Nervous System Nervous System NotesNotes

Ch. 19.1

Functions of the Nervous System

• The nervous system receives information about what is happening both inside and outside you body.

• It also tells your body to respond to information.

• It also helps maintain HOMEOSTASIS!

Receiving Information

• Your nervous system tells you that something is happening around you:– Like a fly buzzing around your head.– Or the wind is blowing– Or a friend is telling a funny joke.

– It also checks your body for glucose levels or when you feel sick.

Responding to Information

• Any change or signal in the environment that makes you react is called a stimulus.

• The fly buzzing is a stimulus.

• When your body REACTS, it is called a response!

• Swatting the fly is a response.

Responding to Information

• There are 2 kinds of responses:

• Voluntary = things you think about doing:– Swatting the fly

• Involuntary = things your body does without thinking:– Heart beats, breathing in your sleep

Maintaining Homeostasis

• The nervous system helps maintain Homeostasis by directing the body to respond appropriately to the information is receives.– If you are hungry, your nervous system tells

you to eat! = homeostasis!– Homeostasis = the things your body does to

keep you alive in that “just right” kind of way.

The Neuron

• Neuron is the name for Nerve Cells!

• They carry messages around your body!

• These messages are called Nerve Impulses!

Neuron Structure

• The neuron is made of 3 major sections:– The cell body– Axon– Axon tips

Structure Cont.

• The Cell body contains– The nucleus (brain of the cell)– Dendrites (thread like extensions that catch

nerve impulses)• There can be MANY dendrites forming a large

“net”.

Axon• The Axon carries the impulses toward

the next Neuron’s cell body.

• It’s like the highway the impulse takes from point A to point B.

• THERE IS ONLY 1 AXON PER NEURON

Axon Tips

• The Axon tips shoot out charged chemicals that act like electricity in the body.

• These chemicals are the messages that are sent through your body.

Kinds of Neurons

• 3 major kinds of neurons–Sensory Neurons

• These neurons “sense” your surroundings and send the message to your SPINAL CORD or BRAIN! They sense pressure or heat and cold.

Cont.

–Interneurons• These neurons carry messages from

one neuron to the next neuron. “Middle Men”

–Motor Neurons• These connect to muscles or glands

to cause a response. (move leg muscle, sweat!)

How a Nerve Impulse Travels

• Nerve impulses can travels as fast as 120 meters per second! THAT’S FAST!

• Messages travel from the Cell Body, down the axon, and to the axon tips!

The Synapse

• After the nerve impulse reaches the axon tip, there is a space between neurons!

• This space is the synapse!

How an Impulse is Transferred

• For a nerve impulse to be carried along at a synapse, it must cross the gap between the axon and the next structure.

• The axon tips release chemicals that carry the impulse across the gap.

• It’s like a car trying to get from one side of the river to the next on a ferry boat!