Motor Neuron Quiz

Paraplegia is the most specific term that identifies the clinical picture described in the question. Paraplegia refers to paralysis of both lower extremities, which matches the examination findings of the 47-year-old man who was involved in an automobile collision. This term specifically indicates the loss of motor function in the lower limbs while the upper limbs remain unaffected. Alternating hemiplegia refers to episodes of paralysis that alternate between the left and right sides of the body, hemiplegia refers to paralysis on one side of the body, monoplegia refers to paralysis of a single limb, and quadriplegia refers to paralysis of all four limbs.

Hyporeflexia is characteristic of lower motor neuron damage. Lower motor neurons are responsible for transmitting signals from the spinal cord to the muscles, and damage to these neurons can result in decreased or absent reflexes. Hyperreflexia, increased tone, and spastic paralysis are more commonly associated with upper motor neuron damage. Increased muscle mass is not a characteristic of lower motor neuron damage.

The fibers that fan out from the internal capsule into the white matter of the hemisphere are represented by the Corona Radiata.

Damage to the corticospinal fibers in the medulla would most likely explain the sudden onset of weakness in the left upper and lower extremities. The corticospinal tract is responsible for voluntary motor control, and it carries signals from the motor cortex to the spinal cord. Damage to this tract would result in a loss of motor function on the opposite side of the body, as the fibers decussate (cross over) in the medulla. Therefore, in this case, the weakness in the left upper and lower extremities is likely due to damage to the corticospinal fibers on the right side of the medulla.

Dysmetria is the correct answer because it refers to the difficulty in controlling the distance, direction, and speed of movements. This can result in overshooting or undershooting a target, as seen in the example of the elderly neighbor struggling to pick up the newspaper and grasp the brandy glass accurately. Akinesia refers to the absence or reduction of voluntary muscle movements, dysdiadochokinesia refers to the inability to perform rapid alternating movements, bradykinesia refers to slowness of movement, and dysphagia refers to difficulty in swallowing.

The woman is displaying upper limb flexion and lower limb extension. Lesions rostral to the red nucleus can result in decerebrate rigidity, which is characterized by stiff extension of the upper limbs and extension of the lower limbs. This is due to disruption of the descending pathways that normally inhibit the extensor muscles and facilitate flexor muscles.

The pyramidal decussation is the point at which the fibers of the corticospinal tract cross over from one side of the brain to the opposite side of the spinal cord. Bilateral weakness of the lower limbs suggests a lesion affecting both sides of the corticospinal tract. Since the lesion is caudal to the pyramidal decussation, it is likely affecting the fibers after they have crossed over, leading to weakness in both lower limbs.

The cell bodies of lower motor neurons innervating the lower limb are located in Lamina VIII, IX. This is indicated by the fact that the patient is unable to move her left leg, suggesting a problem with the lower motor neurons responsible for controlling movement in that limb. The sensory modalities in all of her limbs are retained, indicating that the issue is specific to the motor neurons and not the sensory neurons. Additionally, there is no sign of weakness in her other limbs, further supporting the idea that the problem is localized to the lower limb.

The given scenario describes a patient with weakness of the right lower extremity and loss of pain and thermal sensations on the left side starting at the level of the umbilicus. This pattern of symptoms suggests a lesion on the right side of the spinal cord. The lateral corticospinal tract is responsible for motor control of the contralateral side of the body, meaning that damage to the right lateral corticospinal tract would result in weakness of the right lower extremity. Therefore, the weakness in this man is likely due to damage to the right lateral corticospinal tract.

The most likely location of the lesion in this case is the caudal part of the pyramidal decussation. This is because the patient has bilateral weakness of his lower extremities, indicating a problem with the corticospinal tract. The pyramidal decussation is where the corticospinal fibers cross over from one side of the brain to the opposite side of the spinal cord. Lesions in this area would result in bilateral weakness of the lower extremities, which matches the patient's symptoms. The other options do not explain the bilateral weakness seen in the patient.

The patient's symptoms of weakness, sensory loss, and visual deficit on the left side of the body indicate a lesion on the right side of the brain. The anterior choroidal artery supplies blood to the internal capsule, which contains the corticospinal fibers responsible for motor control. Damage to the corticospinal fibers on the right side would result in weakness on the left side of the body, known as contralateral hemiplegia. Therefore, the weakness in this woman is most likely due to damage to the corticospinal fibers on the right side.

When tapping the patellar tendon, the resulting knee jerk reflex is within a normal range. The sensory organ that is activated in response to this stimulus is the muscle spindle. The muscle spindle is a proprioceptor located within the muscle that detects changes in muscle length and rate of change, allowing for the body to maintain balance and coordination. In this case, the muscle spindle is activated by the stretch of the patellar tendon, leading to the reflexive contraction of the quadriceps muscle and extension of the leg.

The patient's symptoms of slurred speech and right-sided weakness are consistent with a lacunar infarction, which is a small stroke caused by blockage of a small blood vessel in the brain. The specific localization of the infarction is suggested to be in the left genu of the internal capsule. The internal capsule is a white matter tract that contains fibers responsible for motor function. Damage to the left genu of the internal capsule can result in weakness on the opposite side of the body, which is consistent with the patient's right-sided weakness.

The correct answer is Anterolateral area (area of anterolateral system). The extension of the patient's extremities indicates a dominant input to extensor motor neurons through reticulospinal fibers/tracts. The anterolateral area of the spinal cord is responsible for transmitting pain and temperature sensations, as well as controlling involuntary motor movements. In this case, the activation of the reticulospinal fibers in the anterolateral area is causing the extension of the patient's extremities.

Fracture to the vertebral column at the T8 level on the right side would most likely result in damage to the spinal cord at that level. The spinal cord is located within the vertebral column and is responsible for transmitting sensory and motor signals between the brain and the rest of the body. Damage to the spinal cord can lead to loss of sensation and motor function below the level of the injury. In this case, the fracture at T8 on the right side suggests that the spinal cord at that level is most likely affected, resulting in potential loss of function on the right side of the body below that level.

A lesion located in the immediate vicinity of the lateral corticospinal tract would most likely involve the Rubrospinal tract. The Rubrospinal tract is located adjacent to the lateral corticospinal tract in the spinal cord. Both tracts are involved in motor function, with the lateral corticospinal tract primarily responsible for fine motor control and the Rubrospinal tract involved in controlling muscle tone and limb flexion. Therefore, a lesion in this area would likely affect motor function and muscle control.

Damage to the efferent portion of the muscle spindle would involve Ay fibers. The muscle spindle is responsible for providing proprioceptive information about muscle length and tension. The efferent fibers of the muscle spindle, specifically the Ay fibers, transmit signals from the central nervous system to the muscle spindle, allowing for modulation of its sensitivity and function. Therefore, damage to the efferent portion of the muscle spindle would affect the Ay fibers.

The correct answer is "Decerebrate; Medial reticulospinal and lateral vestibulospinal tract". Decerebrate rigidity is characterized by extension of the upper and lower limbs. It is caused by damage to the brainstem, specifically the midbrain. In decerebrate rigidity, the lesion affects the rubrospinal tract, which is responsible for flexor tone, as well as the medial reticulospinal and lateral vestibulospinal tracts, which are responsible for extensor tone. This leads to unopposed extensor tone in the limbs, resulting in the characteristic rigid extension seen in decerebrate rigidity.

The combination of difficulty speaking, deviation of the tongue to the right, and elevation of the soft palate and uvula to the left suggests a lesion in the left side of the brain. The genu of the internal capsule is a structure in the brain that contains motor fibers responsible for controlling movement of the tongue and soft palate. A lesion in the genu of the internal capsule on the left side would result in weakness or paralysis of the muscles on the right side of the body, including the tongue and soft palate, leading to the observed symptoms.

The given symptoms of deviation of the uvula to the left on phonation, deviation of the tongue to the right on the protrusion, and weakness of the facial muscles around the mouth on the right suggest a lesion in the left hypoglossal nerve (CN XII) and right facial nerve (CN VII). These cranial nerves are responsible for the movement of the tongue and facial muscles. Since the hypoglossal nerve also innervates the muscles responsible for turning the head to the opposite side, the most likely additional symptom would be an inability to turn his head to the left against resistance.