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NEURO MIDTERM1 > LECUTRE 6- somatic motor system : proprioceptors and lower motor neurons > Flashcards

LECUTRE 6- somatic motor system : proprioceptors and lower motor neurons Flashcards

1
Q

examples of Sensory proprioceptors/muscle receptors:

A

• Muscle spindles
• Golgi tendon organs

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2
Q

example of motor neurons of the peripheral neuromuscular system

A

• Alpha α motor neurons
• Gamma γ motor neurons

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3
Q

what are the Specialized intrafusal muscle fibers with non- contractile central regions

A

• Dynamic nuclear bag (1a, dynamic γ)
• Static nuclear bag (Ia, II, static γ)
• Nuclear chain (Ia, II, static γ)

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4
Q

what originate from central regions of intrafusal
fibers

A

Large diameter myelinated sensory receptors (Ia &
II)

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5
Q

what innervate the polar contractile regions of intrafusal fibers

A

Small diameter myelinated motor endings (γ)

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6
Q

Typical muscle spindle contains ___ bag and__- chain fibers

A

2-3 and 5

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7
Q

what are Primary sensory endings for muscle spindles

A

la

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8
Q

what type of discharge is Primary sensory endings

A

phasic and tonic discharge

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9
Q

what Responds to changes in muscle length and
steady-state muscle length

A

Primary sensory endings

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10
Q

whtat type of discharge is Secondary sensory endings:

A

tonic discharge

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11
Q

what type of contracture is Secondary sensory endings:

A

II

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12
Q

what ending responds to steady state muscle length

A

Secondary sensory endings:

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13
Q

where does alpha and gamma motor neurons come off of

A

ventral horn/ root of SC

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14
Q

is alpha motor neuron extrafusal or infrafusal

A

extrafusal

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15
Q

is gamma MN infra or extra

A

infra

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16
Q

where are muscle spindles embedded inside of

A

muscle’s
extrafusal fibers

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17
Q

what does muscle spindles monitor

A

muscle length and prevent
over stretching

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18
Q

when does muscle spindles fire

A

Fire even when muscle is relaxed

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19
Q

how does muscle spindles regulate alpha motor neurons?

A

via
feedback mechanism (ex: stretch reflex)

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20
Q

When muscle is loaded, muscle lengthens/is
stretched which causes increased firing of
spindle sensory afferents, what neurons are these ?

A

la & ll

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21
Q

are alpha motor neurons efferent or afferent

A

efferent

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22
Q

how are alpha MN activated

A

by spindles at SC in ventral horn

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23
Q

how happens to the muscle spindle when muscle shortens

A

activity declines

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24
Q

which neuron is in continuum of activation while muscle is shortening

A

la

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25
Q

which MN regulate sensitivity of muscle spindles within intrafusal muscle fibers

A

gamma

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26
Q

what does the dynamic gamma MN innervate and what sensitivity does it increase

A

dynamic nuclear bag fibers & la

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27
Q

which gamma MN innervate both static nuclear bag and chain fibers

A

static

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28
Q

what dies static gamma NM increase activity of

A

tonic activity of la and ll

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29
Q

what Decreases dynamic sensitivity of Ia

A

static gamma MN

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30
Q

what happens to intrafusal fibers if gamma MN were not present?

A

less stretch which decreases spindle activity

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31
Q

what part of the intrafusal fibers do the gamma MNs innervate

A

polar regions ( the ends)

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32
Q

what afferent spindles for the intrafusal muscle fibers contain

A

la & ll

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33
Q

what ensure an appropriate length-tension
relationship during muscle contraction

A

Co-activation of α and γ MNs

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34
Q

if gamma MNs are not active during a alpha -gamma co activation what happens to the spindles

A

they will be slacken and its discharge rate will decrease as muscle shortens

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35
Q

during alpha - gamma co activation what does the gamma MNs adjust

A

sensitivity of muscle spindle
by Ia afferents

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36
Q

what does the motor controls strategy do during the alpha gamma co activation for alpha MNs

A

Reinforces α MN activity through
feedback mechanisms

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37
Q

what happens during reciprocal inhibition

A

When 1 muscle (agonist) contracts, its opposing
muscle (antagonist) is inhibited

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38
Q

during reciprocal inhibition, Muscle spindles of agonist send signal to SC that
activates:

A

activates:
1. Agonist
2. Interneurons that inhibit antagonist

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39
Q

when do reciprocal inhibition happen

A

voluntary and reflexive mvmts

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40
Q

what proprioceptors are Slender, encapsulated structure located at junction between muscle
fibers and tendon (intertwined)

A

golgi tendon organs

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41
Q

what are the golgi tendon organs innervated by

A

Ib sensory fibers

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42
Q

what are the golgi tendon organs sensitive to

A

changes in muscle tension ( stretch of tendon)

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43
Q

what are the 2 motor control strategy of golgi tendon organ

A

afferent signal from GTO inhibit activity of MN and results in muscle relaxation ( via neg
feedback mechanism – autogenic inhibition)

or

activates MN of its own muscle and its synergists via positive feedback

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44
Q

do muscle spindle and GTOs have slow or fast conducting afferent nerves fibers

A

fast

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45
Q

what are the 2 afferent nerve fibers that are fast

A

la and lb

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46
Q

what do the muscle spindle activate directly and what does it cause

A

alpha motor neurons and cause the muscle fibers to contract

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47
Q

what does the GTO provide

A

force feeedback , the more the muscle contracts the more GTO and afferents are activated

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48
Q

Efficacy of length and force feedback
can be regulated independently in

A

SC and via γ MNs

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49
Q

what are called the “final common path”

A

lower motor neurons

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50
Q

where are the motor neurons located and where do they exit

A

in cell bodies in ventral horn of sc and exit thru the ventral root

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51
Q

what are the 2 types of MNs

A

alpha and gamma

52
Q

what are MN pools

A

Clusters of MNs within SC

53
Q

Medially and laterally located pools innervate

A

M- axial and proximal limb muscles, L - distal limb

54
Q

what do the ventral and dorsal located pools innervate

A

V- extensors and D- flexors

55
Q

what are motor units

A

functional unit of voluntary movement

56
Q

how are motor units defined as

A

α MN and muscle fibers it innervates

57
Q

what is a group of muscles innervated by single spinal nerve

A

myotomes

58
Q

what innverate slow twitch fibers

A

smaller MNs

59
Q

do small MNs enervate more or less force than fast twitch fibers

A

less

60
Q

which MN can maintain levels of force for long periods of time

A

Small MNs

61
Q

are large or small MNs important in postural control

A

small

62
Q

what innervates fast twitch fibers

A

large MNs

63
Q

do the large MNs fatigue fast or slow

A

fast

64
Q

what is an area where the motor axon divides into several fine branches

A

neuromuscular junction

65
Q

in the neuromuscular junction, each branch forms multiple swellings called

A

presynaptic boutons

66
Q

the presynapic boutons lay over specaialized region of muscle membrane called what

A

motor endplate

67
Q

what is released at the motor end plate

A

acetylcholine released which causes depolarization of the muscle

68
Q

where do motor axons synapse with muscle fibers

A

neuromuscular junction

69
Q

steps of depolarization of muscle membrane potentials

A

Ach bind w receptors on muscle membrane resulting in membrane depolarization which induces depolarization of T tubes

voltage gated channels open and calcium ions are released from sarcoplasmic reticulum ‘

calcium’s ions bind to receptors on troponins, initiating muscle contraction

70
Q

if you increase the firing rate of MN then there is in _____ in muscle force production

A

increase

71
Q

what is induced by higher firing rate

A

force summation

72
Q

what is tetanus

A

muscle is contracting maximally

73
Q

pertaining to the time to peak-twitch force which twitch is shorter

A

fast twitch MNs shorter than slow twitch MNs

74
Q

pertaining to contraction time which twitch is shorter

A

Fast twitch MNs shorter than slow twitch MNs

75
Q

pertaining to peak force which twitch generated higher forces

A

ast twitch MNs generate higher forces than slow twitch across all frequencies

76
Q

at lower frequencies what forms a better summation force

A

slow twitch MNs

77
Q

what MNs are recruited and fire first

A

smaller MNS first then larger MNs

78
Q

what is ohm’s law

A

V= IR (voltage = current x resistance)

79
Q

Smaller MNs have smaller membrane surface area and few ion channels, and therefore ____
input resistance and then ____ excitatory post-synaptic potential (EPSP)

A

larger 2x

80
Q

how much of synaptic current will be needed to cause the membrane potential of small
MN to reach firing threshold (generation of APs)

A

small amount

81
Q

do smaller MNs have faster or slower conduction velocities

A

faster

82
Q

each muscle fibers consist of ___ and are arranged

A

myofibrils and arranged parallel to long axis of muscle fiber

83
Q

each myofibril consists of

A

sarcomeres

84
Q

sarcomeres are function units of muscle containing….

A

contractile and structural proteins, thick and thin filaments
bounded by Z-lines (disks)

85
Q

what is specialized muscle membrane
that surrounds sarcoplasmic reticulum and allows
propagations of action potentials

A

transverse tube ( t-tube)

86
Q

in the sarcoplasmic reticulum (SR) what is released , what is stored and what does it facilitate?

A

Acetylcholine (Ach) released
• Storage sacs for Ca2+ ions
• Facilitates cross-bridge formation and initiates muscle
contraction

87
Q

what is Fibrous, at end of each sarcomere

A

z line / disk

88
Q

what holds together fibers at sarcomere center

A

M line

89
Q

what Maintains actin/myosin positions to prevent sarcomere from getting pulled apart

A

titin

90
Q

what are the structural proteins in sarcomere

A

z line
M line
titin

91
Q

what are the contractile proteins of the sarcomere

A

myosin
actin
troponin
tropomyosin

92
Q

what do the myosin headed bind with

A

active sites on actin

93
Q

where are actin filaments attached to

A

each end of sarcomere to z-lines

94
Q

within the actin , contractions occur when

A

actin slides relative to myosin, initiated when Ca2+ binds to troponin

95
Q

what changes troponin

A

calcium binding to it

96
Q

when calcium bind to troponin what does it cause

A

tropomyosin to move and uncover active sites on actin

97
Q

what determines the total resistance to stretch

A

Active contractions, titin, and actin-myosin bonds

98
Q

what is Resistance to stretch in resting muscle

A

muscle tone

99
Q

what determines the mortal resting muscle tone

A

Thin/weak actin-myosin bonds and titin

100
Q

the longer the immobility , what happens to the actin - myosin bond

A

there is a weaker bond

101
Q

Healthy innervated muscles will lose sarcomeres when immobilized in shortened position for prolonged time (T or F)

A

T

102
Q

( T/F )Healthy innervated muscles will gain sarcomeres when immobilized in lengthened position for long time

A

True

103
Q

what can restrict movement

A

joint capsules and noncontractile tissues

104
Q

what mvmts are small % of all mvmts

A

reflexive

105
Q

what are spinal reflexes

A

nvoluntary motor response to external stimulus

106
Q

what needs to be present for a reflex to occur

A

receptor, afferent nerve, synapse/s, efferent nerve, and muscle

107
Q

can Spinal reflexes can occur without brain input?

A

yes

108
Q

what is phasic stretch reflex

A

Muscle contraction in response to quick stretch (ex tendon tap)

109
Q

what does fast muscle stretch activate

A

muscle spindles to α MNs of same muscle

110
Q

what is a monosynaptic

A

1 synapse

111
Q

what is a cutaneous withdrawal reflex

A

Another monosynaptic reflex in SC that occurs in response to pain

112
Q

what is a painful contractions lasting sec/min due to overstimulation by sensory and motor tracts

A

muscle cramps

113
Q

what is a Visible fast twitches of all muscle fibers in 1 motor unit

A

Fasciculations

114
Q

Fasciculations can be

A

normal or pathologic

115
Q

fibrillations of single muscle fibers ____ – always pathologic due neuro instability after
denervation

A

not visible

116
Q

what is a Brief contractions of muscles or group of muscles

A

myoclonus

117
Q

what are tremors

A

involuntary rhythmic mvmts

118
Q

when do tremors happen

A

at rest or w movement

119
Q

what are examples of pathologic tremors

A

postural , orthostatic, intention

essential tremor
parkinson’s disease

120
Q

what are the signs of motor neuron lesions

A

• Decrease or loss of reflexes (DTRs)
• Paresis or paralysis
• Muscle atrophy
• Decrease or loss of muscle tone
• Fibrillations

121
Q

what do electrodiagnostic studies differentiate between

A

disorders of MN , NM junction and muscle

122
Q

what does a Electromyography (EMG) differentiate between

A

denervated muscle or myopathy

123
Q

Poliomyelitis and post-polio syndrome (PPS) have what type of MN

A

normal

124
Q

in Poliomyelitis and post-polio syndrome (PPS) there is death of selected MNs due to

A

acute polio

125
Q

in Poliomyelitis and post-polio syndrome (PPS) there is no neuroplasticity of MNs during recovery, forming

A

giant
motor units

NEURO MIDTERM1 (10 decks)

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