12.15.2 The Neuromuscular Junction: The Contraction Is Triggered Flashcards
1
Q
The Neuromuscular Junction: The Contraction Is Triggered
A
- Muscles require nerve stimulus to contract.
- Troponin and tropomyosin work together to prevent myosin from binding to the actin filament.
- The sarcoplasmic reticulum releases calcium that changes the position of tropomyosin allowing myosin to bond to actin. Then muscle contraction can occur.
2
Q
note
A
- Muscles require nerve stimulus to contract. The illustration on the left shows an axon of a motor neuron affecting a single muscle fiber. Motor neurons have many branches and can innervate up to 100 muscle fibers each. Muscle contraction begins when nerve action potentials reach the neuromuscular junction.
- When muscles are at rest, tropomyosin is situated on the actin filament, preventing myosin heads from binding.
- An action potential reaches the muscle, triggering a
depolarization wave through the membrane system of the muscle fiber. During this time, calcium is released from the sarcoplasmic reticulum. Calcium ions then bind to the troponin complex, causing the tropomyosin strand to shift, uncovering the myosin binding sites of the actin filament. When the sites are uncovered, contraction will occur.
3
Q
__________ are extensions of the muscle cell plasma membrane that increse the surface area over which a depolarization spreads.
A
- T tubules
4
Q
True or false?
During muscle contraction, Ca2+ floods the cell, moving tropomyosin away from the binding site between myosin and actin.
A
- true
5
Q
In its relaxed state, the myosin heads are prevented from binding to the actin filaments by
A
- tropomyosin
6
Q
The stimulation of the muscle cell by a neurotransmitter like acetylcholine causes __________ along the muscle cell.
A
- depolarization
7
Q
The critical calcium storage membrane in the muscle cell is the
A
- sarcoplasmic reticulum.
8
Q
Motor neurons stimulate muscle cells by
A
- release of neurotransmitters from the synapse of the motor neuron
