2.21 Motor System 2

Question 1

LMN are only neurons that convey signals to: (specific)

Answer 1

extrafusal and intrafusal skeletal muscle fibers

Question 2

How many types of LMN?

Answer 2

2

Question 3

Cell bodies of LMN are located here

Answer 3

ventral horn of spinal cord

Question 4

two types of motor neurons

Answer 4

• alpha

- gamma

Question 5

alpha motor neurons: cell bodies and axons

Answer 5

• large cell bodies

- large, myelinated axons

Question 6

alpha motor neurons: axons projecting

Answer 6

• project to extrafusal skeletal muscle

- branch into numerous terminals as they approach muscle

Question 7

Normally, an alpha motor neurons releases enough _______ that all the muscle fibers it innervates contracts

Answer 7

ACh

Question 8

gamma motor neurons: axons

Answer 8

• medium sized
• myelinated
• project to intrafusal fibers in the muscle spindle

Question 9

How do most sensory stimuli act?

Answer 9

in ensemble fashion

Question 10

How do sensory stimuli act in an ensemble fashion?

neurons and CNS interaction

Answer 10

• involved neurons can vary

- appropriate levels of CNS interact to produce context-dependent movement

Question 11

What is one way to modify movement response to tendon tap?

Answer 11

changing arousal level

• relaxed: tendon elicits small movement
• anxious: greater movement with same force

Question 12

What are H reflexes?

Answer 12

monosynaptic reflexes elicited by electrically stimulating a nerve

Question 13

purpose of H reflexes

Answer 13

to quantify the level of alpha motor neuron facilitation or inhibition

Question 14

compare H reflexes to tendon reflex

Answer 14

• faster

- doesn’t require activation of spindle receptors

Question 15

What motor signals do UMN provide?

Answer 15

all motor signals from:

• brain to spinal
• from cerebrum to cranial nerve LMNs in the brainstem

Question 16

What UMN activity usually occurs automatically, without conscious effort?

Answer 16

activity controlling posture and gross movements

Question 17

What activity can occur before a person is consciously aware of a stimulus?

Answer 17

medial UMN activity

Question 18

example of medial UMN activity

Answer 18

• a loud noise occurs behind a person

- eyes and face turn toward sound before person is consciously aware of auditory stimulus

Question 19

What are the medial UMN tracts?

Answer 19

• reticulospinal tract
• medial vestibulospinal tracts
• lateral vestibulospinal tract
• medial corticospinal tract

Question 20

reticulospinal tract (overall)

Answer 20

facilitates bilateral LMN innervating postural and gross limb movement of muscles throughout the body

Question 21

medial vestibulospinal tracts (overall)

Answer 21

receives info about head movement and position from vestibular apparatus

Question 22

lateral vestibulospinal tract responds to:

Answer 22

gravity information from vestibular apparatus

Question 23

medial corticospinal tract has direct connection from:

Answer 23

cerebral cortex to spinal cord

Question 24

fractionation

Answer 24

ability to activate individual muscles independently of other muscles

Question 25

What is fractionation essential for? What would happen without it?

Answer 25

• essential for normal movement of the hands

- without it, the fingers and thumb would act as a single unit, as they do when picking up a water bottle

Question 26

What is the lateral UMN tract called?

Answer 26

lateral corticospinal tract

Question 27

major function of LMN

Answer 27

fractionation

Question 28

How does the lateral corticospinal tract fractionate?

Answer 28

by activating inhibitory neurons to prevent unwanted muscles from contracting

Question 29

most important pathway controlling voluntary movements

Answer 29

Lateral corticospinal tract

Question 30

Where do lateral corticospinal fibers arise?

Answer 30

primary motor, premotor, and supplementary motor cortex

Question 31

Where is the primary motor cortex located?

Answer 31

anterior to central sulcus in the precentral gyrus