*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