muscle Flashcards

1
Q

connective tissue of skeletal muscle

A
  • epimysium (surrounding entire muscle)
  • perimysium (surrounding bundles or groups of muscle fibres known as fascicles)
  • endomysium (surrounding each individual muscle fibre)
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2
Q

skeletal muscle made up of

A

SKeltal muscle (organ) is made of

  • Fascicles (bundles)
  • Fibres (muscle cells)
  • Myofibrils (little rods)
  • Sarcomeres (units)
  • Myofilaments (thin filament proteins)
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3
Q

microscopic anatomy of skeletal muscle

A
  • fibres are cylindrical, very thin and up to 30 cm long, with multiple peripheral nuclei and many mitochondria
  • contain glycosomes for glycogen storage and myoglobin for O2 storage
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4
Q

ultrastructure of filaments

A
  • composed or myosin (protein), has a long tail and characteristic head
  • thin filament is a twisted double strand of fibrous protein F actin
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5
Q

sacroplasmic reticulum and T tubules

A
  • sacroplasmis reticulum is a network of smooth ER surrounding each myofibril, regulating Ca2+ levels which is vital for contraction
  • T tubules are invaginations of the cell membrane that penetrate cells interior, conducting nerve impulses deep into every muscle cell
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6
Q

muscle contraction

A
  • contarction is the acitvation of cross-bridges and the generation of force
  • shortening occurs when tension generated by cross bridges on the thin filaments exceeds forces opposing shortening by sliding filaments
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7
Q

requirements for skeletal muscle contraction

A
  • require activation = a neural stimulation (action potential) at the neuromuscular junction (NMJ) by a nerve
  • then excitation-contraction coupling (ECC) = generation and propagation of the action potential along and into each cell, culminating in the release of Ca2+
  • finally, cross-bridge cycling (CBC) resulting in contraction itself
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8
Q

the neuromuscular junction (NMJ)

A
  • where the motor nerve serving the muscle is separated from the muscle fibre itself by a space called the synpase
  • a neurotransmitter (acetylcholine ACh) stimulates the muscle
  • skeletal muscle is stimulated by somatic motor neurons
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9
Q

skeletal muscle contraction = 1. Activation

A
  1. action potential arrives at the end of the nerve (axon terminal)
  2. causes surrounding Ca2+ to enter the nerve, exciting the movement of stored vesicles of acetylcholine
  3. vesicles exocytose, releasing ACh which floats to the synapse and binds ot receptors on the muscle cell membrane
  4. binding opens up protein channels in the sarcolemma, causing Na and K ions to move in and out of the cell (depolarisation)
  5. depolarisation eventually generates another electrical impulse (action potential) which spreads like a wave across the sarcolemma
    muscle fibre cannot be stimulated again intil action potential has finished and repolarisation is complete
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10
Q

skeletal muscle contraction 2. Excitation-contraction coupling (ECC)

A
  • way in which an action potential is transformed into actual physical movement of muscle cell components (sliding of those filaments)
    1. the AP is propagated along entire sarcolemma of each sarcomere and down the T-tubules, deep into the cell interior causing release of large amounts of Ca2+
    2. Ca2+ eventually exposes sites on the thin filament for the thick filament head to bind to forming cross bridges
    3. at this point E-c coupling is over
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11
Q

skeletal muscle contraction. 3. cross bridge cycling

A
  • hoe filaments attach and slide, causing actual muscle shortening
  • involves high energy myosin head attaching to actin thin filament
  • myosin head pivots and pulls thin filament toward the middle of the sacrmere
  • ATP attaches to the myosin head and the cross bridge detaches
  • energy from hydrolysis of ATP cocks the myosin head into high energy state
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12
Q

role of calcium in concentration

A
  • calcium is vital to muscle contraction
  • muscle fibres relax when intracellular ca2+ is low because it blocks binding of thin and thick filaments
  • when ca2+ increases binding allows cross bridge cycling
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13
Q

motor units

A
  • nerve/muscle functional unit

- consisting of a motor neurona nd all four muscle fibres it supplies

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14
Q

twitch and tetany

A
  • stimulation of a muscle fibre by a nerve results in a single contractile response (twitch)
  • as frequency of stimuli increases, muscle doesnt have time to relax between stimuli causing unfused tetany
  • if stimuli are given quickly enough, fused tetany results
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15
Q

isotonic concentration

A
  • muscle shortens because muscle tension exceeds the load

- either concentric (muscle shortens and works) or eccentric (muscle contracts as it lengthens)

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16
Q

isometric concentration

A
  • load is greater than the tension the muscle is able to develop
  • tension increases to the muscles capacity but the muscle neither shortens or lengthens
17
Q

muscle tone

A
  • constant, slightly contracted state of all muscles

- keeps muscles firm, healthy and ready to respond

18
Q

smooth muscle

A
  • found in walls of most hollow organs except heard, inclduing all blood vessels
  • usually in 2 layers (longtiduinal and circular)
19
Q

smooth muscle contractions

A
  • exhibits slow, synchronised contractions
  • sliding filament mechanism still occurs . but the rate and intensity of contraction may be modified by many neural and chemical stimuli
20
Q

location of smooth muscle

A
  • common in thr walls of all hollow organs and in the large airways, large arteries, arrector pili muscles and iris of eye
21
Q

features of smooth muscle

A
  • stress relaxation response, responds to stretch only briefly then adapts to new length so retains the ability to contract on demand
  • length and tension changes, can contract when between half and twice its resting length
  • hyperplasia: smooth muscle cells can divide and increase their numbers
22
Q

cardiac muscle

A
  • striated, short, fat, branche and interconnected

- simple t tubular arrangment and sr arrangment

23
Q

cardiac muscle contraction

A

stimulated by nerve impulse. coordinated contraction of cells so the heart beats as one and also a long refractory period
- more mitochondira = greater dependance on o2

24
Q

developmental aspects of muscle

A
  • all muscle tissues develop from embryonic myoblasts
  • cardiac and skeletal muscle becomes amitotic, but can lengthen and thicken
  • smooth muscle regenerates through life
  • development occurs head to toe and proximal to distal
  • connective tissue increases and muscle fibres decrease
25
Q

muscular dystrophy

A
  • a group of inherited muscle destroying diseases causing muscles to enlarge due to fat and connective tissue deposits, while muscle fibres atrophy