Spinal Reflexes 2

Question 1

Describe the myotactic reflex

Answer 1

The myotatic reflex (stretch reflex) is a tonic contraction of muscle groups in response to a stretching force.

• A myotatic reflex is a monosynaptic reflex
• Afferent Limb: Ia fiber (from muscle spindle)
• Efferent Limb: Alpha motor neuron

Question 2

explain the modulation of the stretch reflex

Answer 2

The stretch reflex constitutes a feedback loop that maintains muscle length and hence dictates posture.

• Descending motor pathways (e.g., corticospinal) comprising upper motor neurons can regulate muscle tone and hence posture by influencing components of the reflex arc.

• Two major modulatory factors in relation to stretch reflexes are: - Descending Fibers
- Gamma motor neurons

Reflex responses mediated via the motor cortex and other surpaspinal structures are termed long-loop reflexes

Input from descending fibers are able to modify the properties of spinal reflexes