Unit3_Motor Systems

Question 1

Small motor unit = _____ alpha-motor neuron → innervate small number of muscle fibers → _____ force

Answer 1

Small motor unit = Small a-motor neuron → innervate small number of muscle fibers → small force

Question 2

An alpha-neurons and the muscle fibers that innervates is called?

Answer 2

Motor Unit

Question 3

T/F?

Muscle fibers of a motor unit are of the same fiber type.

Answer 3

TRUE

Each muscle fiber is only innervated by one motor NEURON

Question 4

What size motor unit preferential innervates slow twitch muscle fibers?

Answer 4

Small motor unit

Question 5

What size motor unit requires more input to drive (recruited later and with larger currents)?

Answer 5

Large Motor Units

Question 6

what motor units preferentially innervate fast twitch glycolytic muscle fibers that are quick to fatigue?

Answer 6

Large motor units

Question 7

______________ : population of a-motor neurons that innervate the muscle fibers within a single muscle

Answer 7

Motor neuron pool

Question 8

Describe the size principle for the recruitment of muscles.

Answer 8

• Systemic recruitment of smaller to larger motor units - generates graded forces.
• Orderly recruitment of increasingly forceful motor units because small neurons have HIGH input resistances → given synaptic current induces larger voltage change in a small motor neuron compared to a large motor neuron

Question 9

The following describes what type of muscle cells/fibers?

non-spiking muscle fibers, shorten extremely slowly, efficiently generate isometric tension with low fatigability.

Answer 9

Tonic

Question 10

The following describes what type of muscle cells/fibers?

Generate APs to twitch, fatigue very slowly, high conc. of myoglobin and many mitochondria

Answer 10

Slow Twitch

Question 11

The following describes what type of muscle cells/fibers?

activate quickly, many mitochondria, fatigue moderately slowly.

Answer 11

Fast Twitch Oxidative

Make up the “Fast Fatigue-Resistant” Motor units.

Question 12

The following describes what type of muscle cells/fibers?

Actives quickly, fatigue rapidly, few mitochondria, depends on anaerobic glycolysis ATP generation.

Answer 12

Fast Twitch Glycolytic

makes up “Fast-Fagtiable” motor units

Question 13

Exercise/Chronic stimulation can shift motor unit phenotype from fast to slow → slows fatigability, ________ endurance capacity

Answer 13

increases

Question 14

What is muscle tone defined as and why is it important?

Answer 14

Muscle tone: defined as resistance to muscle stretch - important for walking, standing, running, etc.

Question 15

The stretch reflex provided resistance to stretch resulting in what?

Answer 15

enhances muscle tone

Question 16

______________ neuron activation → top-down regulation of muscle tone

Answer 16

gamma-motor neuron activation → top-down regulation of muscle tone

Question 17

__________: condition of decreased muscle tone due to damage to 1a sensory afferents innervating spindles or a-motor neurons innervating muscle

Answer 17

Hypotonia

Question 18

What is Hypotonia?

Answer 18

condition of decreased muscle tone d/t damage of 1a sensory afferents innervating spindles or alpha-motor neurons innervating muscles.

Question 19

__________: due to damage to descending motor pathways that influence spinal cord premotor circuits

Answer 19

Hypertonia

Question 20

What is Hypertonia?

Answer 20

d/t damage to descending motor pathways that influences spinal cord pre-motor circuit.

Question 21

What is a muscle spindle?

Answer 21

aka: intrafusal muscle fiber.

proprioceptor embedded within a muscle, composed of muscle fibers.

• Preferentially signals muscle stretch
• Important for maintaining muscle tone
• Feedback system for maintaining muscle strength

Question 22

What type of fibers do muscle spindles use? (intrafusal muscle fibers)

Answer 22

Group 1a and group 2 fibers

Question 23

How do group 1a fibers work?

Answer 23

Ia → synapse on a-motor neurons in spinal cord → trigger muscle contraction of homonymous muscle fiber in response to stretch.

• Have a non-zero firing rate under baseline conditions → maintenance of muscle tone
• Can signal passive stretch by increasing firing rate and passive shortening by decreasing firing rate

Question 24

______________ : special motor neurons that innervate intrafusal muscle fibers

Answer 24

gamma-motor neurons

Question 25

What do alpha and gamma motor neurons do during voluntary contraction?

Answer 25

alpha and gamma neurons fire together! During voluntary contraction, a and y motor neurons fire together → shorten extrafusal AND intrafusal muscle fibers together → maintains spindle sensitivity to stretch

Question 26

Gamma motor neurons do not directly interact with ____ fibers→ not engaged during reflexive contractions

Answer 26

1a fibers.

Question 27

Gamma motor neurons do not directly interact with Ia fibers→ not engaged during __________________.

Answer 27

reflexive contractions

Question 28

______________: collagen structures at junction of muscle and tendon, made up of capsule and collagen fibrils

Answer 28

Golgi tendon organs

Question 29

Golgi tendon organs: ?

Answer 29

collagen structures at junction of muscle and tendon, made up of capsule and collagen fibrils. Important for stabilizing muscle contractions

Question 30

What types of fibers are Golgi tendon organs innervated by?

Answer 30

1b fibers

Question 31

how are GTOs connected to muscle and tendons?

Answer 31

In series

Question 32

GTOs participate in the _______ ________ _________ of muscle tension.

Answer 32

GTOs Participate in negative feedback regulation of muscle tension

Question 33

Are GTOs contractile?

Answer 33

NO!!! GTOs are not innervated by gamma-motor neurons.

Question 34

Hammer tap → stretch muscle spindle→ stimulate Ia sensory axons → activate a-motor neuron in spinal cord → con.tract stretched muscle. What reflex does this describe?

Answer 34

Stretch Reflex Circuit; "Knee-Jerk" reflex Monosynaptic

Question 35

What is Reciprocal Innervation?

Answer 35

1a fibers also innervate other inhibitory interneurons → inhibit other motor neurons → inhibit opposing antagonist muscle

Question 36

In rapid error correction in movements, Heavier than we expect → muscle spindle stretches more than muscle fibers → increase Ia spindle firing → __________ contraction of muscle fibers via a-motor neurons.

Answer 36

increase

Question 37

mismatch between expected and actual muscle stretch detected rapidly and used to correct errors in motor output is called what?

Answer 37

Rapid error correction in movements

Question 38

What reflex protects musculature from over exertion by relaxing the synergistic (homonymous) muscle and contracting the antagonist.

Answer 38

Extensor-Flexor coupling circuit

Question 39

Ib afferents innervate GTOs → GTOs directly innervate inhibitory and excitatory interneurons in spinal cord is the mechanism for what reflex?

Answer 39

Extensor-Flexor coupling circuit

Question 40

Which reflex involves cutaneous sensory/nociceptors receptors that innervate the spinal interneuron motor network?

Answer 40

Crossed-Extensor reflex

Question 41

→ coordinate extensor relaxation and flexor contraction on same side as stimulus and converse extensor contraction and flexor relaxation on contralateral side. Describes what reflex?

Answer 41

Crossed-Extensor reflex

Question 42

_____?_____: neural networks that can produce patterned, rhythmic outputs in absence of sensory or central input - coordinate complex movements

Answer 42

Central Pattern Generator

Question 43

Where is the Central Pattern Generator (CPG) located?

Answer 43

Mesencephalic locomotion center

Question 44

Sensory and descending input from upstream motor centers can modify CPG output, but sensory is ___ necessary for CPGs to generate organized rhythmic motor output

Answer 44

NOT necessary

Question 45

What are the modulary functions of the motor system?

Answer 45

cardiovascular, respiratory control, and sensorimotor reflexes, eye movement, sleep-wake regulation, and coordination of limb/trunk movement

Question 46

What are the pre-motor functions of the motor system?

Answer 46

- Regulate locomotor speed via Input from mesencephalic locomotor region - initiator of CPG activity. - Anticipatory responses to voluntary movement (e.g. flex legs before lifting weight, anticipating change in center of balance). - Important for posture, balance and anticipatory movements.

Question 47

__________ tract: send axons ipsilaterally and innervate medial part of ventral horn

Answer 47

Reticulospinal tract

Question 48

What is the Vestibular nuclei?

Answer 48

vestibular system (vestibulospinal tract) informs brain of head position, orientation, and motion - important for protective responses to falls

Question 49

Sensory info detected by what and sent via 8th cranial nerve to vestibular nuclei

Answer 49

semicircular canals

Question 50

Vestibular nuclei sends info via what tract that regulate eye movement?

Answer 50

descending projections to cranial nuclei 3, 4, 6.

Question 51

Vestibular nuclei sends info via what tract that regulate head orientation and neck muscle activation?

Answer 51

Medial vestibulospinal tracts to medial spinal cord

Question 52

Vestibular nuclei sends info via what tract that control proximal limb musculature.

Answer 52

Lateral Vestibulospinal tract to lateral motor pools.

Question 53

What reflex produces eye movement that counter head movements to keep gaze fixed.

Answer 53

VOR no VOR = brain damage

Question 54

The midbrain structure responsible for orienting gaze and body position is called the?

Answer 54

Superior colliculus/Tectospinal tract: (aka colliculospinal tract). Computes a map merging auditory and visual space onto body coordinates. Descending projections of colliculospinal tract target motor neurons that control axial musculature of neck (e.g. turn head/upper torso towards siren going off)