muscle

Question 1

connective tissue of skeletal muscle

Answer 1

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

Question 2

skeletal muscle made up of

Answer 2

SKeltal muscle (organ) is made of

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

Question 3

microscopic anatomy of skeletal muscle

Answer 3

• 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

Question 4

ultrastructure of filaments

Answer 4

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

Question 5

sacroplasmic reticulum and T tubules

Answer 5

• 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

Question 6

muscle contraction

Answer 6

• 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

Question 7

requirements for skeletal muscle contraction

Answer 7

• 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

Question 8

the neuromuscular junction (NMJ)

Answer 8

• 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

Question 9

skeletal muscle contraction = 1. Activation

Answer 9

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

Question 10

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

Answer 10

• 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

Question 11

skeletal muscle contraction. 3. cross bridge cycling

Answer 11

• 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

Question 12

role of calcium in concentration

Answer 12

• 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

Question 13

motor units

Answer 13

• nerve/muscle functional unit

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

Question 14

twitch and tetany

Answer 14

• 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

Question 15

isotonic concentration

Answer 15

• muscle shortens because muscle tension exceeds the load

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

Question 16

isometric concentration

Answer 16

• 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

Question 17

muscle tone

Answer 17

• constant, slightly contracted state of all muscles

- keeps muscles firm, healthy and ready to respond

Question 18

smooth muscle

Answer 18

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

Question 19

smooth muscle contractions

Answer 19

• 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

Question 20

location of smooth muscle

Answer 20

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

Question 21

features of smooth muscle

Answer 21

• 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

Question 22

cardiac muscle

Answer 22

• striated, short, fat, branche and interconnected

- simple t tubular arrangment and sr arrangment

Question 23

cardiac muscle contraction

Answer 23

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

Question 24

developmental aspects of muscle

Answer 24

• 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

Question 25

muscular dystrophy

Answer 25

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