Download The nervous system - Sonoma Valley High School

THE NERVOUS SYSTEM
35.2
The body’s
communication system
Controls and coordinates
functions throughout the
body.
 Responds to external
and internal messages.
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
Nucleus
Axon
terminals
Cell body
Myelin sheath
Nodes
Axon
Dendrites
FUNCTIONS
Dendrites – carry impulses from the
environment to the cell body
Axons – carry impulses away from the cell
body
Cell body – where the metabolic activity of
the cell takes place
Myelin sheath – an insulating membrane
surrounding the axon
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 cell
Membrane 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
Direction of impulse
axon
• 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.
vesicle
Dendrite of
Adjacent neuron
receptor
Axon terminal
Neurotransmitter
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
Review questions
What are the 4 parts of a neuron?
What is a threshold?
How does a message move from
one neuron to another?