Physiology: Skeletal Muscle Physiology

Question 1

What is tetanus?

Answer 1

Maximal sustained contraction of a muscle fibre that results from repeated stimulations so close together than the fibre does not have time to relax between stimuli

Question 2

What are 𝛾-motor neurons?

Answer 2

Efferent (motor) supply of muscle spindles

Question 3

Describe the structure of skeletal muscle

Answer 3

Parallel muscle fibres (skeletal muscle cells) bundled by connective tissue

Question 4

What causes the striation of skeletal muscle?

Answer 4

Alternating dark bands (myocin) and light bands (actin)

Question 5

Define isometric contraction

Answer 5

Muscle tension develops at constant muscle length

Question 6

Define isotonic contraction

Answer 6

Muscle tension remains constant as the muscle length changes

Question 7

What is excitation-contraction coupling?

Answer 7

The process whereby surface action potential results in activation of the contractile structures of the muscle fibre via Ca2+

Question 8

What are slow oxidative (type I) muscle fibres?

Answer 8

Aerobic fibres used mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking

Question 9

What is electromyography?

Answer 9

Electrodes detect frequency and amplitude of muscle fibre action potentials

Question 10

What is the Z-line of a sarcomere?

Answer 10

The sarcomere is found between two Z lines - connect the thin filaments of 2 adjoining sarcomeres

Question 11

What is isometric contraction used for?

Answer 11

Supporting objects in fixed positions and maintaining body posture

Question 12

What is the A-band of a sarcomere?

Answer 12

Made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments

Question 13

Where do Ca2+ ions bind to in the sliding filament theory of muscle contraction?

Answer 13

Troponin (on actin filaments)

Question 14

What is a muscle spindle (intrafusal fibres)?

Answer 14

Collection of specialised muscle fibres which act as sensory receptors for the stretch reflex

Question 15

What is the sliding filament theory?

Answer 15

Muscle tension is produced by sliding of actin filaments on myocin filaments

Question 16

Which muscle type is non-striated and involuntary?

Answer 16

Smooth muscle

Question 17

How is muscle tension from contraction transmitted to bone?

Answer 17

Via the elastic components of muscle

Question 18

What are fast glycolytic (type IIx) muscle fibres?

Answer 18

Anaerobic fibres used mainly used for short-term high intensity activities e.g. jumping

Question 19

What is the optimal length of skeletal muscle?

Answer 19

The resting length of a skeletal muscle is approximately its optimum length

Question 20

What is ATP required for in the generation of muscle tension?

Answer 20

Contraction (powers cross bridges) and relaxation (release of cross bridges and to pump Ca2+ back into SR)

Question 21

Define a sarcomere

Answer 21

The functional unit of muscle

Question 22

What is the function of 𝛾-motor neurons?

Answer 22

Adjust tension in muscle spindles to maintain sensitivity during contraction, when the muscle shortens

Question 23

Which muscle type is striated and voluntary?

Answer 23

Skeletal muscle

Question 24

What are fast oxidative (type IIa) muscle fibres?

Answer 24

Use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging

Question 25

What are nerve conduction studies?

Answer 25

Determine the functional integrity of peripheral nerves

Question 26

What is a reflex action?

Answer 26

Stereotyped response to a specific stimulus - simplest form of coordinated movement

Question 27

How does a skeletal muscle's function affect the number of muscle fibres per motor unit?

Answer 27

If a muscle serves fine movements, it will have fewer fibres per motor unit, and vice versa

Question 28

What triggers the release of Ca2+ in skeletal muscle?

Answer 28

Action potential reaches T-tubules

Question 29

What are annulospiral fibres?

Answer 29

Sensory nerve endings of muscle spindles

Question 30

What is Ca2+ required for in the generation of muscle tension?

Answer 30

Cross bridge formation

Question 31

Define myotonia

Answer 31

Delayed reaction after voluntary contraction

Question 32

How do Ca2+ ions allow the formation of cross-bridges in the sliding filament theory of muscle contraction?

Answer 32

Bind to troponin which moves tropomyosin aside to uncover the cross-bridge binding sites on the actin, allowing myosin to bind

Question 33

Which muscle type is striated and involuntary?

Answer 33

Cardiac muscle

Question 34

What is the H-zone of a sarcomere?

Answer 34

Lighter area within middle of A-band where thin filaments don't reach

Question 35

When a skeletal muscle fibre receives an action potential, where will Ca2+ be released from?

Answer 35

The lateral sacs of the sarcoplasmic reticulum

Question 36

What are reflex pathways used for in a clinical context?

Answer 36

To identify lesions in the motor system e.g. knee jerk (stretch reflex)

Question 37

What is the I-band of a sarcomere?

Answer 37

Consists of remaining potion of thin filaments that do not project in the A-band

Question 38

What is the M-line of a sarcomere?

Answer 38

Extends vertically down the middle of A-band within the centre of H-zone

Question 39

What is a twitch?

Answer 39

A single contraction of a muscle fibre following a single stimulation

Question 40

What are T-tubules in skeletal muscle?

Answer 40

Extensions of the surface membrane that dip into the muscle fibre

Question 41

What is isotonic contraction used for?

Answer 41

Body movements and moving objects

Question 42

Define a motor unit

Answer 42

A single alpha motor neuron and all the skeletal muscle fibres it innervates

Question 43

Describe the structure of a myofibril

Answer 43

Actin and myocin arranged into sarcomeres

Question 44

Where are muscle spindles found?

Answer 44

In the belly of muscles, run parallel to ordinary muscle fibres

Question 45

What usually attaches skeletal muscles to the skeleton?

Answer 45

Tendons

Question 46

Define myalgia

Answer 46

Muscle pain