Muscle Physiology

Question 1

What are the functions of skeletal muscle?

Answer 1

Movement, posture, moves waste products&nutrients, regulates organ volumes, aids venous return, heat (shivering)

Question 2

Characteristics of skeletal muscle?

Answer 2

Irritability - can receive and respond to stimuli
Contractility - can respond to stimulus by shortening
Extensibility - can be stretched/lengthened
Elasticity - ability of muscle to return to resting length after being stretched

Question 3

Structure of skeletal muscle?

Answer 3

Epimysium - creates structure
Perimysiym - around fibre bundles
Endomysium - around individual fibres

Question 4

What is sarcoplasmic reticulum?

Answer 4

Surrounds myofibril - close to TT’s sarcolemma - stores ca2+ when relaxed, releases it when contracts

Question 5

What is neuromuscular transmission?

Answer 5

Motor nerve impulse - ACh into synaptic cleft - binds with ach receptor in motor end plate of muscle fibre - sarcolemma depolarisation, AP generation in muscle - propagates along muscle fibre

Question 6

What is the command chain?

Answer 6

Brain - spinal cord - peripheral nerve - NMJ - sarcolemma - TT system - SR - Ca2 release - crossbridge formation

Question 7

What is excitation-contraction coupling?

Answer 7

Muscle AP spreads along sarcolemma - Ca2 channels in SR open, Ca2 released - increased sarcoplasmic Ca2 - binds to troponin - actin and myosin bind - contraction

Question 8

What is the sliding filament mechanism?

Answer 8

Thick and thin filaments slide past each other causing contraction - unbind allows relaxation
Myosin heads bind to actin - actin pulled toward M line - sarcomeres shorten - muscle contracts

Question 9

What is length-tension relationship?

Answer 9

Forcefulness of contraction depends on sarcomere length & overlap zone - increase overlap = overstretch, decrease overlap = understretch

Question 10

What are the muscle fibre types?

Answer 10

Slow twitch: type I, slow oxidative, prolonged, continuous muscle activity
Fast twitch: type IIa, fast oxidative-glycolytic
Type IIb, fast glycolysis
Fast twitch = rapid and powerful

Question 11

What is progressive recruitment?

Answer 11

Graduation of muscle force - small steps to start become larger when increase amount of force required

Question 12

What is the sarcoplasm?

Answer 12

Contains mitochondria, glycogen, myoglobin, SR - it’s the cytoplasm of striated muscle cells

Question 13

What is the sarcolemma?

Answer 13

Fine, transparent, tubular sheath covers fibres of skeletal muscle - allows nutrients/gases to pass

Question 14

What is sarcomere?

Answer 14

Stimulated by electrical charge - structural unit of myofibril in striated muscles

Question 15

What are myofibrils?

Answer 15

Longitudinal arrangement containing myofilaments

Question 16

What are myofilaments?

Answer 16

Arranged as sarcomeres between Z disc - interaction causes contraction of muscles - parallel alignment, overlap = striations - actin and myosin - light I band, dark A band, H zone

Question 17

What is myosin?

Answer 17

Thick filament - long body, double head - crossbridges bind to actin, heads swivel - ATPase enzyme, binds ATP

Question 18

Why is actin?

Answer 18

Thin filament, extends from Z disc - myosin binding site - contain regulatory proteins that switch contraction on/off

Question 19

What is tropomyosin?

Answer 19

Myofilament - relaxation, blocks myosin binding site on actin

Question 20

What is troponin?

Answer 20

Activated by binding Ca2+ - moves tropomyosin which exposes binding site, contraction

Question 21

What are transverse tubules?

Answer 21

Sarcolemma invaginations - tubular membrane goes deep in muscle fibre - conducts AP to fibre centre