Skeletal Muscle Physiology

Question 1

What type of muscle is skeletal muscle?

Answer 1

Striated

Voluntary

Question 2

What makes skeletal muscle striated?

Answer 2

Thick myocin filaments

Thin actin filaments

Question 3

What makes skeletal muscle voluntary?

Answer 3

Innervated by somatic nervous system

Question 4

What is the purpose of skeletal muscle?

Answer 4

posture
movement
respiratory movement
heat production
whole body metabolism

Question 5

How are skeletal muscle fibres organised?

Answer 5

into motor units

Question 6

What is a motor unit?

Answer 6

single alpha motor neuron

and all skeletal muscle fibres it innervates

Question 7

Why do fibre numbers differ in motor units?

Answer 7

fewer units for fine movement

lots more unit for gross movement

Question 8

What are the levels of organisation of skeletal muscle?

Answer 8

whole muscle
muscle fibre
myofibril
sarcomere

Question 9

What is a myofibril?

Answer 9

Intracellular structure

contains actin and myosin

Question 10

What is a sarcomere?

Answer 10

functional unit

contains actin and myosin

Question 11

How is contraction initiated and propagated in a skeletal muscle?

Answer 11

Neurogenic initiation to contract motor units
Neuromuscular junctions propagate
NO GAP JUNCTIONS

Question 12

What is a myofibril?

Answer 12

contractile intracellular structure

contains actin and myosin

Question 13

What is a sarcomere?

Answer 13

functional unit
arrangement of actin and myosin
found between 2 Z lines (connecting thin filaments)
4 zones; A band, I band, H zone and M line

Question 14

How does excitation contraction coupling work in skeletal muscle?

Answer 14

Ca2+ entirely

from sarcoplasmic reticulum

Question 15

How does gradation of contraction occur in skeletal muscle?

Answer 15

by motor unit recruitment

summation of contractions

Question 16

What is the neurotransmitter at the NMJ?

Answer 16

Acetylcholine

Question 17

How is Ca2+ released from SR?

Answer 17

Action potential travels down T tubules

Ca2+ released from leteral sacs of SR

Question 18

How is muscle tension produced?

Answer 18

ATP dependant interaction
Excitation causes Ca2+ release
Ca2+ binds to troponin on the tropomysin part of actin filament
Uncovers cross bridge binding site on actin
Binding of actin and myosin at cross bridge causes contraction (sliding)

Question 19

How does the muscle relax?

Answer 19

ATP releases cross bridges
Ca2+ pumped back into SR
relaxation

Question 20

What is the difference in length of action potential and muscle twitch? Why is this useful?

Answer 20

AP much shorter
Can summate muscle twitches (which are weak) through repetitive fast stimulation
Provide more useful mechanism

Question 21

What is muscle tetanus?

Answer 21

muscle fibre stimulated so rapidly
no oppourtunity to relax
maximal sustained contraction occurs

Question 22

When can maximal tetanic contraction be acheived?

Answer 22

When muscle fibre at optimal length

Question 23

What are the 2 types of skeletal muscle contraction?

Answer 23

isotonic contraction

isometric contraction

Question 24

What is isotonic contraction? What is it used for?

Answer 24

tension remains constant as muscle length changes
Body movements
Moving objects

Question 25

What is isometric contraction? What is it used for?

Answer 25

Muscle tension develops at constant muscle length
Support objects
Maintain posture

Question 26

How does the velocity of muscle shortening changes as load changes?

Answer 26

velocity of muscle shortening decreases as load increases

Question 27

How can skeletalmuscle function become impaired?

Answer 27

Intrinsic muscle disease
NMJ disease
Disease of lower motor neurones supllying muscle
Disruption of inputs to motor unit

Question 28

What is a reflex?

Answer 28

Stereotyped response to specific stimulus

Question 29

How can the stretch reflex be illicited?

Answer 29

Tapping muscle tendon with rubber hammer

Question 30

What nerve and spinal segements are responsible for

a) knee jerk
b) ankle jerk
c) biceps jerk
d) brachioradialis
e) triceps jerk?

Answer 30

a) femoral, L3+L4
b) tibial, S1+S2
c) Musculocutaneous, C5+C6
d) Radial, C5+C6
e) Radia, C6+C7

Question 31

What nerve and spinal segements are responsible for

a) knee jerk
b) ankle jerk
c) biceps jerk
d) brachioradialis
e) triceps jerk?

Answer 31

a) femoral, L3+L4
b) tibial, S1+S2
c) Musculocutaneous, C5+C6
d) Radial, C5+C6
e) Radial, C6+C7

Question 32

What are muscle spindles?

Answer 32

sensory receptors for stretch reflex
inrafusal fibres
in the belly of musclesand run parallel to extrafusal fibres (normal ones)
Sensory nerve endings (annuospiral fibres)

Question 33

What is the efferent nerve supply to muscle spindles?

Answer 33

gamma motor neurons

Question 34

What are the differences between skeletal muscle fibres?

Answer 34

enzymatic pathways for ATP synthesis
Resistance to fatigue
Activity of myosin ATPase

Question 35

What are the metabolic pathways for supplying ATP in muscle fibres?

Answer 35

Transfer of high energy creatine phosphate to ADP (immediate source of ATP)
Oxidative phosphorylation when O2 present
Glycolysis when O2 not present

Question 36

What are type 1 fibres and what are they used for?

Answer 36

slow oxidative (slow twitch)
low work aerobic activity eg maintaining posture/walking

Question 37

What are Type 2a fibres and what are they used for?

Answer 37

Fast oxidative (intermediate twitch fibres)
anaerobic and aerobic
moderate activites eg jogging

Question 38

What are type 2x fibres and what are they used for?

Answer 38

Fast glycotic (fast twitch fibres)
Aanaerobic metabolism
short term high intesity eg jumping