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Human Physiology for Exercise Science > Lecture Five > Flashcards

Lecture Five Flashcards

1
Q

What is the primary function of the Muscular System?

A

Produce movement in the body

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2
Q

What are the other functions of the Muscular System?

A
  • Constriction of organs and vessels
  • Cardiac contraction
  • Respiration
  • Postural maintenance
  • Body heat production
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3
Q

What are the types of muscle?

A

Skeletal, smooth, cardiac

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4
Q

What are the functional classification of muscles?

A 
Voluntary= skeletal
Involuntary= cardiac & smooth
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5
Q

What are the is the histological classification of muscles?

A 
Striated= cardiac & skeletal
Non-striated= smooth
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6
Q

What is the Sarcolemma (Plasmalemma), composed of, what does it fuse to, what does it assist and what does it transport??

A
  • Cell membrane is composed of the sarcolemma and basement membrane.
  • Fuses with tendon which connects muscle to bone.
  • Assists with the transmission of action potentials along the muscle.
  • Transports metabolites in and out of cell.
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7
Q

What is the Sarcoplasmic Reticulum and what does to store?

A
  • Specialised smooth endoplasmic reticulum in skeletal muscle, network of tubules run along and around myofibrils.
  • Storage site of calcium
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8
Q

What is the transverse tubules?

A
  • Extensions of the plasmalemma that pass laterally through the cell
  • Allow action potentials to be transmitted into the myofibrils
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9
Q

What are other organelles of the skeletal muscle?

A
  • Sarcoplasm
  • Mitochondria
  • Nucleus
  • Multi-nucleated
  • Myofibrils
  • Myofilaments
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10
Q

What are the Myofibrils?

A

-Complex organelle composed of bundles of myofilaments.

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11
Q

What is the Sarcomere?

A

-Contractile unit of muscle.
o Z-line to Z-line
-Striation of myofibrils reflects overlapping of thick and thin filaments
-M-line: Myosin attachment
-Titin enables the muscle to stretch and recoil

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12
Q

What is myosin?

A

-Thick filaments are bundles of Myosin molecules
-Each globular ‘head’ of the myosin has:
o Myosin ATPase site
o Actin binding site

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13
Q

What is actin?

A

-Thin filaments are paired chains of actin molecules each with a myosin binding site.

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14
Q

What are the binding sites covered with in the sliding filament theory?

A

-At rest the binding sites are covered by the regulatory proteins
o Troponin
o Tropomyosin

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15
Q

What is the role of calcium in the sliding filament theory?

A

-At rest, myosin and actin are unable to bind due to Troponin and Tropomyosin.
o Tropomyosin covers the binding sites on actin
o Troponin holds Tropomyosin in place
-Troponin is the ‘lock’ that keeps binding sites inaccessible
-Calcium is the ‘key’
-Ca2+ is stored in the Sarcoplasmic Reticulum
-Upon release it spreads out in the sarcoplasm and binds to Troponin
o Troponin initiates contraction process by moving Tropomyosin away to expose the Myosin binding sites on actin.

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16
Q

What does calcium do to troponin in an excited sliding filament?

A

-Ca2+ binds to Troponin
o Changes shape exposing the binding sites by moving Tropomyosin aside
o Cross bridging occurs = attachment of Myosin to Actin

17
Q

What are the stages in the sliding filament theory?

A
  1. Exposure of Active Sites
    - Calcium is released
    - Calcium makes it way to troponin which is then unlocked
    - Pulls tropomyosin to uncover the myosin binding sites on actin.
  2. Cross-bridge Formation
    - When myosin binds to binding sites on actin
  3. Power Stroke
    - Energy stored in the myosin head if used to cause the power stroke.
  4. Cross-bridge Release
    - An ATP molecule binds to each head & causes detachment
  5. ATP to ADP and P
    - A chemical reaction causes the P to detach from ATP
  6. Recovery Stroke
    - Myosin head returns to resting position= energy stored in head.
18
Q

What happens if calcium is still attached to troponin?

A

-If calcium is still attached to troponin the cycle starts again
-Repeated cycles of cross-bridge binding and power stroking ‘walks’ the cross bridges along the actin filaments pulling these inward
o Towards M-Line
-Overlap of the filaments increases and sarcomeres shorten

19
Q

What is the role of ATP?

A

-Muscle action is an active process; therefore, it requires energy in the form of ATP.
o Myosin contains a binding site for ATP.
o In a relaxed state, the energised myosin heads are cocked back with ADP + Pi attached.

20
Q

What happens in the power stroke in terms of ATP?

A

-Pi and ENERGY is released causing myosin head to pivot, pulling actin in towards centre of sarcomere; ADP is released from myosin.

21
Q

What happens in the cross bridge stroke in terms of ATP?

A

-A new ATP binds to myosin head to release it from actin

22
Q

What happens in the recovery stroke in terms of ATP?

A

-ATP is broken down by myosin ATPase to form ADP + Pi + energy to re-energise and re-position the head of myosin.

23
Q

What happens to the sarcomere without ATP?

A

-Myosin and actin remain bound
-In rigor mortis, the muscles stiffen because there is no ATP to release the bond.
-When neural muscle stimulation ceases:
o Ca2+ actively transported back into the sarcoplasmic reticulum using ATP
o Tropomyosin will cover binding sites on actin
-Muscle relaxation requires energy supply by ATP

24
Q

What are the functions that require ATP within a muscle?

A
  • Power Stroke
  • Release of myosin from actin after power stroke
  • Transporting calcium back to sarcoplasmic reticulum
25
Q

What does the alpha motor neuron do in neural connection to skeletal muscle?

A
  • Nerve cell innervating skeletal muscle fibres, initiating contraction
  • Cell body located in the central nervous system (CNS)
  • Axon extends to periphery, part of the peripheral nervous system (PNS)
26
Q

What does the motor unit do in neural connection to skeletal muscle?

A
  • α-MN and all the muscle fibres it innervates
  • Neuromuscular Junction
  • Point of the motor neuron and muscle fibres.
27
Q

What is the process in the neural connection to skeletal muscle?

A
  1. An action potential travels along an axon membrane to the neuromuscular junction.
  2. Acetylcholine is released form the presynaptic vesicles.
  3. Acetylcholine stimulates sodium channels on the postsynaptic membrane to open.
  4. Sodium diffuses into the muscle fibre, initiating an action potential that travels along the sarcolemma and T tubule membranes.
  5. Action potential in the T tubules cause the sarcoplasmic reticulum to release calcium.
28
Q

What is excitation-contraction?

A

“Represents the physiologic mechanisms whereby an electrical discharge at muscle initiates chemical events at the cell surface to release intracellular Ca2+ and ultimately produce muscle action”

29
Q

What is the sequence of events that triggers a muscle to contract?

A
  1. Excitation of a motor nerve
  2. Propagation of an action potential
  3. Events at the neuromuscular junction and transfer of action potential
  4. Calcium release from sarcoplasmic reticulum
  5. Sliding of filaments
  6. Muscular contraction
30
Q

Explain in more detail the process of the excitation-contraction events.

A

-The brain/spinal cord triggers a nerve impulse = excitation of a motor neuron.
-Action potential propagates down αMN
-Impulse carried to axon terminal
-Acetylcholine (ACh) released from the synapse
-ACh crosses the synaptic cleft and binds to acetylcholine receptors on the sarcolemma
-Only if sufficient ACh is bound to receptors on the motor end plate on the sarcolemma an ACTION POTENTIAL is generated in the muscle fibre
-The action potential travels along the sarcolemma like a ‘ripple on a pond’ n -Action potential travels down into the T-tubules and into the muscle fibre
-Causes voltage gates of the sarcoplasmic reticulum to open and Ca2+ is released into the sarcoplasm
-Ca2+ binds to troponin tropomyosin complex on actin filaments
-Displaces tropomyosin to allow myosin to bind with actin
-Cross bridge
-Sliding of filaments
= Sarcomeres contract, causing muscle shortening

31
Q

What happens to the cross-bridges if calcium remains high?

A

-Cross bridge activation will continue if Ca2+ remains high, due to continued action potential

32
Q

What happens if the brain signals the muscle to relax?

A
  • The action potential at the neuromuscular junction ceases
  • ATP is required to actively move Ca2+ back into the sarcoplasmic reticulum to await next action potential. Troponin moves tropomyosin to cover binding sites on actin.
  • ATP is required for myosin recovery stroke to take place and for the muscle to remain relaxed.
33
Q

What is skeletal muscle not made up of and what do muscle fibre types differ in?

A
  • Skeletal muscle is not made up of homogenous fibre that share metabolic and contractile properties.
  • Several types differing in mechanism of ATP production, motor neuron innervation, force production capacity.
34
Q

What are the muscle fibre types, give an example of a sport they would be most prevalent in, what type of twitch are they and what is their fatigue rate?

A

Type 1= Long distance, slow twitch & low fatigue rate.
Type 2A=400/800m, fast twitch oxydative & medium fatigue rate.
Type 2B=Short sprints, fast twitch glycolytic & high fatigue rate.

35
Q

What is the predominance of muscle fibre types determined by?

A

-The predominance of muscle fibre types is determined by:
o Function of the muscle
-Postural = Slow-Twitch
-Rapid movement of aerobic nature = Fast twitch
-Rapid, powerful movement = Fast twitch
-Genetics

36
Q

What fibre types do endurance athletes have?

A

-Higher percentage of Type I fibres in the major muscles used in their sport

37
Q

What fibre types do sprint/power athletes have?

A

-Higher percentage of Type II fibres in the major muscles used in their sport

38
Q

What fibre types do middle distance athletes have?

A

-Great range of both Type I and Type II fibres

Human Physiology for Exercise Science (14 decks)

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