2-Spinal Reflexes

Question 1

alpha motor neurons

Answer 1

largest nerve cell bodies in ventral horn of spinal cord > axons end on skeletal muscle fibers

Question 2

gamma motor neurons

Answer 2

smaller nerve cell bodies in ventral horn of spinal cord > axons end on polar contractile region of intrafusal fibers enclosed in muscle spindles

Question 3

reflex

definition

Answer 3

simple response to a specific sensory stimulus
-involuntary
-instantaneous
-protective
-confined to spinal cord so nonconscious

Question 4

reflex arc components

Answer 4

1. receptor @ skin, skeletal muscle, tendon, joint capsule
2. afferent/sensory limb - sensory neuron with cell body in DRG
3. interneuron @ gray matter but not always with reflexes
4. efferent/motor limb- cell body @ ventral horn
5. effector - skeletal muscle

Question 5

extrafusal fibers
have what neurons

Answer 5

alpha motor neurons for motor + pseudouni for sensory

Question 6

intrafusal fibers

Answer 6

nuclear bag- gamma motor + Ia mainly annulospiral sensory + II for flower spray sensory

nuclear chain- gamma motor + Ia annulospiral sensory + II main flower spray sensory

Question 7

muscle stretch reflex

Answer 7

includes 2 neurons (sensory + motor)

elicited by tapping on tendon

Question 8

patellar tendon reflex

Answer 8

aka quadriceps stretch reflex

1. tap patellar tendon = patella moves
2. stretch extrafusal fibers
3. stretch muscle spindles = act receptors in spindles
4. stimulate annulospiral Ia endings to fire
5. Ia fibers stim alpha motors to quads
6. quad contracts = leg extends to compensate muscle stretch

protect from overstretching

Question 9

reciprocal inhibition

patellar tendon reflex

Answer 9

bc central process of sensory neurons bifurcate
-one stims alpha to contract quads
-other stims inhibitory interneuron to inhib another alpha to hamstrings so not stim flexors and extensors at same time

if both stim then no movement

Question 10

autogenic inhibition

patellar tendon reflex

Answer 10

golgi tendon organs act when quad contract and tension on tendon so stretches
-Ib fiber of sensory peripheral process is GTO inn tendon gets act the central process stims inhib interneuron to inhib alpha of quad

GTOs fine tune skeletal muscle contractile force during motor activity

Question 11

flexor reflex

aka withdrawal, nociceptive

Answer 11

receptor cutaneous so either lightly myelinated A delta fibers OR unmye C fibers of pseudouni (cell body in DRG)

1. excitatory interneurons stim alpha to flex hamstrings to contract and flex leg away
2. inhibitory interneurons inhib alpha of extensors

Question 12

crossed extension reflex

Answer 12

with flexor reflex
-will occur in other limb/contralateral so weight of body shifted to it
-engages commissural interneurons so axons cross midline to oppo side spinal cord and synapse with other excit/inhib interneurons

excitatory = alpha > contract extensors to support standing leg and balance
inhibitory inhib flexors to relax

Question 13

muscle tone maintenance

Answer 13

by gamma motor via gamma loop

Question 14

alpha gamma coactivation

Answer 14

maintains spindle sensitivity to muscle stretch regardless of muscle length at onset of muscle stretch