Skeletal Muscle Physiology I

Question 1

What are the physiological functions of skeletal muscle?

Answer 1

Maintenance of posture, purposeful movement in relation to external environment, respiratory movements, heat production, contribution to whole body metabolism

Question 2

What is the largest type of tissue in the body?

Answer 2

Muscle

Question 3

What are the three kinds of muscle in the body?

Answer 3

Skeletal, cardiac, smooth

Question 4

What can all three types of muscle do?

Answer 4

Capable of developing tension and producing movement through contraction

Question 5

Are all muscle types striated?

Answer 5

No - skeletal and cardiac muscle are striated, smooth muscle is unstriated

Question 6

What does striation look like under a light microscope?

Answer 6

Alternating dark (thick myosin) and light (thin actin) bands

Question 7

What are skeletal muscles innervated by?

Answer 7

Somatic nervous system (subject to voluntary control)

Question 8

What are cardiac and smooth muscle innervated by?

Answer 8

Autonomic nervous system (subject to involuntary control)

Question 9

What are some features of skeletal muscle?

Answer 9

Neurogenic initiation of contraction, motor units, neuromuscular junction present, no gap junctions

Question 10

How does excitation contraction coupling work in skeletal muscle?

Answer 10

Ca++ entirely from sarcoplasmic reticulum

Question 11

How is gradation of contraction controlled in skeletal muscle?

Answer 11

By motor units and summation of contractions

Question 12

What are some features of cardiac muscle?

Answer 12

Myogenic (pacemaker potential) initiation of contraction, no neuromuscular junction, gap junctions present

Question 13

How does excitation contraction coupling work in cardiac muscle?

Answer 13

Ca++ from ECF and sarcoplasmic reticulum (ca++ induced Ca++ release)

Question 14

How is gradation of contraction controlled in cardiac muscle?

Answer 14

Depends on the extent of heart filling with blood (preload)

Question 15

Is there continuity of the cytoplasm between nerve and skeletal muscle cells?

Answer 15

No

Question 16

What is the transmitter of neurogenic initiation of skeletal muscle contraction?

Answer 16

Acetylcholine at neuromuscular junction (stimulates alpha motor neuron)

Question 17

How is skeletal muscle organised?

Answer 17

Organised into motor units = motor unit is a single alpha motor neuron and all the skeletal muscle fibre it innervates

Question 18

What determines the number of muscle fibres per motor unit?

Answer 18

The functions served by the muscle = muscles which serve fine movements have fewer fibres per motor unit (about 10 per unit)

Question 19

What does skeletal muscle consist of?

Answer 19

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

Question 20

How much of the muscle do skeletal muscle fibres usually cover?

Answer 20

The entire length of the muscle

Question 21

What normally attaches the skeletal muscle to the skeleton?

Answer 21

Tendons

Question 22

What makes up the lever system that allows the body to move?

Answer 22

Bones, muscles and joints

Question 23

What does each muscle fibre contain?

Answer 23

Many myofibrils = specialised contractile intercellular structures, predominant structure of skeletal muscle

Question 24

What is within each myofibril?

Answer 24

Actin and myosin, arranged into sarcomeres

Question 25

What is the functional unit of an organ?

Answer 25

The smallest component capable of performing all the functions of that organ

Question 26

What is the functional unit of skeletal muscle?

Answer 26

Sarcomeres

Question 27

Where are sarcomeres found in the skeletal muscle?

Answer 27

Between two lines, connect the thin filaments of two adjoining sarcomeres

Question 28

What are the four zones of sarcomeres?

Answer 28

A-band, H-zone, M-line, I-band

Question 29

What is the A-band of sarcomeres?

Answer 29

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

Question 30

What is the H-zone of the sarcomere?

Answer 30

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

Question 31

What is the M-line of the sarcomere?

Answer 31

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

Question 32

What is the I-band of the sarcomere?

Answer 32

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

Question 33

How is muscle tension produced?

Answer 33

By sliding of actin filaments on myosin filaments

Question 34

What does force generation depend on?

Answer 34

ATP-dependent interaction between myosin and actin filaments

Question 35

What is ATP required for in force generation?

Answer 35

For both contraction and relaxation, and to pump Ca++ back into the sarcoplasmic reticulum during relaxation

Question 36

What is Ca++ required for in force generation?

Answer 36

Switching on cross bridge formation

Question 37

What is excitation contraction coupling?

Answer 37

Process whereby the surface action potential results in activation of the contractile structures of the muscle fibre

Question 38

When is Ca++ released from the lateral sacs of the sarcoplasmic reticulum?

Answer 38

When the surface action potential spreads down the transverse (T) tubules

Question 39

What are T-tubules?

Answer 39

Extensions of the surface membrane that dip into the muscle fibre

Question 40

What happens when the muscle is relaxed?

Answer 40

No cross bridge binding because the bridge binding site on actin is physically covered by the troponin-tropomyosin complex

Question 41

What happens when the muscle is excited?

Answer 41

Ca++ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross bridge binding site, cross bridge binding occurs

Question 42

What does the binding of the actin and myosin cross bridge cause?

Answer 42

A power stroke that pulls actin inward during excitation

Question 43

What is the first step of the excitation contraction coupling process?

Answer 43

Acetylcholine released by axon of motor neurons crosses cleft and binds to receptors/channels on motor end plate

Question 44

What is the second step in the excitation contraction coupling process?

Answer 44

Action potential generated in response to binding of acetylcholine and subsequent end-plate potential is propagated across surface membrane and down T-tubules of muscle cells

Question 45

What is the third step of excitation contraction coupling?

Answer 45

Action potential in T-tubules triggers Ca++ release from sarcoplasmic reticulum

Question 46

What is the fourth step in the excitation contraction coupling process?

Answer 46

Calcium ions released from lateral sacs bind to troponin on actin filaments, leads to tropomyosin being physically moved aside to uncover cross bridge binding sites on actin

Question 47

What is the fifth step of excitation contraction coupling?

Answer 47

Myosin cross bridges attach to actin and bend, pulling actin filaments towards centre of sarcomere, powered by energy provided by ATP

Question 48

What is the sixth step in the excitation contraction coupling process?

Answer 48

Ca++ actively taken up by sarcoplasmic reticulum when there is no longer local action potential

Question 49

What is the final step of excitation contraction coupling?

Answer 49

With Ca++ no longer bound to troponin, tropomyosin slips back to its blocking position over binding sites on actin, contraction ends, actin passively slides back to original resting postition