Nerve Impulse Summary

From Neuron to Neuron

The axon ends with many small swellings called axon terminals.

At these terminals, the neuron may make contact with the dendrites

of another neuron with a receptor or with an effector.

Receptors are special sensory neurons in sense organs that receive stimuli from the external environment.

The point of contact at which impulses are passed from one

cell to another are known as the synaptic cleft or synapse.

The axon terminals at a synapse contain tiny vesicles or

sacs. These tiny vesicles are filled with chemicals known

as neurotransmitters.

A neurotransmitter is a chemical substance that is used

by one neuron to signal another. The impulse is changed from

an electrical impulse to a chemical impulse with that chemical being

Ach (Acetycholine.)

When an impulse reaches the axon terminal, dozens of vesicles

fuse with the cell membrane and discharge the neurotransmitter into

the synaptic cleft in a process called exocytosis

The molecules od the neurotransmitter diffuse across the gap and

attach themselves to special receptors on the membrane of the

neuron receiving the impulse.

The minimum level of a stimulus that is required to activate a neuron is called

the threshold.

A nerve impulse follows the all-or-nothing principle.

Threshold

Any stimulus WEAKER than the threshold will produce NO impulse.

Any stimulus STRONGER than the threshold WILL produce an impulse.

Must reach threshold to get

action potential/impulse.

NERVE IMPULSE SUMMARY

BY ERICA WOZNIAK

This allows so many sodium ions to flood into the cell at that location that

A nerve impulse is an electric current that travels

the membrane there is "depolarized," with the local region

inside the cell having a net positive charge and the outside of the cell having

along dendrites or axons due to ions moving through voltage-

a net negative charge.

gated channels in the neuron's plasma membrane.

Dendrites: A short, branched extension of a nerve cell, along which impulses received from other cells at synapses are transmitted to the cell body.

Changes occur behind the action potential to restore

the resting potential. The sodium gates close and

the potassium gates open.

A nerve impulse begins when a stimulus disturbs the membrane on a dendrite,

While other channels allow some flow of potassium ions

back out of the cell,

causing sodium gates to open. Sodium ions flow into the cell, lessening the

the sodium ions cannot easily get back in

charge difference at that location.

to replace the lost positive charges.

The overall result is that

the exterior of the cell has a net positive charge and the

interior has a net negative charge.

Impulse

This is followed by use of sodium-potassium pumps to fully restore the resting potential

and to reestablish proper concentrations of sodium and potassium ions

inside and outside of the cell.

When a neuron is "at rest," a charge difference is maintained between the

inside and outside of the cell.

This allows a rapid flow of potassium ions out of the cell, "repolarizing" the

membrane so that the inside is again negative and the outside positive.

The difference in charge between

the interior and exterior of the cell is called

If the charge is enough,

the resting potential.

The charge difference is produced and maintained

largely by active transport using sodium-potassium

it will cause nearby sodium gates to open.

pumps. The pumps send sodium ions out of the cell

and bring potassium ions in.

This affects neighbouring sodium gates, which then open,

moving the depolarization along the membrane. This moving depolarization

is called an action potential.