Question

Physics/Neuroscience

Using complete sentences and proper vocabulary, describe (in your own words) how neural circuit for knee-jerk reflex works

Answer 1

Neurons never function in isolation; they are organized into ensembles or circuits that process specific kinds of information. Although the arrangement of neural circuits varies greatly according to the intended function, some features are characteristic of all such ensembles.

Neural circuits are both anatomical and functional entities. A simple example is the circuit that subserves the myotatic (or “knee-jerk”) spinal reflex. The afferent limb of the reflex is sensory neurons of the dorsalroot ganglion in the periphery. These afferents target neurons in the spinal cord. The efferent limb comprises motorneurons in the ventral horn of the spinal cord with different peripheral targets: One efferent group projects to flexor muscles in the limb, and the other to extensor muscles. The third element of this circuit is interneurons in the ventral horn of the spinal cord. The interneurons receive synaptic contacts from the sensory afferent neurons and make synapses on the efferent motor neurons that project to the flexor muscles. The synaptic connections between the sensory afferents and the extensor efferents are excitatory, causing the extensor muscles to contract; conversely, the interneurons activated by the afferents are inhibitory, and their activation by the afferents diminishes electrical activity in motor neurons and causes the flexor muscles to become less active. The result is a complementary activation and inactivation of the synergist and antagonist muscles that control the position of the leg.

_In Simple Words

A simple reflex circuit, the knee-jerk response (more formally, the myotatic reflex), illustrates several points about the functional organization of neural circuits. Stimulation of peripheral sensors (a muscle stretch receptor in this case) initiates receptor potentials that trigger action potentials that travel centrally along the afferent axons of the sensory neurons. This information stimulates spinal motor neurons by means of synaptic contacts. The action potentials triggered by the synaptic potential in motor neurons travel peripherally in efferent axons, giving rise to muscle contraction and a behavioral response. One of the purposes of this particular reflex is to help maintain an upright posture in the face of unexpected changes.

Have a look at the reference diafram.