Answer:
The sliding filament model describes the process used by muscles to contract. It is a cycle of repetitive events that causes actin and myosin myofilaments to slide over each other, contracting the sarcomere and generating tension in the muscle.
Explanation:
Step 1) Neuromuscular Control
The axons of the nerve cells of the spinal cord branch and attach to each muscle fiber forming a neuromuscular junction.
i). An action potential passes down the nerve.
ii). The nerve releases Ca++ that results in the release of Acetylcholine (ACh)
Step 2). ACh binds with the sarcolemma.
Step 3). Muscle Fiber Action Potential
i). ACh binds with receptors and opens Na+ channels
Na+ Channels open and Na+ in
There is a decrease in the resting potential
ii). Na + rushes in and the sarcolemma depolarizes.
iii). The regional depolarization spreads rapidly.
The positive patch in the membrane changes the adjacent patch of the membrane.
Thus depolarization spreads.
iv). The K+ channels open and the region repolarizes
Immediately after the action potential passes the membrane permeability changes again.
Na+ channels close and K+ channels open.
K+ rushes out of the cell.
Cell reploraizes
Step 4). Ca++ is released from the sarcoplasmic reticulum.
i). Ca++ is stored in thesarcoplasmic reticulum.
ii). Depolarization releases the Ca++.
iii). The Ca++ clears the actin binding sites.
Step 5). Sliding Filament Theory of Contraction
During muscle contraction the thin actin filaments slide over the thick myosin filament.
When Calcium is present the blocked active site of the actin clears.
Step A: Myosin head attaches to actin. (High energy ADP + P configuration)
Step B: Power stroke: myosin head pivots pulling the actin filament toward the center.
Step C: The cross bridge detaches when a new ATP binds with the myosin.
Step D: Cocking of the myosin head occurs when ATP à ADP + P. Another cross bridge can form.
Actin-Myosin Sliding Filament Theory
The end result is a shortening of the sarcomere.
The distance between the Z discs shortens
The H zone disappears
The dark A band increases because the actin & the myosin overlap more
The light I band shortens.
Sarcomere shortening
Step 6). Ca++ is removed from the cytoplasm
Step 7). Tropomysin blocks the actin site
Answer:
The sliding filament model of contraction involves actin and myosin sliding past each other and partially overlapping
Explanation:
Sliding filament model states that during muscle contraction the myofilaments myosin and actin slide towards each other and overlap. This shortens the sarcomere and the entire muscle/ Muscle cells are shocked by nerve impulses from motor neurons.
The force behind the muscle contraction is the ratchet movement of the tiny myosin heads toward the centre of thei sarcomere. This ratchet movement occurs many times during muscle contraction.
Points of the sliding filament theory will be as follows :
