Synapse and Nerve Fibers

What are the two factors that determine whether a synapse can excite or inhibit the postsynaptic cell?

Depending on which neurotransmitter is used and what receptors are on the postsynaptic neuron

In conclusion: What is the firing frequency and how can this affect the postsynaptic cell's decision to have an action potential?

A neuron can fire repeatedly under certain conditions. The number of action potentials in a given time is the firing frequency. A high firing frequency of a subthreshold input can result in an action potential in the postsynaptic cell.

What is a post synaptic neuron?

A neuron receiving a signal from the axon terminal

What is meant by membrane resting potential?

A signal that exists and is ready for action, but not active.

In conclusion: How does summation occur in a postsynaptic cell?

A single neuron can receive inputs from multiple nerve fibers that have varying strengths. When multiple neurons fire simultaneously, the inputs sum to determine if an action potential occurs. Inhibitory inputs can cancel out excitatory inputs.

In conclusion: What determines whether a synapse is excitatory or inhibitory?

A synapse can excite or inhibit the postsynaptic cell depending on which neurotransmitter they use and what receptors are on the postsynaptic neuron. In the brain, glutamate is generally excitatory and GABA is inhibitory. In the body, Acetylcholine is the primary excitatory neurotransmitter

In conclusion: What are the locations where synapses occur and what are they called?

A synapse can occur between an axon and a dendrite: axodendritic, cell body: axosomatic, or rarely another axon: axoaxonic. Synapses between axons and cell bodies can occur either with other neurons, organs, muscles, or glands.

If enough neurotransmitters are released what is initiated?

An action potential

What occurs at the axon terminal?

An electrochemical signal is converted to a chemical signal

What causes the post-synaptic neuron to depolarize?

An excitatory synapse

In conclusion: What are excitatory and inhibitory synapses?

An excitatory synapse causes the postsynaptic neuron to depolarize. An inhibitory synapse causes the postsynaptic neuron to hyperpolarize, inhibiting action potentials.

What causes the post-synaptic neuron to hyperpolarize?

An inhibitory synapse

In conclusion: What is an electrical synapse?

At electrical synapses cells are joined with gap junctions. Electrical changes in one cell are passed bidirectionally to the next cell through joined membranes. Electrical synapses have the advantage of being fast, but are disadvantaged in that the postsynaptic cell's response is usually lower amplitude.

What can a high firing frequency of a subthreshold input result in?

Can result in an action potential.

What joins together at electrical synapses?

Cells

What 2 events can this binding of neurotransmitters to receptors on the postsynaptic cell cause?

Either an ion channel to open or activation of a second messenger system

In conclusion: How does neural activity propagate between cells without a loss of signal strength?

If enough neurotransmitters are released an action potential is initiated in the post-synaptic neuron in an all-or-nothing fashion. The post-synaptic action potential is as large as the pre-synaptic action potential; the result of this is no loss of signal strength between cells.

In the brain, what neurotransmitter is generally excitatory and what neurotransmitter is generally inhibitory?

In the brain, glutamate is generally excitatory and GABA is inhibitory.

Where are these vesicles with neurotransmitters found?

In the synaptic knob.

What effects do inhibitory inputs have on excitatory inputs?

Inhibitory inputs can cancel out excitatory inputs.

In conclusion: What are neurotransmitters and how are they released?

Neurotransmitters are chemical messengers that neurons use to communicate with each other. Examples are glutamate and acetylcholine. Neurotransmitters are stored in vesicles in the synaptic knob. Action potentials reache the synaptic knob, calcium-dependant release of neurotransmitters occurs.

What happens when an action potential reaches the synaptic knob?

Neurotransmitters are released

In conclusion, How does synaptic fatigue occur?

Neurotransmitters are stored within a limited number of vesicles in the axon terminal. With repeated stimulation, the number of vesicles are depleted. This depletion leads to synaptic fatigue, where the neurons can no longer send a signal.

What is meant by subthreshold inputs?

Signals that do not reach the action potential threshold

When multiple neurons fire simultaneously, what happens to the inputs?

The inputs sum

What determines the firing frequency?

The number of action potentials in a given time

What happens to the number of vesicles during repeated stimulation?

The number of vesicles are depleted

How large is the post-synaptic action potential compared to the presynaptic action potential?

The post-synaptic action potential is as large as the pre-synaptic action potential

What is another name for synaptic knob?

axon terminal

Where can synapses occur?

between an axon and a dendrite, between an axon and a cell body, and between an axon and another axon

Where are axosomatic synapses located?

between two neurons, between neurons and organs, neurons and muscles, or between neurons and glands.

How are electrical signals in one cell passed to the next cell?

bidirectionally using joined membranes.

What method of neurotransmitter release is this?

calcium-dependant release of neurotransmitters

What are neurotransmitters?

chemical messengers that neurons use to communicate with each other.

How is this information sent?

from one neuron's axon to another cell

What are common neurotransmitters?

glutamate, GABA and acetylcholine

In what fashion is the action potential initiated?

in an all-or-nothing fashion.

In what form is the electrochemical signal converted to a chemical signal?

in the form of a neurotransmitter.

Where can this action potential occur?

in the postsynaptic cell

What can a synapse excite or inhibit?

the postsynaptic cell

What is the result of this consistency in the size of the post-synaptic and pre-synaptic action potentials?

the result of this is no loss of signal strength between cells.

In conclusion, What is a synaptic Knob?

the site where an electrochemical signal is converted to a chemical signal in the form of aneurotransmitter.

What is the synapse the site of?

the site where information is sent

What is the purpose of the input summation?

to determine if an action potential occurs.

In what manner do presynaptic cells release neurotransmitters to the postsynaptic cell?

unidirectionally

What are neurotransmitters stored in?

vesicles

Where are these vesicles located?

within the axon terminal

What happens when the membranes resting potential is reduced?

it becomes less negative/more positive

What can a single neuron receive inputs from?

multiple nerve fibers

What is the disadvantage of electrical synapses?

postsynaptic cell's response is usually lower amplitude.

How common are axoaxonic synapses?

rare

What is a post-synaptic cell?

A cell receiving the signal directly from the axon terminal

What is meant by hyperpolarize?

A change in the cell's membrane potential that makes it more negative

What is the result of synaptic fatigue?

A condition where the neurons can no longer send a signal.

In the body, what is the primary excitatory neurotransmitter?

Acetylcholine

What is a synapse that occurs between two axons?

Axoaxonic Synapse

What is a synapse called that occurs between an axon and a dendrite?

Axodendritic synapse

What is meant by nerve fibers?

Axons and the myelin sheath

What is a synapse that occurs between an axon and a cell body?

Axosomatic synapse

What is the most abundant component of the nervous system?

Chemical synapses

What is a common example of a second messenger system?

G-protein signaling.

Where is the axon terminal or synaptic knob located?

Located at the end of an axon

What is meant by the inputs sum?

Means the signal inputs are added together

What is meant by inputs?

Nerve signals

Where is this action potential initiated?

On the post-synaptic neuron

What do Neurotransmitters bind to on the postsynaptic cell?

Receptors

How can neurons fire under certain conditions?

Repeatedly

What situation does this depletion lead to?

Synaptic fatigue

What is meant by depolarize?

The reduction of a membrane's resting potential

What is meant by post-synaptic action potential??

The signal strength after is has left from one neuron to another neuron

What is meant by pre-synaptic action potential?

The signal strength before it leaves to another neuron

In Conclusion: What is a synapse?

The synapse is the site where information is sent from one neuron's axon to another cell either through a chemical or electrical signal.

How abundant are the number of vesicles where neurotransmitters are stored?

There are a limited number of vesicles

What is the advantage of electrical synapses?

They are fast

How are these cells joined together?

Using gap junctions

What types of strengths do these multiple nerve fibers have?

Varying strengths

Where are neurotransmitters stored?

Vesicles

In conclusion: What is a chemical synapse?

Where presynaptic cells release neurotransmitters unidirectionally to the postsynaptic cell. Neurotransmitters bind receptors on the postsynaptic cell. Ion channels open or activation of second messenger system ex. G-protein signaling. Chemical synapses are most abundant in the nervous system.

What does hyperpolarize inhibit?

action potentials

What can multiple subthreshold inputs firing simultaneously cause?

an action potential to occur

What 2 ways can this information be sent?

either through a chemical or electrical signal.

What is meant by a lower amplitude?

lower magnitude of the cells response to the signal