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PHARM 110 > 6 - Muscular Tissue > Flashcards

6 - Muscular Tissue Flashcards

1
Q

3 muscle fiber types

A
  • slow oxidative
  • fast oxidative
  • fast glycolytic
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2
Q

3 phases of muscle twitch

A
  • Latent period - events of E-C coupling
  • Period of contraction - cross bridge formation, tension increases
  • Period of relaxation - Ca re-entry into SR, tension declines to zero
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3
Q

3 types of Muscle tissue

A
  • skeletal, cardiac, smooth
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4
Q

ATP generation - aerobic pathway

A
  • energy source = glucose, pyruvic acid, fatty acid, amino acids
  • uses O2
  • produces 36 ATP per glucose, CO2, H2O
  • Duration hours
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5
Q

ATP generation - anaerobic pathway

A
  • energy source = glucose
  • does NOT use O2
  • produces 2 ATP per glucose, lactic acid
  • duration 30-60s
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6
Q

ATP generation - direct phosphorylation

A
  • energy source = CP
  • does NOT use O2
  • produces 1 ATP per 1 CP
  • duration 15 secs
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7
Q

ATP is regenerated by

A
  • Direct phosphorylation of ADP by creatine phosphate CP
  • Anaerobic pathway (glycolysis)
  • Aerobic respiration
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8
Q

Cardiac muscle cells

A
  • branching chains of cells
  • uninucleate or binucleate
  • striations
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9
Q

Cardiac muscle

A
  • Only in the heart
  • Striated
  • Involuntary
  • Intercalated discs = attachment for cardiac cells
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10
Q

Common characteristics of muscle tissue

A
  • Excitability – ability to receive & 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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11
Q

Dense bodies

A
  • proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals
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12
Q

Endomysium

A
  • fine areolar CT surrounding each muscle fiber
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13
Q

Endurance Training

A
  • Aerobic (endurance) exercise
  • Leads to increased:
    Muscle capillaries
    Number of mitochondria
    Myoglobin synthesis
    May convert fast glycolytic fibers into fast oxidative fibers
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14
Q

Endurance Training

A
  • Typically anaerobic
  • Results in:
    Muscle hypertrophy (increase in muscle fiber size)
    Increased mitochondria
    Myofilaments
    Glycogen stores & CT
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15
Q

Epimysium

A
  • dense irregular CT surrounding entire muscle
  • can form the tendon
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16
Q

EPOC

A
  • excess post exercise consumption
  • replenishment of O2 reserves in muscles
  • ex. breathing heavy post exercise
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17
Q

Fast glycolytic fibers

A
  • fast contraction
  • fast ATPase activity
  • low myoglobin, hgih glycogen stores
  • recruitment order - third
  • white colour
  • large fibers
  • few mitochondria
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18
Q

fast oxidative fibers

A
  • fast contraction
  • fast ATPase activity
  • high myoglobin
  • recruitment order - second
  • red-pink colour
  • many mitochondria
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19
Q

Features of a sarcomere

A
  • Thick filaments – run the entire length of an A band (dArk band)
  • Thin filaments – run the length of the I band & part way into A band (light band)
  • Z disc – coin-shaped sheet of proteins that anchors the thin filaments & connects myofibrils to one another
  • H zone – lighter midregion where the thick & thin filaments do not overlap
  • M line – line of protein myomesin that holds adjacent thick filaments together
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20
Q

Force of contraction is affected by

A
  • Frequency of stimulation - increase frequency allows time for more effective transfer of tension to noncontractile components
  • Number of muscle fibers stimulate (recruitment)
  • Length-tension relationship - muscles contract most strongly when fibers are 80-120% of their normal resting length
  • Relative size of fibers - hypertrophy of cells increase strength (ex. Strength training)
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21
Q

Influence of load

A
  • high load
  • increase latent period, decrease contraction & decrease duration of contraction
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22
Q

Influence of recruitment

A
  • recruitment
  • faster contraction & increased duration of contraction
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23
Q

Is Endplate potential an action potential?

A

NO!!!
- they are different
- end plate potential is at the NMJ, needs to reach threshold to propogate AP down the muscle cell

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24
Q

isometric contraction

A
  • no shortening, muscle tension increases but does NOT exceed the load
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25
Q

Isotonic contraction

A
  • muscles shortens b/c muscle tension exceeds the load
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26
Q

Latent period

A
  • time b/w AP initiation & beginning of contraction
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27
Q

length-tension relationship

A
  • If muscle is already almost fully contracted - it won’t create a lot of tension
  • Excessively stretched – not great overlap, don’t really generate a good amount of tension
  • Optimal overlap -> muscle is about ½ contracted
28
Q

Multiunit Smooth muscle

A
  • Found in - large airways to lungs & large arteries, in arrector pili muscles attached to hair follicles, eye muscles of iris
  • Characteristics:
    Rare gap junctions
    Infrequent spontaneous depol
    Structurally independent muscle fibers
    A rich nerve supply, with multiple fibers forms motor units
    Graded contractions in response to neural stimuli
    act more like skeletal
29
Q

Muscle fatigue

A
  • ionic imbalances - interfere w/ E-C coupling
  • prolonged exercise damages SR & interferes w/ E-C coupling
30
Q

Muscle fatigue from high intensity-short duration exercise

A
  • produces rapid muscle fatigue
  • Na-K pumps cannot restore ionci balances quickly enough
31
Q

Muscle fatigue from low-intensity-long duration exercise

A
  • produces slow-developing fatigue
  • SR damaged & Ca regulation disrupted
32
Q

Muscle functions

A
  • Movement of bones or fluids
  • Maintain posture & body position
  • Stabilizing joints
  • Heat generation (especially skeletal muscle)
33
Q

Muscle responses are graded by…

A
  • Changing the frequency of stimulation
  • Changing the strength of the stimulus
34
Q

Muscle tone

A
  • Constant, slightly contracted state of all muscles
  • Due to spinal reflexes that activate groups of motor units in response to input from stretch receptors in muscles
  • Keeps muscles firm, healthy & ready to respond
35
Q

myofilaments in smooth muscle

A
  • Ratio of thick to thin is 1:13
  • Thick filaments have myosin heads along their entire length
  • No troponin complex - protein calmodulin binds Ca
  • Myofilaments are spirally arranges, causing smooth muscle to contract in a corkscrew manner
36
Q

Nebulin

A
  • ruler in thick & thin filaments, helps maintain length of actin
37
Q

Perimysium

A
  • fibrous CT surrounding fascicles (groups of muscle fibers)
38
Q

Peristalsis

A
  • Alternating contractions & relaxations of smooth muscle layers that mix & squeeze substances through the lumen of hollow organs
39
Q

Response to change in stimulus frequency

A
  • low stimulation frequency -> unfused tetanus
  • high stimulation frequency -> fused (complete) tetanus
40
Q

Responses to change in stimulus strength

A
  • contraction force is controlled by recruitment, brings more fibers into action
  • size principle -> motor units w/ larger fibers are recruited as stimulus intensity increases
41
Q

Role of Calcium in contraction

A
  • low intracellular Ca - tropomyosin blocks active site on actin
  • high intracellular Ca - Ca binds troponin, moves tropomyosin -> events of cross bridge cycling
42
Q

Role of Calcium in Smooth muscle

A
  • Ca binds to & activates calmodulin
  • Activated calmodulin activates myosin (light chain) kinase (MLCK)
  • Activated kinase phosphorylates & activates myosin II
  • Cross bridge interacts w/ actin
43
Q

Sarcomere

A
  • Smallest contractile unit (functional unit) of a muscle fiber
  • Regions of a myofibril b/w 2 successive z discs
  • Composed of thick & thin myofilaments made up of contractile proteins
44
Q

Sarcoplasmic reticulum

A
  • Network of smooth endoplasmic reticulum (SER)
  • Pairs of terminal cisternae form perpendicular cross channels
  • Functions in the regulation of intracellular Ca2+ levels
45
Q

Single Unit smooth muscle

A
  • Cells of a single-unit (visceral muscle)
    Contract rhythmically as a unit
    Electrically coupled via gap junctions
    Spontaneous AP
    Are arranged in opposing sheets & exhibit Stress-relaxation response
46
Q

Skeletal muscle

A
  • Attached to bones & skin
  • Voluntary (conscious control)
  • Striated
  • Powerful
  • Remember: looks like dense regular but has striations
47
Q

Skeletal Muscle cells

A
  • single long cylindrical
  • multinucleate
  • striations
48
Q

sliding filament theory

A
  • relaxed state - thin & thick filaments overlap slightly
  • contraction - myosin head binds actin, detach & binds again - moving filament towards M line
  • H zones & I zones shorten, A band remains the same!!
49
Q

Slow oxidative fibers

A
  • slow contraction
  • slow ATPase activity
  • high myoglobin
  • recruitment order - first
  • red colour
  • many mitochondria
50
Q

Smooth muscle

A
  • In the walls of hollow organs (ex. Stomach, GI, airways)
  • Not striated
  • Involuntary
51
Q

Smooth Muscle (microscopic structure)

A
  • spindle shaped fibers
  • endomysium only
  • SR less developed
  • Caveolae
  • No sarcomeres, myofibrils or T tubules
52
Q

Smooth muscle cells

A
  • single fusiform
  • uninucleate
  • no striations
53
Q

Steps in E-C coupling

A
  1. AP is propagated along the sarcolemma & down T-tubules
    Change in conformation of DHP receptors -> interacts w/ RyR1
  2. Ca ions released
  3. Ca binds to troponin & removes the blocking action of tropomyosin
  4. Contraction begins
54
Q

Steps in generation of AP at NMJ

A
  1. Local depolarization - generation of end plate potential on the sarcolemma
    - MUST reach threshold
  2. Generation & propagation of the action potential
    - Open Na channel, closed K channel -> Na going in, muscle cell getting more depolarized
  3. Repolarization - Closed Na channel, open K channel
    - K going out of cell, less +ve charge inside
55
Q

Steps of contraction in smooth muscle

A
  1. Ca enters from ECF via voltage-dependent/independent channels or from SR
  2. Ca binds to & activates calmodulin
  3. Activated calmodulin, activates MLCK
  4. Activates myosin ATPase
  5. Activated Myosin forms cross-bridge w/ Actin
56
Q

Steps of Cross bridge cycling

A
  1. Cross bridge formation - high-energy myosin head (ATP primed) attaches to thin filament
  2. Working (power) stroke - myosin head pivots & pulls thin filament toward M-line
  3. Cross bridge detachment - ATP attaches to myosin head & cross bridge detaches
  4. Cocking of myosin head - energy from hydrolysis of ATP cocks the myosin head into high-energy state (recharges myosin)
57
Q

Structure of Thick Filament

A
  • 2 myosin
  • Myosin tails - interwoven heavy polypeptide chains
  • Myosin heads - connected to the tails are 2 polypeptide head groups that act as cross bridges during contraction
  • ELC & RLC - can be manipulated, to improve muscle contraction ability, allows fast contractions
58
Q

Structure of Thin Filament

A
  • Twisted double strand of filamentous protein F-actin
  • G-actin make up F-actin
  • Tropomyosin & troponin - regulatory proteins bound to actin
59
Q

T-tubules

A
  • Invagination of sarcolemma
  • Penetrate the cell’s interior at each A band – I band junction
  • Assoicate w/ the paired terminal cisterna to form triads that encircle each sarcomere
60
Q

The overload Principle

A
  • Forcing a muscle to work hard promotes increased muscle strength & endurance
  • Muscles adapt to increased demands
  • Muscle must be overloaded to produce further gains
61
Q

Titin

A
  • interacts w/ M-line throughout the length of Sarcomere (from Z disc to Z disc)
62
Q

Triad Relationship

A
  • T tubule proteins are voltage sensors (DHP receptor)
  • SR foot proteins are gated channels (Ryanodine receptor)
  • 2 receptors bind, release Ca2+ from SR cisternae
63
Q

velocity/duration of contraction influenced by

A
  • muscle fibre type
  • load
  • recruitment
64
Q

What are the events at the Neuromuscular junction?

A
  1. Action potential arrives at axon terminal of motor neuron
  2. Voltage-gated Ca2+ channels open & Ca2+ enters axon terminal
  3. Ca2+ causes synaptic vesicles to release Ach into synaptic cleft
  4. Ach diffuses across synaptic cleft & binds to receptors on sarcolemma
  5. Ach binding opens ion channels that allow Na into muscle fibre & K out
  6. Ach effects are terminated by its enzymatic breakdown in synaptic cleft by acetylcholinesteras
65
Q

what is a muscle twitch?

A
  • response to a single brief threshold stimulus
66
Q

What is excitation-cotnraction (E-C) coupling?

A
  • sequence of events by which transmission of an AP along sarcolemma leads to sliding of myofilaments

PHARM 110 (12 decks)

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