Section 5

Question 1

Functions of skeletal muscles (3)

Answer 1

force generation (locomotion and breathing)
stabilization (posture, rigidity)
thermogenesis

Question 2

Chemical composition of skeletal muscles (3)

Answer 2

75% water
20% protein
5% salts, phosphates, ions, nutrients

Question 3

Gross structure of the muscle (3)

Answer 3

Muscle (covered by epimysium); made of fascicles.
Fascicles (covered by perimysium); made of bundles of muscle fibers.
Muscle Fibers-cell (covered by endomysium and sarcolemma); made up of myofibrils.

Question 4

Cellular and Sub-cellular architecture (5)

Answer 4

Muscle (covered by epimysium); made of fascicles.
Fascicles (covered by perimysium); made of bundles of muscle fibers
Muscle Fibers-cell (covered by endomysium and sarcolemma); made up of myofibrils
Myofibrils (covered by endomysium and sarcolemma); made up of myofilaments
Myofilaments (e.g. protein; actin and myosin)

Question 5

Major proteins (4)

Answer 5

Myosin: contractile
Actin: contractile
Troponin: regulatory
Tropomyosin: regulatory

Question 6

What is the I band? A band? M line? H Zone?

Answer 6

I band: lighter area of the sarcomere; actin only
A band: darker area of the sarcomere; myosin only
M line: middle line of the sarcomere within the H-line (divides the sarcomere in half)
H zone: center of sarcomere (gap between myosins); myosin only

Question 7

Chemical and mechanical events that comprise the excitation contraction coupling process (8)

Answer 7

1. Nerve impulse travels to neuromuscular junction via axon
2. Release ACh (excitatory neurotransmitter) at end of axon into synaptic cleft
3. ACh traverses cleft and binds to receptors on muscle
4. ACh binding results in depolarization muscle fiber and AP
5. AP travel along surface and down the T-tubules
6. Events lead to Ca2+ release from the SR (calcium storage area)
7. Ca2+ binds to troponin-C resulting in a conformational change in tropomyosin, exposing the myosin binding sites on actin.
8. Contraction occurs

Question 8

Results of lack of calcium and lack of ATP (2)

Answer 8

Lack of Ca = NO CONTRACTION

Lack of ATP = NO RELAXTION

Question 9

Explain Lack of Calcium = No contraction

Answer 9

Without calcium, troponin cannot bind with calcium to cause tropomyosin to move from active actin sites allowing for myosin to attach to actin (atrophy).

Question 10

Explain Lack of ATP = No relaxation

Answer 10

Calcium ions cannot be pumped back into the sarcoplasmic reticulum > troponin cannot bind with calcium to occupy active sites of actin > myosin heads have no ATP to bind with so they cannot release from active sites so the muscle fiber stays contracted (dead body in rigor mortis).

Question 11

What is the relationship between sarcomere length and force production?

Answer 11

If sarcomere length is short/under-stretched (using 0/20 myosin), it can’t generate any tension (force).
When it’s stretched to a good length (ex. using 16-20 out of 20 myosin), maximal force is generated.
If it’s over-stretched to its maximal length (myosin doesn’t make contact with actin; 0 myosin used), no tension (force) is generated.