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Musculoskeletal > Skeletal Muscle Physiology I > Flashcards

Skeletal Muscle Physiology I Flashcards

1
Q

What are the physiological functions of skeletal muscle?

A

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

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2
Q

What is the largest type of tissue in the body?

A

Muscle

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3
Q

What are the three kinds of muscle in the body?

A

Skeletal, cardiac, smooth

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4
Q

What can all three types of muscle do?

A

Capable of developing tension and producing movement through contraction

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5
Q

Are all muscle types striated?

A

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

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6
Q

What does striation look like under a light microscope?

A

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

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7
Q

What are skeletal muscles innervated by?

A

Somatic nervous system (subject to voluntary control)

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8
Q

What are cardiac and smooth muscle innervated by?

A

Autonomic nervous system (subject to involuntary control)

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9
Q

What are some features of skeletal muscle?

A

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

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10
Q

How does excitation contraction coupling work in skeletal muscle?

A

Ca++ entirely from sarcoplasmic reticulum

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11
Q

How is gradation of contraction controlled in skeletal muscle?

A

By motor units and summation of contractions

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12
Q

What are some features of cardiac muscle?

A

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

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13
Q

How does excitation contraction coupling work in cardiac muscle?

A

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

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14
Q

How is gradation of contraction controlled in cardiac muscle?

A

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

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15
Q

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

A

No

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16
Q

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

A

Acetylcholine at neuromuscular junction (stimulates alpha motor neuron)

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17
Q

How is skeletal muscle organised?

A

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

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18
Q

What determines the number of muscle fibres per motor unit?

A

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

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19
Q

What does skeletal muscle consist of?

A

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

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20
Q

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

A

The entire length of the muscle

21
Q

What normally attaches the skeletal muscle to the skeleton?

A

Tendons

22
Q

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

A

Bones, muscles and joints

23
Q

What does each muscle fibre contain?

A

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

24
Q

What is within each myofibril?

A

Actin and myosin, arranged into sarcomeres

25
Q

What is the functional unit of an organ?

A

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

26
Q

What is the functional unit of skeletal muscle?

A

Sarcomeres

27
Q

Where are sarcomeres found in the skeletal muscle?

A

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

28
Q

What are the four zones of sarcomeres?

A

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

29
Q

What is the A-band of sarcomeres?

A

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

30
Q

What is the H-zone of the sarcomere?

A

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

31
Q

What is the M-line of the sarcomere?

A

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

32
Q

What is the I-band of the sarcomere?

A

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

33
Q

How is muscle tension produced?

A

By sliding of actin filaments on myosin filaments

34
Q

What does force generation depend on?

A

ATP-dependent interaction between myosin and actin filaments

35
Q

What is ATP required for in force generation?

A

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

36
Q

What is Ca++ required for in force generation?

A

Switching on cross bridge formation

37
Q

What is excitation contraction coupling?

A

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

38
Q

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

A

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

39
Q

What are T-tubules?

A

Extensions of the surface membrane that dip into the muscle fibre

40
Q

What happens when the muscle is relaxed?

A

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

41
Q

What happens when the muscle is excited?

A

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

42
Q

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

A

A power stroke that pulls actin inward during excitation

43
Q

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

A

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

44
Q

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

A

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

45
Q

What is the third step of excitation contraction coupling?

A

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

46
Q

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

A

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

47
Q

What is the fifth step of excitation contraction coupling?

A

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

48
Q

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

A

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

49
Q

What is the final step of excitation contraction coupling?

A

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

Musculoskeletal (57 decks)

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