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Anatomy 403 > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

function of muscle

A

convert chemical energy into mechanical energy

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2
Q

what percent of the total body mass is skeletal muscle?

A

30-40%

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3
Q

largest muscle

A

gluteus maximus

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4
Q

smallest muscle

A

stapedius (inner ear)

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5
Q

muscle generates ____

A

heat

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6
Q

what percent of the body mass is smooth and cardiac muscle?

A

10%

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7
Q

no muscle means

A

no breathing, no chewing, no blinking, no digesting, no circulation, no walking, no talking, no smiling, no sitting up straight

—> NO MOVEMENT

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8
Q

skeletal muscle

A
  • long parallel fibers
  • striated
  • mutinucleated
  • voluntary
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9
Q

cardiac muscle

A
  • short branched fibers
  • striated
  • uninucleated
  • involuntary
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10
Q

smooth muscle

A
  • sheets of cells
  • not striate
  • uninucleate
  • involuntary
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11
Q

whole skeletal muscle

A

bundle of fascicles

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12
Q

fascicle

A

bundle of muscle fibers

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13
Q

muscle fiber

A

bundle of myofibrils (contractile protein bundles)

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14
Q

myofilaments

A
  • contractile proteins

- in the presence of Ca+2 the myosin cross-bridge and actin physically interact to generate tension

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15
Q

scaroplasmic reticulum (smooth ER)

A

stores Ca+2

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16
Q

transverse tubule (T-tubule)

A

in foldings of plasma membrane

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17
Q

sarcolemma

A

plamsa membrane

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18
Q

sarcoplasm

A

cytoplasm

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19
Q

myofibrils

A
  • bundles of myofilaments

- intracellular contractile structures arranged in repeating units)

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20
Q

thin myofilament

A

actin

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21
Q

thick myofilament

A

myosin

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22
Q

sarcomere

A
  • functional units of muscle

- one unit of repeating thin and thick filament pattern within the myofibril

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23
Q

I band

A

actin only (light under the microscope)

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24
Q

M line

A

grey under the microscope

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25
Q

H band

A

myosin only

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26
Q

A band

A
  • both actin and myosin

- dark under the microscope

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27
Q

sarcomere within filament

A

from one z disk to next z disk

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28
Q

what are the “chaperons” regulatory proteins?

A
  • tropomyosin

- troponin

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29
Q

tropomyosin

A
  • covers active sites on 7 actin molecules

- on/off switch for contracted/relaxed muscle

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30
Q

what are the contractile proteins?

A
  • myosin

- actin

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31
Q

muscle contraction order

A
  1. activation of motor neuron
  2. signal transmitted to muscle at Neuromuscular Junction (NMJ)
  3. excitation of muscle fiber
  4. excitation-contraction coupling
  5. contraction (sliding filament mechanism)
  6. relaxation
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32
Q

what division is skeletal muscle in?

A

efferent division

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33
Q

somatic motor

A

skeletal muscle (voluntary)

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34
Q

autonomic motor

A

cardiac and smooth muscle

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35
Q

motor unit

A

one motor neuron and all of muscle fibers it innervates

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36
Q

small motor units

A
  • 3-15 fibers
  • fine motor control
  • eyes
  • hands / fingers
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37
Q

larger motor units

A
  • 100s-1000s
  • for strength and power
  • arms
  • legs
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38
Q

skeletal muscle is always _____

A

excitatory

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39
Q

neuromuscular junction (NMJ)

A

alpha motor neurons originating in CNS terminate on skeletal muscle fibers at a specialized synapse

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40
Q

junctional folds

A

increase SA

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41
Q

motor end place

A

region of muscle membrane directly under axon terminal

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42
Q

what is the first phase of muscle contraction?

A

excitation of muscle fiber

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43
Q

excitation of muscle fiber step 1

A
  • arrival of nerve signal

- Ca+2 enters synaptic knob via VG Ca+2 channels

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44
Q

excitation of muscle fiber step 2

A
  • acetylcholine (ACh) release
  • via exocytosis of synaptic vesicles
  • ACh diffuses across synaptic cleft
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45
Q

excitation of muscle fiber step 3

A

binding of ACh to receptor

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46
Q

excitation of muscle fiber step 4

A
  • opening of ligand-regulated ion gate; creation of end-plate potential
  • Na+ flows in, then K+ flows out
  • More Na+
  • causes local change in potential = end plate potential (EPP)
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47
Q

excitation of muscle fiber step 5

A
  • opening of voltage-regulated ion gates; creation of APs
  • caused by end plate potential
  • APs propagate along muscle membrane
  • muscle fiber = “excited”
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48
Q

Botulinum toxin

A
  1. prevents vesicle exocytosis
  2. skeletal muscle paralysis
  3. respiratory arrest
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49
Q

organophosphates

A
  • pesticides
  • nerves gases (sarin gas)
    1. Inhibits AChE
    2. Na+ channels remain inactive (must repolarize to close)
    3. ACh receptor become desensitized
    4. no additional APs
    5. no contraction
    6. paralysis
    7. respiratory arrest
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50
Q

curare / succinylcholine

A
  1. nACh receptor antagonist
  2. binds to receptor but doesn’t open channel
  3. no AP
  4. no contraction
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51
Q

myasthenia gravis

A
  • autoimmune disorder
    1. auto-antibodies produced against nACh receptor
    2. bind/block/degrades
    3. affects muscles in face/throat/eyes first
    4. caused muscle weakness and fatigue
  • can treat with AChE inhibitor that increase available ACh
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52
Q

what is the second phase of muscle contraction?

A

excitation - contraction coupling

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53
Q

latent period

A

coupling events occur

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54
Q

excitation-contraction coupling

A

events linking muscle AP to cross-bridge (CB) formation

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55
Q

skeletal muscle fiber

A

AP has to travel far/deep inside fiber via T-tubules

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56
Q

Excitation-contraction coupling step 1

A

muscle AP propagated into T-tubules

  • at rest Ca+2 stored in SR
  • free Ca+2 in cytoplasm is very low
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57
Q

excitation-contraction coupling step 2

A
  • activated DHP receptor caused ryandine receptor to open

- Ca+2 is released from SR

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58
Q

DHP receptor

A

VG receptor

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59
Q

Ryanodine receptor

A

Ca+ channel

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60
Q

excitation-contraction coupling step 3

A

increased Ca+2

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61
Q

excitation-contraction coupling step 4

A

binding of calcium to troponin

62
Q

excitation-contraction coupling step 5

A

shifting of tropomyosin; exposure of active sites on actin

63
Q

Cross bridge cycling step 1

A

hydrolysis of ATP to ADP+Pi activation and cocking of myosin head
- at rest, myosin head is already energized

64
Q

cross bridge cycling step 2

A
  • formation of myosin-actin cross-bridge

- increased Ca+2

65
Q

cross bridge cycling step 3

A

power stroke; sliding of thin filament over thick filament

66
Q

cross bridge cycling step 4

A

binding of new ATP; breaking of cross-bridge

67
Q

cross bridge cycling

A
  • if Ca+2 stays high the process will continue

- can cycle about 5x sex if Ca+2 is present

68
Q

rigor mortis

A
  • “stiffness of death”
  • occurs about 3 hours after death
  • peaks at 12 hours
  • unit about 48 hours as muscle decomposes
  • contraction continues as long as there is ATP and Ca+2
  • locked in contracted state because ATP is required to break CB
69
Q

relaxation phase step 1

A

cessation of nervous stimulation and ACh release

70
Q

relaxation phase step 2

A

ACh breaks down by ACHE

71
Q

relaxation phase step 3

A

Ca+2 ATP actively transports Ca+2 back into SR

  • this pump is always on
  • takes time to pump all Ca_2 back in
  • reason why tension generated lasts so long after AP (100 ms)
72
Q

relaxation phase step 4

A

loss of calcium ions from troponin

  • muscle returns to resting length
73
Q

relaxation phase step 5

A

return of tropomyosin to position blocking active sties of actin

74
Q

muscle returns to resting length by:

A
  1. elastic recoil

2. action of opposing muscles

75
Q

costamere

A
  • transmits contrails forces from sarcomeres on one myofiber to another
  • synchronizes contraction of myofiber within a muscle
76
Q

muscular dystrophy (MD)

A
  • mutation in dystrophin gene (X chromosome)
  • Duchenne = dystrophin absent
  • Becker = protein truncated
  • muscle contraction = muscle degeneration and weakening = death from cardiac
77
Q

muscular dystrophy symptoms

A
  • becomes evident when begin walking
  • waddling gait
  • need braces by age 10
  • unable to walk by age 12
  • respiratory arrest
  • cardiomyopathy
78
Q

Duchenne muscular dystrophy lifespan

A

15-20 years

79
Q

Beckers muscular dystrophy lifespan

A

usually normal

80
Q

Gower’s sign

A

affect hip muscles first

81
Q

load

A

force exerted by an object on muscle

82
Q

tension

A

force exerted by muscle on object

83
Q

isometric contraction

A

same length

- CB cycle but bing in same place

84
Q

isotonic contraction

A

change length

- work performed

85
Q

types of isotonic contraction

A
  • concentric

- eccentric

86
Q

concentric isotonic contraction

A
  • shortening

- tension > load

87
Q

eccentric isotonic contraction

A
  • lengthening

- tension < load

88
Q

muscle fiber AP

A

response of a single fiber to one AP

89
Q

skeletal muscle metabolism

A
  1. creatine phosphate
  2. glycolysis
  3. oxidative phosphorylation
    - muscles use lots of ATP
    - different fiber types use different mixtures of ATP sources
90
Q

what system do you use for immediate energy?

A

phosphagen system (direct phosphorylation)

91
Q

phosphagen system

A
  • borrow phosphate from other molecules to make ATP
  • FAST but limited
  • about 5-8 seconds
  • ATP –> ADP + Pi
92
Q

what system do you use for short term energy?

A

glycolysis (anaerobic fermentation)

93
Q

glycolysis

A
  • uses glycogen from muscle and glucose from blood
  • 2 ATP / glucose
  • fast, but not efficient
  • produces lactic acid
  • no oxygen available
  • occurs in cytoplasm
  • 30-40 seconds of intense energy
  • if not intense it will occur longer
94
Q

what system do you use for long term energy?

A

aerobic respiration (oxidative phosphorylation)

95
Q

aerobic respiration

A
  • uses glycogen from muscle and glucose and fatty acids from blood
  • 32 / ATP
  • slower, but most efficient
  • produces CO2
96
Q

muscle fatigue

A

decrease ability to produce tension despite continued stimulation

97
Q

factors associated with fatigue

A
  • decreased glycogen / blood glucose
  • increase lactic acid (increase acidity = decrease enzyme function)
  • increase K+ in ECF (decrease excitability)
  • dehydration / decrease electrolytes (decrease excitability)
  • increase ADP/Pi
    • -> CB slower to release ADP/Pi if Pi increased
    • -> Pi combine Ca+2
  • decrease CNS output to muscles
98
Q

lactic acid

A

decrease enzyme function

99
Q

smooth muscle

A

lines the walls of hollow organs

100
Q

similarities between skeletal and smooth muscle

A
  1. siding filaments (actin, myosin) -> CB’s
  2. ATP power
  3. elevated Ca+2 triggers contraction
101
Q

differences between skeletal and smooth muscle

A
  1. organization of contractile filaments
  2. many inputs can modulate activity
  3. process of EC-coupling
102
Q

smooth muscle difference organization of contractile filaments

A
  • small cells in sheets, single nuclei, no striations

- no sarcomeres, T-tubules, or troponin

103
Q

smooth muscle difference many inputs can modulate activity

A
  • these can be excitatory or inhibitory :
  • ANS (SNS and PSNS)
  • hormones
  • local factors (H+, O2, NO)
  • stretch
  • pacemaker activity
104
Q

smooth muscle difference process of EC-coupling

A
  • relies on Ca+2 from both inside and outside the cell

- cross bridge cycling is controlled by Ca+2 regulated enzyme that phosphorylates myosin

105
Q

smooth muscle contractile properties

A
  1. slow cross bridge cycling: 3 sec twitch & slower removal of Ca+2
  2. slow ATP splitting is economical
  3. activity can be graded by varying Ca+2
    - -> increase Ca+2 = increase tension
  4. broad length-tension relationship
106
Q

latch state phenomenon

A

cross-bridge “latch onto” thin filaments for long periods (up to 60s) = pseudo rigor state

  • maintain high tension without fatigue
  • low ATP consumption = efficient
  • –> these two decrease fatigue because less ATP used over time
107
Q

parallel elastic components function

A
  • absorb tension first

- allows for slow, purposeful development of tension

108
Q

temporal summation

A

increase stimulation of frequency causes increase muscle tension

109
Q

twitch

A

submaximal tension because not all myosin heads find actin before Ca+2 decrease

110
Q

temporal summation / incomplete tetanus

A
  • normal
  • 10-40 / sec
  • physiologically normal stimulus frequency
  • increase tension with particle relaxation between stimuli
111
Q

complete tetanus

A
  • sustained muscle contraction, no relaxation between stimuli
  • max = 3-5x twitch strength
112
Q

overly contracted

A
  • overlapping thin filaments interfere with each other

- Z dics collide with thick filaments

113
Q

optimum resting length

A

overlap that maximizes CB’s formed

114
Q

overly stretched

A
  • decreased overlap between thin/thick filaments
  • decreased number of CB’s formed
  • decreased tension
115
Q

what maintains muscle tone in optimal range?

A

CNS

116
Q

factors that determine muscle fiber tension that can vary from contraction to contraction

A
  • the frequency of stimulation (temporal summation)

- muscle fiber length (length-tension relationship)

117
Q

factors that determine muscle fiber tension that do not vary from contraction to contraction

A
  • metabolic capability
  • fatigue
  • fiber diameter
118
Q

skeletal muscle fibers are categorized by:

A
  1. speed of contraction (depends on myosin isoform) (fast or slow)
  2. metabolic pathway used to form ATP (ox. phosph. or glycolysis)
119
Q

what are the three basic types of skeletal muscle fibers?

A
  1. type I (slow oxidative)
  2. type IIA (fast oxidative-glycolytic)
  3. type IIB (fast glycolytic)
120
Q

slow oxidative

A
  • or known as slow twitch
  • used in posture/antigravity
  • slow to fatigue (aerobic resp)
121
Q

fast oxidative-glycolytic

A
  • intermediate

- used in aerobic exercise activities

122
Q

fast glycolytic

A
  • known as fast twitch
  • fast to fatigue
  • used in high power activities
123
Q

slow oxidative fatigue

A

fatigue slowly but require longer rest periods

124
Q

fast oxidative-glycolytic fatigue

A

intermediate

125
Q

fast glycolytic fatigue

A

fatigue rapidly but recover quickly

126
Q

fiber diameter

A

SO < FOG < FG

- smaller fibers generate less tension

127
Q

endurance training

A

FG –> FOG

128
Q

strength training

A

FOG –> FG

129
Q

adaptations of muscle fibers

A
  1. aerobic exercise induces metabolic changes within fibers, which enable muscle to use O2 more efficiently
    - -> increase number of mitochondria
    - -> increase capillaries
  2. anaerobic, short-duration, high-intensity exercise causes enlargement of fast-glycolytic fibers (muscle hypertrophy)
    - -> increase number of myofibrils per cell
    - -> increase glycolytic enzymes
130
Q

factors that determine muscle tension

A
  1. tension developed by each fiber
    a. AP frequency **
    b. fiber length
    c. fiber diameter
    d. fatigue
  2. number of active fibers
    a. number of fibers per motor size (motor unit size) **
    b. number of active motor units (motor unit recruitment)

** factors that change to modify muscle tension from each contraction

131
Q

motor unit

A

each motor unit contains one muscle fiber type determined by the alpha - motor neuron

132
Q

motor unit size

A

SO < FOG < FG

133
Q

motor unit recruitment

A

primary means of varying tension in whole muscle

134
Q

muscle recruitment order

A

SO –> FOG –> FG

135
Q

higher centers

A

intent

136
Q

higher centers function

A

give “intention” to move

137
Q

higher centers structures

A

sensorimotor areas of cortex and others involved in emotion, memory and motivation
- frontal lobe

138
Q

middle level control

A

coordination

139
Q

middle level control function

A

create a “motor program” based on input from higher centers (intention) and sensory input from muscles, joints, skin, eyes about starting position, space available to move

140
Q

middle level control structures

A

sensorimotor cortex, thalamus, basal nuclei, brainstem, cerebellum

  • with practice, the initial “motor program” is more accurate and the movement becomes skilled
141
Q

local level portal

A

execution

142
Q

local level function

A

provide sensory input and enact the “motor program”

143
Q

local level structures

A
  • muscle spindles
  • Golgi tendon organs
  • other receptors
  • spinal / brainstem interneurons
  • alpha motor neurons
144
Q

muscle spindles

A
  • stretch receptors inside a muscle for proprioception
  • abundant in muscles that control find movement
  • concentrated at ends of muscles near tendons
145
Q

extrafusal muscle fiber

A

regular skeletal muscle fibers innervated by alpha motor neurons

146
Q

stretch reflex

A

muscle spindles provide info on length increase stretch –> contract

147
Q

golgi tendon organs

A

proprioceptors in tendon near junction with muscle = nerve endings embedded in collagen fibers

148
Q

GT reflex

A

increased tension = decreased contraction

149
Q

withdrawal reflex

A

move away from painful stimulus (flexors) = ipsilateral

150
Q

crossed extension reflexes

A

shift body weight to maintain balance (contralateral)

Anatomy 403 (13 decks)

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