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The study of nervous system in all aspects id called neurology.
Nervous tissue :- It fours the nervous system in animals.
It consists (1) neurons, (2) nerve fibers (3) nerves (4) neuralgia (5) ependymal cells and (6) neuro secretary cells.
(1) Nervous:-Neurons or nerve cells form the functional unit of nervous system. A neuron has a cell body, an axon , many dendrites.
Cell body has cytoplasm and a nucleus inside, axon is the middle long part of neuron that takes massage from cell body to synapse (the function b/w the end of a neuron and the other neuron from where massage pass from one neuron to another). And dendrites are short fibers on cell body that transmit impulse coming from other neuron towards cell body.
( Structure of neuron on Pg 317 of NCERT 11)
(2) Nerve fiber:- axon and dendrite of nerve cell is covered with 2 or more sheaths called nerve fiber,
On the basis of no. of axon and dendrites, nerve fibers are of 3 types
Multicolor:-(one axon and 2 or more dendrites)
Bipolar:-(one axon and one dendrite)
Unipolar:-(cell body and one axon only, no dendrite which found only Ph embryonic stage)
On the basis of structure of nerve fiber, they are of 2 types
modulated:-nerve fiber who have Schwann cells, that form a nujlin sheath around axon.
Non-modulated:- nerve fibers who have Schwann cells, that does not form a nujlin (nujelin ) sheath around axon.
Schwann cells:- that covers the axon of nerve fibers.
On the basis of nature of nerve fiber, they are of 3 types
Sensory (afferent ) nerves:- that contain sensory nerve fibers.
Motor (efferent) nerves:- that contain motor nerve fibers.
Mixed nerves:- that contain both sensory and motor nerve fibers.
(3) Neuroglia:-neuro-nerve , glia-glue.
These are the packing and supporting cells of neurons system found in brain and spinal cord. They comprises the 50% of all nerve cells.
(4) Ependymal cells:- they form a layer that lines the cavities of central nervous system.
(5) Neurosecretory cells:-these nerve cells secrete Harmon into the blood stream through their axon ending.
Note :- Invertebrates have simple nervous system than invertebrates and among all invertebrates, insects have most complex nervous system.