Chapter 54

Question 0

1 Alpha motor neuron stimulates 3-100’s of skeletal muscle fibers. Which process is this?

Answer 0

Motor unit

Question 1

What do Alpha motor neurons give rise to?

Answer 1

give rise to large type Aα motor neurons, these are located in the anterior horn of the spinal cord

Question 2

What is the role of the gamma motor neurons?

Answer 2

Transmit impulses through small type Aγ motor fibers which go to small skeletal muscle fibers called intrafusal fibers

Question 3

What is the role of interneurons?

Answer 3

They display many interconnections with each other and they synapse on anterior motor neurons; essential for the integrative function of the spinal cord

Question 4

What is the role of Renshaw cells?

Answer 4

these inhibitory cells transmit inhibitory signals to surrounding motor neurons (lateral inhibition); this focuses the signal and suppresses its lateral spread

Question 5

What is the role of the central portion of the intrafusal muscle fiber?

Answer 5

no actin or myosin; functions as a sensory receptor (afferent)

Question 6

What are the 2 ways to excite the central portion of the intrafusal muscle fiber?

Answer 6

Lengthening the muscles –> stretches the receptor

Even if the length of the muscle does not change, contraction of the end portions –> stretches the receptor

Question 7

What are the roles of the end portions of the intrafusal muscle fiber?

Answer 7

contract; excited by small γ motor neurons which originate from small type A gamma motor neurons (aka gamma efferent fibers) in the anterior horn

Question 8

Which type of neurons innervate the extrafusal fibers?

Answer 8

Aα nerve fibers

Question 9

What is the pirmary ending of the muscle spindle?

Answer 9

large sensory nerve fibers that encircle the central portion of each intrafusal fiber (center of receptor area); type Ia fiber

Question 10

What is the secondary ending of the muscle spindle?

Answer 10

innervate the receptor region on one or both sides of the primary ending ; type II fiber

Question 11

What is the static response to muscle stretch from the intrafusal fibers?

Answer 11

When the sensory receptor of the intrafusal muscle fiber gets stretched slowly, the number of impulses transmitted from both the primary and the secondary endings increases almost directly in proportion to the degree of stretching and the endings continue to transmit these impulses for several minutes.

Question 12

What is the dynamic response to rapid change in intrafusal length?

Answer 12

If the spindle receptor increases in length suddenly, then the primary ending is stimulated powerfully while the secondary ending is not.

Essentially, the primary ending is highly responsive to rapid rate of change in spindle length. Only active while the length is actually increasing

Question 13

What is coactivation?

Answer 13

whenever signals are transmitted from the brain to the alpha motor neurons the gamma motor neurons are stimulated also

Question 14

What is the role of coactivation of alpha and gammaMN’s?

Answer 14

This causes both the extrafusal skeletal muscle fibers and muscle spindle intrafusal muscle fibers to contract at the same time.
Keeps the length of the receptor portion of the muscle spindle from changing during contraction and from opposing the muscle contraction
Maintains proper damping function of the muscle spindle regardless of change in length

Question 15

Hyperreflexia on the knee jerk reflex is indicative of what type of lesion?

Answer 15

UMN

Question 16

Hyporeflexia on the knee jerk reflex is indicative of what type of lesion?

Answer 16

LMN

Question 17

What do golgi tendon organs detect?

Answer 17

detects muscle tension (tensed by contracting or stretching muscles) as reflected by the tension in itself

Question 18

What is the role of the golgi tendon reflex?

Answer 18

Golgi tendon reflex is stimulated by increased tension in the connecting muscle
This reflex is inhibitory and it prevents the development of too much tension on the muscle

Question 19

What is the flexor reflex?

Answer 19

cutaneous sensory stimulus from a limb causes flexor muscles of the limb to contract –> withdrawing the limb from the stimulating object.

Question 20

What is the crossed-extensor reflex?

Answer 20

about .2-.5 seconds after a stimulus elicits a flexor reflex in one limb the opposite limb begins to extend; many interneurons are involved in the circuit between the incoming sensory neuron and the motor neuron of the opposite side of the cord responsible for the crossed extension

Question 21

What is the main cause of local muscle pain?

Answer 21

Muscle spasm

Question 22

What is the mass reflex for the spinal cord?

Answer 22

when the spinal cord suddenly becomes excessively active this may cause massive discharge in large portions/entire of the spinal cord.

(btw, it’s spinal “cord” as a “cord” is a cylindrical object. A “chord” is a musical tone. just fyi to everyone because that bugs the shit outta me).

Question 23

What are the 4 effects of the mass reflex?

Answer 23

Major portion of the body’s skeletal muscles goes into strong flexor spasm
Colon and bladder are likely to evacuate
Arterial pressure often rises to maximal values (systolic 200 mmHg)
Large areas of the body break out into profuse sweating

Question 24

What are the immediate effects of spinal cord tansection?

Answer 24

All cord functions (inc. reflexes) immediately become depressed (total silence) –> spinal shock
Non communication between higher centers and cord neurons via reticulospinal tracts, vestibulospinal tracts, and corticospinal tracts

Question 25

What are the long term effects of spinal cord transections?

Answer 25

In human it typically results in hyperexcitability of some or all cord functions
Blood pressure (Drop to 40 mmHg initially  normal w/in days)