2. Muscle Functions
ā¢ Produce body movements
ā¢ Stabilize body position
ā¢ Regulate organ volume
ā¢ Move fluids and solid food and
wastes in the body
ā¢ Produce heat
25. From: Principles of Anatomy & Physiology Tortora & Grabowsky
Neuromuscular Junction
SEM 1650x
26. Events Leading up to Muscle Contraction
ā¢ Nerve impulse arrives at end
of motor nerve axon causing
ā¢ Acetylcholine(ACh) release
into synapse via exocytosis
ā¢ ACh floods across synaptic
gap and attaches to receptors
on the sarcolemma
ā¢ Permeability of sarcolemma
changes and Na+ enters cell
ā¢ A muscle impulse is
triggered
ā¢ Muscle impulse travels via the
transverse tubules throughout
the muscle cell
ā¢ Ca++ diffuses from SR and
binds to troponin on actin
ā¢ Myosin cross bridges link
with actin and muscle
contracts
NMJ
Muscle fiber
29. Fig. 9.9
3 Myosin heads bind to actin forming cross-bridges
ADP + P ADP + P
P
ADP
P
ADP
Cross-bridges pull thin filament (power stroke),
ADP and P released from myosin
ADP + P
4
30. ATP
ATP ATP ATP
New ATP binds to myosin, releasing linkages
5
6 ATP splits, which provides power toācockā the myosin cross-bridges
ADP + P ADP + P
Fig. 9.9
33. Muscle Fiber Excitation
ā¢ Nerve impulse arrives at axon terminal
ā¢ Triggers release of Ach by exocytosis
ā¢ ACh diffuses across synaptic cleft
ā¢ ACh binds to receptors on muscle motor end plate
ā¢ Sarcolemma becomes more permeable to Na+
ā¢ Na+ triggers release of muscle action potential
ā¢ Muscle action potential travels along outside of
sarcolemma and into T tubules
ā¢ Action potential triggers Ca++ release from SR
ā¢ Ca++ binds to troponin on thin filament
ā¢ Tropomyosin is pulled aside, revealing binding
sites
ā¢ Myosin links to & pulls actin to contract muscle
Muscle Fiber Relaxation
ā¢ Acetylcholinesterase decomposes ACh
in synapse
ā¢ Action potential (impulse) ends
ā¢ SR actively pumps Ca++ back into SR
ā¢ Tropomyosin moves back to cover
binding sites
ā¢ Myosin heads detach
ā¢ Muscle fiber returns to its longer resting
length