1. The Nervous System

2. Neurons
Cell body- produces energy that fuels the activity of the cell.
Dendrites- receive information from other neurons and pass the message through the cell body.
Axon- carries messages away.
Neurons- nerve cells that run through our entire body and communicate with each other.
They consist of a cell body, dendrites, and an axon.

3. Anatomy of a neuron

4. Myelin sheath- a casing of myelin, a white fatty substance, that protects the axon and helps speed up the transmission of the message.
Axon terminals- small fibers that branch out at the end of the axon.

5. The communication process
Messages are sent from the axon terminal of one neuron to the dendrites of other neurons. It does this by crossing the synapse.
Synapse- the junction between the axon terminal of one neuron and the dendrites of another neuron.
Messages travel in only one direction.
Neurons send messages across synapses by releasing neurotransmitters.
Neurotransmitters- are chemical messengers that carry impulses across the synaptic gap between neurons.

7. Central nervous system
Central Nervous System (CNS)- consists of the neurons of the spinal cord and the brain.
Spinal Cord- extends form the back of the brain down the back. It is a column of nerves as thick as a thumb protected by the spine. It transmits messages between the brain and the muscles and glands throughout the body.

8. Peripheral nervous system
Peripheral Nervous System (PNS)- lies outside the CNS and is responsible for transmitting messages between the CNS and all parts of the body. It has two main divisions.
The Somatic Nervous System- connects the CNS with sensory receptors, muscles, and skin. It is activated by touch, pain, changes in temperature, and changes in body position. It enables us to move and change position.

9. The Autonomic Nervous System- regulates body function, such as respiration, heartbeat, and digestion. These functions occur automatically and keep us alive. There are two divisions .
Sympathetic Nervous System- “fight or flight” response. Increases heart rate, respiration, and blood pressure.
Parasympathetic Nervous System- restores the body’s reserves of energy after an action has occurred. Heart rate, breathing, and blood pressure are normalized.