Spinal Cord and Reflexes

Question 1

cervical and lumbar enlargements

Answer 1

more grey matter in the areas connected to limbs- white matter drastically decreases all the way down

Question 2

what type of neural fibers arise from muscle spindle

Answer 2

1a, Aa, faster than 100 m/s, myelinated

sensory

Question 3

what type of neural fibers arise from golgi fibers

Answer 3

1b, Aa, faster than 100 m/s, myelinated

sensory

Question 4

motor pools

Answer 4

all of the motor neurons going to a single muscle. spans several spinal segments

spinal cord organized into motor pools

Question 5

describe the topographical distribution of motor neurons in the cervical segment for the arm

Answer 5

hand most lateral, shoulder and distal most medial

extensor more ventral, flexor more ventral

Question 6

motor unit

Answer 6

all of the muscle fibers innervated by a single motor neuron

Question 7

compare type 1 and 2 muscle fibers

Answer 7

type 1 (red)- small fibers, small neurons, slower contraction, low tension/fiber, highly aerobic, fatigue resistant

type 2 (white)- opposite

Question 8

what governs the type of muscle fibers?

Answer 8

the neuron innervating it

Question 9

muscle spindles

Answer 9

intrafusal fibers- much smaller than normal fibers. innervated by gamma motor neurons.

ends of the fibers contain contractile elements,- contraction causes a stretch on the middle of the fiber.

middle of the fiber innervated by annulospiral sensory ending (1A afferent fiber)- activated by stretch of the intrafusal fiber

Question 10

stretch reflex

Answer 10

stretch causes excitation of the annulospiral sensory nerves on the intrafusal fibers, exciting the 1A afferent neuron. this synapses directly on the motor neurons going to the muscle. collateral branches will synapse on interneurons that will inhibit antagonist muscles and activate agonist muscles

net effect- stabilize movement and prevent unintentended movement

Question 11

gamma motor neurons in intrafusal fibers

Answer 11

contract intrafusal fibers to “reset” the annulospiral stretch receptor when muscle is contracted

alpha-gamma coactivation

Question 12

gamma loop

Answer 12

gamma activation of muscle results in tension on annulospinal endings, activating the stretch reflex, activating that muscle and inhibiting its antagonists

efficient way to change length of a muscle and muscle will maintain new length

Question 13

overactivity of gamma motor neurons results in what?

Answer 13

spasticity

typically result from damage to descending projections from brainstem that inhibit gamma motor runs

Question 14

where are golgi tendon organs found?

Answer 14

connective tissue that attaches muscle fiber to muscle tendon

Question 15

what type of afferent nerve do golgi tendon organs have?

Answer 15

1B afferent fiber, slightly slower than 1A

Question 16

what is the purpose of the golgi tendon organ?

Answer 16

signal muscle tension

only signals when the limit of the muscle compliance is reached (ie when the CT is about to tear)

results in the inhibition of the activated muscle and the activation of the antagonists

Question 17

clasp knife phenomena

Answer 17

overactive GTO reflex results in a “giving way” of passively stretched muscles

Question 18

withdrawal reflex

Answer 18

physiologic flexion of limbs in response to painful stimuli

causes extension of opposite limb

Question 19

example of overactive withdrawal reflex

Answer 19

babinski reflex- extension of big toe w/ stroke of bottom of foot

Question 20

central pattern generators

Answer 20

interneurons encode patterns that represent movements with limited input from descending tracts

very important for things like locomotion