4.1 Neuromuscular Junction Flashcards
What is a neuromuscular junction?
A specialised synapse/connection between a motor neuron and a muscle fiber
Whats the purpose of a neuromuscular junction?
The point where the nervous system communicates w/ muscular system to initiate muscle contraction
In short, how does the process of the neuromuscular junction convert a neural signal into a muscle contraction?
- Acetylcholine is released from the motor neuron
- Acetylcholine diffuses across the synaptic cleft
- Acetylcholine binds to the receptors on the muscle fiber, initiating an action potential which leads to muscle contraction
- The enzyme, acetylcholinesterase terminates the signal & allows the muscle to relax
Explain the role of neurotransmitters in stimulating skeletal muscle contraction.
4.1.2
Neurotransmitter Release:
-acetylcholine is released when the action potential arriving at the presynaptic membrane triggers the opening of the voltage-gated calcium channels. The release of the calcium ions into the neuron fuses the presynaptic membrane with the synaptic vessels, releasing acetylcholine into the synaptic cleft.
Synaptic Cleft Transmission
-Acetylcholine travels across the synaptic cleft, the narrow space between the presynaptic terminal and postsynaptic membrane
Muscle Fiber Activation
-reaching postsynaptic membrane of muscle fiber, acetylcholine binds to specific receptors on the postsynaptic membrane, causing a sodium ion influx which enter the fiber, generating an action potential -> causes muscle contraction
Signal Termination
-Acetylcholinesterase in the synaptic cleft breaks down acetylcholine, ending the muscle stimulation and allowing the muscle to relax.
Label a diagram of a motor unit.
4.1.1
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What are the functions of the labelled components of the motor unit?
(node of ranvier & myelin not required)
*this is mainly for actually understanding this concept
The dentrides is the area where neurons receive information.
-> have receptors that pick up signals from other neurons, come in chemical forms: neurotransmitters
-> signals cause electrical changes in neurons, the changes are interpreted by the soma/cell body
soma/cell body contains nucles,dna, takes the signal received by dentrides -> if signal is strong enough it gets send down the body of the neuron, the axon
if a signal is sent down the axon, the signal is now called an action potential (the myelin sheaths prevent the signal from degrading). the axon gives out many branches -> supplying multiple muscle fibers
motorendplate: chemical synapse between nerve terminal & specialized muscle cell membrane
What are the main components of the neuromuscular junction?
Presynaptic terminal ~ of motor neuron
Synaptic cleft
Postsynaptic membrane~ of muscle fiber
Where is the presynaptic terminal located? What does it contain?
Located at the end of the motor neuron. It contains synaptic vessels that are filled with neurotransmitters, acetylcholine (ACh)
What is the synaptic cleft?
The narrow space between the presynaptic terminal and the postsynaptic membrane.
Where is the postsynaptic membrane located? What does it contain?
The postsynaptic membrane is located at the muscle fibers. It contains the receptors which acetylcholine binds to.
Explain step 1 of the neuromuscular junction.
Hint: Its called the “Arrival of an ____ ____at the pre…_____ ____”
Step 1: Arrival of an action potential at the presynaptic terminal
The action potential reaches the presynaptic terminal -> triggers the opening of voltage-gated calcium channels. This opening of the voltage-gated calcium channels allows the calcium ions to enter the neuron.
Explain step 2, of the neuromuscular junction.
Hint: its called the “Release of _____ into the _____ ____”
Step 2: Release of acetylcholine into the synaptic cleft
The influx of the calcium ions causes the synaptic vessicles (those located in the presynaptic terminal) to fuse w/ the presynaptic membrane. This fussion releases the neurotransmitter acetylcholine into the synaptic cleft.
Explain step 3, of the neuromuscular junction.
Hint: its when “Acetylcholine _____ to the ____ at the postsynaptic membrane”
Step 3: Acetylcholine binds to the receptors at the postsynaptic membrane
The acetylcholine released from the motor neuron diffuses across the synaptic cleft to reach the postsynaptic membrane. The postsynaptic membrane contains the receptors for acetylcholine. The binding of acetylcholine to those receptors, causes an influx of sodium ions into the muscle fibers, initiating an action potential that travels along the muscle fibers, finally leading to the muscle contraction.
Explain step 4, of the neuromuscular junction.
Hint: its when “Acetylcholine is ____ by the enzyme ____”
Step 4: Acetylcholine is broken down by the enzyme acetylcholinesterase.
After acetylcholine binds to the receptors, it quickly gets broken down by the enzyme acetylcholinesterase. This enzyme is located in the synaptic cleft.
Purpose: The breakdown of acetylcholine (by acetylcholinesterase) stops the signal and allows the muscle fiber to relax.
