Dr Gawad Online MCQ Exam. Stretch Reflex, Umnl & Lmnl

A lower motor neuron lesion refers to damage or dysfunction of the motor neurons in the spinal cord or the nerves that extend from it to the muscles. This type of lesion typically affects a localized group of muscles, as the motor neurons innervate specific muscle groups. It does not affect muscles on the contralateral side because the motor neurons on each side of the spinal cord control muscles on the same side of the body. Additionally, a lower motor neuron lesion can lead to a decrease or absence of tendon jerk reflexes, rather than an exaggeration.

In vascular lesions of the internal capsule, the correct statement is that contralateral muscles are hypertonic. The internal capsule is a crucial pathway that carries motor fibers from the cerebral cortex to the spinal cord, controlling voluntary movements. When a vascular lesion occurs in this area, it can disrupt the motor pathway, leading to muscle abnormalities. In this case, the contralateral side of the body, opposite to the lesion, experiences increased muscle tone or hypertonicity. This is known as spasticity and is a common symptom of damage to the internal capsule.

The Golgi tendon organ is a sensory receptor located in the tendons that connect muscles to bones. It is responsible for detecting changes in muscle tension. When muscle tension increases, the Golgi tendon organ is stimulated and sends signals to the brain, which allows for the regulation and control of muscle contraction. Therefore, the correct answer is "Increase in muscle tension."

The correct answer is "the nuclear bag stimulation leads to dynamic stretch reflex." This is because the nuclear bag fibers are responsible for detecting changes in muscle length and initiating the stretch reflex. When these fibers are stimulated, they send signals to the spinal cord, which then activates the motor neurons to contract the muscle and prevent overstretching. The gamma neuron, on the other hand, is responsible for regulating the sensitivity of the muscle spindle, but it is not the center of the reflex. The statement about the nuclear chain afferent being of type II fibers only is incorrect, as both type I and type II fibers can be found in the nuclear chain.

A vascular lesion of the internal capsule can result in damage to the motor pathways, leading to various motor deficits. Hypotonia, or decreased muscle tone, may be present due to the disruption of signals from the brain to the muscles. Deep reflexes may also be absent because the lesion can affect the transmission of sensory information to the spinal cord. The absence of muscle wasting suggests that there is no degeneration or atrophy of the muscles, which further supports the possibility of a vascular lesion. Therefore, all of the given options may be found in a male patient with a vascular lesion of the internal capsule.

The correct answer is "both α- and γ-motor neurons are activated by descending stimulatory tracts." This means that a servo-assistant device activates both α- and γ-motor neurons through descending stimulatory tracts. α-motor neurons innervate extrafusal muscle fibers, which are responsible for generating force in muscles, while γ-motor neurons innervate intrafusal muscle fibers, which are involved in muscle spindle function. Activation of both types of motor neurons allows for precise control and coordination of muscle activity, which is essential for the functioning of a servo-assistant device.

The stretch reflex is a monosynaptic reflex that occurs when a muscle is stretched, causing a contraction to prevent overstretching. It does not involve after discharge, which is the continuation of neural activity after the stimulus has ended. It also does not involve irradiation, which is the spread of reflex activity to other muscles. However, it does involve reciprocal innervation, which is the simultaneous contraction of one muscle and relaxation of its antagonist. Therefore, the correct answer is "no reciprocal innervations."

The correct answer is "Gamma efferent neuron is considered as the efferent of stretch reflex." This statement is false because the efferent of the stretch reflex is actually the alpha motor neuron, not the gamma efferent neuron. The gamma efferent neuron is responsible for adjusting the sensitivity of the muscle spindle, but it is not directly involved in the stretch reflex itself.

UMNL stands for Upper Motor Neuron Lesion, while LMNL stands for Lower Motor Neuron Lesion. The given statement is true because if the lesion in the descending tracts is at the level of the spinal cord, the UMNL can be ipsilateral, meaning it affects the same side of the body. This is because the descending tracts in the spinal cord carry motor signals from the brain to the muscles, and if there is a lesion at the level of the spinal cord, it can disrupt the motor signals on the same side.