Physiology of muscle contractions
Muscle contraction is initiated by nervous system.
Contraction of skeletal muscle is controlled by nervous system.
Mechanism of Muscle contraction
Steps
1. Depolarization and calcium ion release
2. Actin and myosin bridge formation
3. Sliding mechanism of actin and myosin filaments
4. Sarcomere shortening (muscle contraction)
Nervous control of muscle contraction
1. Motor unit
2. Neuromuscular junction/ myoneural junction
3. Motor end plates
4. Synaptic gutter
5. Synaptic cleft
6. Acetylcholine
7. Subneural clefts
1. Motor unit
Motor neuron together with muscle fibers. It innervates (supply with nerve) is called motor unit.
In human, a motor unit composed of about 6 to 30 fibers (in eye muscles).
To over 1000 fibers (in powerful leg muscles).
2. Neuromuscular junction
Junction between motor nerve ending and muscle fibre called neuromuscular junction.
End branches of motor neuron (axon terminal) gain access to muscle fibre through endomysium.
At the junction between muscle fiber and motor neuron, muscle fibre forms motor end plate.
3. Motor end plate
Motor neuron Connects to muscle fibers.
It is specialized portion of sarcolemma of muscle fibers.
Mitochondria are abundant near motor end plate.
4. Synaptic gutter
Turned inside out area of sarcolemma under i.e reach close to muscle fiber sarcolemma.
5. Subneural clefts
Small fold of the sarcolemma are present at the bottom of synaptic gutter.
These clefts increases surface area of synaptic gutter.
6. Synaptic cleft
At Motor end plate, nerve endings are separated from sarcolemma of muscle fiber by tiny gap called synaptic cleft.
It is 20-30 nm wide.
7. Acetylcholine
Acetylcholine is released from synaptic vesicles of nerve endings.
It bridge synaptic cleft and flows into folds of sarcolemma.
Acetylcholine attached to receptor site in sarcolemma.
Initiating electrochemical impulse across sarcolemma of muscle cells, so that Na+ ions moves into sarcoplasm and K+ move out.
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