Physiology of Muscle Contraction

Question 1

myofibril

Answer 1

• make up the muscle fibers (1000s of myofibrils per muscle fiber)
• cylindrical sections that run the length of muscle fibers
• contain sarcomeres

Question 2

sarcomere

Answer 2

• contractile unit of myofibrils
• contains 2 types of protein myofilaments
• measured from one z-line to the next

Question 3

myosin

Answer 3

thick protein myofilaments of sarcomere

held together by m-line

Question 4

actin

Answer 4

• thin protein myofilaments of sarcomere

- parallel bands connected by z-lines

Question 5

z- line

Answer 5

• vertical lines that divide one sarcomere from the next

- during muscle contraction, move closer to the center M line

Question 6

A band

Answer 6

• dark band (dark when stained)

- contains thick + think filaments

Question 7

steps of muscle contraction

Answer 7

1. nerve impulse sent to neuromuscular junction of muscle fiber
2. acetylcholine released from motor nerve ending
3. acetylcholine binds to receptors on muscle cell and opens sodium channels
4. sodium flows inside the sarcoplasm, causing action potential in sarcolemma
5. action potential causes calcium ions to be released from sarcoplasmic reticulum
6. calcium ions cause cross-bridges of myosin filaments to bend backward and attach to actin filaments
7. cross-bridges bend forward (50-100x) and pull actin filaments to center of sarcomere
8. movement of actin filaments –> muscle contraction

Question 8

sarcoplasmic reticulum

Answer 8

smoother ER in striated muscle

Question 9

acetylcholine

Answer 9

• neurotransmitter, released from motor nerve ending
• binds to receptors on muscle cell
• opens sodium channels

Question 10

sodium channel

Answer 10

when open, allow sodium ions to flow into sarcoplasm

Question 11

sarcolemma

Answer 11

cell membrane of the muscle fiber