Physiology Quiz (Reflexes -- Sleep)

Clonus refers to a rhythmic, involuntary muscle contraction and relaxation that occurs due to the hyperexcitability of the stretch reflex. It is commonly observed in upper motor neuron lesions (UMNLs), which are conditions that affect the motor pathways in the central nervous system. UMNLs can result from various causes such as stroke, spinal cord injury, or multiple sclerosis. Therefore, the statement "Clonus is a sign of UMNLs" is true, as clonus is often associated with these conditions.

The clasp-knife sign is not observed in LMNLs. The clasp-knife phenomenon refers to the resistance encountered when attempting to passively extend a joint, which is commonly seen in upper motor neuron lesions (UMNLs). In LMNLs, such as peripheral nerve injuries, there is typically a decrease in resistance during passive movement, known as the "clasp-knife effect." Therefore, the correct answer is false.

The parieto-occipital cortex shows remarkably alpha waves. Alpha waves are a type of brainwave that occurs when a person is awake but in a relaxed state with their eyes closed. They are typically associated with a calm and relaxed mental state, and can be observed during meditation or when a person is daydreaming. Alpha waves are characterized by a frequency range of 8-12 Hz and are often seen in the parieto-occipital region of the brain, which is involved in visual processing and spatial awareness.

The stretch reflex is a rapid and involuntary response to a sudden stretching of a muscle. It involves a sensory receptor called a muscle spindle that detects the stretch and sends a signal to the spinal cord. The short latent period refers to the quick response time between the stretch stimulus and the activation of the motor neurons in the spinal cord, resulting in a rapid muscle contraction. This property allows for a fast and automatic adjustment of muscle length, helping to maintain posture and balance.

Thiopental is a barbiturate that is commonly used as an anesthetic. Unlike the other options listed, thiopental does not increase the activity of the Renin-Angiotensin System (RAS). Adrenaline, caffeine, and thyroid hormone have all been shown to stimulate RAS activity. Adrenaline activates the release of renin, an enzyme that plays a key role in RAS. Caffeine inhibits the breakdown of cyclic adenosine monophosphate (cAMP), leading to increased renin release. Thyroid hormone enhances the production and release of renin as well. Therefore, thiopental is the exception as it does not have any effect on RAS activity.

Irradiation refers to the phenomenon where a stimulus of greater intensity can spread and evoke a response in neighboring areas. In the context of reflexes, it means that a stronger stimulus can cause a response not only in the specific area it was applied to, but also in adjacent areas. This property allows for a wider distribution of the reflex response and is related to the relationship between the intensity of the stimuli and the degree of response.

The sucking reflex from the breast in newly born infants is not classified as a conditioned reflex. It is actually classified as an innate or natural reflex. This reflex is present in infants from birth and does not require any prior conditioning or learning. It is a natural instinct that helps infants obtain nourishment from their mothers. Therefore, the correct answer is false.

Brown-Sequard syndrome is a neurological condition caused by damage to one side of the spinal cord. It typically presents with paralysis of voluntary movement on the same side below the level of the lesion, as well as loss of fine touch sensation on the same side below the level of the lesion. Additionally, there is hyperesthesia (increased sensitivity to stimuli) on one segment on the same side above the level of the lesion. However, it is not true that there is a loss of pain sensation on the opposite side at the level of the lesion.

Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness and sudden attacks of sleep. Orexin, also known as hypocretin, is a neuropeptide that regulates wakefulness and arousal. A deficiency of orexin is believed to be the primary cause of narcolepsy. This deficiency can be caused by the destruction of orexin-producing cells in the brain, leading to disrupted sleep-wake cycles and uncontrollable sleep attacks. Therefore, the correct answer is orexin.

The correct answer is "They carry sensory innervation from the central non-contractile part of the nuclear chain." Annulospiral fibers are a type of sensory nerve fibers found in muscle spindles. They are responsible for conveying information about muscle length and changes in muscle length to the central nervous system. The central non-contractile part of the nuclear chain is where the annulospiral fibers are located, and they transmit sensory information from this region.

The statement is false. The stage of spinal shock after complete cord transection is not due to the sudden withdrawal of inhibitory tonic discharge from the brain. Instead, it is caused by the temporary loss of all neurological activity below the level of the injury. This loss of activity leads to a temporary loss of reflexes, muscle tone, and sensation.

The locus ceruleus is a small nucleus in the brainstem that plays a crucial role in regulating arousal, attention, and stress response. It is known to secrete noradrenaline, a neurotransmitter that is involved in various physiological processes, including the "fight or flight" response. Noradrenaline helps to increase heart rate, blood pressure, and alertness, preparing the body for action. It also plays a role in mood regulation and is implicated in conditions such as anxiety and depression. Therefore, it is the correct answer in this case.

Orexin is not an inducer of sleep. It is actually a neuropeptide that promotes wakefulness and regulates arousal. Galanin, melatonin, and adenosine are all substances that play a role in promoting sleep. Galanin is a neurotransmitter that helps regulate sleep-wake cycles, melatonin is a hormone that helps regulate the sleep-wake cycle, and adenosine is a chemical that builds up in the brain during wakefulness and promotes sleep.

Ib fibers are responsible for transmitting sensory impulses from the muscle tendon. These impulses provide information about the tension or stretch in the muscle, allowing the body to monitor and regulate muscle contraction. By detecting changes in muscle tension, the Ib fibers play a crucial role in protecting the muscle from damage by initiating reflexes that inhibit excessive muscle contraction.

The lateral reticulospinal tract inhibits the activity of gamma-motor neurons. Gamma-motor neurons are responsible for controlling the sensitivity of muscle spindles, which are sensory receptors in muscles. By inhibiting these neurons, the lateral reticulospinal tract reduces the sensitivity of muscle spindles, leading to a decrease in muscle tone and reflex activity. This allows for more precise control of voluntary movements and prevents unwanted muscle contractions.

The statement "sensory impulses are carried by flower spray Ia fibres" is not true. Sensory impulses in the static stretch reflex are actually carried by the type Ia afferent fibers, not flower spray Ia fibers. The type Ia afferent fibers are responsible for relaying sensory information from the muscle spindle receptors to the central nervous system. Flower spray Ia fibers do not exist and are not involved in the static stretch reflex. The other statements in the question are true, such as the receptor being located in the nuclear chain fibers, alpha motor neurons in the ventral horn being the center, the reflex being implemented by the contraction of extrafusal fibers, and it maintaining muscle tone.

The question is asking for the property that is not shown by the initiated reflex when applied to an injurious cutaneous stimulus. The properties listed in the options are irradiation, reciprocal innervation, poly-synaptic central delay, and after discharge. The correct answer is "none of the above," which means that all of the listed properties are exhibited by the initiated reflex. Therefore, the initiated reflex may show all of these properties when applied to an injurious cutaneous stimulus.

Caffeine is a competitive antagonist of adenosine. Adenosine is a neurotransmitter that promotes sleep and relaxation by binding to adenosine receptors in the brain. Caffeine, on the other hand, blocks these receptors and prevents adenosine from binding to them. This leads to increased alertness and wakefulness, as caffeine stimulates the central nervous system and inhibits the effects of adenosine.

Interneurons are responsible for transmitting signals between sensory and motor neurons, allowing for the coordination of reflex actions. Reciprocal innervation refers to the simultaneous contraction of one muscle and the relaxation of its antagonist, which is facilitated by interneurons. Recruitment refers to the activation of additional motor units to increase the strength of a muscle contraction, which is also mediated by interneurons. After-discharge refers to the continued firing of neurons after the initial stimulus has ceased, and interneurons are involved in this process as well. Irradiation refers to the spread of a reflex response to adjacent muscles, and interneurons facilitate this as well. Therefore, all of the reflex properties mentioned are influenced by interneurons, except for D.

The Jendrassik maneuver is a technique used to enhance reflex responses. It involves the patient clenching their teeth and interlocking their fingers while attempting to pull them apart. This maneuver is found to stimulate gamma-motor neurons in the spinal cord. Irradiation refers to the spread of excitation from the stimulated neurons to nearby neurons, leading to a stronger and more widespread response. Therefore, the action of Jendrassik maneuver stimulating gamma-motor neurons can be explained by the reflex property of irradiation.

UMNLs, or upper motor neuron lesions, are characterized by certain manifestations. Spastic ipsilateral paralysis refers to muscle weakness and stiffness on the same side of the body as the lesion, which is consistent with UMNLs. Exaggeration of the abdominal reflex, hypertonia (increased muscle tone), and a positive Babinski sign (toes flex upward when the sole of the foot is stimulated) are also manifestations consistent with UMNLs. However, rapid dis-use atrophy, which is the wasting away of muscles due to lack of use, is not typically associated with UMNLs. Therefore, it is not a manifestation consistent with UMNLs.

The pathway of the stretch reflex may contain inhibitory interneurons. These interneurons play a crucial role in regulating the reflex response by inhibiting the activity of certain motor neurons. This inhibition helps to prevent excessive muscle contraction and maintain balance and coordination. By inhibiting the opposing muscles, the inhibitory interneurons help to fine-tune and control the stretch reflex.