Animals-Nervous System

Table Of Contents

Introduction to the Nervous System

Nervous System Classification

Animals have a complex nervous system. It receives and interprets the signals from the surroundings, and sends the messages to the brain. The structure of the nervous system depends upon the body plan of an organism e.g. animals that do not have a defined head or tail, they have web-like arrangements of nerve cells throughout the body. Animals with a defined head have the nervous system divided into three parts: the Central Nervous System, Peripheral Nervous System, and Autonomous Nervous System.

  • Central Nervous System– It comprises of the brain and neurons. It is located in the head and continues along the back
  • Peripheral Nervous System– It includes all the nerves continuing from the central nervous system to the entire body.
  • Autonomous Nervous System– It consists of sympathetic and parasympathetic nerves.

In all the vertebrates, the central nervous system comprises the brain and the spinal cord. The brain contains centres that process the signals received, regulate the homeostasis, and control emotions and intelligence.

The spinal cord helps in the transfer of information to and from the brain.

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Nervous System Functions

The nervous system consists of different parts performing different functions, listed below are the functions of various parts.

Nervous System Parts And Functions

Human Brain 

The brain consists of the following parts performing the following functions:

  • Cerebral Cortex – Voluntary movement, reasoning, language, perception and thought are a few functions.
  • Cerebellum – It is involved in maintaining balance, movement and body posture. The cerebellum is split into two hemispheres wherein the cortex envelopes the hemispheres.
  • Hypothalamus –  This region is responsible for the regulation of the temperature of the body, hunger centre, emotions, regulation of the circadian rhythms etc. It serves as a thermostat which senses the body temperature and projects signals to manage the temperature.
  • Medulla oblongata or Brain stem – It controls heart rate, breathing and blood pressure and consists of the pons, medulla, tectum, tegmentum and reticular formation.
  • Thalamus – It integrates the motor and sensory information and obtains the sensory information which inturn carries forward the information to the cerebral cortex. The information it receives from the cerebral cortex is transmitted by it to the other areas of the spinal cord and the brain
  • Limbic system – It assists in regulating the response to emotions and includes the hippocampus, cingulate gyrus and mammillary bodies. The hippocampus is vital for memory and learning.
  • Basal Ganglia –  It regulates the movements and balance and includes the caudate nucleus, globus pallidus, putamen, substantia nigra and subthalamic nucleus.
  • Midbrain – It controls hearing, vision, body movement, eye movement. It consists of the red nucleus, inferior and superior colliculi.

Cerebrospinal Nervous System

It consists of 12 pairs of cranial nerves which are connected to the brain having particular functions. The following are the nerves and their respective functions:

  • Optic – Sight
  • Oculomotor – Eyeball, pupils and lens movement
  • Olfactory – Smell
  • Trochlear – Motion of the eye muscles (superior oblique)
  • Trigeminal – Supplies with nerves for eyes, jaws, cheeks and governs chewing
  • Abducens – Outward gaze, movement of the lateral rectus muscles in humans
  • Facial – movement of the facial muscles, regulates salivary glands, taste sensation from the anterior of the tongue
  • Glossopharyngeal – Sensation of taste
  • Acoustic – Maintains balance, hearing
  • Vagus – Supplies with nerves for the organs in the abdomen and the chest
  • Spinal Accessory –  Shoulder and head movement
  • Hypoglossal – Regulate muscles of the tongue

Autonomic Nervous System

This system is segregated into parasympathetic and sympathetic nervous systems which have contrasting effects on the same organ set. The parasympathetic nervous system is linked with a relaxed condition such as the contraction of the pupils, slowing of the heart rate, energy for food digestion etc.

The sympathetic nervous system is necessary during a crisis and is linked with “fight or flight reaction”. Increased rate of breathing, pupil dilation, Increase in the heart rate, Increased rate of salivation and perspiration etc.

Parts of Nervous System


A neuron is the structural and functional unit of a nervous system. It has the capacity to receive and dispatch electrochemical signals. They have three basic parts:

Cell Body

This is the main part of the neuron and consists of a nucleus, mitochondria, endoplasmic reticulum, and ribosomes. If the cell body dies, the neuron does not survive.


An axon or a nerve cell is a long cylindrical structure that conducts nerve impulses away from the cell body. It is covered with a thin layer of insulated electrical wire known as myelin. Myelinated neurons are found in the peripheral nervous system, while non-myelinated neurons are found in the brain and the spinal cord.


These are located on either side of the neuron. These are small branch-like projections used to connect with the adjacent neuron.

Also read: Neuron 

Types Of Nerves

When several axon fibres are bundled together they form a nerve. Nerves are of three types:


When the direction of impulse is from the receptor to the brain or spinal cord, the nerve fibres are called sensory. For eg., nerves in the eyes, nerves, and ears.


When the impulse is directed from the brain or spinal cord to the gland or muscle, it is known as a motor neuron.


A mixed nerve contains both the sensory and the motor nerves. For eg., spinal nerves

Also refer: Nerves

Parts of Human Brain

The human brain receives signals from the sense organs and transmits them back to the nerves. The brain is placed in the skull which contains the cerebrospinal fluid to protect the brain from any mechanical shocks. It is divided into three regions:


It receives the impulses from the receptors. It has specific areas to analyze the different signals like hearing, smelling, etc. The process of thinking also takes place here. The incoming signals are interpreted and transmitted to the respective regions.


Our body performs various voluntary and involuntary functions. Voluntary actions like running and pushing are under human control. Involuntary actions such as blinking, breathing are automatic, and not under human control.


The hindbrain contains the medulla and the cerebellum. These control breathing, salivation, blood pressure, etc.

Also refer: Brain diseases

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