INTRODUCTION
Neurons are important in psychiatry because they are the messengers that send information
throughout the brain, spinal cord and body. Their communication plays an important role in
mental illness and mental well-being as well as physical health and illness.
DEFINITION
Neuron or nerve cell is defined as the structural and functional unit of nervous system.
Neuron is similar to any other cell in the body, having nucleus and all other organelle in
cytoplasm. However, it is different from other cells by two ways:
i. Neuron has branches or processes called axon and dendrite.
ii. Neuron does not have centrosome. So, it cannot undergo division.
CLASSIFICATION
• Depending upon the number of poles
a. Unipolar neurons: Has only one pole. Axon and dendrite arise from one pole.
Example: nerve cell in embryonic stage, sensory neurons
b. Bipolar neurons: Neurons with 2 poles are known as bipolar neurons. Axon arises
from one pole and dendrite from the other.
Example: Interneurons
c. Multipolar neurons: Motor neurons
• Depending upon the function
a. Motor and efferent neuron: Which carry the motor impulses from CNS to
peripheral effector organs like muscles, glands, blood vessels etc.
Generally motor neuron has a long axon and short dendrites.
b. Sensory or afferent neurons: Which carry the sensory impulses from periphery to
CNS.
Generally sensory neuron has a short axon and long dendrites.
• Depending upon the length of axon
a. Golgi type I neurons (having longer axon)
b. Golgi type II neurons (having shorter axon)
STRUCTURE OF NEURON:
Neuron is made up of three parts:
1) Nerve cell body
2) Dendrite
3) Axon
1) Nerve cell body:
→ Nerve cell body also known as soma or Perikaryon. It is irregular in shape.
→ Like any other cell it is constituted by a mass of cytoplasm called Neuroplasm.
→ Cytoplasm of nerve cell body contains:
➢ A large nucleus
➢ Nissl bodies They both are only found in nerve cell
➢ Neurofibrils and not any other cells
➢ Mitochondria
➢ Golgi apparatus
→ Nucleus: It is centrally placed; has one or two prominent nucleoli and does not
contain centrosome. So, they can’t multiply like other cells.
→ Nissl bodies: They are the small granules only present in nerve cell, containing
ribosome and concerned with protein synthesis
→ Neurofibrils: They are thread like structures present in the form of network in the
soma and nerve processes.
→ Mitochondria: They are present in the soma and also in axon. It is the power house
of the cell.
→ Golgi apparatus: Golgi apparatus of nerve cell concerned with processing and
packing of proteins into granules.
2) Dendrite:
→ Dendrite are the short processes of neuron. It may be sometimes present or absent.
→ It transmits impulse towards the nerve cell body from synapse.
3) Axon:
→ Axons are the long processes of nerve cell.
→ Axon transmits impulses away from the nerve cell body to the synapse.
Myelin sheath:
It is a thick lipoprotein sheath that insulate the myelinated nerve fiber. It is not continuous
and absent at regular intervals, called Node of Ranvier.
→ It is responsible for faster conduction of impulse through the nerve fibers.
→ High insulating capacity that restricts the nerve impulse within single nerve fiber.
Neurilemma:
Neurilemma sheath covers all the axon and also the myelin sheath. It also known as sheath of
Schwann.
Synapse:
→ Synapse is the junction between two neurons.
→ Information is transmitted through the body from one neuron to another.
→ The small space between the axon terminals of one neuron and the cell body or
dendrites of another is called the synaptic cleft.
→ Neurons conducting impulses toward the synapse are called pre-synaptic neurons and
those conducting impulses away are called post-synaptic neurons.
→ A chemical called neurotransmitter, is stored in the axon terminals of the pre-synaptic
neuron.
→ An electrical impulse through the neuron causes the release of this neurotransmitter
into the synaptic cleft.
→ The neurotransmitter then diffuses across the synaptic cleft and combines with
receptor sites that are situated on the cell membrane of the post synaptic neuron.
→ This combination of neurotransmitter and receptor site determines whether or another
electrical impulse will be generated or not to transmit the impulse.
→ If one is generated the result is called an excitatory response and if one is not
generated the result is called inhibitory response.
→ The cell body or dendrite of the post-synaptic neuron also contains a chemical
inactivator that is specific to the neurotransmitter that has been released by pre-
synaptic neuron.
→ When the synaptic transmission has been completed, the chemical inactivator quickly
inactivates the neurotransmitter to prevent unwanted continuous impulses.
→ Then the neurotransmitter back to the pre-synaptic neuron and stored for reuse. This is
called reuptake.
Fig: Impulse transmission at synapse
Neurotransmitters:
They are the chemicals that convey information across synaptic clefts to neighboring target
cells.
Some neurotransmitters are
i. Cholinergic
• Acetylcholine
ii. Monoamines
• Norepinephrine
• Dopamine
• Serotonin
• Histamine
iii. Amino acids
• Inhibitory – GABA or Gama Amino Butyric Acid and Glycine
• Excitatory – Glutamate and Aspartate
iv. Neuropeptides
• Opioid peptides
• Substance P
• Somatostatin
CONCLUSION
Neurons have specialized structures known as dendrites and axons, designed to receive and
transmit information. Neurons release chemical messengers known as neurotransmitters into
synapses, or the space between nerve cells, to communicate with each other.
The structure of neurons is important in psychiatry because structural and functional
alterations in neurons are associated with psychiatric illnesses.
BIBLIOGRAPHY
1) Townsend C. Mary. Psychiatric Mental Health Nursing. 8th edition. New Delhi: Jaypee
Brothers Medical Publisher (P) Ltd; 2018; Page no-47-77
2) Sembulingam K, Sembulingam Prema.Essentials of Medical Physiology. 6th edition. New
Delhi: Jaypee Brothers Medical Publisher (P) Ltd; 2013; Page no-759-763
3) https://en.wikipedia.org/wiki/Neuron
A PRACTICE TEACHING
STRUCTURE OF
SUB: NURSING EDUCATION
Submitted By,
Subhra Maity
Roll No.: 24027010023
Registration No.: 010920142015
M.sc nursing 1st year (2023-2024)
Govt. CON, BSMC, Bankura
