35.2. controls and coordinates functions throughout the body. responds to external and internal...
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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?
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