Muscle Spindle Fun Facts

Question 1

Muscles involved in fine movement (hand) have more or less spindles than coarse moving muscles (back)?

Answer 1

Have MORE

Question 2

Stretch Reflex–> if the muscle is stretched then what happens??

Answer 2

1-a axon is stimulated and this sends impulses to the ventral horn

Question 3

What does the 1-a axon stimulate in the ventral horn?

Answer 3

alpha motor neuron (Again remember this is on the EXTRAFUSAL fiber) and this will tell the stretched muscle it needs to contract

Question 4

In addition to the 1-a neuron stimulating alpha motor neurons of the muscle, what does the 1-a neuron send inhibitory interneurons to?

Answer 4

Inhibit the alpha motor neuron of the antagonist muscle (this is known as reciprocal innervation)

Question 5

Again when the alpha motor is stimulated, the muscles does what??

Answer 5

shortens or contracts

Question 6

When the alpha and gamma motor are both stimulated, what does the muscle do?

Answer 6

the intrafusal (gamma) and the extrafusal fibers (alpha) will contract together

Question 7

Now for 1-b fibers in the golgi tendon organ, if the muscle is contracted or shortened then what happens with 1-b axons??

Answer 7

this increases the firing rate of the 1-b axon

Question 8

An increase 1b axon firing rate will cause what???

Answer 8

Increase inhibition on the alpha motor neuron

Question 9

What effect does 1-b firing having on patients?

Answer 9

ensures even distribution of tension and contraction as well as avoiding excessive contract to the point of damage (known as reverse myotactic reflex)

Question 10

The number of muscle fibers in a motor unit increases or decreases with increasing fine motor control???

Answer 10

DECREASES (muscles of hand are about 10 fibers) (So remember more spindles but less fibers)

Question 11

Type 1 muscle??

Answer 11

Slow twitch muscle fibers, low tension; fatigue resistance; aerobic; innervated by large motor neurons and axons

Question 12

Type IIA muscle??

Answer 12

Fast fatigue-resistant; large tension

Question 13

Type IIB muscle??

Answer 13

Fast Fatigable; large tension (running from a bear situation)

Question 14

Hypotonia is due to damage to what?

Answer 14

1a afferent or alpha motor efferent

Question 15

The cell bodies of all muscle afferent are where?

Answer 15

DRG

Question 16

What are the two major sensory organs?

Answer 16

Muscle Spindle –> measures length 1a fiber

Golgi tendon –> measures tension: 1-b fiber

Question 17

where are muscle spindles located?

Answer 17

Encapsulated structures found in most skeletal muscles used to monitor its length

Question 18

what are the components of the spindle?

Answer 18

Small group of 2-12 intrafusal fiber
large diameter myelinated sensory axon (1a-axon) with sensory ending in the intrafusal belly
small diameter myelinated motor axon that innervate the distal contractile regions

Question 19

What are Renshaw cells?

Answer 19

are inhibitory interneurons of the anterior horn that receive collaterals form the alpha motor neuron and work to avoid damage in the event of excessive contraction (golgi)

Question 20

A motor axon branches at its muscles and what happens to the fibers that these branches connect with?

Answer 20

each fiber receives only one ending of the branching

Question 21

Where is the NMJ located?

Answer 21

in the center of the muscle fiber and is where AP are generated

Question 22

The force developed by the muscle fiber increases with?

Answer 22

increasing firing rate of the motor neuron

Question 23

The force will also increase as more what are recruited

Answer 23

more motor units are recruited to the excited state