Muscle spindles

Question 1

What are Muscle Spindles?

Answer 1

Specialized muscle fibers containing contractile elements

Question 2

Muscle spindles are encased in what?

Answer 2

Connective tissue sheath

Question 3

Where are muscle spindles anchored to?

Answer 3

The endomysium and perimysium that surrounds the fascicles of the muscle

Question 4

Contractile fibers within the muscle spindle are referred to as…

Answer 4

Intrafusal Muscle Fibers

Question 5

Fibers that make up the bulk of a muscle are referred to as…

Answer 5

Extrafusal Muscle Fibers​

Question 6

True or False:

Both intrafusal and extrafusal muscle fibers have a typical sarcomere arrangement

Answer 6

True

Question 7

True or False:

A muscle spindle contains several intrafusal muscle fibers within it.

Answer 7

True

Question 8

Where are the Contractile Elements of the intrafusal fibers located at?

Answer 8

At the poles or ends of each fiber

Question 9

Intrafusal fibers are multinucleated with all of the nuclei being located where?

Answer 9

Centrally (equatorially)

Question 10

Muscle spindles have how many types of nuclear arragnements?

Answer 10

Two

1. ) Nuclear bag
2. ) Nuclear Chain

Question 11

Nuclear Bag filaments are characterized by the nuclei looking like what?

Answer 11

“Clumped” in th emiddle forming a “bag-like” enlargement of the sarcolemma

Question 12

Nuclear Chain filaments are characterized by the nuclei looking like what?

Answer 12

Arranged linearly in a “Chain-like” arrangement

Question 13

Each filament has at least two sensory receptors. Explain the location of each

Answer 13

Located either:

1. ) Centrally around the nuclear groups (primary)
2. ) Peripherally near the contractile elements (secondary)

Question 14

Primary receptors in the muscle spindle are located where?

Answer 14

Centrally

—around the nuclear groups

Question 15

Secondary receptors in the muscle spindle are located where?

Answer 15

Peripherally

—near the contractile elements

Question 16

The stimulus during a stretch is actually what?

Answer 16

Mechanical deformation of the afferent ending

Question 17

Some of the primary endings are highly responsive to _____________ in muscle length, and in turn encode ____________.

Answer 17

—Rate of change

—Velocity of the muscle stretch

Question 18

Primary endings that are responsive to the rate of change are also referred to as what?

Answer 18

Dynamic or phasic endings

Question 19

The histological name for dynamic or phasic endings is what?

Answer 19

Annulospiral rings

Question 20

Secondary endings (and some primary) are responsive to what?

Answer 20

The static muscle length

Question 21

Secondary endings that are responsive to static muscle length are also refered to as what?

Answer 21

Static or Tonic endings

Question 22

Static or Tonic endings have what histological name?

Answer 22

Flower Spray endings

Question 23

Information from primary endings are carried into the CNS by what fiber type?

Answer 23

Type Ia

Question 24

Information from secondary endings are carried by what fiber type?

Answer 24

Type II

Question 25

Each fiber in the muscle spindle recieves an ending from what type of motor neuron?

Answer 25

γ motor neuron

Question 26

Where does the muscle spindle recieve the ending of the γ motor neuron?

Answer 26

On each contractile component of each fiber

Question 27

What do the γ motor neurons act to control?

Answer 27

The contraction of each spindle

Question 28

Activiation of the γ motor neuron results in what?

Answer 28

Contraction of the intrafusal fibers

Question 29

γ motor neurons can be used to adjust what within the muscle spindle?

Answer 29

The sensitivity of each receptor with the muscle spindle

Question 30

True or False:

The adjustment of sensitivity by the γ motor neurons are specific and seperate to the dynamic and static receptors

Answer 30

True

Question 31

What is the purpose of the motor activation within muscle spindles?

Answer 31

To prevent unloading of the receptor during extrafusal muscle contraction

Question 32

The process of preventing “unloading” of the receptor during extrafusal muscle contraction is refered to as what?

Answer 32

Alpha-gamma coactivation

Question 33

Explain alpha gamma co-activation

Answer 33

At the time of alpha motor neuron firing, the appropriate γ motor neuron are also activated.

—Resulting in muscle spindle adjustment that parallels the contraction of the extrafusal muscle fiber

Question 34

Muscle spindle adjustment that parallels the contraction of the extrafusal muscle fiber occurs because of what?

Answer 34

Alpha gamma co-activation

Question 35

If stimulation of the γ motor neuron takes place in a situation other than alpha-gamma coactivation what is the result?

Answer 35

An increase in the sensitivity of both the primary and secondary endings

Question 36

What can influence an increase in the sensitivity of both the primary and secondary endings?

Answer 36

CNS pathways or cutaneous stimulation

—this allows for fine tuning of the spindle as the difficulty of the motor task increases