The Nervous System Class 5 Notes

All organs in each body system must work together within that system, and every body system must work together with every other body system for humans to function.

 The nervous system is the system which coordinates each body system within its own system and with the other systems through signal transmissions.

Parts of Nervous System

The vertebrate nervous system is divided into a number of parts.

  •  The central nervous system includes the brain and spinal cord. 
  • The peripheral nervous system consists of all body nerves. Motor neuron pathways are of two types: somatic (skeletal) and autonomic (smooth muscle, cardiac muscle, and glands).

The Brain

The  brain is the most remarkable organ in our body. 

  • It is protected by the bony skull.
  •  It looks like a walnut and is the control center for your whole body.
  •  It is like a supercomputer
  • . It controls everything that goes on in your body.
  •  It stores a lot of information and can recall the information when needed. This is called memory. What you are reading right now is getting stored in your brain!


Structure of brain 

The brain is divisible into three main regions:

  • Forebrain (Prosencephalon)is the anterior part of brain which consists mainly of cerebrum
  • Midbrain (Mesencephalon)
  • Hindbrain (Rhombencephalon)It is the posterior most part of the brain which consists of cerebellum, pons varolii and medulla oblongata.

Functions of brain 

The brain is a complex organ that controls thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger and every process that regulates our body. Together, the brain and spinal cord that extends from it make up the central nervous system, or CNS.               


  • It is the largest  and uppermost part of the brain occupying about 80% of the brain.
  • The cerebrum consists of the cerebral  hemispheres and accounts for two-thirds of the total weight of the brain.
  •  One hemisphere, usually the left, is functionally dominant, controlling language and speech. The other hemisphere interprets visual and spatial information.


  • The cerebellum (which is Latin for “little brain”) is a major structure of the hindbrain that is located near the brainstem. 
  • This part of the brain is responsible for coordinating voluntary movements.
  •  It is also responsible for a number of functions including motor skills such as balance, coordination, and posture.
  • Although the cerebellum only accounts for roughly 10% of the brain’s total weight, this area is thought to contain more neurons (nerve cells) than the rest of the brain combined.


  • It is located at the base of the brain. 
  • This area connects the cerebrum and the cerebellum to the spinal cord, acting as a relay station for these areas. 
  • The brainstem works by regulating automatic functions such as sleep cycles, breathing, body temperature, digestion, coughing, and sneezing.

The Spinal Cord 

The spinal cord is a long bundle of nerves and cells that extends from the lower portion of the brain to the lower back.It remains protected by the vertebral column.

Structure of Spinal Cord 

The length of the spinal cord varies from person to person. According to some estimates, females have a spinal cord of about 43 centimetres (cm), while males have a spinal cord of about 45 cm.

The spinal cord comprises three parts: the cervical (neck), thoracic (chest), and lumbar (lower back) regions.

Three layers of tissue protect the spinal cord: the dura mater, arachnoid mater, and pia mater. Doctors call these layers “meninges.” 

Functions of Spinal Cord 

The spinal cord plays a vital role in various aspects of the body’s functioning. Examples of these key functions include:

  • Carrying signals from the brain: The spinal cord receives signals from the brain that control movement and autonomic functions.
  • Carrying information to the brain: The spinal cord nerves also transmit messages to the brain from the body, such as sensations of touch, pressure, and pain.
  • Reflex responses: The spinal cord may also act independently of the brain in conducting motor reflexes. One example is the patellar reflex, which causes a person’s knee to involuntarily jerk when tapped in a certain spot.

These functions of the spinal cord transmit the nerve impulses for movement, sensation, pressure, temperature, pain, and more.

vertebra class 5

The Nerves 

A nerve is a cable-like structure within the body designed to conduct nerve impulses that relay information from one part of the body to another.

Neuron is the unit of the nervous system.

Function of nerves

  • The primary function of nerves to conduct an electrochemical impulse and convey information. These impulses are carried by the individual neurons that make up the nerve.
  • These impulses travel from one neuron to another by crossing a synapse. The messages are converted from electrical to chemical and then back to electrical.
  • The sensory nerves carry information from the receptor to the central nervous system where the information gets processed.
  • The motor nerves, on the other hand, carry information from the central nervous system to the muscles.

Types of nerves 

There are three types of nerves

  1. Sensory nerves
  2.  Motor nerves
  3. Mixed nerves. 


Sensory nerves or afferent nerves:

  • These are the nerves that send messages to the brain or the spinal cord from the sense organs.
  •  These are enclosed in the form of a bundle like structures or nerve fibres in the peripheral nervous system.
  •  They carry information from the PNS to the CNS( Central Nervous System).
  •  The brain studies the messages and tells you what your sense organs have seen, heard, tasted, smelt or felt. 

Motor nerves or efferent nerves:

  • Motor nerves are those nerves that carry the messages in the form of a response from the brain or the spinal cord to other parts of the body such as the muscles and glands.
  •  They are responsible for carrying the information from the CNS to the PNS.
  • . If your sensory nerves report that your eyes have seen a stone about to hit you, the brain will immediately send a message through the motor nerves to your leg muscles to get out of the way. 

Mixed nerves or relay nerves:

  • Mixed nerves are the nerves that perform both the action of sensory nerves as well as a motor nerve. 
  • They carry messages between the sensory nerve cells and the motor nerve cells.
  • Generally, the mixed nerves transmit impulses at the rate of 120 metres per second or 432 kilometres per hour.
  • They are present in the brain and spinal cord. 

 Reflex Actions

When you touch a hot object or when a pin pricks your finger, what is your immediate reaction? Of course, you remove your hand away from the source of pain, either the hot object or the pin. In situations like these, your reactions are always immediate, involuntary and sudden. They happen without much of a thinking process. In scientific terms, a reflex is an involuntary and rapid response to the stimulus. It is a crucial component of the famed survival instinct.

Also Check – Class 5 – Nervous System Question Answers  

Why Reflex actions are important 

  • Many situations require quick reactions. There is no time to think and act. In such cases, reflex actions are important.
  •  A reflex action is an automatic (involuntary) and rapid response to a stimulus, which minimises any damage to the body from potentially harmful conditions, such as touching something hot. 
  • Reflex actions are therefore essential to the survival of many organisms.

Examples of reflex action  

  • When light acts as a stimulus, the pupil of the eye changes in size.
  • Sudden jerky withdrawal of hand or leg when pricked by a pin.
  • Coughing or sneezing, because of irritants in the nasal passages.
  • Knees jerk in response to a blow or someone stamping the leg.
  • The sudden removal of the hand from a sharp object.
  • Sudden blinking when an insect comes very near to the eyes.

The Sense Organs 

Specialised organs consisting of sensory cells that respond to the external stimuli to convey impulses to the nervous system of the body are known to be sense organs.  Sense organs play an important role in a variety of functions and help in perceiving our surroundings. These are an integral part of our bodies that enable us to sense the environment  around us.

We have five primary sensory organs and the sense organs names are:

  • Ears

  • Eyes

  • Nose

  • Tongue

  • Skin

The Eyes: the Sensory System for Vision.

Functions of Eyes :

  • Eyes are the body’s camera:  It collects light from the visible world around us and converts it into nerve impulses. The optic nerve transmits these signals to the brain, which forms an image thereby providing sight.
  • Light Detection:.The human eye is only able to pick up on a small range of this light, called the visible spectrum.
  • Night Vision:The less light there is, the less the items will reflect for the eyes, making nighttime or darkness harder to see. The human eye has specialised cells called rods that allow for night vision. 
  • Focus:The eye, like a camera, has a lens. This lens allows for light to be focused on a light receptor, the retina. 
  • Depth Perception: The human body has two eyes located on the front of the body. This close positioning of the eyes allows them to see the same object from a slightly different view — stereo vision. Having this type of vision is necessary for driving, throwing, catching and building a 3-D object. Loss of vision in one eye can lead to a loss of depth perception.
  • Balance: The eye is a small part of the vestibular system — the balance system of the body. Loss of vision can alter balance. This is quickly tested by standing on one leg with eyes open and eyes closed. As soon as the eyes are closed, balance becomes more difficult.

Parts Of Eyes 


An eyelid is a thin fold of skin that covers and protects an eye.


  • It looks like a circle with an opening in the middle (pupil). Iris consist of muscles that change pupil size by constricting and relaxing. 
  • It is a part of the eye choroid. 
  • Iris is responsible for the colour of the eyes (if it is blue this means it contains few pigment cells, if brown – a lot).
  •  Its function is the same as aperture in a camera – to adjust light flow.


  •  A small opening in the iris is known as a pupil. Its size is controlled by the help of iris.
  •  It controls the amount of light that enters the eye.
Also Check – Class 5 – Nervous System – worksheet 


  •  Behind the pupil, there is a transparent structure called a lens. By the action of ciliary muscles, it changes its shape to focus light on the retina.
  • It becomes thinner to focus distant objects and becomes thicker to focus nearby objects.

Function of lens

  • The primary function of the lens is to bend and focus light to create a sharp image. 
  • To do that, the lens uses the help of ciliary muscles to stretch and thin out when focusing on distant objects, or to shrink and thicken when focusing on near objects.  
  • When light enters the eye, the lens will bend and focus incoming light directly on the retina, which is how the clearest possible image is produced.


 It is a light-sensitive layer that consists of numerous nerve cells. It converts images formed by the lens into electrical impulses. These electrical impulses are then transmitted to the brain through optic nerves.

Functions Of Retina 

  •  The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition.
  • The retina processes light through a layer of photoreceptor cells. These are essentially light-sensitive cells, responsible for detecting qualities such as colour and light-intensity.

Optic Nerve 

  • Optic nerves are of two types. These include cones and rods.
  1. Cones: Cones are the nerve cells that are more sensitive to bright light. They help in detailed central and colour vision.
  2. Rods: Rods are the optic nerve cells that are more sensitive to dim lights. They help in peripheral vision.

How to take Care of Eyes

Don’t take your eyes for granted. Take these easy steps to keep your peepers healthy.

1. Eat Well

Good eye health starts with the food on your plate. Nutrients like omega-3 fatty acids, zinc, and vitamin C and E might help ward off age-related vision problems like cataracts. To get them, fill your plate with:

  • Green leafy vegetables like spinach, kale, and collards
  • Salmon, tuna, and other oily fish
  • Eggs, nuts, beans, and other non meat protein sources
  • Oranges and other citrus fruits or juices
  • Oysters and pork

A well-balanced diet also helps you stay at a healthy weight. That lowers your odds of obesity and related diseases like type 2 diabetes, which is the leading cause of blindness in adults.

2. Wear Sunglasses

The right pair of shades will help protect your eyes from the sun’s ultraviolet (UV) rays.Choose a pair that blocks 99% to 100% of UVA and UVB rays. 

3.Look Away From the Computer Screen

Staring at a computer or phone screen for too long can cause:

  • Eyestrain
  • Blurry vision
  • Trouble focusing at a distance
  • Dry eyes
  • Headaches
  • Neck, back, and shoulder pain

The Ears :Sensory System for Hearing

Also known as the auditory sense organs, ears play an important role in hearing or perceiving sounds. After detecting sound waves or vibrations in the air, our auditory system helps us in hearing sounds. The ear is also important for our sense of balance (equilibrium) as it is known that the vestibular system, also known as the organ of balance, is found inside the inner ear.

Functions of Ears 

The ears are organs that provide two main functions — hearing and balance — that depend on specialised receptors called hair cells.

  • Hearing: The eardrum vibrates when sound waves enter the ear canal. Ossicles, three tiny bones (including the stapes, the smallest bone in the body), pass vibrations to the oval window, which is a membrane at the entrance to the inner ear.
  • Balance: Balance is achieved through a combination of the sensory organ in the inner ear, visual input, and information received from receptors in the body. The information processed in the cerebellum and cerebral cortex of the brain allows the body to cope with changes in speed and the direction of the head.

Parts of ears

  Three parts of the ear are namely-
  • Outer EarIt consists of the visible portion known as auricle or pinna, and a short external auditory canal (eardrum) enclosed by the tympanic membrane.

Function of Outer Ear : 

 The outer ear collects sound waves and makes these reach the tympanic membrane.

  • Middle Ear It is a narrow air-filled cavity in the temporal bone and surrounded by three tiny bones that include hammer (malleus), anvil (incus), and stirrup (stapes). Auditory ossicles are the name given to the combination of these bones.

Function of Middle Ear :

The middle ear is important because it is filled with numerous air spaces, which provide routes for infections to travel.

 It is also the location of the Eustachian tube, which equalizes the air pressure between the inner and outer surfaces of the tympanic membrane.

  • Inner Ear Two functional units of the inner ear are the vestibular apparatus having vestibule and semicircular canals, and cochlea having sense organs of hearing. 

How to take care of ears 

Maintaining ear health is a lifelong process. Taking steps to protect your hearing can help you enjoy music and conversation without strain, and having healthy ears might even enable you to have better balance and a reduced risk of accidents and falls in your senior years.

1. Use Ear Protection

Ear protection is vital for individuals who work in certain occupations. Musicians, construction workers, and others who work in noisy environments are at a higher risk for early hearing loss due to their jobs. If you work in a noisy environment, use hearing protection aids like  ear plugs and over-the-ear style muffs to reduce noise levels.

2. Reduce the Volume

Hearing loss is increasing among young people, and researchers believe this may be due to the large amount of time many younger individuals spend listening to music with earbuds. For optimal ear health, doctors recommend people who are using earbuds only wear these for a maximum of one hour a day, and the music should be played at a volume of 60 percent.

3. Leave Earwax Removal to the Professionals

Earwax helps to protect the ears from pollutants, irritants, and even insects. Some patients believe that removing earwax is an important part of personal hygiene. However, the ears are naturally self-cleaning, and earwax does not normally need to be manually removed. Attempting to remove it could cause it to be pushed deep into the ear canal, and this might lead to an impaction. Impacted earwax should be removed by an ear health professional who is trained in this procedure. 

The Nose :  Sensory System for Smell

Known as an Olfactory organ,the nose is the primary organ of smell and functions as an important respiratory organ in the body. Besides this, it is also involved in functions such as tasting. 

How it works:

We inhale air through the nose and as it passes over olfactory cells (chemoreceptors), the brain recognizes and identifies different smells. Hairs in the nose called cilia, move back and forth to take out the mucus from the sinuses and back of the nose. 

Function of Nose 

  • Helps in Inhalation

The process of respiration starts in the nose. The oxygen enters into the nose through the nostrils and exits the same way during exhalation.

  • Purification of air:

 The nose warms, moistens and cleans air before it enters the lungs. It protects the airway by trapping and removing incoming dirt particles.

  • Organ of Smell

The inhaled air comes in contact with the olfactory epithelium and the nerve fibres extending from the olfactory receptors accumulate the molecules containing the odour to  the olfactory region of the brain and are decoded so that the smell is identified.

  • Sense of Taste

While chewing, the food releases certain chemicals that travel up to the nose and activate the olfactory receptors inside the nose. They work in coordination with the taste buds to identify the actual flavor of the food.

How to take care of Nose :

  • Preserving respiratory health begins with a healthy environment. Here are a few tips to reduce the number of threats in your environment:
  • avoid carpets as much as possible
  • don’t let dust accumulate in your home
  • clean your house regularly
  • Keep  your nostrils clean by blowing your nose gently. 
  • The hair inside the nose keep out dust that is present in the air, so breathe through your nose
  • Do not pick your nose.
  • Inhale steam to clear a blocked nose. 

The Tongue: Sensory System for Taste

The tongue is a muscular organ in the mouth covered with a moist, pink tissue called the mucosa.

  •  It is involved in licking, tasting, breathing, swallowing, and speaking.
  •  The papillae present on the tongue gives it a rough texture
  •  It is covered by a number of taste buds.
  •  There are several nerves in the tongue that help in transmitting taste signals to the brain, and thus helps in taste sensation.

Structure of Tongue

The human tongue is about 3.3 inches in men and 3.1 inches in women. It is located in the oral cavity. The tongue is divided into three parts:

  • Tip
  • Body
  • Base

Function Of Tongue

Following are the important tongue functions:

  • The tongue helps in chewing.
  • It helps in swallowing food.
  • The tongue transmits taste signals to the brain and helps in sensing taste.
  • It is an important organ that facilitates speech.
  • It secretes mucous and serous fluid which keeps the mouth moist.

Taste Buds 

Taste buds are sensory organs that are found on your tongue and allow you to experience tastes that are sweet, salty, sour, and bitter. The average person has about 10,000 taste buds and they’re replaced every 2 weeks or so.

The Skin  – Sensory System for Touch

The largest sense organ of our body is Skin and it relates to the sense of touch. It is a flexible outer covering of the body that comprises hair follicles, nerves, nails, and glands.

How it Works

It consists of sensory nerve structures or receptors that detect surface temperature, pain, physical touch, and chemical stimuli.

Functions of Skin
  • Provides a protective barrier against mechanical, thermal and physical injury and hazardous substances.
  • Prevents loss of moisture.
  • Reduces harmful effects of UV radiation.
  • Acts as a sensory organ (touch, detects temperature).
  • Helps regulate temperature.
  • An immune organ to detect infections etc.
  • Production of vitamin D.
How to take care of Skin 
  •  Soap and water are enough to remove dirt and sweat from the skin. 
  •  Dry yourself thoroughly after bathing and wear clean and comfortable clothes.
  •  Clothes should be loose enough for the passage of fresh air when the weather is warm. 
  •  A scratch or cut on the skin should be treated with an antiseptic lotion to prevent infection. 

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