The neurons may be of different types based on their structure and functions.

Structurally the neurons may be of the following types:
(i) Unipolar neurons
(ii) Bipolar neurons
(iii) Multipolar neurons
(i) Unipolar neurons:
i) Only one nerve process arises from the cyton which acts as both axon and dendron. 
ii) Unipolar neurons found in early embryos but not in adults.
(ii) Bipolar neurons:
i) The cyton gives rise to two nerve processes of which one acts as an axon while another as a dendron. 
ii) Bipolar neurons found in retina of eye and olfactory epithelium of nasal chambers.
(iii) Multipolar neurons:
i) The cyton gives rise to many dendrons and an axon. 
ii) Multipolar neurons found in cerebral cortex of brain.

(i) All the information from the environment ate detected by the receptors located in our sense organs such as the eyes, the nose, the skin etc.
(ii) Information from the receptors is transmitted as electrical impulse and is received by the dendritic tips of the neuron.
(iii) This impulse travels from the dendrite to the cell body and then along the axon to its terminal end
(iv) On reaching the axonal end, it causes the nerve endings to release a chemical (neurotransmitter) which diffuses across a synapse and starts a similar electrical impulse in the dendrites of the next neuron, then to their cell body to be carried along the axon.
(v) In this way, the electrical signal reaches the brain or spinal cord. The response from brain (or spinal cord) is similarly passed on to the effector organs such as the muscle or gland cell, that undergoes the desired response.
(vi) The flow of nerve impulses from axonal end of one neuron to dendrite of another neuron through a synapse is called synaptic transmission.
(vii) Neurotransmitters are the chemicals which allow the transmission of nerve impulse.
(viii) The important neurotransmitter released by neurons is called Acetylcholine.

Spinal Cord :

i) Spinal cord is a cylindrical structure lying in the neural canal of the vertebral column.
ii) It is also covered by meninges.
iii) It extends from the lower end of medulla oblongata to the first lumbar vertebra.
iv) The posterior most region of spinal cord tapers into a thin fibrous thread like structure called filum terminale.
v) Internally, the spinal cord contains a cerebrospinal fluid filled cavity known as the central canal.
vi) The grey matter of spinal cord is 'H' shaped.
vii) The upper end of letter 'H' forms posterior horns and lower end forms anterior horns.
viii) A bundle of fibres pass into the posterior horn forming dorsal or afferent root.
ix) Fibres pass outward from the anterior horn forming ventral or efferent root.
x) These two roots joins to form spinal nerves.
xi) The white matter is external and have bundle of nerve tracts.
xii) Spinal cord conducts sensory and motor impulses to and from the brain.
xiii) It controls reflex actions of the body.

A human brain is formed of three main parts:
(a) forebrain
(b) midbrain and
(c) hindbrain.
(1) Forebrain:
A. Cerebrum(cortex)
B. Diencephalon
i) Thalamus ii) Hypothalamus
(2) Midbrain
(3) Hindbrain:
A. Cerebellum
B. Pons
C. Medulla Oblongata

(i) Nerve cells or neurons
(ii) Axon and Dendrites
(iii) Synapse
(iv) The chemical is Acetylcholine