Muscle physiology

Question 1

Name the four phases of muscle contraction.

Answer 1

Excitation
Excitation-contraction coupling
Contraction
Relaxation

Question 2

Provide short definition of excitation

Answer 2

process in which nerve action potentials lead to muscle action potentials

Question 3

Provide short definition of excitation-contraction coupling

Answer 3

link aps on sarcolemma to activation of myofilaments- prep them to contract

Question 4

Provide short definition of contraction

Answer 4

muscle fibre develops tension & may shorten

Question 5

Provide short definition of relaxation

Answer 5

stimulation ends - muscle fibre relaxes & returns to its resting length

Question 6

Describe what occurs in the excitation phase

Answer 6

-Ap arrives at synaptic terminal.
-Acetylcholine (ACh) released, changing membrane perm
-ACh crosses synaptic cleft, binding to ACh receptors on sarcolemma.
-Na+ ions rush in, generating an ap.

Question 7

Describe what occurs during the excitation-contraction coupling phase

Answer 7

-Ap spreads along T tubules.
-Ca+ binds to troponin, shifting tropomyosin and exposing active sites.

Question 8

Describe what occurs at contraction phase

Answer 8

-Energized myosin heads bind to F-actin active sites
-forms cross-bridges.
-myosin heads pivot towards the M line=contraction cycle

Question 9

Describe what occurs at relaxation phase

Answer 9

-Myosin heads split ATP, releasing energy to ‘cock’ the heads.
-ATP binds to myosin, breaking actin-myosin link and exposing active sites for new cross-bridges.