Neuromuscular Junction

Events that occur during synaptic activity are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Voltage-gated calcium channels open (b) Neurotransmitter binds to receptors (c) Action potential arrives at axon terminal (d) Neurotransmitter is removed from the synaptic cleft (e) Neurotransmitter released into synaptic cleft (f) Graded potential generated in postsynaptic cell

(c) Action potential arrives at axon terminal (a) Voltage-gated calcium channels open (e) Neurotransmitter released into synaptic cleft (b) Neurotransmitter binds to receptors (f) Graded potential generated in postsynaptic cell (d) Neurotransmitter is removed from the synaptic cleft

Neurotransmitter binds to receptors on the postsynpatic cell. These chemically gated channels open, allowing the transfer of the "signal" from a presynaptic neuron to the postsynaptic cell

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When an action potential reaches the synaptic terminal voltage-gated channels open and calcium enters the cell. Calcium causes vesicles to fuse with the presynaptic membrane and release neurotransmitter into synaptic cleft.

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Using the images for help, place in the correct order of occurrence from left to right the events that occur at the neuromuscular junction after the action potential reaches the axon terminal

1) Ca2+ enters the axon terminal 2) Synaptic vesicles release ACh

Drag the labels to identify the sequence of events that occur at a synapse

1) an action potential arrives at the synaptic terminal 2) calcium channels open, and calcium ions enter the synaptic terminal 3) Vesicles containing neurotransmitter fuse with the plasma membrane of the sending neuron 4) neurotransmitters molecules diffuse across the synaptic cleft 5) the neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, causing channels there to open

How is acetylcholine (ACh) removed from the synaptic cleft?

simple diffusion away from the synaptic and acetylcholinesterase (AChE, enzyme)

What type of channel on the postsynaptic membrane binds neurotransmitter?

a chemically gated channel

A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?

a neuron

Facts about neuron

a neuron is the only type of presynaptic cell. Neurons release neurotransmitters, effectively changing an electrical signal or action potential into a chemical signal that can communicate across the synaptic cleft to the postsynaptic cell

Synaptic vesicles at the neuromuscluar junction contain__

acetlycholine

In a neuromusclar junction, synaptic vesicles in the motor neuron contain which neurotransmitter?

acetylcholine (ACh)

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?

an exocytosis

the binding of a neurotransmitter to receptors on the motor end plate causes which of the following to occur?

binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell

What is the primary mechanism by which ACh is cleared from the synaptic cleft?

broken down by acetylcholinesterase

What are most directly causes synaptic vesicles to release acetlycholine into the synpatic cleft?

calcium entering the axon terminal

What is the role of calcium in synaptic activity?

calcium influx into the synaptic terminal causes vesicle fusion

Acetlycholine receptors are best characterized as what type of channel?

chemically gated Na+-K channels

Which component has a role in the postsynpatic cell during synaptic activity?

chemically gated channels

Neurotransmitters is released from presynaptic neurons through what mechanism?

exocytosis

skeletal muscles cells are grouped into bundles called___

fascicles

what would happen if acetylcholine was not removed from the synaptic cleft?

multiple action potentials would occur in the muscle fiber

What is the direct role of neurotransmitter at a chemical synapse?

neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane.

In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?

reuptake and degraddation

ACh receptors are found mainly in the __________.

sarcolemma

when the chemically gated ion channels open, which ion is mainly responsible for depolarizing the sacrolemma?

sodium

The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?

terminal cisterns (cisternae) of the sacroplasmic reticullum

When an action potential arrives at the axon terminal of a motor neuron, which ions channels open?

voltage-gated calcium channels