The Myotatic reflex

Question 1

What motor reflexes are done by the cortex

Answer 1

placing reaction

Hopping reaction

Question 2

What motor reflexes are done by the brainstem/midbrain

Answer 2

vestibular

righting reflex

suckle

yawn

eye/head movements

Question 3

What reflexes are done by the spine

Answer 3

stretch (myotatic)

golgi tendon reflex

crossed extensor

Question 4

General characteristics of motor control reflexes

Answer 4

protective
movement thats required even without voluntary motor control
fast
reflexes must be very precise to make it look like volitional movement

Question 5

What is a myotactic reflex

Answer 5

contraction of a stretched muscle

purpose is to protect the muscle from tearing

Characteristics:

• initiated by muscle spindle
• monosynaptic, segmental reflex

Question 6

What is a muscle spindle

Answer 6

found in the skeletal muscle, embedded in a fusiform capsule

in parallel to the muscle fibers

contain both afferent (sensory) and efferent (contractile) components

Question 7

intrafusal fibers vs extrafusal fibers

Answer 7

the fibers within the fusiform capsule of the muscle are the intrafusal fibers

the fibers that make up the bulk of the muscle are called the extrafusal fibers

Question 8

what components do intrafusal fibers have

Answer 8

contain both a motor and sensory component

Question 9

What are the components of the sensory portion of a muscle spindle

Answer 9

not contractile
portion is sensitive to length

2 sensors:

• nuclear bag fiber (middle)
• nuclear chain fiber (outside part)

Question 10

Primary afferent characteristics of a myotic reflex

Answer 10

innervates both the nuclear bag and the nuclear chain
large myelinated Ia fiber

sensitive to: length of muscle and how fast the length is changing

sends more action potentials if the muscle stretches and even more with a rapid stretch

Question 11

The secondary afferent characteristics of a myotic reflex

Answer 11

smaller, myelinated Group II fiber
innervates only the nuclear chain fiber
sensitive only to the length of the muscle

Question 12

Motor portion of the intrafusal muscle fibers

Answer 12

innervated by a gamma motor neuron
controls the length of the sensory portion of the muscle spindle

by contracting the intrafusal muscles we stretch the sensory portion of the muscle making the primary and secondary afferent more sensitive to a superimposed stretch

Question 13

what do the gamma motor neurons do and versus alpha motor neuron

Answer 13

control the sensitivity of the Ia and II fibers to stretch
activity causes contraction
activity does not directly lead to motion

vs. alpha
innervates the extrafusal skeletal muscle fibers
responsible for activating muscle
activity directly leads to motion

Question 14

how does the primary afferent synapse on the agonist alpha motor neuron

Answer 14

the Ia afferent neuron will synapse directly onto the alpha motor neuron in the ventral body of the spinal cord (the Ia will release an EAA neurotransmitter)

therfore the alpha motor neuron will contract the muscle and relieve the stretch that the Ia afferent neuron detected in the muscle spindle

Question 15

How does the primary afferent synapse on the alpha motor neuron on the antagonist alpha motor neuron

Answer 15

the Ia afferent neuron synapse on an inhibitory interneuron which will be excited from the EAA and release GABA on the alpha motorneuron antagonist muscle which will then relax the antagonist muscle (allowing for that muscle to lengthen)