THE NERVOUS SYSTEM35.2

Controls and coordinates functions throughout the body.

Responds to external and internal messages.

The body’s communication system

NEURONS

•Specialized cells of the nervous system• Transmit electrical signals called impulses in only one direction.•3 types

– sensory neurons-send signals from sensory receptors brain– motor neurons – send signals from the brain muscles & glands– interneurons –carry impulses between sensory & motor neurons

NEURON ANATOMY

Axon terminals

Nodes

Myelin sheath

Cell body

Axon Dendrites

Nucleus

FUNCTIONS

Axons – carry impulses away from the cell body

Myelin sheath – an insulating membrane surrounding the axon

Cell body – where the metabolic activity of the cell takes place

Dendrites – carry impulses from the environment to the cell body

NERVE IMPULSE – RESTING NEURON • A nerve impulse is similar to the flow of electrical current through a wire.• When the neuron is NOT sending an impulse, the inside is negative and the outside is positive

Na+ and K+ ions move across the cellMembrane via the sodium-potassium pump

The Moving impulse An impulse begins when a neuron is

stimulated by another neuron or the environment

Action potential - When an impulse is sent the charge reverses inside the cell – it becomes positive

Threshold – the amount of stimulus required to activate the neuron

The moving impulse

An impulse begins when a neuron is stimulated strong enough to reach a threshold. The impulse travels rapidly down the axon towards the terminal end.

THE SYNAPSE • Where impulses are transferred from one neuron to another.•Chemicals diffuse across a small gap between the cells •Neurotransmitters- are the chemicals that transfer impulses from one neuron to another.•Receptors of the neighboring neuron pick up the chemical message, and a new impulse begins.

axon

Neuro-transmitter

Direction of impulse

receptor

Axon terminal

vesicle

Dendrite ofAdjacent neuron

In a fraction of a second after binding to the receptors, the neur0transmitter molecules are released.

They are re-absorbed back into the axon terminal

What are the 4 parts of a neuron?

What is a threshold?How does a message move

from one neuron to another?

Review questions