8 - Neuromuscular junction
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- impulses from the motor neurons
- What causes skeletal muscle cells to contract?
- neuromuscular junction
- What is the place called where a motor neuron stimulates a muscle cell?
- by endomysium
- How are skeletal muscle cells are electrically insulated from each other?
- motor neuron
- A single nerve cell that extends from the brain or spinal cord to a muscle or gland and carries movement instructions to muscle. An efferent neuron.
- The axon. A elongated portion of the neuron
- What part of the motor neuron carries impulses to the muscle? Describe its structure.
- T-tubules
- Invaginations of the sarcolemma penetrating deep into the interior of the muscle cell.
- Synaptic cleft
- The space between the axon terminal and the motor end plate.
- Axon terminal
- swollen distal end of the motor neuron axon.
- Sarcolemma
- The muscle cell membrane.
- Synaptic vesicles
- Structures within the axon terminal that contain the neurotransmitter acetylcholine.
- Sarcomere
- The contractile unit of the muscle cell that extends from one Z line to the next.
- S.R. & terminal cisternae
- Structures within skeletal muscle cells that serve as reservoirs of calcium ions.
- Motor end plate
- A folded region of the sarcolemma at the neuromuscular junction.
- polarized membrane
- A condition in which a difference in electrical charge exist across a cell membrane.
- It is when the + & - sign indicate a polarized condition. More + on outside & more - on inside.
- Describe the resting membrane potential with respect the neuromuscular junction?
- They are polarized
- Describe the T Tubules when they are at resting membrane potential.
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_____ e. An action potential arrives at the axon terminal
_____ c. Acetyl choline is released from the axon terminal into the synaptic cleft.
_____ a. The motor end plate is depolarized.
_____ d. The depolarization trigge -
List the following events in the order they occur:
_____ a. The motor end plate is depolarized.
_____ b. The sarcomeres contract.
_____ c. Acetyl choline is released from the axon terminal into the synaptic cleft.
_____ d. The depolarization triggers an action potential which propagates along the sarcolemma and the T tubules.
_____ e. An action potential arrives at the axon terminal - The voltage change of the membrane opens voltage-regulated Ca++ channels, allowing Ca++ ions to enter the axon terminal.
- What happens at the neuromuscular junction when the action potential arrives at the axon terminal?
- causes synaptic vesicles to fuse w/the membrane of the axon terminal.
- What is the effect of the presence of calcium ions inside the axon terminal?
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1. Ach is liberated (released) by exocytosis into the synaptic cleft.
2. Ca++ is pumped out of the axon terminal. - What two events happen after the synaptic vesicles fuse with the membrane of the axon terminal?
- It binds to receptor sites of the chemically-regulated ion channels on the motor end plate.
- What happens to acetylcholine after it is released into the synaptic cleft?
- Cause channel to open, permitting an influx of Na+ ions and a small flux of K+ ions. This causes a local depolarization of motor end plate.
- What happens after the acetylcholine binds to the acetylcholine receptor on the motor end plate?
- when Ach diffuses away from the receptor.
- When does the chemically regulated ion channel on the motor end plate close?
- It is degraded by acetylcholinesterase.
- What happens to the acetyl choline after it diffuses away from its receptor on the motor end plate?
- it initiates an action potential which propagates along the sarcolemma all directions and down the T-tubules.
- The movement of the sodium ions through the chemically regulated ion channel initiates a depolarization of the motor end plate. What happens after this depolarization is generated?
- it causes the release of Ca++ ions from the terminal cisternae into the cytosol.
- What happens as the action potential moves down the T Tubules?
- it contracts
- What happens when calcium ion is present in the cytosol of the muscle cell?
- F, J, C, A, H, D, E, B, G, I.
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Place the following events in their proper sequence:
_____ a. Acetyl choline is released into the synaptic cleft.
_____ b. Action potential propagates along the sarcolemma and down the T Tubules.
_____ c. Synaptic vesicles fuse to membrane of axon terminal.
_____ d. Motor end plate becomes depolarized.
_____ e. Action potential is initiated on the sarcolemma.
_____ f. Action potential arrives at the axon terminal.
_____ g. Calcium ions are released from the terminal cisternae.
_____ h. Acetylcholine binds to receptor sites on the motor end plate.
_____ i. The muscle cell contracts.
_____ j. Calcium ions enter the axon terminal.