The document discusses nerve physiology and chemical coordination. It describes how neurons are the basic structural and functional units of the nervous system. Neurons have dendrites, a cell body, and an axon. The neural system ranges from simple networks in lower invertebrates to more complex brains and ganglia in insects and vertebrates. There are different types of neurons based on their structure, including unipolar, multipolar, and bipolar neurons. Axons can be myelinated or unmyelinated. Neurons transmit electrical signals to coordinate functions in the body.

1. Shri Shivaji Education Society, Amravati's
Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly. Dist. Buldana
Topic: Nerve Physiology and Chemical Coordination
Class: B.Sc-III, Sem-V
Shantaram Bhoye
Assistant Professor, Department of Zoology
M.Sc., NET-JRF, SET, M.A.(Eng.)

2. Nerve Physiology and Chemical Coordination:
 The neural system of all animals is composed of highly specialised cells called neurons which can detect,
receive and transmit different kinds of stimuli.
 The neural organization is very simple in lower invertebrates. For example, in Hydra it is composed of a
network of neurons.
 The neural system is better organized in insects, where a brain is present along with a number of ganglia
and neural tissues.
 The vertebrates have a more developed neural system.
Neuron:
 Neurons are the structural and functional unit of the nervous system.
 All neurons have three different parts – dendrites, cell body and axon.
 A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized
connections called synapses.
 “Neurons are the fundamental unit of the nervous system specialized to transmit information to different
parts of the body.”
Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

3. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

4.  A neuron is a microscopic structure composed of three major parts, namely, cell body, dendrites and axon.
 The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl’s
granules.
 Short fibres which branch repeatedly and project out of the cell body also contain Nissl’s granules and are
called dendrites.
 These fibres transmit impulses towards the cell body.
 The axon is a long fibre, the distal end of which is branched.
 Each branch terminates as a bulb-like structure called synaptic knob which possess synaptic vesicles
containing chemicals called neurotransmitters.
 The axons transmit nerve impulses away from the cell body to a synapse or to a neuro-muscular junction.
 Based on the number of axon and dendrites, the neurons are divided into three types, i.e., multipolar (with
one axon and two or more dendrites; found in the cerebral cortex), bipolar (with one axon and one dendrite,
found in the retina of eye) and unipolar (cell body with one axon only; found usually in the embryonic
stage).
 There are two types of axons, namely, myelinated and nonmyelinated.
Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

5.  The myelinated nerve fibres are enveloped with Schwann cells, which form a myelin
sheath around the axon.
 The gaps between two adjacent myelin sheaths are called nodes of Ranvier.
 Myelinated nerve fibres are found in spinal and cranial nerves.
 Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath
around the axon, and is commonly found in autonomous and the somatic neural systems.
Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

6. Types of neurons:
Based on structure include.
1) Unipolar neurons:
 These neurons have a single long axon that is
responsible for sending electrical signals.
 The axon in unipolar neurons is myelinated, which
allows for rapid signal transmission.
2) Multipolar neurons:
 These neurons are able to receive impulses from
multiple neurons via dendrites.
 The dendrites transmit the signals through the
neuron via an electrical signal that is spread down
the axon.
Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

7. 3) Bipolar neurons:
 These neurons send signals and receive information from
the world.
 Examples include the neurons in the eye that receive light
and then transmit signals to the brain.
4) Pseudo-unipolar neurons:
 The cyton develops one axon and one axon like dendron,
but the impulses do not pass through the cyton.
 These neurons relay signals from the skin and muscles to
the spinal cord.
 They are the primary neurons responsible for coordinating
movement of the arms and legs using input from the brain.
Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana