Question

Velocity Assessment.

Part A. Describe the pathway that the patellar reflex travels and explain why it is so fast .

Part B. Explain why the blink reflex (involuntary blinking elicited by touching the cornea) might be faster? Explain your reasoning.

Answer 1

Ans part 1

Patellar jerk reflex is an example of Monosynaptic stretch reflex.

Monosynaptic stretch reflex, or deep tendon reflex, is a reflex arc that provides direct communication between sensory and motor neurons innervating the muscle

A 'reflex arc' which is made up of 5 components:
Receptor – muscle spindle.
Afferent fibre – muscle spindle afferent.
Integration centre – lamina IX of spinal cord.
Efferent fibre – α-motoneurones.
Effector – muscle.

Patellar Reflex

Striking of the patellar tendon with a below the patella stretches the muscle spindle in the quadriceps muscle which carries signal to the spinal cord and synapses (without interneurons) at the level of L3 in the spinal cord.

From there, an alpha motor neuron conducts an efferent impulse back to the quadriceps femoris muscle, triggering contraction which is coordinated with the relaxation of the antagonistic flexor hamstring muscle which causes the leg to kick.

Spinal control of the stretch reflex means the signal returns to the muscle from the same spinal cord segment as where it entered the spinal cord. This is the shortest distance for a reflex signal to travel, thus creating a fast response.

Ans Part 2 --

Corneal reflex or blink reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea.

Stimulation should elicit both a direct and consensual response (response of the opposite eye).

The reflex is mediated by:

Afferent Nerve --- Nasociliary branch of the ophthalmic branch (V1) of the trigeminal nerve.

Efferent Nerve ---- temporal and zygomatic branches of the facial nerve (CN VII)

Center is located in the pons of the brainstem.

This is a Protective reflex and its purpose is to protect the eyes from foreign bodies, thats why it is very fast.