Nervous system - spinal level reflexes

Question 1

stretch reflex (myotatic)

Answer 1

stim = muscle stretch
arc = afferent 1a fiber from muscle spindle to alpha motor neurons projecting back to muscle of origin (monosynaptic)

• function for maintenance of muscle tone, support agonist muscle contraction, and provide feedback about muscle length.
• same stretch reflex stimulus inhibits the antagonist muscle = reciprocal inhibition

Question 2

inverse stretch reflex (myotatic)

Answer 2

stim = muscle contraction
arc = afferent 1b fiber from GTO via inhibitory interneuron to muscle of origin (polysynaptic)

-functions to provide agonist inhibition, diminution of force of agonist contraction, stretch protection reflex

Question 3

gamma reflex loop

Answer 3

• stretch relax forms part of this loop
• allows muscle tension to come under control of descending pathways (reticulospinal, vestibulospinal, and others)

-descending pathways excite gamma motor neurons, causing contraction of muscle spindle, and in turn increased stretch sensitivity and increased rate of firing from spindle afferents; impulses are then conveyed to alpha motor neurons

Question 4

Flexor (withdrawal) reflex

Answer 4

stim = cutaneous sensory stimuli
arc = cutaneous receptors via interneurons to largely flexor muscles; multisegment response involving groups of muscles (polysynaptic) 

-functions as a protective withdrawal mechanism to remove body part from harmful stimuli

Question 5

Crossed extension reflex

Answer 5

stim = noxious stimuli and reciprocal action of antagonists; flexors of one side are excited, causing extensors on the same side to be inhibited; opposite response occur in opposite limb

arc = cutaneous and muscle receptors diverging to many spinal cord motor neurons on same and opposite side (polysynaptic)

-also coordinates reciprocal limb activities such as gait.