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PHARM110 > Muscle Tissue > Flashcards

Muscle Tissue Flashcards

1
Q

Skeletal Muscle Tissue characteristics

A 
attached to bones and skin
voluntary (conscious control)
striated 
powerful
multi nucleated
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2
Q

cardiac muscle tissue characteristics

A

only in the heart
striated
involuntary
uni-or-binucleated

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3
Q

smooth muscle tissue characteristics

A

in the walls of hallow organs (stomach, GI, urinary, airways)
not striated
involuntary
uninucleated

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4
Q

what are the 4 special characteristics of muscle tissue?

A

excitability - ability to receive and respond to stimuli
contractility - ability to shorten when stimulated
extensibility - ability to be stretched
elasticity - ability to recoil to resting length

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5
Q

what are the 4 muscle functions?

A

movement of bones or fluids
maintaining posture and body position
stabilizing joints
heat generation

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6
Q

epimysium

A

dense irregular connective tissue surrounding entire muscle

connective tissue sheath

surrounds the whole muscle and is continuous with the tendon

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7
Q

perimysium

A

fibrous connective tissue surrounding fascicles (groups of muscle fibers)

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8
Q

endomysium

A

fine areolar connective tissue surrounding each muscle fiber

surrounds each cell

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8
Q

what are the 2 ways muscles attach?

A
  1. directly - epimysium of muscle is fused to the periosteum of bone or perichondrium of cartilage
  2. indirectly - connective tissue wrappings extend beyond the muscle as a rope-like tendon or sheetlike aponeurosis
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9
Q

skeletal muscle fiber characteristics

A

10 to 100um in diameter, up to 30cm long
multiple peripheral nuclei

results from the fusion of hundreds of embryonic precursor cells called myoblasts

a cell made from the fusion of many others is known as syncytium

glycosomes for glycogen storage, myoglobin for oxygen storage

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10
Q

what are myofibrils?

A

densely packed, rodlike elements that take up ~80% of muscle fiber

very fine contractile fibers, groups of which extend in parallel columns along the length of striated muscle fibers

made up of thick and thin myofilaments which give the muscle its striped appearance

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11
Q

what are sarcomeres?

A

the smallest contractile unit (functional unit) of muscle fiber

the region of a myofibril between 2 successive z discs

each sarcomere contains 2 types of
myofilaments
- thick filaments: composed of myosin
- thin filaments: composed to actin

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12
Q

thick filament characteristics

A

made up of myosin

myosin has a hinge that separates the tail and head

runs the entire length of an A band

dark band

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13
Q

thin filament characteristics

A

run the length of the I band and partway into the A band

associated with actin filaments

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14
Q

Z disc vs H zone vs M line

A

z disc - coin-shaped sheet of proteins that anchors thin filaments and connects myofibrils to one another

H zone - lighter midregion where the thick and thin filaments do not overlap

M line: line of protein myomesin that holds adjacent thick filaments together

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15
Q

describe what filaments are in each part of a sarcomere

A

I band - only thin filaments
H zone - only thick filaments
M line - thick filaments with accessory proteins
Outer edge of A band - thick and thin filaments overlap

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16
Q

what is the structure of a thick filament?

A

composed of myosin
has 2 myosin tail that are 2 interwoven heavy polypeptide chains
myosin heads are connected to the tails, and act as cross bridges during contraction
- binding sites for actin
- binding sites for ATP
- ATPase enzymes

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17
Q

structure of a thin filament

A

twisted double strand of filamentous protein F-actin

F-actin consists of globular actin subunits

G-actin bears active sites for myosin head during contraction

tropomyosin and troponin are regulatory proteins bound to actin

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18
Q

what are the 2 proteins bound to actin

A

tropomyosin and troponin

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19
Q

sarcoplasmic reticulum

A

network of smooth endoplasmic reticulum (SER)

pairs of terminal cisternae form perpendicular cross channels

functions in the regulation of intracellular calcium levels

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20
Q

t-tubules

A

continuous with sarcolemma

penetrate the cell’s interior at each A band - I band junction

associate with the paired terminal cisternae to form triads that encircle each sarcomere

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21
Q

what is in each triad

A

t-tubule

terminal cisternae of the SR (2)

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22
Q

what are the relationships associated with triads

A

t-tubules conduct impulses deep into muscle fiber

integral membrane proteins protrude into the intermembrane space between T-tubule and SR cisternae membranes

T-tubule proteins are voltage sensors

SR foot proteins are gated channels that regulate calcium release from the SR cisternae

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23
Q

sliding filament model of contraction

A

relaxed state - when thick and thin filaments overlap only slightly

contraction - myosin heads bind to actin, detach and bind again propelling thin filaments toward the M line
- contraction occurs when tension generated by cross bridges on the thin filaments exceeds the forces opposing shortening

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24
Q

voltage sensors - DHP receptor

A

DHP: dihydropyridine
calcium channel voltage sensor
interacts with proteins found in the cisternae

in the transverse tubule
- interact with sarcoplasmic reticulum protein

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25
Q

ryanodine receptors

A

interacts to bind with the sarcoplasmic protein

located in the sarcoplasmic reticulum membrane and responsible for the release of calcium from intracellular stores during excitatio-contraction coupling in both cardiac and skeletal muscle

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26
Q

what happens during contraction?

A

contraction occurs when tension generated by cross bridges on the thin filaments exceeds the forces opposing shortening

brings the 2 z-discs together to basically close in the H zone

relaxes sarcomere - some overlap between the thick and thin filaments, and H zone is easily seen

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27
Q

characteristics of a contracted sarcomere

A

I band is very small

H zone can disappear

the filaments are closer as they are contracted together

Z discs become closer together

Dark A band does not change (constant)

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28
Q

Neuromuscular junction characteristics

A

skeletal muscles are stimulated by somatic motor neurons

each motor neuron axon forms several branches as it enters a muscle and its ending forms a neuromuscular junction (NMJ) with a muscle fiber

NMJ is situated midway along the length of a muscle fiber

axon terminal and muscle fiber are separated by a gel-filled space called the synaptic cleft

synaptic vesicles in axon terminal have the neurotransmitter acetylcholine (ACh)

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29
Q

what are the 6 events that occur at the neuromuscular junction?

A
  1. action potential arrives at axon terminal of motor neuron
  2. voltage-gated calcium channels open and calcium enters the axon terminal
  3. calcium causes synaptic vesicles to release ACh
  4. ACh diffuses across the synaptic cleft and binds to receptors in the sarcolemma
  5. ACh binding opens ion channels that allow simultaneous passage of sodium into the muscle fiber and potassium out
  6. ACh effects are terminated by its enzymatic breakdown in the synaptic cleft by acetylcholinesterase
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30
Q

what are the 3 events of the generation of an action potential?

A
  1. local depolarization: generation of the endplate potential on the sarcolemma
  2. generation and propagation of the action potential
  3. repolarization
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31
Q

repolarization

A

once the action potential happens, need to repolarize the channel for the next action potential

sodium channels will close, and then potassium channels reopen which leads to repolarization

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32
Q

what is resting potential?

what do you need to reach for the channels to open?

A

-70mV

once activated, the voltage gated sodium channels open when you reach a threshold of -55mV

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33
Q

what is the generation of the action potential accredited to?

A

sodium entry

sodium flows in, potassium flows out

non selective

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34
Q

what is the role of calcium in contraction? *low calcium concentration

A

low intracellular calcium concentration - tropomyosin blocks the active sites on actin

myosin heads cannot attach to actin

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35
Q

what is the role of calcium in contraction? *high calcium concentration

A

calcium binds to troponin and changes shape and moves tropomyosin away from active sites

events of the cross bridge cycle occur

when nervous stimulation ceases, calcium is pumped back into the SR and contraction ends

calcium-activated troponin undergoes a conformational change that moves tropomyosin away from actins binding sites

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36
Q

what are the 6 actions that happen with excitation-contraction (EC) coupling?

A
  1. Action potential is propagated along the sarcolemma and down the T-tubules
  2. Activate DHPR – voltage sensitive tubule protein
    a. Activate the receptors in the T-tubule
  3. Calcium ions are released by the Ryanodine receptor (RyR1)
    a. Found on SR
    b. Goes into the cytoplasm to lead to muscle contraction
  4. Calcium binds troponin and removes the blocking action of tropomyosin
  5. Binds to troponin and ship the tropomyosin out of the area
  6. Add calcium, shifts tropomyosin away and active sites are exposed and ready for myosin binding
  7. Myosin can bind to actin molecules and continue to contract the muscle until maximal contraction
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37
Q

latent period

A

time between action potential starting and the beginning of a contraction

38
Q

what is excitation contraction coupling?

A

sequence of events by which transmission of an action potential along the sarcolemma leads to sliding of the myofilaments

action potential is propagated along sarcomere to T-tubules

voltage sensitive proteins stimulate calcium release from SR (calcium is necessary for contraction)

39
Q

cross bridge formation

A

high-energy myosin head attaches to thin filament

40
Q

working (power) stroke of the cross bridge cycle

A

myosin head pivots and pulls thin filament toward M-line

41
Q

cross bridge detachment of the cross-bridge cycle

A

ATP attaches to myosin head and the cross bridge detaches

42
Q

cocking of the myosin head of the cross bridge cycle

A

energy from hydrolysis of ATP cocks the myosin head into the high-energy state

43
Q

cross bridge cycle steps

A
  1. cross bridge formation (myosin attaches to the thin filament)
  2. the power stroke happens, and ADP + P are released
  3. cross bridge detachment
  4. cocking of myosin head causes ATP hydrolysis
44
Q

isometric contraction

A

no shortening; muscle tension increases but does not exceed the load

the load is greater than the tension the muscle is able to develop

muscle neither shortens nor lengthens

45
Q

isotonic contraction

A

muscle shortens because muscle tension exceeds the load

46
Q

what is a motor unit

A

a motor neuron and all (4-several hundred) muscle fibers it supplies

a motor unit extends from the motor neuron cell body (spinal cord), extends by the motor neuron axon, to the muscle fibers to activate it

muscle fibers from a motor unit are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle

47
Q

small motor unit

A

muscles that control fine movements (fingers, eyes)

48
Q

what are the 3 types of troponin?

A

troponin I - interacts with actin
Troponin C - interacts with calcium
Troponin T - interacts with tropomyosin

49
Q

large motor unit

A

large weight-bering muscles (thighs and hips)

50
Q

what are the 3 phases of a muscle twitch?

A

latent period: events of excitation-contraction coupling

period of contraction: cross-bridge formation; tension increases

period of relaxation: calcium reentry into the SR; tension declines to 0

51
Q

what is a muscle twitch?

A

response of a muscle to a single, brief threshold stimulus

simplest contraction observable in the lab

52
Q

why are there differences in muscle twitch?

A

different strength and duration of twitches are due to variations in metabolic properties and enzymes between muscles

extraocular muscle - eye movements (want a fast twitch that goes on and off quickly)

53
Q

what are graded muscle responses? what are they graded by?

A

variations in the degree of muscle contraction

required for proper control of skeletal movement

responses are graded by:

  1. changing the frequency of stimulation
  2. changing the strength of the stimulus
54
Q

what is the response of a single stimulus?

A

single stimulus - single twitch

muscle contractions and relaxes

55
Q

what is the response of an increase in frequency of stimulus?

A

muscle does not have time to relax between stimuli

calcium release stimulates further contraction -> temporal summation (wave)

further increase in stimulus frequency - unfused tetanus

low stimulation frequency - causes unfused tetanus

56
Q

what is the response of multiple quick stimuli?

A

high stimulation frequency causes fused (complete) tetanus

57
Q

threshold stimulus

A

stimulus strength at which the first observable muscle contraction occurs

contraction force is precisely controlled by recruitment (multiple motor unit summation), which brings more and more muscle fibers into action

58
Q

size principle

A

motor units with larger and larger fibers are recruited as stimulus intensity increases

59
Q

what is the force of concentration affected by?

A

frequency of stimulation - increased frequency allows time for more effective transfer of tension to noncontractile componetns

number - the number of muscle fibers controlled (recruitment)

length-tension relationship - muscles contract most strongly when muscle fibers are 80-120% of their normal resting length

relative size of fibers - hypertrophy of cells increase length

60
Q

what increases contractile force?

A

large number of muscle fibers activated

large muscle fibers

high frequency of stimulation

muscle and sarcomere stretched slightly over 100% of resting length

61
Q

muscle tone

A

constant, slightly contracted state of all muscles

due to spinal flexes that activate groups of motor units alternately in response to input from stretch receptors in muscles

keep muscles firm, healthy, ready to respond

62
Q

isotonic contractions are either….

A

concentric - the muscle shortens and does not work

eccentric - the muscle contracts as it lengthens

63
Q

describe the resistance and speed of contraction

A

there is an inverse relationship between the amount of resistance and the speed of contraction

when the load exceeds the ability of the muscle to move it, the velocity of shortening becomes zero and the contraction is isometric

64
Q

isotonic vs isometric

A

isotonic - concentric contraction and eccentric contraction (muscle changes shape)

isometric - muscle does not change length

65
Q

what are 3 ways ATP is regenerated?

A
  1. direct phosphorylation of ADP by creatine phosphate (CP)
  2. Anaerobic pathway (glycolysis)
  3. Aerobic respiration
66
Q

direct phosphorylation of ADP

A

-Coupled reaction of creatine phosphate (CP) and ADP

-Requires creatine kinase – to generate ATP
oCan buffer the ATP generation

  • Creatine phosphate gives its phosphate to ADP to form ATP
  • Energy source: CP
  • Oxygen use: None
  • Products: 1 ATP per CP, creatine
  • Duration of energy provision: 15 seconds
67
Q

aerobic pathway

A

-Produces 95% of ATP during rest and light to moderate exercise

-Fuels:
oStored glycogen
oThen bloodborne glucose, pyruvic acid from glycolysis and free fatty acids

  • Duration of energy provisions: Hours
  • Glucose comes from glycogen or blood, then converted to pyruvic acid (no oxygen)

-Respiration in the mitochondria requires oxygen, and can generate a lot of ATP per glucose molecule

  • Can also use fatty acid and amino acids as an energy source
  • Can be used for running, long duration exercise

-Exercise gets easier here after 5 minutes, once the aerobic pathway kicks in

68
Q

anaerobic pathway: lactic acid and 70% maximum contractile activity

A

at 70% maximum contractile activity

  • bulging muscles compress blood vessels
  • oxygen delivery is impaired
  • pyruvic acid is converted into lactic acid

Lactic acid

  • diffuses into bloodstream
  • used as fuel by the liver, kidneys, heart
  • converted back into pyruvic acid by the liver
69
Q

anaerobic pathway characteristics

A

energy source - glucose
derived from what is in the muscle cell or from glycogen
- breaking down glucose decreases blood glucose, then enters the metabolic pathway to glycolysis
- oxygen use: none (not oxygen required)

products: 2 atp per glucose, lactic acid
duration: 60 seconds

70
Q

muscle fatigue occurs when..

A

ionic imbalances (potassium, calcium, phosphate) interfere with E-C coupling

prolonged exercise damages the SR and interferes with calcium regulation and release

71
Q

low intensity exercise vs high intensity exercise muscle fatigue

A

high intensity-short duration exercise produces rapid muscle fatigue (with rapid recovery)

  • sodium potassium pumps cannot restore ionic balances quickly enough
  • dysregulation of ionic substances

Low intensity long duration exercise produces slow developing fatigue
- SR is damaged and calcium regulation is disrupted

72
Q

muscle fatigue characteristics

A

physiological inability to contract

rarely because of a lack of ATP

total lack of ATP occurs rarely, during states of continuous contraction and causes contractures (continuous contractions)

73
Q

oxygen deficit

A

-Extra oxygen needed after exercise for:
oReplenishment of oxygen reserves, glycogen stores, ATP and CP reserves, and conversion of lactic acid to pyruvic acid, glucose, glycogen

-EPOC – excess post-exercise oxygen consumption
oWhen you are done exercising, still feel winded with some energy
oNeed to replace oxygen reserves and glycogen stores

74
Q

velocity and duration of contraction is

A

muscle fiber type
load
recruitment

75
Q

what are the 2 characteristics of muscle fiber type

A

Speed of contraction: slow or fast, according to:

  • Speed at which myosin ATPases split ATP
  • Pattern of electrical activity for the motor neurons

Metabolic pathways for ATP synthesis

  • Oxidative fibers – use aerobic pathways
  • Glycolytic fibers - use anaerobic glycolysis
76
Q

slow oxidative fibers

A 
Soleus muscle 
Aerobic pathway 
High myoglobin in muscle cells 
Low glycogen stores
Do not need a lot of contraction to activate 
Red colour
77
Q

fast oxidative fibers

A 
Intermediate between the slow and fast 
Can be both aerobic and anaerobic 
Intermediate glycogen stores
High myoglobin 
Pink colour
78
Q

fast glycolytic fibers

A 
Rapid on, rapid off
Does not use oxygen primarily 
Low myoglobin
High glycogen stores 
Need a lot of stimulation to be able to contract 
White in colour
Use glycogen store levels (high levels)
79
Q

aerobic (endurance) exercise results in

A

Leads to increased:

  • Muscle capillaries
  • Number of mitochondria
  • Myoglobin synthesis

Results in greater endurance, strength, and resistance to fatigue

May convert fast glycolytic fibers into fast oxidative fibers

Little hypertrophy but biochemical adaptations within muscle fibers
Concentration and activities of oxidative enzymes (succinate dehydrogenase, SDH)

80
Q

SDH activity

A

low activity is light

high activity is dark

81
Q

effects of resistance exercise

A

Resistance exercise (typically anaerobic) results in:

  • Muscle hypertrophy (increase in fiber size)
  • Increased mitochondria
  • Myofilaments
  • Glycogen stores and connective tissue
82
Q

overload principle

A

forcing a muscle to work hard promotes increased muscle strength and endurance

muscles adapt to increased demands

muscles must be overloaded to produce further gains

83
Q

smooth muscle

A

found in walls of most hollow organs (except heart)
- usually 2 layers (longitudinal and circular)

Longitudinal - looks like cubes

  • along the length
  • shortening of the tube when contracted

Circular - very stretched out

  • interior of the smooth muscle cell
  • pinches of the tube diameter smaller
84
Q

peristalsis

A

Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through the lumen of hollow organs

Longitudinal layer contracts; organ dilates and shortens

Circular layer contracts: organ constricts and elongates

Pinching of the layer

Moves the bolus movement along the tube through shortening (like pushing toothpaste out)

85
Q

innervation of smooth muscle

A

Pouch like structures as the neuron moves into the layer: Varicosities

In each varicosity, have a lot of neurons and mitochondrion

Varicosities: release their neurotransmitters into a wide synaptic cleft (diffuse junction)

Norepinephrine gets released by the sympathetic nerve on the alpha-adrenergic receptors (smooth muscle cell)

86
Q

myofilaments in smooth muscle

A

Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:6)

Thick filaments have myosin heads along their entire length

No troponin complex; protein calmodulin binds calcium
- Troponin is associated with thin filaments

Myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner

Dense bodies: protein that anchor non-contractile intermediate filaments to sarcolemma at regular intervals
- Membrane structures in SR

87
Q

contraction of smooth muscle

A

Slow, synchronized contractions

Some cells are electrically coupled by jap junctions

Some cells are self-excitatory and act as pacemakers for sheets of muscle

Rate and intensity of contraction may be modified by neural and chemical stimuli

Sliding filament mechanism

  • Overlap between thick and thin filaments, pulling of actin filaments along the length of the thick filament which contains myosin
  • Final trigger is an increase in intracellular calcium
  • Calcium is obtained from the SR and extracellular space

Calcium enters the cytosol from the extracellular fluid via voltage-dependent or voltage-independent calcium channels or from scant SR

Calcium binds to and activates calmodulin

Activated calmodulin activates MLCK

The activated kinase enzymes catalyze transfer of phosphate to myosin, activating the myosin ATPases
- 2 phosphate molecules added to the myosin head

Activated myosin forms cross bridges with actin of the thin filaments and shortening begins

  • Very energy efficient (slow ATPases)

Myofilaments may maintain a latch state for prolonged contractions

88
Q

role of calcium ions in smooth muscle

A
  • Calcium binds to and activates calmodulin
  • Activated calmodulin activates myosin (light chain) kinase (MLCK)
  • Activated kinase phosphorylates and activates myosin 2
  • Cross bridges interact with actin
  • Source of calcium comes from extracellular sources to lead to muscle contraction, and internal stores
  • Unlike skeletal and cardiac (only get calcium from SR), smooth muscle has 2 sources of calcium to utilize
  • Outside the cell and internal stores
89
Q

regulation of contraction

A

Neural regulation

  • Neurotransmitter binding – increases concentration of calcium in sarcoplasm; either graded (local) potential or action potential
  • Response depends on neurotransmitter released and type of receptor molecules

Hormones and local chemicals

  • May bind to G-protein-linked receptors
  • May either enhance or inhibit calcium entry
90
Q

special features of smooth muscle contraction

A

Stress-relaxation response

  • Responds to stretch only briefly, then adapts to new length
  • Retains ability to contract on demand
  • Enables organs such as the stomach, and bladder to temporarily store contents

Length and Tension changes
- Can contract when between half and twice its resting length

Hyperplasia

  • Smooth muscle cells can divide and increase their numbers
  • Example: estrogen effects on uterus at puberty and pregnancy
91
Q

types of smooth muscle: single unit

A

The cells of single-unit smooth muscle: visceral muscle

  • Contract rhythmically as a unit
  • Are electrically coupled to one another via gap junctions
  • Spontaneous AP
  • Are arranged in opposing sheets and exhibit stress-relaxation response
92
Q

types of smooth muscle: multiunit

A

Multiunit smooth muscles are found

  • In large airways to the lungs and large arteries
  • In arrector pili muscles attached to hair follicles
  • Eye muscles of the iris

Characteristics include

  • Rate gap junctions
  • Infrequent spontaneous depolarizations
  • Structurally independent muscle fibers
  • A rich nerve supply, which, with several muscle fibers, forms motor units
  • Graded contractions in response to neural stimuli

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