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The Brain

Home | The Brain | Neurons | Neurotransmitters | Cerebrum | Lobes | Cerebellum | Brain Stem | Limbic System


Neurons are the basic building blocks of the brain.
The parts of a neuron are very similar to the parts of any other cell.
A neuron has a cell body, which contains a nucleus.
Extensions, which branch off the cell body, are called dendrites.
Dendrites receive messages from other neurons. The membrane between the dendrites and the cell body is called the post-synaptic membrane.
On the other side of the neuron connected to the cell body, is the axon.  The axon sends messages to other neurons. The point at which the axon releases the neurotransmitters is the pre-synaptic membrane. Also located at the axon terminal.
An axon is covered by the myelin sheath, which is a fatty cell layer wrapped around the axon. This alos speeds up the rate at which neurotransmitters travel through the axon.
The neuron either fires or it doesn't. Also, intesity of a sensation doesn't determine how much, or how fast a neuron fires.
A neuron can not fair immidieately after it has already fired, it must return to a state of polarity before it can fire again.
To upset this polarity a threshold must be reached before a neuron can fire, thus the fire or non-firing of a neuron.


Types of Neurons
Sensory Neurons-carry sensory information to the brain and spinal cord.
Motor Neurons-control skeletal muscles.
Interneurons-sends signals back and forth between parts of the body.
Basic Reflex: (hand over flame.)
1) Flame meets threshold of neurons in the hand.
2) Sensory Information is sent to the spinal chord.
3) This information is passed onto interneurons which take the information to the sensory cortex.
4) Interneurons move from the motor cortext to the spinal chord.
5) The interneurons give information to the motor neurons.
6) Motor Neurons travel back down the arm causing the muscles to contract pulling the hand away from the fire.