Nerves
Nerves are bunches of neurons stuck together.
There are 3 types of nerves:
1. Sensory or Afferent nerves. These nerves transmit impulses sent by your sense organs (such as your eyes and ears). Sense receptors in your sense organs stimulate sensory nerves, which then send information to the spinal cord and brain.
Look at Bob, who's been kind enough to have his skull removed so we
can see what's going on.
Bob notices the pretty candle and reaches out to touch the flame with
his fingertip. Sense receptors in his
fingertip stimulate sensory nerves
that travel down his arm, into his spinal cord, and possibly to his brain.
He thinks "Ow!"
2. Motor or efferent nerves. These nerves transmit orders from the brain or spinal cord to our muscles and organs.
If you were Bob's spinal cord and brain, what would you do when he touched
the flame?
I know what I'd do. I'd send an order down the motor or efferent nerves
to my arm, saying "pull our hand away!"
3. Interneurons. These exist only in the brain and spinal cord. They receive signals from sensory neurons and send information to other interneurons or to motor neurons.
The Big Picture
Sense receptors in the sensory organs
stimulate sensory neurons.
Sensory neurons then stimulate interneurons
in the spinal cord and brain.
Interneurons stimulate each other in
reflexes and thought, and eventually send impulses to motor
neurons.
Motor neurons send messages to muscles;
this leads to behaviors.
The Nervous System
Central Nervous system:
Brain and spinal cord.
The spinal cord does two things:
1. It contains sense or afferent nerves carrying information to the
brain, and motor/efferent nerves carrying information from the brain to
our muscles and glands. It also contains interneurons. These are all used
to communicate between the brain, our senses, and our muscles and glands.
2. It controls reflexes: fast reactions that don't have to involve the brain. Sometimes the information from sense nerves doesn't have to reach our brain for us to react. Sometimes the interneurons in our spine are hooked up to automatically carry out certain signals without the brain having to participate:
Peripheral Nervous System:
Part of the nervous system that connects your sensory organs, other organs, glands, and muscles, to the central nervous system.
The peripheral nervous system is made up of somatic and autonomic nervous system.
Somatic nervous system:
Connects central nervous system to voluntary muscles: things you have
control over, like moving your hands or your eyes.
Autonomic nervous system:
Connects central nervous system to internal organs, glands, and muscles
that we don't control consciously, like how big our pupils get, whether
we release certain digestive acids, etc. It is made up of the sympathetic
and parasympathetic nervous systems.
Sympathetic nervous system:
Prepares the body for using energy: stimulation of the sympathetic
nervous system increases heartbeat, raises blood pressure, increases breathing,
releases sugar into the blood, stops digestion and relaxes your bladder.
Parasympathetic nervous system: works to conserve energy: slows
heartbeat, lowers blood pressure, slows breathing, start digestion.