USMLE Step 1 Qs (12)

Clonidine has long been used effectively for the treatment of hypertension. The other choices listed are compounds that can induce panic attacks and are, therefore, inappropriate for the treatment for this patient. Clonidine is an adrenergic agonist whose functions are mediated by its actions upon 2 receptors. Administration of this drug results in an overall decrease in noradrenergic transmission. Although the precise mechanism by which the effects of clonidine become manifest is unknown, it may be that it reduces noradrenergic transmission by acting upon 2 presynaptic receptors, which typically produce autoinhibition of the noradrenergic pathways.

Herb's drooping eyelid, small pupil, and lack of sweating on the right side are examples of Horner's syndrome. This is caused by the interruption of sympathetic fibers anywhere along their course from the hypothalamus and brainstem, to the intermediolateral cell column in the upper thoracic levels of the spinal cord where neurons, supplying sympathetic innervation to the pupil, the levator palpebrae superioris muscle of the eyelid and sweat glands of the face, are located. Interruption of this sympathetic innervation will result in the drooping of the upper eyelid (ptosis), pupillary constriction (miosis; due to unopposed action of the parasympathetic innervation of the circular muscles of the iris), and lack of sweating on the face. Parasympathetic or oculomotor damage causes pupillary dilation, rather than constriction. Herb could close his eyes tightly because this function is mediated by the seventh nerve, which is not damaged by this lesion. Preganglionic sympathetic neurons are predominantly cholinergic, and postganglionic sympathetic neurons are predominantly noradrenergic. Horner's syndrome may be caused by either a preganglionic or postganglionic lesion. The location may be determined by the use of eyedrops specifically targeted at a particular neurotransmitter. One cause of interruption of the sympathetic fibers is a tumor of the apex (top portion) of the lung, called a Pancoast tumor. Because the apex of the lung is in close proximity to the spine, a Pancoast tumor may compress the upper thoracic spinal cord where the sympathetic fibers exit from it. Compression of the adjacent spinal nerves between C8 and T2, entering the brachial plexus, also interrupts the nerve supply to the hand and triceps muscle, causing numbness and weakness in these areas. Pancoast tumors do not often cause respiratory symptoms early on in their course because they are located far from the mainstem bronchi. Because these tumors have this unique location, the neurological abnormalities often predate the respiratory problems. The neurologist suspected that Herb may have a Pancoast tumor in the lung because of his long history of smoking.

The MRI of Susan's head revealed a pituitary microadenoma, a benign tumor arising from the anterior pituitary or adenohypophysis. This particular tumor consisted of cells that secrete the hormone prolactin, which is not only the stimulating factor for lactation, but inhibits menstruation when levels are high. It is common for this tumor's symptoms to be manifested during the child-bearing years. The visual problem is called bitemporal hemianopsia. Since the pituitary gland is in very close proximity to the optic chiasm, pituitary tumors often invade this structure. Since only the medial fibers (which perceive the temporal field of each eye) in each optic nerve cross, these are the fibers damaged by these tumors, and the patient will be unable to see either temporal visual field. Both the central scotoma (an island of visual loss surrounded by normal vision in one eye), which is usually seen with lesions of the retina or optic nerve, and the papilledema (blurring of the optic disc margin when viewed by fundoscopic examination due to increased intracranial pressure) would not be caused by damage to the optic chiasm. The optic chiasm can be compressed by pituitary tumors, causing bitemporal hemianopsia. The prolactin-releasing factor is found in the arcuate nucleus of the hypothalamus and activates the lactotropic cells of the anterior pituitary gland. Several different peptides, including dopamine, have the capacity to raise the level of prolactin in the blood. Specifically, the tuberoinfundibular dopaminergic system regulates prolactin secretion through direct projection to the pituitary. For this reason, a newer treatment for prolactin-secreting microadenomas is the drug bromocriptine, a dopamine agonist commonly used in the treatment of Parkinson's disease. By giving a dopamine agonist, serum prolactin increases, inhibiting production by the tumor cells, and eventually the tumor size shrinks. This has become either an alternative or first-line treatment prior to trying radiation or surgery.

Clonidine has long been used effectively for the treatment of hypertension. The other choices listed are compounds that can induce panic attacks and are, therefore, inappropriate for the treatment for this patient. Clonidine is an adrenergic agonist whose functions are mediated by its actions upon 2 receptors. Administration of this drug results in an overall decrease in noradrenergic transmission. Although the precise mechanism by which the effects of clonidine become manifest is unknown, it may be that it reduces noradrenergic transmission by acting upon 2 presynaptic receptors, which typically produce autoinhibition of the noradrenergic pathways.

This individual who suffers a paralysis of the soft palate and pharynx, as well as loss of the carotid sinus reflex, sustains damage that includes cranial nerve X. It should be noted that several of these symptoms could have been incurred by damage to cranial nerve IX as well. However, in this question, cranial nerve IX was not listed as a choice. The axons of the nucleus ambiguus of cranial nerve X innervate the soft palate and pharynx. Damage to these neurons would frequently cause dysphagia, hoarseness, and paralysis of the soft palate. In addition, damage to the dorsal motor nucleus of the vagus constitutes an efferent limb for expression of the carotid sinus reflex. Thus, damage to these two nuclear groups would produce the constellation of deficits described for this case. The nucleus ambiguus is classified as a special visceral efferent fiber because it innervates skeletal muscle and it is derived from a visceral arch, while the dorsal motor nucleus innervates thoracic and abdominal viscera and is therefore classified as a general visceral efferent fiber.

This is an example of Bell's palsy, or damage to the facial nerve distal to its nucleus in the pons. The motor weakness is LMN because of the involvement of the upper one-third of the face (this has bilateral innervation within the CNS). The loss of taste on the anterior two-thirds of the tongue and the hyperacusis (sensitivity to noise) point to damage that is distal to the brainstem because these are functions whose nerves join the facial nerve distal to its exit from the pons. This type of palsy may be caused by a virus and is more common among people with diabetes. This type of facial paralysis, involving the upper one-third of the facial muscles, is characteristic of an LMN facial nerve lesion. Since there is bilateral innervation within the CNS, from the prefrontal gyrus bilaterally until their synapse at the facial nerve nucleus, all UMN facial weakness spares the forehead. Since there is motor weakness of the face and since the chorda tympani nerve (which subserves taste) joins the facial nerve, it is likely that the lesion exists proximal to where the chorda tympani joins the facial nerve. A lesion in the lingual nerve (a branch of the trigeminal) would result in a loss of taste as well, but would also result in a loss of sensation to the face, not motor weakness. If the lesion occurred distal to the chorda tympani nerve, taste would have been spared. The facial nerve sends a branch to the stapedius muscle distal to the geniculate ganglion, but proximal to the chorda tympani nerve. Lesions proximal to this branch will cause weakness of the stapedius muscle. Contraction of this muscle normally serves as a mechanism for dampening the motion of the ossicles, thus lowering the amount of stimulation reaching the organ of Corti. If this muscle is paralyzed, hyperacusis, or increased acuity, as well as hypersensitivity to low tones will occur. Since the genu of the facial nerve is in close proximity to the nucleus of the abducens nerve, the pons is a likely location for this particular type of combination of findings. Since the damage to the facial nerve has occurred distal to the facial nerve nucleus, an LMN facial palsy is present. The lack of hyperacusis and the presence of normal taste imply that the lesion is proximal to the geniculate ganglion. Therefore, the lesion must be between the facial nerve nucleus and the geniculate ganglion, and the location in the pons is the most likely choice. If this clinical picture is present, then an infarct or tumor in the pons must be suspected, and, in this case, an imaging study would be more appropriate.

This is an example of Bell's palsy, or damage to the facial nerve distal to its nucleus in the pons. The motor weakness is LMN because of the involvement of the upper one-third of the face (this has bilateral innervation within the CNS). The loss of taste on the anterior two-thirds of the tongue and the hyperacusis (sensitivity to noise) point to damage that is distal to the brainstem because these are functions whose nerves join the facial nerve distal to its exit from the pons. This type of palsy may be caused by a virus and is more common among people with diabetes. This type of facial paralysis, involving the upper one-third of the facial muscles, is characteristic of an LMN facial nerve lesion. Since there is bilateral innervation within the CNS, from the prefrontal gyrus bilaterally until their synapse at the facial nerve nucleus, all UMN facial weakness spares the forehead. Since there is motor weakness of the face and since the chorda tympani nerve (which subserves taste) joins the facial nerve, it is likely that the lesion exists proximal to where the chorda tympani joins the facial nerve. A lesion in the lingual nerve (a branch of the trigeminal) would result in a loss of taste as well, but would also result in a loss of sensation to the face, not motor weakness. If the lesion occurred distal to the chorda tympani nerve, taste would have been spared. The facial nerve sends a branch to the stapedius muscle distal to the geniculate ganglion, but proximal to the chorda tympani nerve. Lesions proximal to this branch will cause weakness of the stapedius muscle. Contraction of this muscle normally serves as a mechanism for dampening the motion of the ossicles, thus lowering the amount of stimulation reaching the organ of Corti. If this muscle is paralyzed, hyperacusis, or increased acuity, as well as hypersensitivity to low tones will occur. Since the genu of the facial nerve is in close proximity to the nucleus of the abducens nerve, the pons is a likely location for this particular type of combination of findings. Since the damage to the facial nerve has occurred distal to the facial nerve nucleus, an LMN facial palsy is present. The lack of hyperacusis and the presence of normal taste imply that the lesion is proximal to the geniculate ganglion. Therefore, the lesion must be between the facial nerve nucleus and the geniculate ganglion, and the location in the pons is the most likely choice. If this clinical picture is present, then an infarct or tumor in the pons must be suspected, and, in this case, an imaging study would be more appropriate.

This is an example of Bell's palsy, or damage to the facial nerve distal to its nucleus in the pons. The motor weakness is LMN because of the involvement of the upper one-third of the face (this has bilateral innervation within the CNS). The loss of taste on the anterior two-thirds of the tongue and the hyperacusis (sensitivity to noise) point to damage that is distal to the brainstem because these are functions whose nerves join the facial nerve distal to its exit from the pons. This type of palsy may be caused by a virus and is more common among people with diabetes. This type of facial paralysis, involving the upper one-third of the facial muscles, is characteristic of an LMN facial nerve lesion. Since there is bilateral innervation within the CNS, from the prefrontal gyrus bilaterally until their synapse at the facial nerve nucleus, all UMN facial weakness spares the forehead. Since there is motor weakness of the face and since the chorda tympani nerve (which subserves taste) joins the facial nerve, it is likely that the lesion exists proximal to where the chorda tympani joins the facial nerve. A lesion in the lingual nerve (a branch of the trigeminal) would result in a loss of taste as well, but would also result in a loss of sensation to the face, not motor weakness. If the lesion occurred distal to the chorda tympani nerve, taste would have been spared. The facial nerve sends a branch to the stapedius muscle distal to the geniculate ganglion, but proximal to the chorda tympani nerve. Lesions proximal to this branch will cause weakness of the stapedius muscle. Contraction of this muscle normally serves as a mechanism for dampening the motion of the ossicles, thus lowering the amount of stimulation reaching the organ of Corti. If this muscle is paralyzed, hyperacusis, or increased acuity, as well as hypersensitivity to low tones will occur. Since the genu of the facial nerve is in close proximity to the nucleus of the abducens nerve, the pons is a likely location for this particular type of combination of findings. Since the damage to the facial nerve has occurred distal to the facial nerve nucleus, an LMN facial palsy is present. The lack of hyperacusis and the presence of normal taste imply that the lesion is proximal to the geniculate ganglion. Therefore, the lesion must be between the facial nerve nucleus and the geniculate ganglion, and the location in the pons is the most likely choice. If this clinical picture is present, then an infarct or tumor in the pons must be suspected, and, in this case, an imaging study would be more appropriate.

Sam has Parkinson's disease, a degenerative condition caused by progressive loss of dopaminergic cells in the substantia nigra, pars compacta. This is an area that controls the speed and spontaneity of movement, so damage to this area can produce deficits that include: a slow shuffling gait with a tendency to move progressively faster (festinating gait); problems with maintaining size in handwriting, with a tendency to write with small letters (micrographia); masklike facial expression with a paucity of eyeblinks; and difficulty getting out of a chair. Other problems include a soft, monotonous voice; muscle rigidity (lead-pipe rigidity); a tremor at rest that is "pill-rolling"; and a combination of a tremor and rigidity, especially in the arms, which, when flexion is attempted, elicits a "cogwheeling" property. Failure to swallow with a normal frequency makes drooling a problem. Dementia (senility) is also a problem with Parkinson's patients, especially later in the course of the disease. The blood supply to the substantia nigra arises from the posterior circulation, specifically the posteromedial branches of the posterior cerebral artery and branches of the posterior communicating artery. The lenticulostriate branches of the middle cerebral artery supply other portions of the basal ganglia, such as the striatum and the globus pallidus. The anterior choroidal artery also supplies some of the telencephalic nuclei of the basal ganglia. The majority of cells that are lost in this disease are dopaminergic cells in the substantia nigra, pars compacta. Only the pars compacta region of the substantia nigra contains dopaminergic neurons. Medications are currently available to lessen the symptoms of Parkinson's disease. Some of these medications contain various concentrations of L-dopa, an immediate precursor to dopamine. Dopamine itself doesn't cross the blood-brain barrier, so it cannot be directly replaced. Medications that antagonize the breakdown of catecholamines by monoamine oxidase can increase the amount of dopamine available for the remaining cells in the substantia nigra.

Cranial nerve IX, the glossopharyngeal nerve, innervates the skeletal muscles of the pharynx. The motor component involved arises from the nucleus ambiguus of the medulla. This cranial nerve also contains afferents, a component of which arises from the superior ganglion. These sensory neurons convey somatosensory sensation, including pain afferents that ultimately synapse in the spinal trigeminal nucleus. The motor component of the glossopharyngeal nerve mediating swallowing and coughing constitutes a special visceral efferent (because it is derived from a visceral arch), and the sensory component conveying pain is referred to as a general somatic afferent fiber

One of the drugs that has been used effectively for the treatment of epilepsy, especially complex partial seizures involving the temporal lobe, has been vigabatrin. The other choices of drugs are ones that enhance convulsive activity either by facilitating excitatory transmitter function or by inhibiting inhibitory transmitter functions. Vigabatrin functions by enhancing GABA-mediated inhibition of neurons, perhaps by the inhibition of GABA-transaminase.

The MRI of Susan's head revealed a pituitary microadenoma, a benign tumor arising from the anterior pituitary or adenohypophysis. This particular tumor consisted of cells that secrete the hormone prolactin, which is not only the stimulating factor for lactation, but inhibits menstruation when levels are high. It is common for this tumor's symptoms to be manifested during the child-bearing years. The visual problem is called bitemporal hemianopsia. Since the pituitary gland is in very close proximity to the optic chiasm, pituitary tumors often invade this structure. Since only the medial fibers (which perceive the temporal field of each eye) in each optic nerve cross, these are the fibers damaged by these tumors, and the patient will be unable to see either temporal visual field. Both the central scotoma (an island of visual loss surrounded by normal vision in one eye), which is usually seen with lesions of the retina or optic nerve, and the papilledema (blurring of the optic disc margin when viewed by fundoscopic examination due to increased intracranial pressure) would not be caused by damage to the optic chiasm. The optic chiasm can be compressed by pituitary tumors, causing bitemporal hemianopsia. The prolactin-releasing factor is found in the arcuate nucleus of the hypothalamus and activates the lactotropic cells of the anterior pituitary gland. Several different peptides, including dopamine, have the capacity to raise the level of prolactin in the blood. Specifically, the tuberoinfundibular dopaminergic system regulates prolactin secretion through direct projection to the pituitary. For this reason, a newer treatment for prolactin-secreting microadenomas is the drug bromocriptine, a dopamine agonist commonly used in the treatment of Parkinson's disease. By giving a dopamine agonist, serum prolactin increases, inhibiting production by the tumor cells, and eventually the tumor size shrinks. This has become either an alternative or first-line treatment prior to trying radiation or surgery.

Sam has Parkinson's disease, a degenerative condition caused by progressive loss of dopaminergic cells in the substantia nigra, pars compacta. This is an area that controls the speed and spontaneity of movement, so damage to this area can produce deficits that include: a slow shuffling gait with a tendency to move progressively faster (festinating gait); problems with maintaining size in handwriting, with a tendency to write with small letters (micrographia); masklike facial expression with a paucity of eyeblinks; and difficulty getting out of a chair. Other problems include a soft, monotonous voice; muscle rigidity (lead-pipe rigidity); a tremor at rest that is "pill-rolling"; and a combination of a tremor and rigidity, especially in the arms, which, when flexion is attempted, elicits a "cogwheeling" property. Failure to swallow with a normal frequency makes drooling a problem. Dementia (senility) is also a problem with Parkinson's patients, especially later in the course of the disease. The blood supply to the substantia nigra arises from the posterior circulation, specifically the posteromedial branches of the posterior cerebral artery and branches of the posterior communicating artery. The lenticulostriate branches of the middle cerebral artery supply other portions of the basal ganglia, such as the striatum and the globus pallidus. The anterior choroidal artery also supplies some of the telencephalic nuclei of the basal ganglia. The majority of cells that are lost in this disease are dopaminergic cells in the substantia nigra, pars compacta. Only the pars compacta region of the substantia nigra contains dopaminergic neurons. Medications are currently available to lessen the symptoms of Parkinson's disease. Some of these medications contain various concentrations of L-dopa, an immediate precursor to dopamine. Dopamine itself doesn't cross the blood-brain barrier, so it cannot be directly replaced. Medications that antagonize the breakdown of catecholamines by monoamine oxidase can increase the amount of dopamine available for the remaining cells in the substantia nigra.

Sam has Parkinson's disease, a degenerative condition caused by progressive loss of dopaminergic cells in the substantia nigra, pars compacta. This is an area that controls the speed and spontaneity of movement, so damage to this area can produce deficits that include: a slow shuffling gait with a tendency to move progressively faster (festinating gait); problems with maintaining size in handwriting, with a tendency to write with small letters (micrographia); masklike facial expression with a paucity of eyeblinks; and difficulty getting out of a chair. Other problems include a soft, monotonous voice; muscle rigidity (lead-pipe rigidity); a tremor at rest that is "pill-rolling"; and a combination of a tremor and rigidity, especially in the arms, which, when flexion is attempted, elicits a "cogwheeling" property. Failure to swallow with a normal frequency makes drooling a problem. Dementia (senility) is also a problem with Parkinson's patients, especially later in the course of the disease. The blood supply to the substantia nigra arises from the posterior circulation, specifically the posteromedial branches of the posterior cerebral artery and branches of the posterior communicating artery. The lenticulostriate branches of the middle cerebral artery supply other portions of the basal ganglia, such as the striatum and the globus pallidus. The anterior choroidal artery also supplies some of the telencephalic nuclei of the basal ganglia. The majority of cells that are lost in this disease are dopaminergic cells in the substantia nigra, pars compacta. Only the pars compacta region of the substantia nigra contains dopaminergic neurons. Medications are currently available to lessen the symptoms of Parkinson's disease. Some of these medications contain various concentrations of L-dopa, an immediate precursor to dopamine. Dopamine itself doesn't cross the blood-brain barrier, so it cannot be directly replaced. Medications that antagonize the breakdown of catecholamines by monoamine oxidase can increase the amount of dopamine available for the remaining cells in the substantia nigra.

Research conducted over the past 2 decades has shown that the actions of morphine are mediated through opioid mu receptors, while other opioid receptors appear not to play a significant role. Likewise, dopamine receptors are not involved in this process. The region of the brain where concentrations of opioid receptors are very heavily concentrated is the midbrain periaqueductal gray. This region plays an important role in the modulation of pain and is particularly responsive to opioid activation by morphine.

Research conducted over the past 2 decades has shown that the actions of morphine are mediated through opioid receptors, while other opioid receptors appear not to play a significant role. Likewise, dopamine receptors are not involved in this process. The region of the brain where concentrations of opioid receptors are very heavily concentrated is the midbrain periaqueductal gray. This region plays an important role in the modulation of pain and is particularly responsive to opioid activation by morphine.

Cranial nerve IX, the glossopharyngeal nerve, innervates the skeletal muscles of the pharynx. The motor component involved arises from the nucleus ambiguus of the medulla. This cranial nerve also contains afferents, a component of which arises from the superior ganglion. These sensory neurons convey somatosensory sensation, including pain afferents that ultimately synapse in the spinal trigeminal nucleus. The motor component of the glossopharyngeal nerve mediating swallowing and coughing constitutes a special visceral efferent (because it is derived from a visceral arch), and the sensory component conveying pain is referred to as a general somatic afferent fiber

The third cranial nerve (oculomotor) controls four of the six extraocular muscles that move the eye. When this nerve fails to function, the eye remains deviated laterally due to the unopposed action of the other two extraocular muscles. When the eyes no longer move together, patients have double vision because the visual cortex now receives two different images. In addition, fibers originating in the third nerve nucleus innervate the levator palpebrae superioris, a muscle that helps to lift the eyelid. Damage to the optic nerve causes loss of vision, blurred vision, and a central scotoma (blind spot in the center of the visual field). Damage to the cervical sympathetic fibers causes Horner's syndrome, consisting of ptosis (drooping of the eyelid), miosis (constriction of the pupil), and anhydrosis (loss of sweating), not eye movement abnormalities. The actions of the superior oblique, the muscle innervated by the trochlear nerve, include intorsion, depression, and abduction. The abducens nerve mediates the lateral rectus muscle, which abducts the eye. The eye is depressed and abducted due to the unopposed actions of the superior oblique and lateral rectus muscles, which together move the eye downward and abduct it (see earlier discussion for the actions of these muscles). The other four muscles are innervated by the oculomotor nerve, which presumably has been damaged. This is an example of Weber's syndrome, or a lesion involving the third cranial nerve outflow tract, and the corticospinal and corticobulbar tracts in the cerebral peduncles of the midbrain. Weber's syndrome may occur as a result of an occlusion of the interpeduncular branches of the posterior cerebral artery (which supply this portion of the midbrain), a tumor pressing on this area, an aneurysm (circumscribed dilation of an artery) of the posterior communicating artery, or a plaque (lesion) related to multiple sclerosis. Fibers from the Edinger-Westphal nucleus are affected by lesions of the midbrain as well, and because they are instrumental in constricting the pupil, this lesion causes the patient to have a dilated pupil. If there is a mass that is external to the midbrain, but pressing on the oculomotor nerve, then the preganglionic parasympathetic fibers traveling to the ciliary ganglion, which, in turn, innervate the pupillary constrictor muscles, can be damaged, also causing a dilated pupil. Cervical sympathetic fibers cause pupillary dilatation, so damage to these fibers causes pupillary constriction (see Horner's syndrome, earlier). Involvement of the cerebral peduncle causes damage to the corticospinal and corticobulbar tracts, resulting in weakness of the contralateral face, arm, and leg. The motor deficit is contralateral because the corticospinal tracts cross in the medullary pyramids, below the level of the lesion. The upper portion of Mike's face was spared in this case (as well as in any other UMN lesion) because the face is innervated bilaterally until the level of the caudal pons, so a unilateral lesion results in sparing of this portion of the face. The combination of a third-nerve palsy and contralateral hemiparesis can only occur in the midbrain. The observed effects relating to cranial nerve III could not be accounted for by cortical damage. Likewise, damage to the cervical cord would not affect the third nerve.

This is an example of Bell's palsy, or damage to the facial nerve distal to its nucleus in the pons. The motor weakness is LMN because of the involvement of the upper one-third of the face (this has bilateral innervation within the CNS). The loss of taste on the anterior two-thirds of the tongue and the hyperacusis (sensitivity to noise) point to damage that is distal to the brainstem because these are functions whose nerves join the facial nerve distal to its exit from the pons. This type of palsy may be caused by a virus and is more common among people with diabetes. This type of facial paralysis, involving the upper one-third of the facial muscles, is characteristic of an LMN facial nerve lesion. Since there is bilateral innervation within the CNS, from the prefrontal gyrus bilaterally until their synapse at the facial nerve nucleus, all UMN facial weakness spares the forehead. Since there is motor weakness of the face and since the chorda tympani nerve (which subserves taste) joins the facial nerve, it is likely that the lesion exists proximal to where the chorda tympani joins the facial nerve. A lesion in the lingual nerve (a branch of the trigeminal) would result in a loss of taste as well, but would also result in a loss of sensation to the face, not motor weakness. If the lesion occurred distal to the chorda tympani nerve, taste would have been spared. The facial nerve sends a branch to the stapedius muscle distal to the geniculate ganglion, but proximal to the chorda tympani nerve. Lesions proximal to this branch will cause weakness of the stapedius muscle. Contraction of this muscle normally serves as a mechanism for dampening the motion of the ossicles, thus lowering the amount of stimulation reaching the organ of Corti. If this muscle is paralyzed, hyperacusis, or increased acuity, as well as hypersensitivity to low tones will occur. Since the genu of the facial nerve is in close proximity to the nucleus of the abducens nerve, the pons is a likely location for this particular type of combination of findings. Since the damage to the facial nerve has occurred distal to the facial nerve nucleus, an LMN facial palsy is present. The lack of hyperacusis and the presence of normal taste imply that the lesion is proximal to the geniculate ganglion. Therefore, the lesion must be between the facial nerve nucleus and the geniculate ganglion, and the location in the pons is the most likely choice. If this clinical picture is present, then an infarct or tumor in the pons must be suspected, and, in this case, an imaging study would be more appropriate.

Damage to the trochlear nerve causes weakness of the superior oblique muscle, resulting in the inability of the orbit to deviate downward when the eye is intorted. To compensate for the classically vertical double vision, the patient tends to tilt his head to the contralateral side, causing the contralateral eye to intort. The trochlear nerve supplies the superior oblique muscle. The trochlear nerve is the only nerve to decussate peripherally, and also to emerge from the dorsal aspect of the brainstem. In this case, the damaged nerve emerged from the right (contralateral) dorsal midbrain. The action of the superior oblique muscle is to rotate the orbit medially and downward. Because the trochlear nerve is not only the smallest cranial nerve but also has the longest course of any cranial nerve, it is especially vulnerable to trauma. One of the most common causes of trochlear nerve palsy is trauma.

The MRI of Susan's head revealed a pituitary microadenoma, a benign tumor arising from the anterior pituitary or adenohypophysis. This particular tumor consisted of cells that secrete the hormone prolactin, which is not only the stimulating factor for lactation, but inhibits menstruation when levels are high. It is common for this tumor's symptoms to be manifested during the child-bearing years. The visual problem is called bitemporal hemianopsia. Since the pituitary gland is in very close proximity to the optic chiasm, pituitary tumors often invade this structure. Since only the medial fibers (which perceive the temporal field of each eye) in each optic nerve cross, these are the fibers damaged by these tumors, and the patient will be unable to see either temporal visual field. Both the central scotoma (an island of visual loss surrounded by normal vision in one eye), which is usually seen with lesions of the retina or optic nerve, and the papilledema (blurring of the optic disc margin when viewed by fundoscopic examination due to increased intracranial pressure) would not be caused by damage to the optic chiasm. The optic chiasm can be compressed by pituitary tumors, causing bitemporal hemianopsia. The prolactin-releasing factor is found in the arcuate nucleus of the hypothalamus and activates the lactotropic cells of the anterior pituitary gland. Several different peptides, including dopamine, have the capacity to raise the level of prolactin in the blood. Specifically, the tuberoinfundibular dopaminergic system regulates prolactin secretion through direct projection to the pituitary. For this reason, a newer treatment for prolactin-secreting microadenomas is the drug bromocriptine, a dopamine agonist commonly used in the treatment of Parkinson's disease. By giving a dopamine agonist, serum prolactin increases, inhibiting production by the tumor cells, and eventually the tumor size shrinks. This has become either an alternative or first-line treatment prior to trying radiation or surgery.

Sam has Parkinson's disease, a degenerative condition caused by progressive loss of dopaminergic cells in the substantia nigra, pars compacta. This is an area that controls the speed and spontaneity of movement, so damage to this area can produce deficits that include: a slow shuffling gait with a tendency to move progressively faster (festinating gait); problems with maintaining size in handwriting, with a tendency to write with small letters (micrographia); masklike facial expression with a paucity of eyeblinks; and difficulty getting out of a chair. Other problems include a soft, monotonous voice; muscle rigidity (lead-pipe rigidity); a tremor at rest that is "pill-rolling"; and a combination of a tremor and rigidity, especially in the arms, which, when flexion is attempted, elicits a "cogwheeling" property. Failure to swallow with a normal frequency makes drooling a problem. Dementia (senility) is also a problem with Parkinson's patients, especially later in the course of the disease. The blood supply to the substantia nigra arises from the posterior circulation, specifically the posteromedial branches of the posterior cerebral artery and branches of the posterior communicating artery. The lenticulostriate branches of the middle cerebral artery supply other portions of the basal ganglia, such as the striatum and the globus pallidus. The anterior choroidal artery also supplies some of the telencephalic nuclei of the basal ganglia. The majority of cells that are lost in this disease are dopaminergic cells in the substantia nigra, pars compacta. Only the pars compacta region of the substantia nigra contains dopaminergic neurons. Medications are currently available to lessen the symptoms of Parkinson's disease. Some of these medications contain various concentrations of L-dopa, an immediate precursor to dopamine. Dopamine itself doesn't cross the blood-brain barrier, so it cannot be directly replaced. Medications that antagonize the breakdown of catecholamines by monoamine oxidase can increase the amount of dopamine available for the remaining cells in the substantia nigra.

An ataxic gait is an unsteady gait. Gaits due to motor weakness or spasticity tend to involve circling of the weak leg (circumduction); festinating or shuffling gaits, which are often due to parkinsonism or disease of the basal ganglia, involve a stooped posture with shuffling of the feet and very small steps. An ataxic gait may result from motor incoordination due to cerebellar disease, or from lack of proprioception in the lower extremities due to disease in the posterior column system (gait becomes unsteady when a patient is unable to detect the location of his or her feet). Degeneration of both systems may occur due to alcoholism, although in this case, we are told that John does not have any sensory deficits when this modality is tested in isolation. This is an example of alcoholic cerebellar degeneration. It is caused by degeneration (probably through nutritional deficiency) of neurons in the cerebellar cortex, particularly of the Purkinje cells, and is usually restricted to anterior and superior parts of the vermis, as well as anterior portions of the anterior lobes. For this reason, most of the deficits in this syndrome involve midline structures such as the trunk, which are represented most in the vermis. Trunk instability usually causes problems with gait. In addition, because the cerebellar homunculus represents the legs in the anterior portion of the anterior lobe, the legs are affected more than the arms. Loss of volume within the vermis of the cerebellum is readily visualized, especially on an MRI of the brain, because this technique allows good visualization of the posterior fossa. If these changes are visualized, then the condition is most likely chronic (as also indicated by the history) and most likely irreversible. However, it is important to make sure that the patient is well nourished, takes vitamins, and stops drinking in order to prevent other neurologic problems from occurring. Damage to other brain regions listed do not cause such damage. The spinocerebellum receives sensory inputs from the spinal cord and is instrumental in controlling posture and movement. It includes the vermis and the intermediate hemisphere. The cerebrocerebellum consists of the lateral hemispheres and is instrumental in the planning of movement. The dentate nucleus comprises the cell bodies that form the superior cerebellar peduncle. The brachium pontis corresponds to the middle cerebellar peduncle. The spinocerebellar cortical (Purkinje) cells project to the fastigial and interposed nuclei. Purkinje cells are found in the cerebellar cortex. None of the other choices are cells that are found in the cerebellum.

Amyotrophic lateral sclerosis is characterized by a progressive loss of motor functions, first seen as weakness in limb muscles, especially those of the fingers, and later of the other limbs. Sensory functions are not significantly affected. Over time, there is wasting, atrophy, and fasciculations of limb muscles followed by UMN signs. Electromyogram abnormalities can also be observed of the upper and lower extremities. In MS, there is also sensory loss, such as loss or blurring of vision, as well as bladder problems. Poliomyelitis and myasthenia gravis involve LMN symptoms, while a cerebral cortical stroke would result in a UMN disorder without LMN signs. In ALS, there is damage initially to ventral horn cells of the spinal cord, producing LMN signs. As the disease progresses, there is involvement of UMNs located in the lateral columns of the spinal cord (i.e., corticospinal dysfunction), thereby producing UMN signs such as an increase in tendon reflexes and the presence of an extensor plantar response. Sensory neurons are not involved in this disorder.

This is an example of Bell's palsy, or damage to the facial nerve distal to its nucleus in the pons. The motor weakness is LMN because of the involvement of the upper one-third of the face (this has bilateral innervation within the CNS). The loss of taste on the anterior two-thirds of the tongue and the hyperacusis (sensitivity to noise) point to damage that is distal to the brainstem because these are functions whose nerves join the facial nerve distal to its exit from the pons. This type of palsy may be caused by a virus and is more common among people with diabetes. This type of facial paralysis, involving the upper one-third of the facial muscles, is characteristic of an LMN facial nerve lesion. Since there is bilateral innervation within the CNS, from the prefrontal gyrus bilaterally until their synapse at the facial nerve nucleus, all UMN facial weakness spares the forehead. Since there is motor weakness of the face and since the chorda tympani nerve (which subserves taste) joins the facial nerve, it is likely that the lesion exists proximal to where the chorda tympani joins the facial nerve. A lesion in the lingual nerve (a branch of the trigeminal) would result in a loss of taste as well, but would also result in a loss of sensation to the face, not motor weakness. If the lesion occurred distal to the chorda tympani nerve, taste would have been spared. The facial nerve sends a branch to the stapedius muscle distal to the geniculate ganglion, but proximal to the chorda tympani nerve. Lesions proximal to this branch will cause weakness of the stapedius muscle. Contraction of this muscle normally serves as a mechanism for dampening the motion of the ossicles, thus lowering the amount of stimulation reaching the organ of Corti. If this muscle is paralyzed, hyperacusis, or increased acuity, as well as hypersensitivity to low tones will occur. Since the genu of the facial nerve is in close proximity to the nucleus of the abducens nerve, the pons is a likely location for this particular type of combination of findings. Since the damage to the facial nerve has occurred distal to the facial nerve nucleus, an LMN facial palsy is present. The lack of hyperacusis and the presence of normal taste imply that the lesion is proximal to the geniculate ganglion. Therefore, the lesion must be between the facial nerve nucleus and the geniculate ganglion, and the location in the pons is the most likely choice. If this clinical picture is present, then an infarct or tumor in the pons must be suspected, and, in this case, an imaging study would be more appropriate.

The MRI of Susan's head revealed a pituitary microadenoma, a benign tumor arising from the anterior pituitary or adenohypophysis. This particular tumor consisted of cells that secrete the hormone prolactin, which is not only the stimulating factor for lactation, but inhibits menstruation when levels are high. It is common for this tumor's symptoms to be manifested during the child-bearing years. The visual problem is called bitemporal hemianopsia. Since the pituitary gland is in very close proximity to the optic chiasm, pituitary tumors often invade this structure. Since only the medial fibers (which perceive the temporal field of each eye) in each optic nerve cross, these are the fibers damaged by these tumors, and the patient will be unable to see either temporal visual field. Both the central scotoma (an island of visual loss surrounded by normal vision in one eye), which is usually seen with lesions of the retina or optic nerve, and the papilledema (blurring of the optic disc margin when viewed by fundoscopic examination due to increased intracranial pressure) would not be caused by damage to the optic chiasm. The optic chiasm can be compressed by pituitary tumors, causing bitemporal hemianopsia. The prolactin-releasing factor is found in the arcuate nucleus of the hypothalamus and activates the lactotropic cells of the anterior pituitary gland. Several different peptides, including dopamine, have the capacity to raise the level of prolactin in the blood. Specifically, the tuberoinfundibular dopaminergic system regulates prolactin secretion through direct projection to the pituitary. For this reason, a newer treatment for prolactin-secreting microadenomas is the drug bromocriptine, a dopamine agonist commonly used in the treatment of Parkinson's disease. By giving a dopamine agonist, serum prolactin increases, inhibiting production by the tumor cells, and eventually the tumor size shrinks. This has become either an alternative or first-line treatment prior to trying radiation or surgery.

This individual who suffers a paralysis of the soft palate and pharynx, as well as loss of the carotid sinus reflex, sustains damage that includes cranial nerve X. It should be noted that several of these symptoms could have been incurred by damage to cranial nerve IX as well. However, in this question, cranial nerve IX was not listed as a choice. The axons of the nucleus ambiguus of cranial nerve X innervate the soft palate and pharynx. Damage to these neurons would frequently cause dysphagia, hoarseness, and paralysis of the soft palate. In addition, damage to the dorsal motor nucleus of the vagus constitutes an efferent limb for expression of the carotid sinus reflex. Thus, damage to these two nuclear groups would produce the constellation of deficits described for this case. The nucleus ambiguus is classified as a special visceral efferent fiber because it innervates skeletal muscle and it is derived from a visceral arch, while the dorsal motor nucleus innervates thoracic and abdominal viscera and is therefore classified as a general visceral efferent fiber.

One of the drugs that has been used effectively for the treatment of epilepsy, especially complex partial seizures involving the temporal lobe, has been vigabatrin. The other choices of drugs are ones that enhance convulsive activity either by facilitating excitatory transmitter function or by inhibiting inhibitory transmitter functions. Vigabatrin functions by enhancing GABA-mediated inhibition of neurons, perhaps by the inhibition of GABA-transaminase.

Herb's drooping eyelid, small pupil, and lack of sweating on the right side are examples of Horner's syndrome. This is caused by the interruption of sympathetic fibers anywhere along their course from the hypothalamus and brainstem, to the intermediolateral cell column in the upper thoracic levels of the spinal cord where neurons, supplying sympathetic innervation to the pupil, the levator palpebrae superioris muscle of the eyelid and sweat glands of the face, are located. Interruption of this sympathetic innervation will result in the drooping of the upper eyelid (ptosis), pupillary constriction (miosis; due to unopposed action of the parasympathetic innervation of the circular muscles of the iris), and lack of sweating on the face. Parasympathetic or oculomotor damage causes pupillary dilation, rather than constriction. Herb could close his eyes tightly because this function is mediated by the seventh nerve, which is not damaged by this lesion. Preganglionic sympathetic neurons are predominantly cholinergic, and postganglionic sympathetic neurons are predominantly noradrenergic. Horner's syndrome may be caused by either a preganglionic or postganglionic lesion. The location may be determined by the use of eyedrops specifically targeted at a particular neurotransmitter. One cause of interruption of the sympathetic fibers is a tumor of the apex (top portion) of the lung, called a Pancoast tumor. Because the apex of the lung is in close proximity to the spine, a Pancoast tumor may compress the upper thoracic spinal cord where the sympathetic fibers exit from it. Compression of the adjacent spinal nerves between C8 and T2, entering the brachial plexus, also interrupts the nerve supply to the hand and triceps muscle, causing numbness and weakness in these areas. Pancoast tumors do not often cause respiratory symptoms early on in their course because they are located far from the mainstem bronchi. Because these tumors have this unique location, the neurological abnormalities often predate the respiratory problems. The neurologist suspected that Herb may have a Pancoast tumor in the lung because of his long history of smoking.

Herb's drooping eyelid, small pupil, and lack of sweating on the right side are examples of Horner's syndrome. This is caused by the interruption of sympathetic fibers anywhere along their course from the hypothalamus and brainstem, to the intermediolateral cell column in the upper thoracic levels of the spinal cord where neurons, supplying sympathetic innervation to the pupil, the levator palpebrae superioris muscle of the eyelid and sweat glands of the face, are located. Interruption of this sympathetic innervation will result in the drooping of the upper eyelid (ptosis), pupillary constriction (miosis; due to unopposed action of the parasympathetic innervation of the circular muscles of the iris), and lack of sweating on the face. Parasympathetic or oculomotor damage causes pupillary dilation, rather than constriction. Herb could close his eyes tightly because this function is mediated by the seventh nerve, which is not damaged by this lesion. Preganglionic sympathetic neurons are predominantly cholinergic, and postganglionic sympathetic neurons are predominantly noradrenergic. Horner's syndrome may be caused by either a preganglionic or postganglionic lesion. The location may be determined by the use of eyedrops specifically targeted at a particular neurotransmitter. One cause of interruption of the sympathetic fibers is a tumor of the apex (top portion) of the lung, called a Pancoast tumor. Because the apex of the lung is in close proximity to the spine, a Pancoast tumor may compress the upper thoracic spinal cord where the sympathetic fibers exit from it. Compression of the adjacent spinal nerves between C8 and T2, entering the brachial plexus, also interrupts the nerve supply to the hand and triceps muscle, causing numbness and weakness in these areas. Pancoast tumors do not often cause respiratory symptoms early on in their course because they are located far from the mainstem bronchi. Because these tumors have this unique location, the neurological abnormalities often predate the respiratory problems. The neurologist suspected that Herb may have a Pancoast tumor in the lung because of his long history of smoking.

The third cranial nerve (oculomotor) controls four of the six extraocular muscles that move the eye. When this nerve fails to function, the eye remains deviated laterally due to the unopposed action of the other two extraocular muscles. When the eyes no longer move together, patients have double vision because the visual cortex now receives two different images. In addition, fibers originating in the third nerve nucleus innervate the levator palpebrae superioris, a muscle that helps to lift the eyelid. Damage to the optic nerve causes loss of vision, blurred vision, and a central scotoma (blind spot in the center of the visual field). Damage to the cervical sympathetic fibers causes Horner's syndrome, consisting of ptosis (drooping of the eyelid), miosis (constriction of the pupil), and anhydrosis (loss of sweating), not eye movement abnormalities. The actions of the superior oblique, the muscle innervated by the trochlear nerve, include intorsion, depression, and abduction. The abducens nerve mediates the lateral rectus muscle, which abducts the eye. The eye is depressed and abducted due to the unopposed actions of the superior oblique and lateral rectus muscles, which together move the eye downward and abduct it (see earlier discussion for the actions of these muscles). The other four muscles are innervated by the oculomotor nerve, which presumably has been damaged. This is an example of Weber's syndrome, or a lesion involving the third cranial nerve outflow tract, and the corticospinal and corticobulbar tracts in the cerebral peduncles of the midbrain. Weber's syndrome may occur as a result of an occlusion of the interpeduncular branches of the posterior cerebral artery (which supply this portion of the midbrain), a tumor pressing on this area, an aneurysm (circumscribed dilation of an artery) of the posterior communicating artery, or a plaque (lesion) related to multiple sclerosis. Fibers from the Edinger-Westphal nucleus are affected by lesions of the midbrain as well, and because they are instrumental in constricting the pupil, this lesion causes the patient to have a dilated pupil. If there is a mass that is external to the midbrain, but pressing on the oculomotor nerve, then the preganglionic parasympathetic fibers traveling to the ciliary ganglion, which, in turn, innervate the pupillary constrictor muscles, can be damaged, also causing a dilated pupil. Cervical sympathetic fibers cause pupillary dilatation, so damage to these fibers causes pupillary constriction (see Horner's syndrome, earlier). Involvement of the cerebral peduncle causes damage to the corticospinal and corticobulbar tracts, resulting in weakness of the contralateral face, arm, and leg. The motor deficit is contralateral because the corticospinal tracts cross in the medullary pyramids, below the level of the lesion. The upper portion of Mike's face was spared in this case (as well as in any other UMN lesion) because the face is innervated bilaterally until the level of the caudal pons, so a unilateral lesion results in sparing of this portion of the face. The combination of a third-nerve palsy and contralateral hemiparesis can only occur in the midbrain. The observed effects relating to cranial nerve III could not be accounted for by cortical damage. Likewise, damage to the cervical cord would not affect the third nerve.

Damage to the trochlear nerve causes weakness of the superior oblique muscle, resulting in the inability of the orbit to deviate downward when the eye is intorted. To compensate for the classically vertical double vision, the patient tends to tilt his head to the contralateral side, causing the contralateral eye to intort. The trochlear nerve supplies the superior oblique muscle. The trochlear nerve is the only nerve to decussate peripherally, and also to emerge from the dorsal aspect of the brainstem. In this case, the damaged nerve emerged from the right (contralateral) dorsal midbrain. The action of the superior oblique muscle is to rotate the orbit medially and downward. Because the trochlear nerve is not only the smallest cranial nerve but also has the longest course of any cranial nerve, it is especially vulnerable to trauma. One of the most common causes of trochlear nerve palsy is trauma.

Glutamate has been implicated in ischemia-induced brain damage following brain trauma such as a stroke. It has also been shown that administration of NMDA-receptor antagonists following a stroke is effective in the treatment of stroke by reducing tissue infarction and neuronal cell death. The NMDA-receptor antagonist is effective, in part, by decreasing disruption of the blood-brain barrier. It has been suggested that this becomes manifest by a blockade of the neuronal production of reactive oxygen species that occurs as a result of activation of NMDA receptors. The other choices listed for the question have no known relationship to the process in question.

Amyotrophic lateral sclerosis is characterized by a progressive loss of motor functions, first seen as weakness in limb muscles, especially those of the fingers, and later of the other limbs. Sensory functions are not significantly affected. Over time, there is wasting, atrophy, and fasciculations of limb muscles followed by UMN signs. Electromyogram abnormalities can also be observed of the upper and lower extremities. In MS, there is also sensory loss, such as loss or blurring of vision, as well as bladder problems. Poliomyelitis and myasthenia gravis involve LMN symptoms, while a cerebral cortical stroke would result in a UMN disorder without LMN signs. In ALS, there is damage initially to ventral horn cells of the spinal cord, producing LMN signs. As the disease progresses, there is involvement of UMNs located in the lateral columns of the spinal cord (i.e., corticospinal dysfunction), thereby producing UMN signs such as an increase in tendon reflexes and the presence of an extensor plantar response. Sensory neurons are not involved in this disorder.

Cranial nerve IX, the glossopharyngeal nerve, innervates the skeletal muscles of the pharynx. The motor component involved arises from the nucleus ambiguus of the medulla. This cranial nerve also contains afferents, a component of which arises from the superior ganglion. These sensory neurons convey somatosensory sensation, including pain afferents that ultimately synapse in the spinal trigeminal nucleus. The motor component of the glossopharyngeal nerve mediating swallowing and coughing constitutes a special visceral efferent (because it is derived from a visceral arch), and the sensory component conveying pain is referred to as a general somatic afferent fiber

An ataxic gait is an unsteady gait. Gaits due to motor weakness or spasticity tend to involve circling of the weak leg (circumduction); festinating or shuffling gaits, which are often due to parkinsonism or disease of the basal ganglia, involve a stooped posture with shuffling of the feet and very small steps. An ataxic gait may result from motor incoordination due to cerebellar disease, or from lack of proprioception in the lower extremities due to disease in the posterior column system (gait becomes unsteady when a patient is unable to detect the location of his or her feet). Degeneration of both systems may occur due to alcoholism, although in this case, we are told that John does not have any sensory deficits when this modality is tested in isolation. This is an example of alcoholic cerebellar degeneration. It is caused by degeneration (probably through nutritional deficiency) of neurons in the cerebellar cortex, particularly of the Purkinje cells, and is usually restricted to anterior and superior parts of the vermis, as well as anterior portions of the anterior lobes. For this reason, most of the deficits in this syndrome involve midline structures such as the trunk, which are represented most in the vermis. Trunk instability usually causes problems with gait. In addition, because the cerebellar homunculus represents the legs in the anterior portion of the anterior lobe, the legs are affected more than the arms. Loss of volume within the vermis of the cerebellum is readily visualized, especially on an MRI of the brain, because this technique allows good visualization of the posterior fossa. If these changes are visualized, then the condition is most likely chronic (as also indicated by the history) and most likely irreversible. However, it is important to make sure that the patient is well nourished, takes vitamins, and stops drinking in order to prevent other neurologic problems from occurring. Damage to other brain regions listed do not cause such damage. The spinocerebellum receives sensory inputs from the spinal cord and is instrumental in controlling posture and movement. It includes the vermis and the intermediate hemisphere. The cerebrocerebellum consists of the lateral hemispheres and is instrumental in the planning of movement. The dentate nucleus comprises the cell bodies that form the superior cerebellar peduncle. The brachium pontis corresponds to the middle cerebellar peduncle. The spinocerebellar cortical (Purkinje) cells project to the fastigial and interposed nuclei. Purkinje cells are found in the cerebellar cortex. None of the other choices are cells that are found in the cerebellum.

Rigidity can occur by experimentally producing a decerebrate preparation (i.e., severing the brainstem at the level of the pons) and it appears clinically as well. In both situations, there has to be extensive destruction of brain tissue below the midbrain in the region of the pons, but which spares the medulla. In this way, the lateral vestibulospinal tract remains intact. This pathway powerfully facilitates extensor motor neurons and extensor reflexes, thus contributing significantly to the expression of decerebrate rigidity, in particular, when the descending inhibitory pathways, which arise from more rostral levels, are disrupted by the experimental procedure or stroke.

The cranial nerve that was directly affected was the glossopharyngeal nerve (cranial nerve IX). This is a mixed and complex nerve containing: (1) special visceral efferents from the nucleus ambiguus that supply the stylopharyngeus muscle (for elevation of pharynx in speech); (2) special visceral afferent fibers that transmit taste impulses from the posterior third of the tongue, general visceral afferent fibers associated with the inferior ganglion whose receptors lie in the carotid sinus that regulates cardiovascular functions; (3) general somatic afferents whose cell bodies lie in the superior ganglion of cranial nerve IX, and which mediate somatosensory information, including pain from the pharynx; and (4) general visceral efferent fibers that originate in the inferior salivatory nucleus, which are preganglionic and synapse in the otic ganglion. The postganglionic fiber from the otic ganglion innervates the parotid gland and mediates, in part, salivation. Thus, when this nerve is affected by an infectious agent, it results in the constellation of symptoms presented earlier in this case. Since the cell bodies of motor (or visceral motor) fibers (mediating motor and visceral effects) as well as the terminals of sensory afferents (mediating pain from the pharynx) lie in different regions of the medulla, it is very unlikely that such an effect could be the result of damage centrally. A much more likely occurrence is that the infectious agent produced disruption of the glossopharyngeal nerve peripherally, such as at the base of the skull or jugular foramen, where all the components run together and can be more easily affected.

Herb's drooping eyelid, small pupil, and lack of sweating on the right side are examples of Horner's syndrome. This is caused by the interruption of sympathetic fibers anywhere along their course from the hypothalamus and brainstem, to the intermediolateral cell column in the upper thoracic levels of the spinal cord where neurons, supplying sympathetic innervation to the pupil, the levator palpebrae superioris muscle of the eyelid and sweat glands of the face, are located. Interruption of this sympathetic innervation will result in the drooping of the upper eyelid (ptosis), pupillary constriction (miosis; due to unopposed action of the parasympathetic innervation of the circular muscles of the iris), and lack of sweating on the face. Parasympathetic or oculomotor damage causes pupillary dilation, rather than constriction. Herb could close his eyes tightly because this function is mediated by the seventh nerve, which is not damaged by this lesion. Preganglionic sympathetic neurons are predominantly cholinergic, and postganglionic sympathetic neurons are predominantly noradrenergic. Horner's syndrome may be caused by either a preganglionic or postganglionic lesion. The location may be determined by the use of eyedrops specifically targeted at a particular neurotransmitter. One cause of interruption of the sympathetic fibers is a tumor of the apex (top portion) of the lung, called a Pancoast tumor. Because the apex of the lung is in close proximity to the spine, a Pancoast tumor may compress the upper thoracic spinal cord where the sympathetic fibers exit from it. Compression of the adjacent spinal nerves between C8 and T2, entering the brachial plexus, also interrupts the nerve supply to the hand and triceps muscle, causing numbness and weakness in these areas. Pancoast tumors do not often cause respiratory symptoms early on in their course because they are located far from the mainstem bronchi. Because these tumors have this unique location, the neurological abnormalities often predate the respiratory problems. The neurologist suspected that Herb may have a Pancoast tumor in the lung because of his long history of smoking.

The third cranial nerve (oculomotor) controls four of the six extraocular muscles that move the eye. When this nerve fails to function, the eye remains deviated laterally due to the unopposed action of the other two extraocular muscles. When the eyes no longer move together, patients have double vision because the visual cortex now receives two different images. In addition, fibers originating in the third nerve nucleus innervate the levator palpebrae superioris, a muscle that helps to lift the eyelid. Damage to the optic nerve causes loss of vision, blurred vision, and a central scotoma (blind spot in the center of the visual field). Damage to the cervical sympathetic fibers causes Horner's syndrome, consisting of ptosis (drooping of the eyelid), miosis (constriction of the pupil), and anhydrosis (loss of sweating), not eye movement abnormalities. The actions of the superior oblique, the muscle innervated by the trochlear nerve, include intorsion, depression, and abduction. The abducens nerve mediates the lateral rectus muscle, which abducts the eye. The eye is depressed and abducted due to the unopposed actions of the superior oblique and lateral rectus muscles, which together move the eye downward and abduct it (see earlier discussion for the actions of these muscles). The other four muscles are innervated by the oculomotor nerve, which presumably has been damaged. This is an example of Weber's syndrome, or a lesion involving the third cranial nerve outflow tract, and the corticospinal and corticobulbar tracts in the cerebral peduncles of the midbrain. Weber's syndrome may occur as a result of an occlusion of the interpeduncular branches of the posterior cerebral artery (which supply this portion of the midbrain), a tumor pressing on this area, an aneurysm (circumscribed dilation of an artery) of the posterior communicating artery, or a plaque (lesion) related to multiple sclerosis. Fibers from the Edinger-Westphal nucleus are affected by lesions of the midbrain as well, and because they are instrumental in constricting the pupil, this lesion causes the patient to have a dilated pupil. If there is a mass that is external to the midbrain, but pressing on the oculomotor nerve, then the preganglionic parasympathetic fibers traveling to the ciliary ganglion, which, in turn, innervate the pupillary constrictor muscles, can be damaged, also causing a dilated pupil. Cervical sympathetic fibers cause pupillary dilatation, so damage to these fibers causes pupillary constriction (see Horner's syndrome, earlier). Involvement of the cerebral peduncle causes damage to the corticospinal and corticobulbar tracts, resulting in weakness of the contralateral face, arm, and leg. The motor deficit is contralateral because the corticospinal tracts cross in the medullary pyramids, below the level of the lesion. The upper portion of Mike's face was spared in this case (as well as in any other UMN lesion) because the face is innervated bilaterally until the level of the caudal pons, so a unilateral lesion results in sparing of this portion of the face. The combination of a third-nerve palsy and contralateral hemiparesis can only occur in the midbrain. The observed effects relating to cranial nerve III could not be accounted for by cortical damage. Likewise, damage to the cervical cord would not affect the third nerve.

The third cranial nerve (oculomotor) controls four of the six extraocular muscles that move the eye. When this nerve fails to function, the eye remains deviated laterally due to the unopposed action of the other two extraocular muscles. When the eyes no longer move together, patients have double vision because the visual cortex now receives two different images. In addition, fibers originating in the third nerve nucleus innervate the levator palpebrae superioris, a muscle that helps to lift the eyelid. Damage to the optic nerve causes loss of vision, blurred vision, and a central scotoma (blind spot in the center of the visual field). Damage to the cervical sympathetic fibers causes Horner's syndrome, consisting of ptosis (drooping of the eyelid), miosis (constriction of the pupil), and anhydrosis (loss of sweating), not eye movement abnormalities. The actions of the superior oblique, the muscle innervated by the trochlear nerve, include intorsion, depression, and abduction. The abducens nerve mediates the lateral rectus muscle, which abducts the eye. The eye is depressed and abducted due to the unopposed actions of the superior oblique and lateral rectus muscles, which together move the eye downward and abduct it (see earlier discussion for the actions of these muscles). The other four muscles are innervated by the oculomotor nerve, which presumably has been damaged. This is an example of Weber's syndrome, or a lesion involving the third cranial nerve outflow tract, and the corticospinal and corticobulbar tracts in the cerebral peduncles of the midbrain. Weber's syndrome may occur as a result of an occlusion of the interpeduncular branches of the posterior cerebral artery (which supply this portion of the midbrain), a tumor pressing on this area, an aneurysm (circumscribed dilation of an artery) of the posterior communicating artery, or a plaque (lesion) related to multiple sclerosis. Fibers from the Edinger-Westphal nucleus are affected by lesions of the midbrain as well, and because they are instrumental in constricting the pupil, this lesion causes the patient to have a dilated pupil. If there is a mass that is external to the midbrain, but pressing on the oculomotor nerve, then the preganglionic parasympathetic fibers traveling to the ciliary ganglion, which, in turn, innervate the pupillary constrictor muscles, can be damaged, also causing a dilated pupil. Cervical sympathetic fibers cause pupillary dilatation, so damage to these fibers causes pupillary constriction (see Horner's syndrome, earlier). Involvement of the cerebral peduncle causes damage to the corticospinal and corticobulbar tracts, resulting in weakness of the contralateral face, arm, and leg. The motor deficit is contralateral because the corticospinal tracts cross in the medullary pyramids, below the level of the lesion. The upper portion of Mike's face was spared in this case (as well as in any other UMN lesion) because the face is innervated bilaterally until the level of the caudal pons, so a unilateral lesion results in sparing of this portion of the face. The combination of a third-nerve palsy and contralateral hemiparesis can only occur in the midbrain. The observed effects relating to cranial nerve III could not be accounted for by cortical damage. Likewise, damage to the cervical cord would not affect the third nerve.

The MRI of Susan's head revealed a pituitary microadenoma, a benign tumor arising from the anterior pituitary or adenohypophysis. This particular tumor consisted of cells that secrete the hormone prolactin, which is not only the stimulating factor for lactation, but inhibits menstruation when levels are high. It is common for this tumor's symptoms to be manifested during the child-bearing years. The visual problem is called bitemporal hemianopsia. Since the pituitary gland is in very close proximity to the optic chiasm, pituitary tumors often invade this structure. Since only the medial fibers (which perceive the temporal field of each eye) in each optic nerve cross, these are the fibers damaged by these tumors, and the patient will be unable to see either temporal visual field. Both the central scotoma (an island of visual loss surrounded by normal vision in one eye), which is usually seen with lesions of the retina or optic nerve, and the papilledema (blurring of the optic disc margin when viewed by fundoscopic examination due to increased intracranial pressure) would not be caused by damage to the optic chiasm. The optic chiasm can be compressed by pituitary tumors, causing bitemporal hemianopsia. The prolactin-releasing factor is found in the arcuate nucleus of the hypothalamus and activates the lactotropic cells of the anterior pituitary gland. Several different peptides, including dopamine, have the capacity to raise the level of prolactin in the blood. Specifically, the tuberoinfundibular dopaminergic system regulates prolactin secretion through direct projection to the pituitary. For this reason, a newer treatment for prolactin-secreting microadenomas is the drug bromocriptine, a dopamine agonist commonly used in the treatment of Parkinson's disease. By giving a dopamine agonist, serum prolactin increases, inhibiting production by the tumor cells, and eventually the tumor size shrinks. This has become either an alternative or first-line treatment prior to trying radiation or surgery.

An ataxic gait is an unsteady gait. Gaits due to motor weakness or spasticity tend to involve circling of the weak leg (circumduction); festinating or shuffling gaits, which are often due to parkinsonism or disease of the basal ganglia, involve a stooped posture with shuffling of the feet and very small steps. An ataxic gait may result from motor incoordination due to cerebellar disease, or from lack of proprioception in the lower extremities due to disease in the posterior column system (gait becomes unsteady when a patient is unable to detect the location of his or her feet). Degeneration of both systems may occur due to alcoholism, although in this case, we are told that John does not have any sensory deficits when this modality is tested in isolation. This is an example of alcoholic cerebellar degeneration. It is caused by degeneration (probably through nutritional deficiency) of neurons in the cerebellar cortex, particularly of the Purkinje cells, and is usually restricted to anterior and superior parts of the vermis, as well as anterior portions of the anterior lobes. For this reason, most of the deficits in this syndrome involve midline structures such as the trunk, which are represented most in the vermis. Trunk instability usually causes problems with gait. In addition, because the cerebellar homunculus represents the legs in the anterior portion of the anterior lobe, the legs are affected more than the arms. Loss of volume within the vermis of the cerebellum is readily visualized, especially on an MRI of the brain, because this technique allows good visualization of the posterior fossa. If these changes are visualized, then the condition is most likely chronic (as also indicated by the history) and most likely irreversible. However, it is important to make sure that the patient is well nourished, takes vitamins, and stops drinking in order to prevent other neurologic problems from occurring. Damage to other brain regions listed do not cause such damage. The spinocerebellum receives sensory inputs from the spinal cord and is instrumental in controlling posture and movement. It includes the vermis and the intermediate hemisphere. The cerebrocerebellum consists of the lateral hemispheres and is instrumental in the planning of movement. The dentate nucleus comprises the cell bodies that form the superior cerebellar peduncle. The brachium pontis corresponds to the middle cerebellar peduncle. The spinocerebellar cortical (Purkinje) cells project to the fastigial and interposed nuclei. Purkinje cells are found in the cerebellar cortex. None of the other choices are cells that are found in the cerebellum.

Damage to the trochlear nerve causes weakness of the superior oblique muscle, resulting in the inability of the orbit to deviate downward when the eye is intorted. To compensate for the classically vertical double vision, the patient tends to tilt his head to the contralateral side, causing the contralateral eye to intort. The trochlear nerve supplies the superior oblique muscle. The trochlear nerve is the only nerve to decussate peripherally, and also to emerge from the dorsal aspect of the brainstem. In this case, the damaged nerve emerged from the right (contralateral) dorsal midbrain. The action of the superior oblique muscle is to rotate the orbit medially and downward. Because the trochlear nerve is not only the smallest cranial nerve but also has the longest course of any cranial nerve, it is especially vulnerable to trauma. One of the most common causes of trochlear nerve palsy is trauma.

Damage to the trochlear nerve causes weakness of the superior oblique muscle, resulting in the inability of the orbit to deviate downward when the eye is intorted. To compensate for the classically vertical double vision, the patient tends to tilt his head to the contralateral side, causing the contralateral eye to intort. The trochlear nerve supplies the superior oblique muscle. The trochlear nerve is the only nerve to decussate peripherally, and also to emerge from the dorsal aspect of the brainstem. In this case, the damaged nerve emerged from the right (contralateral) dorsal midbrain. The action of the superior oblique muscle is to rotate the orbit medially and downward. Because the trochlear nerve is not only the smallest cranial nerve but also has the longest course of any cranial nerve, it is especially vulnerable to trauma. One of the most common causes of trochlear nerve palsy is trauma.

Damage to the trochlear nerve causes weakness of the superior oblique muscle, resulting in the inability of the orbit to deviate downward when the eye is intorted. To compensate for the classically vertical double vision, the patient tends to tilt his head to the contralateral side, causing the contralateral eye to intort. The trochlear nerve supplies the superior oblique muscle. The trochlear nerve is the only nerve to decussate peripherally, and also to emerge from the dorsal aspect of the brainstem. In this case, the damaged nerve emerged from the right (contralateral) dorsal midbrain. The action of the superior oblique muscle is to rotate the orbit medially and downward. Because the trochlear nerve is not only the smallest cranial nerve but also has the longest course of any cranial nerve, it is especially vulnerable to trauma. One of the most common causes of trochlear nerve palsy is trauma.

Glutamate has been implicated in ischemia-induced brain damage following brain trauma such as a stroke. It has also been shown that administration of NMDA-receptor antagonists following a stroke is effective in the treatment of stroke by reducing tissue infarction and neuronal cell death. The other choices listed in the question are not known to relate to the reversal of the deleterious effects of stroke. The NMDA-receptor antagonist is effective, in part, by decreasing disruption of the blood-brain barrier. It has been suggested that this becomes manifest by a blockade of the neuronal production of reactive oxygen species that occurs as a result of activation of NMDA receptors.

The cranial nerve that was directly affected was the glossopharyngeal nerve (cranial nerve IX). This is a mixed and complex nerve containing: (1) special visceral efferents from the nucleus ambiguus that supply the stylopharyngeus muscle (for elevation of pharynx in speech); (2) special visceral afferent fibers that transmit taste impulses from the posterior third of the tongue, general visceral afferent fibers associated with the inferior ganglion whose receptors lie in the carotid sinus that regulates cardiovascular functions; (3) general somatic afferents whose cell bodies lie in the superior ganglion of cranial nerve IX, and which mediate somatosensory information, including pain from the pharynx; and (4) general visceral efferent fibers that originate in the inferior salivatory nucleus, which are preganglionic and synapse in the otic ganglion. The postganglionic fiber from the otic ganglion innervates the parotid gland and mediates, in part, salivation. Thus, when this nerve is affected by an infectious agent, it results in the constellation of symptoms presented earlier in this case. Since the cell bodies of motor (or visceral motor) fibers (mediating motor and visceral effects) as well as the terminals of sensory afferents (mediating pain from the pharynx) lie in different regions of the medulla, it is very unlikely that such an effect could be the result of damage centrally. A much more likely occurrence is that the infectious agent produced disruption of the glossopharyngeal nerve peripherally, such as at the base of the skull or jugular foramen, where all the components run together and can be more easily affected.

Cranial nerve IX, the glossopharyngeal nerve, innervates the skeletal muscles of the pharynx. The motor component involved arises from the nucleus ambiguus of the medulla. This cranial nerve also contains afferents, a component of which arises from the superior ganglion. These sensory neurons convey somatosensory sensation, including pain afferents that ultimately synapse in the spinal trigeminal nucleus. The motor component of the glossopharyngeal nerve mediating swallowing and coughing constitutes a special visceral efferent (because it is derived from a visceral arch), and the sensory component conveying pain is referred to as a general somatic afferent fiber

Rigidity can occur by experimentally producing a decerebrate preparation (i.e., severing the brainstem at the level of the pons) and it appears clinically as well. In both situations, there has to be extensive destruction of brain tissue below the midbrain in the region of the pons, but which spares the medulla. In this way, the lateral vestibulospinal tract remains intact. This pathway powerfully facilitates extensor motor neurons and extensor reflexes, thus contributing significantly to the expression of decerebrate rigidity, in particular, when the descending inhibitory pathways, which arise from more rostral levels, are disrupted by the experimental procedure or stroke.