Nervous System
The nervous system or the neural system is a complex network of
neurons specialized to carry messages. The complexity of the
nervous system increases as we move towards higher animals.
For instance, cnidarians
such as jellyfish have relatively simple nerve nets spread throughout their
body. Crabs have a more complicated nervous system in the form of 2 nerve
centers called dorsal ganglion and ventral ganglion.
As we move further up
the ladder, higher organisms such as vertebrates have a developed brain.
Moreover, it is one of the most complicated structures in the animal kingdom,
containing billions of neurons, all intricately connected.
In the human body, the
neural system integrates the activities of organs based on the stimuli, which
the neurons detect and transmit. They transmit messages in the form of electrical
impulses and convey messages to and from the sense organs. Thus, the nervous
coordination involves the participation of the sense organs, nerves, spinal
cord, and brain.
Diagram of the Human
Nervous System
One
of the most complex organ system to ever evolve, the human nervous system
consists of two parts, namely:
- Central Nervous System (consists of the
brain and spinal cord)
- Peripheral Nervous System (includes all
the nerves of the body)
Central
Nervous System
Central Nervous System (CNS) is often
called the central processing unit of the body. It consists of the brain and
the spinal cord.
Brain
Brain is the important and central organ of human body.
It is control unit of nervous system.
Human Brain is composed of three major parts:
1. Forebrain: The anterior part of the brain, consists of Cerebrum,
Hypothalamus and Thalamus.
2.
Midbrain: The smaller and
central part of the brainstem, consists of Tectum and Tegmentum.
3.
Hindbrain: The central region of
the brain, composed of Cerebellum, Medulla and Pons.
Spinal
Cord
The spinal cord is a cylindrical bundle of nerve fibers and
associated tissues enclosed within the spine and connect all parts of the body
to the brain. It begins in continuation with the medulla and extends downwards.
It is enclosed in a bony cage called vertebral column and surrounded by
membranes called meninges. The spinal cord is concerned with spinal reflex
actions and the conduction of nerve impulses to and from the brain.
Peripheral Nervous System
Peripheral Nervous System (PNS) is the lateral part of the
nervous system that develops from the central nervous system which connects
different parts of the body with the CNS. We carry out both voluntary and
involuntary actions with the help of peripheral nerves.
Also
refer: Peripheral Nervous System
PNS
includes two types of nerve fibers:
- Afferent nerve
fibers –
These are responsible for transmitting messages from tissues and organs to
the CNS.
- Efferent
nerve-fibers – These are responsible for conveying messages
from CNS to the corresponding peripheral organ.
Neuron
A Neuron is a structured and functional unit of the nervous system and unlike other cells, neurons are irregular in shape and able to conduct electrochemical signals. The different parts of a neuron are discussed below.
- Axon is the longest thread on
the cell body of a neuron and has an insulating and protective sheath of
myelin around it.
- Cell body consists of cytoplasm
and nucleus.
- Synapse is the microscopic gap
between a pair of adjacent neurons over which nerve impulses pass, when
moving from one neuron to the other.
Nerves
Nerves
are thread-like structures that emerge from the brain and spinal cord. It is
responsible for carrying messages to all the parts of the body. There are three
types of nerves. Some of these neurons can fire signals at speeds of over 119
m/s or above 428 km/h.
- Sensory nerves send messages from all
the senses to the brain.
- Motor nerves carry messages from the
brain to all the muscles.
- Mixed nerves carry both sensory and
motor nerves.
Cranial
nerves begin from the brain as these nerves carry
impulses to start from the central nervous system.
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