NETTER - Neuroscience Flash Cards

Spinal Somatic Reflex Pathways
Type of Reflex Responses
1. Afferent inhibition
2. Muscle stretch reflex
3. Recurrent inhibition
4. Golgi tendon organ reflex
5. Flexor reflex withdrawal reflex
6. Renshaw cell bias
Comment: Somatic spinal cord reflexes consist of a sensory input,
a motor output, and possible intermediate neurons in the spinal
cord. The muscle stretch reflex involves stimulation of Ia afferents
from the muscle spindles responding to stretch of the homonymous
muscle, synapsing on corresponding lower motor neurons (LMNs) to
elicit contraction of the muscle whose tendon has been stretched.
This reflex is the most commonly tested reflex in neurology. Ia
afferents from flexor or extensor muscles can reciprocally inhibit the
activity in their counterpart, called reciprocal or afferent inhibition.
The Golgi tendon organ reflex is a disynaptic reflex stimulated
by high threshold stretch of a tendon, leading to inhibition of the
homonymous LMN pool to muscle and excitation of the antagonist
LMN pool. This reflex is observable in patients with a pathological
condition such as spasticity. The flexor reflex withdrawal response
is a polysynaptic reflex elicited from sensory activation (particularly
noxious stimuli) that results in appropriate reflex withdrawal of the
body part from potential harm also accompanied by reciprocal
inhibition. Renshaw cells provide a mechanism for controlling LMN
excitability by inhibiting an LMN that has just been excited by a
reflex activation or activation from a descending pathway. The
Renshaw cell receives input from axon collaterals of both flexor and
extensor LMNs, and in turn exerts an inhibitory bias toward extensor
LMNs with a reciprocal excitation of flexor LMNs. This system
favors flexor movements and helps to inhibit extensor movements,
especially powerful antigravity muscle activity.
Regional Neuroscience See book 10.8