Thursday 1 - Fitz - Muscle receptors and spinal reflexes pre-recorded

Question 1

What are muscle spindles

where are they

Answer 1

sensory afferents

in intrafusal muscle fiber in the core of the muscle

Question 2

Is a muscle spindle contractile?

Answer 2

The core is NOT (intrafusal fibers), but it is attached to contractile units on either end (extrafusal fibers).

Question 3

two receptor type in muscle spindle fibers

Answer 3

1 (primary, IA) anulospiral endings - detect velocity,

• Dynamic movements
• Stop firing completely when stretch is released

2 (secondary, II) flower spray

• Amplitude of stretch
• Static

Question 4

What innervates muscle spindle fibers

Answer 4

Gamma motor neurons for intrafusal fibers

alpha motor neurons for extrafusal

Question 5

golgi tendon organs

where

what happens in the inverse stretch reflex

Answer 5

at the juction of the muscle and tendon, in series with extrafusal fibers

inverse - depolarization of the golgi tendon organ increases the activity of an inhibitory interneuron. This decreases activity of alpha and gamma motor neurons

Question 6

Do spindles have no activity if the muscle is relaxed?

Answer 6

no, they just have reduced activity

Question 7

Steps in “monosynaptic reflex stretch”

Answer 7

1 - muscle stretches
2 - depolarization in spindle afferent
3 - activation of both alpha and gamma motor neurons
4 - contration of the extraafusal muscle fibers (this maintains tension in the spindle, allowing the spindle to continue to be responsive. Its like the adaptation motor in the hair cells. intrafusal fiber pulls on the spindle afferent section of the intrafusal fiber and maintain tension)
5 - (maintenance of tension) muscle tone

Question 8

What happens if you eliminate the alpha motor neurons

Answer 8

flaccid paralysis, cannot control the muscles anymore

Question 9

What happens if the gamma motor neurons are overactive

Answer 9

spastic paralysis

Question 10

two causes of spastic paralysis from lecture

Answer 10

elimination of descending inhibition

overactive gamma motor neurons

Question 11

muscle reflex arc

Answer 11

sensory receptor
primary afferent neuron
1 - 3 CNS synapses
motor neuron
muscle

Question 12

Recurrent inhibition

Answer 12

motor neurons that transmit impulses to muscle can also send signals to “renshaw cells” which inhibit the muscle neuron as well as adjacent neurons

Question 13

Lengthening reaction

light and heavy weights

modded by ?

Answer 13

light weight
moderate stretch
stretch reflex
contraction

heavy weight
strong stretch
inverse stretch reflex
relaxation

Modulated by gamma motor neurons

Question 14

withdrawl reflex

pathways

Answer 14

noxious stimulus
withdrawl of limb via:

contraction of flexers via monosynaptic pathway

relaxation of extensors via multisynaptic pathways

Question 15

Spinal shock

Answer 15

initially spinal shock prevents any reflexes

start to come back, primitive first

Question 16

Crossed extension reflex

Answer 16

step on a nail, lean on other foot ya dingus