Neuromotor System

Question 1

The basal ganglia is involved in voluntary motor movements and procedural learning, as well as forming habits, emotion, and cognition - to where does it almost exclusively project its signals?

Answer 1

thalamus

Question 2

type of muscle fiber that is innervated by alpha motor neurons and generates tension by contracting, thereby moving skeletal elements

Answer 2

extrafusal muscle fiber

Question 3

a collection of all motor neurons that innervate a single

muscle is called a what?

Answer 3

motor pool

Question 4

type of muscle fiber that is embedded in main muscle fibers that is involved in proprioception and facilitating muscle tone

Answer 4

intrafusal muscle fiber (muscle spindle)

Question 5

these neurons terminate on the contractile end portions of muscle spindle fibers and take part in the process of muscle contraction, representing about 30% of fibers going to muscle

Answer 5

gamma (γ) motor neurons (fusimotor system)

Question 6

muscle spindle fiber that contains cell nuclei jumbled together in the middle, and in response to stretch encodes the rate of change (velocity) of muscle length

Answer 6

nuclear bag fiber

Question 7

muscle spindle fiber that contains cell nuclei aligned in a single row, and in response to stretch conveys information about static length of the muscle

Answer 7

nuclear chain fiber

Question 8

what type of information do type Ia afferent spindle fibers provide the CNS?

Answer 8

muscle length and velocity (they wrap around both nuclear chain and nuclear bag fibers)

Question 9

what type of information do type II afferent spindle fibers provide the CNS?

Answer 9

only immediate muscle length information (they do not innvervate nuclear bag fibers, which convey information about muscle velocity)

Question 10

restoring tautness to muscle spindles following stretch is achieved via coactivation of alpha and gamma neurons by what system?

Answer 10

corticospinal system (and other supraspinal systems)

Question 11

Muscle tone is fine-tuned by tonic discharge of

gamma motor neurons activated by what brainstem pathways?

Answer 11

reticulospinal and vestibulospinal

Question 12

states that increases in the rate of action potentials of

motor neurons allows for as much as a 4-fold increase in muscle force (from single twitch to fused tetanic contraction)

Answer 12

rate code

Question 13

states that with increasing strength of input, motor neurons are recruited from smallest (fewer ion
channels) to largest (most ion channels).

Answer 13

size principle

Question 14

_____ sized neurons innervate fast-twitch, fatigue resistant fibers (for normal movements)

Answer 14

medium

Question 15

____ sized neurons innervate fast-twitch, fatigable

fibers (for bursts of energy)

Answer 15

large

Question 16

____ sized neurons innervate slow-twitch fibers (for

postural control)

Answer 16

small

Question 17

in the ventral horn, ____ groups of motor neurons innervate flexors while _____ groups innervate extensors.

Answer 17

dorsal; ventral

Question 18

in the ventral horn, _____ groups of motor neurons innervate axial (proximal) muscles while ______ groups
innervate more distal muscles

Answer 18

medial; lateral

Question 19

the intermediate zone of the spinal cord is heavily populated by propriospinal neurons, which are the major players in these networks, responsible for complex stereotypic movements involving multiple muscle groups

Answer 19

central pattern generators

Question 20

True or false: in most spinal cord injuries involving central pattern generators, the problem is degradation of the CPG network.

Answer 20

False. usually the problem is loss of command signal by supraspinal inputs (ie, corticospinal system) necessary to voluntarily activate pattern generators for stereotypic movements

Question 21

regulate stereotypic movements of the head (ie, swallowing, respiration, chewing, saccadic eye movements)

Answer 21

brainstem central pattern generators

Question 22

maintenance of upright posture by constant, automatic corrections of axial and limb muscles is based on control of what kind of neurons that increase tone?

Answer 22

gamma motor neurons

Question 23

descending motor pathway whose fibers pass through the posterior limb of the internal capsule; involved in individual muscle control, facilitation of flexors, and CPG command

Answer 23

corticospinal system

Question 24

descending motor pathway whose fibers pass through the genu of the internal capsule; primary function is to control voluntary movements of the eyes, jaw muscles of facial expression, swallowing and voice modulation, and tongue mobility

Answer 24

corticobulbar system

Question 25

True or false: most fibers of the corticospinal/bulbar systems contact alpha motor neurons directly.

Answer 25

False. Only 20% directly contact alpha motor neurons; the rest contact interneurons in the intermediate zone (corticospinal) and pontine/medullary reticular formation (corticobulbar)

Question 26

Why is it that unilateral corticobulbar lesions usually produce no clinical effect?

Answer 26

Most CN motor nuclei receive bilateral corticobulbar inputs (with the exception of the facial and hypoglossal nuclei, which receive mainly crossed input from the opposite motor cortex)

Question 27

descending pathway that originates in the red nucleus, whose presence and function is only clinically significant during decerebrate and decorticate rigidity

Answer 27

rubrospinal system

Question 28

descending pathway that is involved in postural control, regulation of muscle tone, and CPG coordination

Answer 28

reticulospinal system

Question 29

the pontine (medial) reticulospinal tract facilitates extensor muscle activity to _______ muscle tone, while the medullary (lateral) reticulospinal tract suppresses extensor activity to ____ muscle tone.

Answer 29

increase; decrease

Question 30

While the corticospinal tract is thought to activate CPGs,

this tract is heavily involved in integrating the motor systems for coordination of automatic locotomor movements.

Answer 30

reticulspinal tract

Question 31

the descending system that is involved in reflexive head turn toward or away a visual or auditory stimulus

Answer 31

tectospinal tract

Question 32

descending lateral and medial pathways that target intermediate zone and medial motor neurons that maintain upright posture (vestibulo-spinal reflex) and maintain head in upright position (vestibulo-collic reflex; ends at T1)

Answer 32

vestibulospinal tracts

Question 33

two systems that together function in postural control through facilitation of extensors, as well as coordination of head, neck, and axial spine movements

Answer 33

vestibulospinal and tectospinal systems