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SR2002 - The Science Of Sports Performance > Muscles > Flashcards

Muscles Flashcards

1
Q

How many skeletal muscles do humans have?

A

~660 skeletal muscles

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2
Q

What is the average muscle mass in adult females?

A

13-30 kg

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3
Q

What is the average muscle mass in adult males?

A

18-40 kg

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4
Q

What is the diameter range of muscle fibers?

A

10-100 μm

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5
Q

What is the length range of muscle fibers?

A

1-500 mm

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6
Q

What are the three layers of connective tissue surrounding muscle fibers?

A
  • Epimysium: Encloses muscles. (The connective tissue)
  • Perimysium: Surrounds the groups of fibres that form muscle fascicles.
  • Endomysium: Encloses each muscle fibre, and it consists of Extracellular matrix (made of collagen).
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7
Q

What is the basic contractile unit of muscle?

A

Sarcomere: Consists of myofilaments within myofibrils which are arranged in a series of repeating units.

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8
Q

What type of proteins are troponin and tropomyosin classified as?

A

Regulatory proteins

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9
Q

What are the two types of myofilaments found in myofibrils?

A
  • Thick filaments
  • Thin filaments
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10
Q

What proteins make up thick and thin filaments?

A

Thick Filaments: Myosin and Myosin-binding proteins (C protein, H protein, M protein, myomesin).

Thin filaments: Actin, tropomyosin, and troponin complex (TN-T, TN-I, TN-C).

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11
Q

What is the primary function of dystrophin in muscle fibers?

A

Force transmission

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12
Q

What are the three types of muscle contractions?

A
  • Eccentric contraction: muscle generates force when lengthening. (Where muscle force is at its greatest.
  • Isometric contraction: Muscle generates force while length stays the same.
  • Concentric contraction: Muscle shortens and generates force.
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13
Q

In which type of contraction does the muscle generate force while lengthening?

A

Eccentric contraction

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14
Q

What is myosin?

A

A myosin molecule is composed of six proteins:
- Two myosin heavy chains (MyHC)
- One essential myosin light chain (MLC) on each MyHC
- One regulatory myosin light chain (MLC) on each MyHC

MyHC contains ATP- and actin-binding sites (essential for muscle contraction)

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15
Q

What is the role of titin in muscle fibers?

A

Acts as a molecular spring permitting return of stretched sarcomeres to ‘optimal’ length.

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16
Q

What occurs during the power stroke in the cross-bridge cycle?

A

Dissociation of Pi results in 5-10 nm displacement

17
Q

True or False: Muscle force is greatest during concentric contractions.

A

False

18
Q

What is the relationship between force and velocity during muscle contraction?

A

Speed of contraction decreases with increasing resistance

19
Q

What does the sarcoplasmic reticulum do in muscle fibers?

A

Surrounds myofibrils and stores calcium

20
Q

What is the average resting myoplasmic calcium concentration?

A

~0.1 µM

21
Q

What is the maximum contraction myoplasmic calcium concentration?

A

~2 µM

22
Q

What is the delay between action potential and initiation of muscle contraction?

A

~20 ms

23
Q

What slows down the relaxation after fatiguing contractions?

A

Decrease in ATP concentration

24
Q

What provides the framework for actin and myosin filaments in the sarcomere?

A

Cytoskeletal proteins

25
Q

What links to the endomysium?

A

Structural Intracellular proteins of muscle fibre link to the endomysium via focal adhesions. (This is important for force transmission).

26
Q

What is the Contractile machinery of the muscle?

A
  • Muscle fibres (10-100 μm) are covered by sarcolemma (≈7.5 nm thick).
  • T-tubules are invaginations of sarcolemma.
  • Sarcoplasmic reticulum is a network of tubes surrounding myofibrils.
  • Sarcoplasm is fluid enclosed within the fibre.
  • Myofibrils (~1 μm) are packed bundles of myofilaments running along the fibre.
27
Q

What do the different filaments in the sarcomere do?

A
  • Thin filaments at one end project into the sarcomere while another connects the Z line.
    -Thin filaments contain troponin and tropomyosin proteins that participate in blocking and unblocking of thin filaments (regulatory proteins).
  • Thick filaments (myosin) are in the centre of sarcomere and overlap thin filaments from both sides
28
Q

Muscle Contraction:

A

Myosin heads drag thin filaments from both ends towards each other
•The distance between Z lines shortens (sarcomere shortens)
•Shortening of sarcomeres in series add up.

•Example
–10-cm fibre contains ~4,000,000 sarcomeres
–Each sarcomere shortening by 1 µm shortens the fibre to 6 cm.

29
Q

How is force produced: the cross-bridge cycle

A
  1. ATP hydrolysis increases affinity of myosin for actin.
  2. Following Ca++ release from SR myosin binds actin.
  3. ATP binds to myosin decreasing its affinity for actin.
  4. Myosin dissociates from actin, ATP is hydrolysed.
30
Q

Why does eccentric contraction generate more force than concentric?

A

Eccentric - all associated cross-bridges contribute.
Concentric - “power stroke” cross-bridges contribute.

31
Q

What slows down the relaxation after fatiguing contractions?

A

Possible cause of slowing relaxation is a decrease in concentration ATP leading to impaired dissociation of these metabolites from the myosin.

32
Q

Where is the muscle contractile force transmitted through?

A

Through the connective tissue: Endomysium, perimysium, epimysium, tendons).

SR2002 - The Science Of Sports Performance (2 decks)

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