Reflexes

Question 1

Describe the stretch reflex.

Answer 1

The stretch reflex is a protective and automatic response that helps maintain muscle length and posture. When a muscle is stretched, the muscle spindle detects the change and activates a monosynaptic reflex arc, leading to muscle contraction that resists the stretch. This reflex is critical for muscle tone regulation, injury prevention, posture maintenance and coordination of movement.

Question 2

Describe the reflex mediated by Golgi tendon organs.

Answer 2

The Golgi tendon reflex helps protect muscles and tendons from excessive force or tension by inducing muscle relaxation through autogenic inhibition. When the Golgi tendon organ detects excessive tension during muscle contraction, it sends a signal to the spinal cord, where it inhibits the alpha motor neurons innervating the muscle, reducing contraction and preventing injury. This reflex is essential for muscle safety, preventing overload, and maintaining proper muscle function during activities that involve heavy lifting or high levels of force.

Mechanism:
- Detection of Muscle Tension
- Sensory Signal to the Spinal Cord
- Inhibition of the Muscle (Autogenic Inhibition): In response to the detected tension, the Golgi tendon organ activates an inhibitory interneuron in the spinal cord. This interneuron then inhibits the activity of the alpha motor neurons that innervate the muscle. The alpha motor neurons are responsible for causing muscle contraction, so their inhibition leads to a reduction in muscle contraction.
- Relaxation of the Muscle: As the alpha motor neurons are inhibited, the muscle relaxes, reducing the tension on the tendon. This is known as autogenic inhibition, as the reflex causes the same muscle to relax and decrease the force it is exerting on the tendon, protecting the muscle from injury due to excessive tension.

Question 3

Explain the role of interneurones.

Answer 3

Interneurons are essential for processing, integrating, and modulating neural signals within the central nervous system. They allow the nervous system to perform complex tasks, such as reflex actions, movement coordination, sensory integration, and higher cognitive functions. By forming circuits that connect different neurons, interneurons play a central role in shaping behavior, regulating muscle function, and maintaining balance within neural networks.

Question 4

Describe ipsilateral and contralateral reflexes.

Answer 4

• Ipsilateral Reflex:
• Occurs on the same side of the body as the stimulus.
• Example: Patellar reflex, stretch reflex (e.g., knee-jerk), where the muscle contracts to resist stretching.
• Contralateral Reflex:
• Occurs on the opposite side of the body from the stimulus.
• Example: Crossed extensor reflex, where one leg withdraws from a painful stimulus and the other leg extends to help support the body.

Both reflex types are important for maintaining balance, posture, and protection from injury. Ipsilateral reflexes are crucial for simple, localized adjustments, while contralateral reflexes help with coordination and balance in more complex situations.

Question 5

Describe the flexor-withdrawal reflex.

Answer 5

• Steps in the Reflex Process:
• Noxious stimulus (e.g., stepping on a sharp object) activates pain receptors.
• Pain signals are sent via sensory neurons to the spinal cord.
• Sensory neurons synapse onto interneurons in the spinal cord.
• The interneurons send signals to motor neurons, activating the flexor muscles on the same side (ipsilateral flexion), causing the withdrawal of the limb.
• Simultaneously, interneurons stimulate extensor muscles on the opposite side (contralateral extension) to help maintain balance.
• The reflex occurs automatically, without input from the brain.

The flexor-withdrawal reflex is a rapid, automatic response to a noxious stimulus, causing the affected limb to withdraw from the source of pain. This reflex involves the activation of flexor muscles on the stimulated (ipsilateral) side and extension of the opposite (contralateral) limb to maintain balance. It is an essential protective reflex that operates at the spinal level to minimize injury and maintain coordination during sudden, potentially harmful events.

Question 6

Explain the roles of higher centres in reflexes

Answer 6

Higher centers in the brain play an essential role in modulating, facilitating, and inhibiting reflex responses. These centers include the cerebral cortex, brainstem, basal ganglia, and cerebellum. While reflexes are primarily spinal (automatic and rapid), higher centers allow the body to adjust these reflexes based on context, experience, and voluntary control. This allows for more adaptive, coordinated, and context-sensitive responses, ensuring that reflexes work in harmony with voluntary movements and helping maintain balance, posture, and motor control during complex tasks.