Dr Gawad Physiology Course (Stretch Reflex, Umnl & Lmnl) Online Exam

Gamma motor neuron activity affects muscle spindle sensitivity. Gamma motor neurons are a type of motor neuron that innervate the intrafusal fibers within muscle spindles. These intrafusal fibers are responsible for detecting changes in muscle length and relaying this information to the central nervous system. When gamma motor neurons are activated, they cause the intrafusal fibers to contract, increasing the sensitivity of the muscle spindle. This increased sensitivity allows for more precise control of muscle contraction and helps to maintain muscle tone. Therefore, the statement that gamma motor neuron activity affects muscle spindle sensitivity is true.

Primary fibers are indeed the afferent (sensory) component of both the muscle spindle and stretch reflex. The muscle spindle is a sensory receptor located within the muscle that detects changes in muscle length and sends signals to the central nervous system. The stretch reflex is a reflexive response that occurs when a muscle is stretched, and it involves the activation of the muscle spindle. Therefore, primary fibers play a crucial role in both the muscle spindle and stretch reflex.

Lower motor neuron lesions typically affect a localized group of muscles. This is because lower motor neurons are responsible for directly innervating and controlling specific muscles or muscle groups. When these neurons are damaged or disrupted, the muscles they innervate may experience weakness, atrophy, or paralysis, leading to a localized impact on motor function. In contrast, upper motor neuron lesions tend to affect muscles more diffusely and can result in more widespread motor deficits.

The Golgi tendon organ is a sensory receptor located in the tendons that connect muscles to bones. Its main stimulus is an increase in muscle tension. When muscle tension increases, the Golgi tendon organ detects this change and sends signals to the central nervous system. This mechanism helps to prevent excessive muscle contraction and potential damage to the muscle or tendon. Therefore, an increase in muscle tension is the correct answer as it accurately describes the main stimulus for Golgi tendon organ activation.

Gamma motor neurons do not directly initiate muscle contraction. Instead, they regulate the sensitivity of muscle spindles, which are sensory receptors located within muscles. By adjusting the tension in the muscle spindles, gamma motor neurons help to control the sensitivity and responsiveness of the muscle to changes in length. This allows for precise control of muscle contraction and helps to maintain muscle tone. Therefore, the statement that gamma motor neurons initiate contraction directly is false.

Vascular lesions in the internal capsule can result in contralateral hypertonicity of muscles. The internal capsule is a pathway that carries motor fibers from the brain to the spinal cord, and damage to this area can disrupt the signals sent to the muscles. As a result, the muscles on the opposite side of the body from the lesion may become excessively tense and rigid, leading to hypertonicity. This can cause difficulties with movement and coordination on the affected side of the body.

The correct answer is "the nuclear bag stimulation leads to dynamic stretch reflex." This is because the stretch reflex is a rapid and automatic response to a stretching stimulus in a muscle. The nuclear bag fibers are specialized muscle fibers that detect changes in muscle length and are responsible for initiating the dynamic stretch reflex. The gamma neuron, on the other hand, is responsible for regulating the sensitivity of the muscle spindle fibers, which are involved in the stretch reflex but not directly responsible for its initiation. The statement that the nuclear chain afferent is of type II fibers only is incorrect, as both type I and type II fibers can be found in the nuclear chain afferents.

The dynamic stretch reflex is important for rapid correction of position. This reflex allows the muscles to quickly respond and adjust to changes in position or movement, helping to maintain balance and stability. Unlike the static stretch reflex, which helps to maintain posture and muscle tone, the dynamic stretch reflex is specifically involved in rapid adjustments to prevent falls or maintain proper body alignment during movements.

The statement is true because the alpha motor neuron is indeed the center of the stretch reflex. The stretch reflex is a reflexive response to a sudden stretching of a muscle. When a muscle is stretched, sensory receptors called muscle spindles detect the change in muscle length and send signals to the spinal cord. The alpha motor neuron, located in the spinal cord, receives these signals and sends motor signals back to the muscle, causing it to contract and resist the stretching. Therefore, the alpha motor neuron plays a central role in the stretch reflex.

In a male patient with a vascular lesion of the internal capsule, it is unlikely to find muscle wasting. This is because the internal capsule is responsible for relaying motor signals from the brain to the muscles, and a lesion in this area may result in weakness or paralysis but not muscle wasting. Hypotonia, or decreased muscle tone, may be present due to the disruption of motor signals. Additionally, deep reflexes may be absent as a result of the lesion. Therefore, all of the above options may be found in this patient except for muscle wasting.

UMNL refers to upper motor neuron lesions, while LMNL refers to lower motor neuron lesions. The given answer states that UMNL may be ipsilateral if the lesion in the descending tracts is at the level of the spinal cord. This means that if the lesion occurs in the descending tracts of the spinal cord, the effects of the UMNL may be seen on the same side of the body as the lesion. This is because the descending tracts carry motor signals from the brain to the spinal cord, and if there is a lesion in these tracts, it can affect the motor function on the same side.

The correct answer is "all of the above". The term "servo-assistant device" refers to a mechanism that helps in the coordination and control of muscle movements. The increased activity of both primary and secondary afferent nerve endings from muscle spindle is essential for providing sensory feedback to the central nervous system. The absence of reciprocal innervation in positive supporting reaction ensures that the muscles involved in supporting the body weight are activated without any interference from opposing muscles. Finally, the activation of both α- and γ-motor neurons by descending stimulatory tracts is necessary for the precise control of muscle contraction and relaxation.

The statement is false because the gamma motor neuron is not the efferent of the stretch reflex. The efferent of the stretch reflex is the alpha motor neuron. The gamma motor neuron, on the other hand, is responsible for regulating the sensitivity of the muscle spindle, which is involved in the stretch reflex.

The stretch reflex is a monosynaptic reflex that involves the contraction of a muscle in response to its stretching. It is a rapid and automatic response that helps maintain posture and balance. After the initial contraction, there is no after discharge, meaning that the muscle quickly returns to its resting state. There is also no irradiation, which refers to the spread of the reflex response to other muscles. However, reciprocal innervation is a key component of the stretch reflex, where the muscle that is stretched is contracted while the antagonist muscle is inhibited. Therefore, the correct answer is "no reciprocal innervations."

The Jendrassik maneuver is a technique used to increase gamma sensitivity. It involves the patient interlocking their fingers and trying to pull them apart while a reflex test is being conducted. This maneuver activates the reticular formation in the brainstem, which in turn enhances the sensitivity of the gamma motor neurons. This increased sensitivity allows for a stronger contraction of muscle spindles, leading to a more pronounced reflex response. The crossed reticulospinal tract and Golgi botthel organ do not directly contribute to gamma sensitivity.

The correct answer is "Gamma efferent neuron is considered as the efferent of stretch reflex." This statement is false because the alpha efferent neuron is considered as the efferent of the stretch reflex, not the gamma efferent neuron. The gamma efferent neuron is responsible for regulating the sensitivity of the muscle spindle, which is involved in the stretch reflex.

The correct answer is "its action is mainly dependent on potassium and chloride ions." The inverse stretch reflex is a neural mechanism that helps to prevent excessive muscle contraction. It occurs when the muscle spindle, which detects changes in muscle length, sends signals to the spinal cord. These signals inhibit the alpha motor neurons that stimulate muscle contraction. The inhibitory effect is mainly dependent on the flow of potassium and chloride ions, which regulate the excitability of the alpha motor neurons. This allows for a controlled response to muscle length changes and prevents overstretching or damage to the muscle.