The nervous system controls and coordinates all the essential functions of the body.
The nervous system receives and relays information about activities within the body and monitors and responds to internal and external changes.

The nervous system is divided into 2 parts: the central and peripheral.
The central consists of the brain and spinal cord.
The peripheral consists of the sympathetic, parasympathetic and cerebrospinal.

Motor neurons carry impulses from the brain and spinal cord to muscles or glands.
Interneurons connect sensory and motor neurons and carry impulses between them.

Divisions of the Nervous System...
The Central Nervous System
The nervous system is shown here as a cell body in the brain or
Autonomic Nervous System
This is the autonomic nervous system. It is necessary for movement.
The Autonomic Nervous System
The autonomic nervous system functions mainly in a reflexive manner.
Touch a hot stove = jerk your hand back.
That’s a function of the autonomic nervous system. Simple.
The ANS is divided into 3 parts: the sympathetic, parasympathetic and cerebrospinal nervous systems.

Sympathetic Nervous System
The sympathetic nervous system functions in emergencies. Being attacked by a bear for example, would trigger the function of this system. You might run away or wet your pants, but they’re both results of sympathetic nervous system responses.

Parasympathetic
The parasympathetic nervous system functions in the opposite way.
It is for ‘rest and digest’ situations. Sleeping, lying down, any sort of relaxing situation will trigger the parasympathetic system.
It slows down the heart rate and breathing, works on digesting and tries to save your body some energy. Nice huh…

Cerebrospinal Nervous System
The cerebrospinal nervous system is part of the spinal cord.
It controls sense and voluntary movement.

The Enteric Nervous System
Here is the enteric nervous system, the part which works internally.
An example of its existence is a stomach ache caused by anxiety.

Neurons
The body is made up of billions of cells. Cells of the nervous system, called neurons, are specialized to carry "messages" through an electrochemical process. The human brain has about 100 billion neurons.
Neurons contain a nucleus, nucleolus, nissl bodies, endoplasmic reticulum, golgi apparatus, microfilaments, and mitochondria.

More About Neurons…
Neurons communicate with each other through an electrochemical process.
Neurons contain some specialized structures (for example, synapses) and chemicals (for example, neurotransmitters).

Types of Neurons
Unipolar neurons have 1 process extending from them.
A process is a nerve fiber.
More Types of Neurons!
Bipolar neurons have two processes extending from the cell body (examples: retinal cells, olfactory epithelium cells).

Types of Neurons!
Pseudounipolar cells (example: dorsal root ganglion cells). Actually, these cells have 2 axons rather than an axon and dendrite. One axon extends centrally toward the spinal cord, the other axon extends toward the skin or muscle.
Types of Neurons!
Multipolar neurons have many processes extending from the cell body, although only one of these is the axon (example: spinal motor neurons).
Synapses
The synapse is the gap between the axon and dendrite. It consists of:
1. A presynaptic ending that contains neurotransmitters, mitochondria and other cell organelles,
2. A postsynaptic ending that contains receptor sites for neurotransmitters and,
3. The synaptic cleft: a space between the presynaptic and postsynaptic endings.
Electrical Trigger
For communication between neurons to occur, an electrical impulse must first travel down an axon to the synaptic terminal.
Neurotransmitter Release…
Here at the synaptic terminal, the electrical impulse will trigger the migration of vesicles containing neurotransmitters toward the presynaptic membrane. The vesicle membrane will fuse with the presynaptic membrane releasing the neurotransmitters into the synaptic cleft.
  neurons!