Author Question: Sometimes, when it is difficult to initiate a knee-jerk reflex by tapping the patellar tendon, a ... (Read 30 times)

AEWBW · **on:** Feb 28, 2019

Sometimes, when it is difficult to initiate a knee-jerk reflex by tapping the patellar tendon, a patient will be asked to voluntarily make a fist. Then the reflex will be easily evoked. What does this illustrate about the relation between voluntary and involuntary reflex movement?

Question 2

What is a reflex arc? What components must be present to qualify?

Missbam101 · **Reply #1 on:** Feb 28, 2019

Answer to Question 1

Descending motor tracts that excite the motor neurons that activate forearm and hand muscles also send excitatory impulses to motor neurons lower down the spinal cord. These EPSPs spatially summate with the excitatory inputs from the muscle spindles to quadriceps motor neurons, bringing the quadriceps neurons to threshold, and thus generate a brisk knee-jerk response.

Answer to Question 2

A reflex arc is the wiring pattern of neurons that underlie a particular reflex. A reflex arc consists of three elements at the minimum: (1 ) a sensory receptor and neuron to carry afferent information to the CNS; (2 ) an excitatory synapse on a motor neuron; (3 ) the motor neuron to generate an action potential and conduct the impulse to an effector such as a skeletal muscle motor unit.