M3b L29-30

Question 1

Describe the structure of the sarcomere

Answer 1

Myofibrils: Actin and myosin
Myofibers (muscle cells)
Multinucleated muscle cells 1-40 mm long
Formed from the fusion of precursor muscle cells, it has more than one nuclei
Bundles of Thick (myosin) and thin (F-actin + other proteins) filaments
Specialized muscle structure responsible for contraction
Z disc joins sarcomeres

Question 2

Explain the symptoms of rigor mortis

Answer 2

contracted muscle, caused by myosin being bound to f-actin
no ATP being made results in muscle-cell death and muscle stiffening

Question 3

Describe energy sources for muscle contraction

Answer 3

Cellular ATP supplies are limited
Oxidative phosphorylation generates ATP for normal aerobic muscle contraction
Substrate level phosphorylation supplies some ATP; short bursts only of anaerobic metabolism
Creatine phosphate (PCr) supplies a fast acting reserve of ATP
glycogen

Question 4

Describe excitation-contraction coupling

Answer 4

Sodium channels and potassium channels responsible for the nerve signal
They work together to transfer the action potential down the T-tubule
It is sensed by DHPR. voltage sensor
DHPR is connected to RyR (Ryanodine receptor), voltage change is passed via chemical interaction to RyR in the SR membrane, opens and releases calcium to myofibrils

Question 5

Explain the roles of the sarcoplasmic reticulum and
transverse tubules in muscle cells

Answer 5

t tubules are used to ensure connection
Action potential travels across sarcolemma/muscle cell membrane to the T tubules

Question 6

Describe the swinging cross-bridge mechanism for muscle contraction, including the role of ATP

Answer 6

Muscle contraction by bands/zones
H zone decreases in length via contraction
Focus on 1 monomer not all simultaneous, as muscle contracts, the myosin binds, generates force, myosin pulls on F-actin then release and reset, if they all release at the same time the f-actin will slip back again
Cyclic mechanism, can start at any step
Each myosin head goes through these 6 steps every 0.2 seconds, lots of ATP used

Question 7

Describe the sliding filament mechanism for muscle
contraction

Answer 7

Key proteins; actin and myosin, form the thin and thick filaments in muscle Sliding filament mechanism a series of filaments sliding on top of one another, results in muscle cells getting longer

Question 8

Describe motor neuron initiation and Ca2+ regulation of muscle contraction/relaxation

Answer 8

Ca2+ signaling controls muscle contraction via the troponin complex & tropomyosin
excitation-contraction coupling
Sodium channels and potassium channels responsible for the nerve signal
They work together to transfer the action potential down the T-tubule
It is sensed by DHPR. Voltage change is passed via chemical interaction to RyR in the SR membrane, opens and releases calcium to myofibrils
Green pump is SERCA
To enable the membrane bound DHPR to come into close enough contact with the cytoplasm bound receptor