Neuro 5-Somatic Motor System

Question 1

Alpha and gamma neurons are what kind of neurons?

Answer 1

Motor

Question 2

What is the difference between Golgi tendon organs and Muscle Spindles

Answer 2

Both are sensory organs
Muscle spindle- detect stretch in muscle
GTO- Detect stretch in tendon

Question 3

What are the joint kinesthetic receptors

Answer 3

Pacinian and ruffini corpusle

bare endings

Question 4

Muscle spindles are ______ muscle fibers

Answer 4

Intrafusal

Question 5

True or false: muscle spindles contract in their central region

Answer 5

False, the central region is non-contractile

Question 6

Type 2 sensory fibers go to what muscle spindles?

Answer 6

Nuclear chain and STATIC nuclear bag fibers

(not dynamic nuclear bag)

Question 7

Type 1a fibers go to what muscle spindles?

Answer 7

All 3

Nuclear chain, static, and dynamic nuclear bag

Question 8

Static gamma neurons innervate the contractile endings of what muscle spindles?

Answer 8

Static nuclear bag and nuclear chain

Question 9

Dynamic gamma neurons innervate the contractile endings of what muscle spindles?

Answer 9

dynamic nuclear bags

Question 10

True or false: Sarcomeres are found inside of intrafusal muscle fibers

Answer 10

Sarcomeres are present in extrafusal muscle fibers and the polar regions of intrafusal fibers.

Extrafusal fibers are the standard muscle fibers responsible for muscle contraction and movement, and they contain sarcomeres throughout their entire length.

Intrafusal fibers, on the other hand, are found within muscle spindles and are involved in proprioception (sense of muscle stretch). Sarcomeres are **only present in the polar ends **of intrafusal fibers, not in the central region, which functions to detect stretch

Question 11

What do gamma motor neurons innervate?

Answer 11

The contractile ends of muscle spindles

slide says: “polar regions of intrafusal fibers”

Question 12

large? diameter Alpha motor neurons (also called lower motor neurons) innervate what?

Answer 12

Extrafusal skeletal muscle fibers

Question 13

Large diameter 1a and 2 fibers originate from the _____ region of muscle spindles

Answer 13

Central regions

Question 14

A typical muscle spindle contains ____ nuclear bag and ____ chain fibers

Answer 14

2-3 nuclear bag and 5 chain fibers

Question 15

Muscle spindles measure the velocity of stretch from phasic discharge of ____ fibers

Answer 15

1a

Question 16

Muscle spindles measure the steady state length of muscle from tonic discharge of _______ fibers

Answer 16

1a and 2

Question 17

1a’s have both ____ and _____ discharges

whereas 2’s only have ____ discharges

Answer 17

1a: Phasic and tonic

2: only tonic

Question 18

True or false: Muscle spindles fire even when muscle fibers are relaxing

Answer 18

True

Question 19

Muscle spindles regulate _____________ neurons via feedback mechanism/stretch reflex

Answer 19

alpha motor neurons

Question 20

Muscle spindles send input via sensory neurons to the spinal cord at the _________ horn and the spinal cord relays information to the muscle via alpha motor neurosn from the _______ horn

Answer 20

Dorsal horn (afferent)

Ventral horn (efferent)

Question 21

Gamma motor neurons control the ______ of the muscle spindles

Answer 21

Sensitivity

Question 22

Dynamic gamma motor neurons increase the dynamic sensitivity of…

Answer 22

1a fibers

Question 23

Static gamma motor neurons increase the tonic activity of….

Answer 23

Type 1a and 2

Note: also decreases the dynamic sensitivity of 1a

Question 24

When extrafusal fibers shorten the intrafusal fibers _______

Answer 24

Are slack, do not fire as much

Note: less stretch = less firing

Question 25

Without the sensory afferents of muscle spindles, the CNS cannot monitor information about....

Answer 25

Muscle length/position

Question 26

coactivation of gamma and alpha motor neurons ensure

Answer 26

appropriate length/tension relationship

Question 28

What causes reciprocal inhibitor? Golgi Tendon Organs OR Muscle Spindles

Answer 28

Muscle Spindles

Question 29

How does reciprocal inhibition work?

Answer 29

Muscle spindles of agonist (example:quads) send signal to spinal cord From the spinal cord a signal is sent that activates further contraction at the quads AND it sends a signal via inter neurons to inhibit contraction of the antagonist (example:hamstrings)

Question 30

True or false: reciprocal inhibition can occur voluntarily AND reflexively

Answer 30

True

Question 31

Where are golgi tendon organs found?

Answer 31

At the junction between muscle fibers and tendons

Question 32

What kind of neurons innervate the Golgi Tendon Organs?

Answer 32

1b fibers

Question 33

What do Golgi tendon organs do?

Answer 33

Autogenic inhibition or activation The respond to force/muscle tension at the junction between the muscle and its tendon They can either inhibit or activate the same muscle that they’re found in.

Question 34

True or false: both the Golgi tendons and the muscle spindles use *fast conducting* afferent nerves

Answer 34

True

Question 35

What is the ratio of muscles to motor neuron pool?

Answer 35

1:1

Question 36

all motor neurons within the muscle neuron pool innervate ____

Answer 36

a single muscle

Question 37

MNs innervating the axial muscles are located where in the ventral horn? what about distal muscles?

Answer 37

located medially located laterally

Question 38

where are flexor muscles located in the ventral horn? extensors?

Answer 38

flexors located dorsally extensors ventrally

Question 39

describe a motor unit

Answer 39

one alpha motor neuron and all the muscle fibers it innervates

Question 40

small motor units (not very many muscle fibers innervated) are used for what type of movement? what about larger motor units?

Answer 40

small = fine movements large = gross movement

Question 41

What determines if a muscle fiber is fast/slow twitch?

Answer 41

the neuron innervating the muscle motor neurons/UNITS (both) are classified as slow twitch or fast twitch depending on speed of contraction so "both".... but motor neurons.

Question 42

which fiber (type 1 or 2) can maintain levels of force for long periods of time?

Answer 42

type 1 (endurance)

Question 43

which muscle fiber (type 1 or 2) has a larger axon diameter?

Answer 43

type 2 (fast) larger forces but fatigue quickly

Question 44

which muscle fibers are used for postural control?

Answer 44

endurance - type 1

Question 45

What NT is released from the presynaptic neuron in the NMJ?

Answer 45

Ach

Question 46

After being released into the NMJ, Ach binds to the muscle membrane, causing what?

Answer 46

Depolarization of the muscle membrane and then depolarization of the T-tubules in the muscle fiber

Question 47

What happens following the depolarization of T-tubules in the muscle cell?

Answer 47

voltage-gated channels open, releasing Ca+ from the sarcoplasmic reticulum (SR)

Question 48

To initiate a muscle contraction, ___ (what ion) binds to ___

Answer 48

Ca+ troponins

Question 49

What is rate coding?

Answer 49

MN signals amount of force to be exerted by muscle (frequency of firing determines contraction strength)

Question 50

Tetanus

Answer 50

muscle is contracting maximally

Question 51

Force summation is caused by

Answer 51

higher firing rate

Question 52

How do slow vs fast twitch MNs compare with time to peak-twitch force contraction time peak force relative force summation

Answer 52

time to peak force: fast twitch have shorter time contraction time: fast twitch have shorter twitch time peak force: fast twitch generates higher forces relative force summation: at lower frequencies, slower twitch form better summation

Question 53

What is recruited first, smaller or larger MNs? Why is this the case?

Answer 53

smaller V = IR, smaller motor neurons have large resistance ("R"), so a smaller current ("I") will still lead to higher V small amount of synaptic current will be sufficient to cause the potential of small MN to reach the firing threshold

Question 54

Z lines are ____ and are at the end of each sarcomere Titin is ____ and anchors Z and M lines

Answer 54

fibrous elastic

Question 55

Which filament has the "head" and which one slides inwards towards M line? (thick or thin)

Answer 55

Myosin heads connect with actin, pulling actin towards center

Question 56

What does Ca+ bind to in order to open active sites on actin?

Answer 56

Ca+ binds to troponin, causing tropomyosin to move off active sites

Question 57

Resistance to stretch in resting muscle is

Answer 57

muscle tone

Question 58

what determines the amount of muscle tone?

Answer 58

weak actin/myosin bonds at rest as well as titin

Question 59

How does contraction or immobility impact muscle tone/resistance to stretch?

Answer 59

resistance to stretch increases for a short time after prolonged contraction or immobility longer immobility = more weak actin-myosin bonds exist (Think about when you exercise and feel your muscles, and how you feel stiff in the morning getting out of bed)

Question 60

How are sarcomeres affected when patients are immobilized in a shortened position vs a lengthened positioned for a long time?

Answer 60

in a shortened position - lose sarcomeres lengthened position - gain sarcomeres

Question 61

What 3 things in your body can restrict movement?

Answer 61

joint capsules, noncontractile tissue and antagonist muscles (co-contraction)

Question 62

T/F Cocontraction is a normal part of stabilizing a joint in function

Answer 62

T

Question 63

Reflexive movements make up a __ (small or large) percentage of our movements. Define reflexive movements

Answer 63

small involuntary motor response to an external stimulus

Question 64

Spinal reflexes occur without what?

Answer 64

brain input

Question 65

T/F: patients with SCI can have spinal reflexes after time

Answer 65

T

Question 66

Describe the phasic stretch reflex

Answer 66

fast muscle stretch activates signals from the muscle spindles to alpha MNs for the same muscle causing a contraction monosynaptic

Question 67

Describe the cutaneous withdrawal reflex

Answer 67

monosynaptic reflex in the SC that occurs in response to pain/noxious stimuli before conscious awareness of pain

Question 68

The following are examples of what? - muscle cramps - fasciculations - myoclonus - abnormal movements generated by dysfunctional basal ganglia - fibrillations - tremors

Answer 68

spontaneous involuntary muscle contractions

Question 69

What causes muscle cramps?

Answer 69

high frequency discharges of MNs overstimulated by sensory and motor input healthy or pathologic

Question 70

What are fasciculations?

Answer 70

VISIBLE fast twitches of all muscle fibers in one motor unit healthy or pathologic

Question 71

What is myoclonus?

Answer 71

brief involuntary contraction - muscle jerks when falling asleep, hiccups healthy or pathologic

Question 72

what are fibrillations

Answer 72

NONVISIBLE, random, brief contraction so single muscle fibers PATHOLOGIC FIBRILation sounds like FIBER, single fiber

Question 73

What are tremors? List the three types

Answer 73

involuntary rhythmic movement that can occur at rest or with movement postural - body part maintained against gravity (usually upper limb) orthostatic - standing, (usually lower limbs) intention - absent at rest, worsen when target is approached

Question 74

Conditions affecting the ___ ____ and ______ (what two brain structures) also present with tremor?

Answer 74

basal ganglia and cerebellum

Question 75

List common signs of lower motor neuron lesions

Answer 75

hypoflexia or areflexia paresis or paralysis muscle atrophy decrease or loss of muscle tone (hypotonia/flaccidity) fibrillations

Question 76

What do motor nerve conduction velocities/studies measure?

Answer 76

measure the speed and strength of electrical signals traveling through MNs to muscles

Question 77

Why might an EMG be done for a patient with motor issues?

Answer 77

diagnostically differentiate between denervated muscle or myopathy "muscle not working does not mean the neuron is not working"

Question 78

What part of the nervous system does polio attack?

Answer 78

LMNs (at the ventral horn)

Question 79

What are the affects of the polio virus and how does it lead to PPS? (post-polio syndrome)

Answer 79

polio causes death of selected MNs, your body then forms giant motor units from remaining MNs (neuroplasticity effect) PPS - over time the giant MNs die off due to their excessive oxygen needs, causing fatigue, weakness and pain