Motor System

Question 1

How does graded recruitment of motor neurons work?

Answer 1

small neurons have high input resistances (R) –> given current will cause a larger change in these neurons –> will be brought to threshold with less synaptic input than the larger motor neuron

Question 2

A motor unit is defined as ________.

Answer 2

an α motor neuron and the muscle fibers it innervates

Question 3

Corticospinal axons course through the ______ then gather into the cerebral peduncle on the ventral surface of the midbrain.

Answer 3

internal capsule

Question 4

____ is highly activated during mental rehearsal of movement.

Answer 4

The supplementary motor cortex

Question 5

Activation of α motor neurons ____.

Answer 5

maintains muscle tone

Question 6

What are the 2 general functions of the reticular formation?

Answer 6

1. modulatory functions
2. premotor functions

Question 7

During ______, α and ɣ motor neurons fire together, shortening both the extrafusal (normal skeletal muscle) and intrafusal (spindle) muscle fibers together.

Answer 7

voluntary contraction

Question 8

The ______ is responsible for many anticipatory responses to a voluntary movement that help maintain postural control and balance.

Answer 8

reticular formation

Question 9

What is mirror neuron activity?

Answer 9

selective neural responses are observed in response to the subject simply watching an action with an intended consequence

Question 10

Degeneration of ______ is the hallmark of amyotrophic lateral sclerosis (ALS) which is characterized by progressive weakness and wasting of skeletal muscles.

Answer 10

α motor neurons

Question 11

The vestibular nuclei project bilaterally to the _____.

Answer 11

abducens nuclei

Question 12

______ is communicated to the spinal cord through group Ia and group II sensory afferents.

Answer 12

Stretch of the muscle spindle

Question 13

During voluntary contraction, ___ and ____ motor neurons fire together, shortening both the extrafusal (normal skeletal muscle) and intrafusal (spindle) muscle fibers together.

Answer 13

α and ɣ

Question 14

Ia sensory afferents contact ____ motor neurons in the spinal cord, which trigger muscle contraction of the homonymous muscle fiber in response to stretch.

Answer 14

α

Question 15

What is a muscle spindle?

Answer 15

a specialized type of sensory receptor, known as a proprioceptor, that is embedded within a muscle and detects muscle stretch

Question 16

Do intrafusal muscle fibers detect stretch in a contracted or relaxed muscle?

Answer 16

both

Question 17

Descending projections of the ______ tract target motor neurons that control the axial musculature of the neck to generate coordinated orienting responses.

Answer 17

colliculospinal (aka tectospinal)

Question 18

Explain the steps in the knee-jerk reflex.

Answer 18

hammer tap stretches the muscle spindles –> 1a sensory axons stimulated –> α motor neurons in the spinal cord activated –> contraction of the stretched muscle

Question 19

fall –> vestibular system detects downward acceleration –> arms push out and head pulls up

Answer 19

the vestibulocervical/vestibulospinal reflex

Question 20

The _____ informs the brain of head position, orientation, and motion.

Answer 20

vestibular system

Question 21

Stretch of the muscle spindle is communicated to the spinal cord through ______ sensory afferents.

Answer 21

group Ia and group II

Question 22

These are circuits in the spinal cord that contribute to bilateral organized rhythmic behaviors.

Answer 22

central pattern generators (CPGs)

Question 23

1a spindle afferents branch and diverge in the spinal cord to contact large populations of motor neurons which innervate ______ of muscle fibers to create the reflex motion.

Answer 23

populations

Question 24

Slow twitch muscle fibers generate action potentials to twitch, but fatigue very slowly owing to _____.

Answer 24

high concentrations of myoglobin and many mitochondria

Question 25

The vestibular system informs the brain of \_\_\_\_\_.

Answer 25

head position, orientation, and motion

Question 26

The ______ is a collection of loosely connected areas that lie within the midbrain tegmentum.

Answer 26

reticular formation

Question 27

Explain the crossed extension reflex.

Answer 27

cutaneous/nociceptive sensory receptors activated --\> spinal interneurons activated --\> extensor relaxation with flexor contraction on the same side AND flexor relaxation with extensor contraction on the contralateral side

Question 28

What are the modulatory functions of the reticular formation?

Answer 28

* cardiovascular control * respiratory control * some sensorimotor reflexes * eye movement coordination * sleep wake regulation * coordination of limb and trunk movements

Question 29

\_\_\_\_\_\_ muscle fibers of the spindle are innervated by a special type of motor neurons called ɣ motor neurons.

Answer 29

Intrafusal

Question 30

Corticospinal axons course through the internal capsule then gather into the ______ on the ventral surface of the midbrain.

Answer 30

cerebral peduncle

Question 31

\_\_\_\_\_\_ cell bodies reside in the ventral horn of the spinal cord and brainstem cranial motor nuclei.

Answer 31

α motor neuron

Question 32

A _____ is defined as an α motor neuron and the muscle fibers it innervates.

Answer 32

motor unit

Question 33

What is the Golgi tendon organ sensitive to?

Answer 33

muscle tension

Question 34

Tonic muscle fibers are a type of non-spiking muscle fibers that shorten _____ and efficiently generate isometric tension with _____ fatigability.

Answer 34

shorten extremely slowly; low fatigue

Question 35

A small α motor neuron will innervate ______ muscle fibers, forming a motor unit that generates small forces.

Answer 35

a small number of

Question 36

1a sensory afferents directly contact _____ motor neurons in the spinal cord.

Answer 36

α

Question 37

Give an example of a vestibulocervical/vestibulospinal reflex.

Answer 37

fall --\> vestibular system detects downward acceleration --\> arms push out and head pulls up

Question 38

What are central pattern generators (CPGs)?

Answer 38

circuits in the spinal cord that contribute to bilateral organized rhythmic behaviors

Question 39

A given muscle fiber is innervated by how many motor neurons?

Answer 39

one

Question 40

α motor neuron cell bodies reside in the _____ of the spinal cord and brainstem cranial motor nuclei.

Answer 40

ventral horn

Question 41

The vestibular nuclei project to which cranial nuclei?

Answer 41

3 (oculomotor), 4 (trochlear), and 6 (abducens)

Question 42

GTOs are situated _____ with the muscle and tendon, in contrast to the _____ arrangement of the muscle spindles.

Answer 42

GTO = in series; muscle spindle = in parallel

Question 43

The knee-jerk reflex is an example of a _____ reflex arc.

Answer 43

monosynaptic

Question 44

Fast twitch oxidative muscle fibers activate quickly, have many mitochondria and fatigue ______ because they contain _____ mitochondria.

Answer 44

fatigue slowly; lots of mitochondria

Question 45

What does the vestibular ocular reflex (VOR) do?

Answer 45

produces eye movements to counter head movements to keep the gaze fixed

Question 46

Degeneration of α motor neurons is the hallmark of _____ which is characterized by progressive weakness and wasting of skeletal muscles.

Answer 46

amyotrophic lateral sclerosis (ALS)

Question 47

What activates ɣ motor neurons?

Answer 47

descending command axons executing voluntary movements

Question 48

Fast twitch glycolytic fibers activate _____ and fatigue ______ owing to few mitochondria and a dependence of anaerobic glycolysis ATP generation.

Answer 48

quickly; rapidly

Question 49

Intrafusal muscle fibers of the spindle are innervated by a special type of motor neurons called ____ motor neurons.

Answer 49

ɣ

Question 50

\_\_\_\_\_\_ muscle fibers activate quickly, have many mitochondria, and fatigue moderately slowly because they contain lots of mitochondria.

Answer 50

Fast twitch oxidative

Question 51

Skeletal muscle contraction is driven by _____ neurons that innervate skeletal muscle cells.

Answer 51

α motor neurons

Question 52

\_\_\_\_\_ muscle fibers generate action potentials to twitch, but fatigue very slowly owing to high concentrations of myoglobin and many mitochondria.

Answer 52

Slow twitch

Question 53

Stimulation of premotor cortex elicits \_\_\_\_\_.

Answer 53

more complex, compound movements that involve multiple joints

Question 54

What is a muscle spindle made of? Where are they located?

Answer 54

a specialized muscle fiber called intrafusal muscle fibers; they run in parallel with the main “extrafusal” muscle fibers

Question 55

What is the size principle?

Answer 55

the systematic recruitment of smaller-to-larger motor units

Question 56

\_\_\_\_\_ muscle fibers are a type of non-spiking muscle fibers that shorten extremely slowly and efficiently generate isometric tension with low fatigability.

Answer 56

Tonic

Question 57

Fast twitch oxidative muscle fibers activate \_\_\_\_\_, have ______ mitochondria and fatigue moderately slowly because they contain lots of mitochondria.

Answer 57

activate quickly; many mitochondria

Question 58

cutaneous/nociceptive sensory receptors activated --\> spinal interneurons activated --\> extensor relaxation with flexor contraction on the same side AND flexor relaxation with extensor contraction on the contralateral side

Answer 58

the crossed extension reflex

Question 59

The ______ is critical for orienting gaze and body position.

Answer 59

superior colliculus (aka tectum)

Question 60

\_\_\_\_\_ sensory afferents contact α motor neurons in the spinal cord, which trigger muscle contraction of the homonymous muscle fiber in response to stretch.

Answer 60

Ia

Question 61

Fast twitch glycolytic fibers activate quickly and fatigue rapidly owing to ____ mitochondria and a dependence of \_\_\_\_\_\_.

Answer 61

few; anaerobic glycolysis ATP generation

Question 62

A large α motor neuron will innervate ______ muscle fibers, forming a motor unit that generates large forces.

Answer 62

a large number of

Question 63

This is a specialized type of sensory receptor, known as a proprioceptor, that is embedded within a muscle and detects muscle stretch.

Answer 63

a muscle spindle

Question 64

The reticular formation is responsible for many anticipatory responses to a voluntary movement that help maintain \_\_\_\_\_\_.

Answer 64

postural control and balance

Question 65

The superior colliculus (aka tectum) is critical for \_\_\_\_\_\_.

Answer 65

orienting gaze and body position

Question 66

Ia sensory afferents contact α motor neurons in the spinal cord, which trigger \_\_\_\_\_.

Answer 66

muscle contraction of the homonymous muscle fiber in response to stretch

Question 67

Activation of _____ maintains muscle tone.

Answer 67

α motor neurons

Question 68

The population of α motor neurons that innervates the muscle fibers within a single muscle is called the _____ for that muscle.

Answer 68

‘motor neuron pool’

Question 69

During voluntary contraction, α and ɣ motor neurons fire together, shortening both the ____ and _____ muscle fibers together.

Answer 69

extrafusal (normal skeletal muscle) and intrafusal (spindle)

Question 70

What are the targets of the vestibular nuclei?

Answer 70

1. the medial vestibulospinal tract --\> medial spinal cord --\> head and neck orientation 2. lateral vestibulospinal tract --\> lateral motor pools --\> proximal limb musculature

Question 71

What allows for rapid error-correction in muscle movement and contraction?

Answer 71

α and ɣ motor neuron coactivation

Question 72

What is the target of the 8th cranial nerve?

Answer 72

the vestibular nuclei

Question 73

Force increases the tension on collagen strands and pinches the intertwined afferent fibers, causing \_\_\_\_.

Answer 73

them to fire

Question 74

What is the Golgi tendon organ made of? Where are they found?

Answer 74

collagen; at the junction of a muscle and a tendon

Question 75

This produces eye movements to counter head movements to keep the gaze fixed.

Answer 75

the vestibular ocular reflex (VOR)

Question 76

This is when selective neural responses are observed in response to the subject simply watching an action with an intended consequence.

Answer 76

mirror neuron activity

Question 77

The reticular formation is a collection of loosely connected areas that lie within the \_\_\_\_\_.

Answer 77

midbrain tegmentum

Question 78

1a spindle afferents branch and diverge in the spinal cord to contact ______ of motor neurons which innervate populations of muscle fibers to create the reflex motion.

Answer 78

large populations

Question 79

Slow twitch muscle fibers generate action potentials to twitch, but fatigue ____ owing to high concentrations of myoglobin and many mitochondria.

Answer 79

very slowly

Question 80

Is motor unit type plastic?

Answer 80

yes- exercise and chronic stimulation can shift motor unit phenotype from fast to slow

Question 81

What innervates the Golgi tendon organ?

Answer 81

type Ib sensory afferents that wind around and within the collagen strands

Question 82

\_\_\_\_\_\_\_ fibers activate quickly and fatigue rapidly owing to few mitochondria and a dependence of anaerobic glycolysis ATP generation.

Answer 82

Fast twitch glycolytic

Question 83

Descending projections of the colliculospinal (aka tectospinal) tract target motor neurons that control the ______ to generate coordinated orienting responses.

Answer 83

axial musculature of the neck

Question 84

Gradients from small to large motor units exist, generating \_\_\_\_\_.

Answer 84

graded forces

Question 85

Are small or large motor units recruited first?

Answer 85

small- think about grabbing something delicate