spinal reflexes

Question 1

central pattern generators

Answer 1

rythmic movements generators

coordinate these movements to free motor cortex

Question 2

alpha motor neurons

Answer 2

intervate extrafusal muscle fibers, generate force

Question 3

gamma motor neurons

Answer 3

intrafusal muscle fibers - components of muscle spindles
don’t generate force
co-activated with alpha-motor neuron
control how sensitive spindle is to stretch by directly altering the length of the intrafusal fibers and altering tension

Question 4

muscle spindles

Answer 4

muscle stretch receptors that monitor absolute and rate of change muscle length
contribute to kinesthesia, locomotion, and muscle tone
located deep in muscle belly
nuclear chain and bag fibers (2:1 ratio)
innervated by group 1a and 2 afferents
efferent innervation by gamma motor neurons

Question 5

kinesthesia

Answer 5

sense of position and movement of limbs

Question 6

locomotion

Answer 6

feedback to CNS on muscle length to help CNS correct movement errors

Question 7

muscle tone

Answer 7

degree to which muscle resists passive lengthening

Question 8

group 1a afferents

Answer 8

primary endings
innervate both chain and bag fibers
sensitive to onset of muscle stretch by discharge slowly with maintained stretch
->steady state muscle length and velocity of length change

Question 9

group 2 afferents

Answer 9

secondary endings
nuclear chain only
sensitive to absolute length

Question 10

alpha gamma coactivation

Answer 10

prevents loss of information when alpha motor neurons cause contraction of extrafusal muscles, gamma-motor neurons cause simultaneous contraction so that tension on the intrafusal fibers is maintained and info reaches the CNS

Question 11

golgi tendon organ

Answer 11

monitor tension in a muscle at jcn of muscle and tendon
tension depends on length, load, degree of muscle fatigue
innervated by 1 group ab afferent axon that is unmyelinated in the golgi tenon organ
are in series with extrafusal fibers and tension increases when muscle contracts
no activation during passive stretch

Question 12

large afferent fiber neuropathy

Answer 12

gait impairment and gross errors in positioning and force esp in fine movements

Question 13

spinal reflexes

Answer 13

reflex arc

fast, automatic, stereotyped

Question 14

stretch reflexes

Answer 14

automatic contractions of a muscle in response to passive lengthening of the same muscle
myotatic reflex-
1. autogenic excitation - monosynaptic connectiong from group 1a afferents cause homonymous muscle contractions
2. synergistic activation - group 1a from primary muscle excites alpha-motor neurons of synergistic muscles causing contraction
3. reciprocal innervation - inhibitory spinal cord interneurons cause inhibition of alpha-motor neurons to antagonistic m.

Question 15

clinical stretch reflexes

Answer 15

knee jerk reflex
tells us that afferent fibers, synaptic input to the motor neurons, motors neurons, neuromuscular junction, muscles themselves all work
others: biceps, brachioradialis, tricpes, ankle jerk

Question 16

spinal local circuits

Answer 16

negative feedback control loops - return a variable to set-point or dampen oscillations in a perturbed system

a. recurrent inhibition - renshaw cells are inhibitory interneurons that use glycine, whenever motor neuron is excited, it excites inhibitory renshaw cell decreasing motor neuron activity, stabilizes firing rate, excitability of cells regulated by descending pathways
b. reciprocal inhibiion - relax antagonistic muscles during movements - enhance speed and efficiency
c. co-contraction - contract prime move and antagonist for fine control, precision, joint stabilization

Question 17

clostridium tetani

Answer 17

inhibits release of glycine by renshaw cells by the tetanus toxin produced by the bacteria
increase in muscle tension and rigidity

Question 18

strychnine

Answer 18

acts on renshaw cells ability to control alpha-motor neuron by binding to glycine receptor
tetanic contractions

Question 19

tendon reflex

Answer 19

inverse myotatic reflex or golgi tendon reflex
contraction of extrafusal muscle fibers increase tension in golgi tendon organ
group 1b afferents synapse on inhibitory interneurons in spinal cord that innervate contracting homonymous m. - autogenic inhibition
also have excitation of antagonistic m.
reduce tension, contribute to fine adjustments

Question 20

flexion reflex- spinal pathway

Answer 20

crossed-extension reflex
input causes excitatory spinal interneurons that innervate flexors in inpsilateral limb to activation
inhibits antagonistic extensor muscles in that limb
commissural interneuorns on contralateral side extend

Question 21

flexor-withdrawal reflex

Answer 21

nociceptive stimulus causes reflex withdrawalof affected limb away from stimulus
local sign- strength of stimulus = strength of response