Neuromuscular junction

Question 1

Describe extrafusal fibers

Answer 1

They are striated multi-nucleated muscle fibers

Question 2

What innervates extrafusal fibers

Answer 2

Alpha lower motor neuron

Question 3

Describe intrafusal fibers

Answer 3

They have an enlarged middle portion called a muscle spindle and they contain nuclear bag and nuclear chain receptors

Question 4

What innervates intrafusal fibers?

Answer 4

Gamma motor neuron

Question 5

Which type of fibers is found in nuclear bag receptors?

Answer 5

Type 1a motor afferent fiber

Question 6

Which type of fibers is found in nuclear chain receptors?

Answer 6

Type Ia and Type 2 motor afferent fibers

Question 7

Describe Type 1 fibers

Answer 7

Large diameter, highest degree of myelination, highest conductivity

Question 8

Describe Type 1a fibers

Answer 8

Run in parallel and set muscle length, tell CNS about the rate of change of muscle length

Question 9

Describe Type 1b fibers

Answer 9

Run in series with extrafusal fibers and set muscle tension

Question 10

Describe Type 3 fibers

Answer 10

Smallest diameter, least myelinated, least conductivity

Question 11

Describe Type 4 fibers

Answer 11

Unmyelinated

Question 12

Describe Type 2 fibers

Answer 12

They tell the CNS about the length of the muscle and if there has a been a change in muscle length

Question 13

Describe myotatic reflex

Answer 13

Myotatic reflex is 1a reflex, it regulates the length of the muscle

Question 14

Examples of myotatic reflexes

Answer 14

Autogenic excitation
Synergist excitation
Reciprocal inhibition
Renshaw inhibition

Question 15

Which myotatic reflex does not involve an interneuron?

Answer 15

Autogenic excitation

Question 16

Role of reciprocal inhibiton

Answer 16

Inhibit antagonist muscle so that when the synergist muscle is contracted, the antagonist doesn’t get in the way

Question 17

Another name for Renshaw inhibition

Answer 17

Local Feedback inhibition

Question 18

What is Renshaw inhibition?

Answer 18

It is an inhibitory interneuron

Question 19

What happens if only gamma fibers are stimulated

Answer 19

Contraction of intrafusal fibers and the spindle gets stretched

Question 20

Characteristics of Reverse Myotatic Reflex

Answer 20

Has a Golgi Tendon Organ, the GTO is in series with the muscle

Question 21

Which fiber innervates Golgi Tendon Organ?

Answer 21

Type 1b fiber

Question 22

What happens if only alpha fibers are stimulated

Answer 22

The muscle contracts, the spindle gets squished and cannot sense the change in length

Question 23

What happens if both alpha and gamma fibers are stimulated

Answer 23

The spindle stays the same length

Question 24

How many firing frequencies are there in a Type Ia fibers?

Answer 24

Three firing frequencies