Question

In a paragraph describe the neural circuitry responsible for the “deep
tendon reflex” -- a reflexive movement of a limb elicited by briefly striking a
tendon (e.g., the patellar tendon)

Answer 1

Deep tendon reflex is an example of stretch reflex. Stretch reflex refers to the reflex contraction of a muscle that is stretched. It is a type of monosynaptic reflex. Stretch reflex is the quickest of all the reflexes. the time taken for the reflex activity to traverse the spinal cord in stretch reflex is only 0.6 to 0.9 seconds. It is well developed in antigravity muscles such as extensor group of muscles of legs and flexor group of muscles of arm.

Neural circuitry:-

1. Afferent limb consists of receptor and afferent nerve. Receptor is muscle spindle. It detects the degree and rate of muscle stretch. Afferent nerve is the nerve supply of muscle spindle. Two types of fibres supply muscle spindle-Ia and II fibres. The nerve fibres emerging from the muscle spindle travel along the spinal nerve and enter the spinal cord through the dorsal root and send branches to every alpha motor neuron that goes to the muscle from which Ia originated.
2. Centre for stretch reflex is ventral gray Horn area of spinal cord, where the afferent nerve ends and synapses directly with Alpha motor neuron. does Alpha motor neurone is the final common pathway serving as both integrating centre and efferent pathway.
3. Efferent limb consists of efferent Nerve and effector organ. The axons of Alpha motor neurons form the efferent nerve fibres which leave the spinal cord through the ventral root and supply the skeletal muscle fibres. Effector organs are both extension and flexion muscles. there occurs a reciprocal inhibition of the antagonist muscle.