Skeletal Muscle Flashcards
What surrounds: muscle; muscle fascicle; muscle fiber?
Epimysium; Perimysium; Endomysium.
Control and appearance of Skeletal muscle?
Voluntary control; striated.
Muscle fibers contain?
Myofibrils.
smallest unit of contraction?
Sarcomere.
Skeletal muscles controlled by what neurons?
Somatic motor neurons - voluntary control.
Tension: contraction and relaxation?
Shortening and lengthening myofibrils (sarcomeres).
5 “areas” of sarcomere?
Z-discs; M-line; H-zone; A-band; I-band.
Elastic structure of sarcomere?
Titin
Proteins regulating contraction?
Troponin and Tropomyosin.
Filaments present in areas?
A-band: thick partially overlapping thin (across M-line and H-zone) H-zone: only thick I-band: only thin Z-disc: thin attached (toward M-line) M-line: thick attached (toward Z-disc)
Area(s) unchanged (constant length) during contraction?
Area(s) shorten during contraction?
A-band.
H-zone & I-band.
Stimulus for contraction?
Calcium.
Process of crossbridge cycling
- Myosin bound to actin (rigor state)
- ATP bind to myosin head - detachment from thin actin filament
- ATPase activity of myosin hydrolyses ATP. ADP and Pi remain bound.
- Hydrolysis causes conformational change - head swivel and bind to actin.
- Release of Pi causes power stroke
- ADP released - head bound in rigor state to actin
What binds to troponin to move tropomyosin from MBS?
Calcium.
Triad consists of?
T-Tubule and 2 cisternae.
Calcium release from which channels to cause contraction?
Ryanodine receptors (RyRs)
Calcium uptake through which ATP dependent structure to cause relaxation?
SERCA pump
Calcium is stored in which structure?
Sarcoplasmic Riticulum
Membrane resting potential of Skeletal Muscle?
-70mV
Distribution of ions across cell membrane?
Na+ outside and K+ inside cell.
Depolarisation caused by?
Na+ influx through voltage gated sodium channels.
Repolarisation caused by?
K+ efflux through voltage gate Potassium channels.
Neurotransmitter that crosses synapse? Receptor that receives it?
Acetylcholine (Ach) and Nicotinic Receptors.
Exocytosis of vesicles caused by?
AP and influx of Ca2+.
On motor end plate, Na+ and K+ move through which channel?
Nicotinic receptor (opened by binding of Ach).
Excitation-Contraction process?
- Ach released - bind to Nicotinic Receptors
- AP reach T-tubules - activate membrane protein (DHPR) or (LTCC) which opens RyRs.
- Ca2+ released from SR
- Ca2+ bind to troponin, move tropomyosin and expose MBS
- Myosin bind to actin - contraction occurs
- SERCA take up Ca2+ into SR
- MBSs covered by tropomyosin - no crossbridge cycling
- Contraction ends
- Relaxation - lengthening of sarcomere
How many APs in one twitch?
+/- 5 - 50 (AP: 2msec; twitch: 10-100msec)
Tetanus caused by?
Summation (repeated stimulation)
Greatest tension at what sarcomere length?
2.0-2.3micrometers (resting length)
What is a muscle unit?
1 somatic motor neuron and all myofibers it innervates
Most ATP generated when?
Glycolysis coupled with oxidative phosphorylation
Skeletal muscle prefer glucose or fatty acids to generate ATP?
Glucose (aerobic and anaerobic)
Types of fatigue?
Central fatigue and peripheral fatigue.
