Muscles Flashcards
Describe the structure of muscle
Each muscle fibre is a single multinucleated cell called sarcolemma
Contractile unit is a sarcomere
Thin filament: made of actin, tropomyosin, and troponin. Forms I bands ->shrink with contraction
Thick filament: made from myosin. Forms A bands-> DOES NOT shrink with contraction
H band: pure thick filaments
M line: middle of H band
Z line: where thin filaments are attached
Describe the steps of contraction of skeletal muscle
- discharge of motor neuron
- release of transmitter Ach at motor end plate
- binding of Ach to nictotinic Ach receptors
- Increased Na+K conductance in end plate membrane
- Generation of end plate potential which initiates AP along muscle fibres
- Inward spread of depolarisation along T tubule
- Release of calcium from terminal cisterns of sarcoplasmic reticulum and diffusion to thick and thin filaments
- lateral movement of tropomyosin
- Binding of calcium to troponin C uncovering myosin binding sites on actin
- formation of cross links between actin and myosin
How does muscle relax after contraction?
Calcium actively pumped back into sarcoplasmic reticulum
How does muscle work increase during vigorous exercise?
Efficiency of nutrient energy into muscle work is 20-25%
Oxygen consumption may increase 20x in a trained athlete
Heatstroke will develop when body temp>41 degrees
what is the resting membrane potential of a muscle cell?
-90mv
AP last 2-4ms
How do action potentials affect fast and slow muscle fibres differently?
A single AP causes a muscle twitch
Fast fibres twitch lasts 7.5ms
slow fibres twitch lasts 100ms
How do the different elements of a sarcomere change during a muscle contraction?
Width of A band: constant
Z lines: move closer together
Contraction occurs when myosin heads bind firmly to actin (needs ATP as energy)
Why is all the energy of an isometric muscle contraction dissipated as heat?
No external work is done in an isometric contraction
How is smooth muscle different to skeletal?
No striations
No Z lines
Fewer mitochondria
Calmodulin is regulatory calcium binding protein
Calcium pump is slow compared to the pump in skeletal muscle
How do muscular arteries adapt to changing requirements for blood flow in distal tissue?
Muscular arteries sense and adapt to the flow and pressure in their lumen
How is cardiac muscle different to skeletal?
Intercalated disks
Gap junctions
T system at z lines rather than at A-I junction
Contraction due to influx of calcium rather than release of stored calcium from SR
AP different (4 stages, prolonged plateau phase due to slower opening calcium channels
How does digoxin interfere with the cardiac action potential?
Decreases Na-K ATPase
Decreases sodium influx
If sodium cant get in, calcium cant get out (Na-Ca exchange)
Therefore increased intracellular calcium and increased strength of contraction of cardiac muscle
How do catecholamines increase cardiac function?
Increase cAMP production
Leading to influx of calcium in cardiac cells which increases contraction. Also increases active transport of calcium to sarcoplasmic reticulum which accelerates which increases diastolic filling time
Where does the heart get its energy from?
<1% by anaerobic metabolism (increased to 10% during hypoxia)
35% from carbohydrate oxidation
5% from ketones and amino acids
60% from fat (1/2 of which from FFA)
Which types of muscle have spontaneous electrical activity?
Cardiac muscle
Visceral smooth muscle
