*13) Objective 3 Neuromuscular junction*
Nerve impulses elicit a muscle action potential in the following way
1) Release the acetylcholine 2) Activation of ACh receptors 3) Production of muscle action potential 4) Termination of ACh activity
Activation of ACh receptors
- binding of ACh to the receptor on the motor end plate opens and ion channel - Allows Na+ to flow into the muscle cell
Production of muscle action potential
- the inflow of Na+ makes the inside of the muscle fiber more positively charges, triggering a muscle action potential - the muscle action potential then propagates to the SR to stimulate the release its stored Ca++
Motor end plate
- the region of the muscle cell membrane opposite the synaptic end bulbs - contains ACh receptors -Neuromuscular junctions, also called motor end plates, are specialised chemical synapses formed at the sites where the terminal branches of the axon of a motor neuron contact a target muscle cell.
The Neuromuscular Junction
-Motor neurons have a threadlike axon that extends from the brain or spinal cord to a group of muscle fibers - is a chemical synapse formed by the contact between a motor neuron and a muscle fiber. - Action potentials arise at the interface of the motor neuron and muscle fiber. Called the synapse
Termination of ACh activity
Ach efffects last only briefly because it is rapidly broken down by the enzyme acetylcholinesterase (AChE)
Neurotransmitter
Chemical released by the motor neuron. For motor neurons the neurotransmitter is called acetylcholine
Synaptic Cleft
Gap that separates the motor neuron and muscle fiber. Where action potentials arise at the interface of the motor neuron and muscle fiber (synapse)
chemical gated sodium ion channels
open in response to a neurotransmitter (ACh)
voltage gated ion channels
open in response to voltage change or an action potential
Motor neurons are
cells that send action potentials to the muscle fiber
the neurotransmitter that is released into the synaptic cleft binds to a _________________________________
chemical gated sodium ion channel
motor unit
a motor neuron plus all the muscle fibers it innervates
For motor neurons the neurotransmitter is called....
acetylcholine
calcium ions
are free floating surrounding the axon termial
first an action potential travels down to the
axon terminal
axon terminal
is the end of a motor neuron
A muscle is controlled by ______________ motor neurons
many
Skeletal muscle contraction when stimulated by
motor neurons
sarcolemma
muscle cell membrane; this the outer most part of the motor end plate; on this you will find chemical gated sodium ion channels
release of acetylcholine
nerve impulses arriving at the synaptic end bulbs causes many synaptic vesicles to release ACh into the synaptic cleft
A place where the action potential is transferred from a motor neuron to a muscle fiber is called.....
neuromuscular junction (synapse between a motor neuron and a muscle fiber)
motor end plate
place where the motor neuron synapses with the muscle fiber
synaptic vesicles
sacs suspended within the synaptic end bulb containing molecules of acetylcholine (ACh)
At the end of an axon terminal you will find an open space where neurotransmitter diffuses across
synaptic cleft
are inside the axon terminal and are filled with the neurotransmitter acetylcholine
synaptic vesicles
calcium ions in the axon terminal then stimulate ___________________________ to fuse to the presynaptic membrane of the axon terminal then releasing the neurotransmitter into the synaptic cleft
synaptic vesicles
the binding to neurotransmitter to the chemical gated sodium ion channel causes ________________________
the gate to open allowing sodium to diffuse across the sarcolemma and thus creating a new action potential within the muscle fiber
2nd the action potential stimulates the opening of _______________________________ and when open allows the flow of calcium into the axon terminal
voltage gated ion calcium ion channels