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Muscle, Efferent (motor) somatic nervous system - Coggle Diagram
Muscle
Major functions
Mobility - interaction with external environment
Motility - movement of materials through the body
Temperature regulation
3 Types
Smooth muscle
Skeletal muscle
Cardiac muscle
Anatomy
Sarcolemma
(cell or plasma membrane of muscle fibre)
Sacroplasm -
contains particularly high concentrations of glycogen and myoglobin
- 10^-7 Ca2+ at rest
Organelles
Myofibrils -
1-2 micrometres in diameter -> occupy approximately 80% of sacroplasm
Thin filaments - 5-8nm in diameter, 1 micron length
actin (components that make up thin filament)
tropomyosin
troponin complex
calcium binding site
Actin binding site
tropomyosin binding site
myosin binding site
Thick filaments - 12-18nm in diameter, 1.6 micron length
Myosin filament (200 myosin protiens)
cross-bridges
Actin binding site
ATPase
Sacroplasmic reticulum -
storage site for calcium
-> typically contains 10^-3M Ca2+
Transverse (or T-) tubule -
Important in iniation of muscle fibre contraction
Lateral sacs -
two enlarged regions
Largest diameter Myelinated neurones
Mechanics
A. motor unit recruitment
B. Action potential frequency
C. length-tension relationship
Fibre Types
Slow-twitch (type 1)
Fast-twitch (type 2)
Neuromuscular transmission
Action potential moves down axon of motoneurone and depolarises sarcolemma of muscle fibre
Triggers opening of voltage-gated Ca2+ channels
Ca2+ flows down concentration gradient from extracellular into axon terminal then binds to proteins that enable synaptic vesicles to fuse with the neuronal plasma membrane
results in exocytosis of acetylcholine into synaptic cleft, seperating axon terminal and motor end plate
Acetylecholine diffuses across synaptic cleft binding to nicotinic acetylcholine receptors in the folds on the sarcolemma
opens ion channel in each receptor. Causes depolarising graded potential in muscle fibre -> end-plate potential (reason being binding of acetylcholine triggers opening of non-selective cation channel).
Na+ flows into cell (sarcoplasm) and K+ out -> electrochemical gradient difference results in more Na+ flowing into the cell than K+ out= net positive charge
In most instances end-plate potential 3-4 times greater than required action potential threshold.
excitation-contraction coupling
action potential traveling along muscle fibre meets t-tubule, flows down t-tubules into middle of muscle fibre
Presence of action potential in t-tubules triggers opening of voltage-gated Ca2+ channels in walls of sarcoplasmic reticulum
opening of Ca2+ channels enables Ca2+ to run down concentration gradient into sarcoplasm -> causes sarcoplasmic Ca2+ concentration to increase from resting 10^-7 to 10^-4M
increase in Ca2+ concentration triggers molecular processes causing myofibril to shorten
when action potentials stop flowing down t-tubules, a calcium pump in the membrane of sarcoplasmic reticulum pumps calcium out of the sarcoplasm and back into the sarcoplasmic reticulum
Ca2+ concentration within sarcoplasmic reticulum returns to resting levels, myofibrils return to normal length
The Muscle relaxes
Sliding-Filament Mechanism
Rest
- prior to action potential arriving in the muscle fibres sarcoplasmic Ca2+ concentration is low - Tropomyosin molecules cover myosin-binding sites however, cross-bridges are in primed (energised) state due to splitting of ATP-ADP->potential energy
Binding
- release of Ca2+ from sarcoplasmic reticulum -> sarcoplasmic Ca2+ increases to 10^-4M, some calcium binds to calcium biding sites on troponin complex -> this process allows myosin cross-bridges to bind to thin filaments -> thick & thin filaments are now coupled
Power Stroke
- myosin cross-bridge swings over, binds weakly to a new actin molecule -> at 90 degree angle relative to thin filament. Inorganic phosphate released in this process initiates 'power stroke'. ending in ADP being released
Deattachment
- Release of ADP from ATPase allows new ATP molecule to bind to myosin with breaks link between actin and myosin
Relaxation
- if no Ca2+ bound to troponin complex will return original shape, tropomyosin filament return to blocked state over myosin binding site (passive)
Efferent (motor) somatic nervous system