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Chapter: 12th Nursing : Chapter 1 : Human Anatomy and Physiology

Sensory system

There are five sense organs in the human body. It includes, • Skin • Eye • Ear • Tongue • Nose

Sensory system

It is an organ of the body which response to external stimuli by conveying impulses through the sensory neuron to the appropriate places within the sensory nervous system.

There are five sense organs in the human body. It includes,

•      Skin    

•      Eye     

•      Ear

•      Tongue   

•   Nose



The human skin is the outer covering of the body and is the largest organ of the integumentary system. The main functions are protection, regulation and sensation.


Anatomy of the Eye

The eye is a sensory organ. It absorbs light rays from our environment and transforms them in such a way that the information in the brain can be processeced further.

·              The eye has many parts work together to produce clear vision.

·               The sclera or white part of the eye protects the eyeball.

·              The pupil or black dot at the center of the eye is a hole through which light can enter the eye.

·              The iris or coloured part, surrounding the pupil. It controls how much light enters the eye by changing the size of the pupil.

·              The cornea, a clear window at the front of the eye covers the iris and pupil.

·              A clear lens, located behind the pupil, acts like a camera lens by focusing light in to the retina at the back of the eye.

·              The retina is a light sensitive inner lining at the back of the eye. Ten different layers of cells work together in the retina to detect light and turn it into electrical impulses.

·              The retina has special cells called cones and rods are located in the retina. These all are known as photoreceptors and help absorb light.

·              Cones cone cells help us see colour and detail.

·              Rods rod cells allow us to see in poor lighting and give us our night vision.


Functions [Physiology] of the Eye

1.            Light reflects of the object we are looking at

2.            Light rays enter the eye through the cornea at the front of the eye.

3.            The light passes through a watery fluid and enters the pupil to reach the lens.

4.            The lens can change in thickness to bend the light, which will focus it on to the retina at the back of the eye.

5.            On the way to the retina, light passes through a thick, clear fluid called a vitreous humour. The vitreous humor fills the eyeball and helps maintain its round shape.

6.            The light then reaches the back of the eyes and hits the retina. The retina translates the light into electrical impulses which are then carried to the brain by the optic nerve.

Finally, the visual cortex of the brain interprets these impulses at what we see.



The ear is the organ for hearing. It is divided into three parts.

·              Outer ear-pinna /auricle, auditory canal

·              Middle ear-ear drum, ossicles, Eustachian tube

·              Inner ear- cochlea, vestibule and semicircular canal.

The outer ear

Pinna: receives sound waves that travel the auditory canal or ear canal.

The curved formation on the outside [the pinna] helps funnel sound down the ear canal to the ear drum.

Auditory canal

Acts as a funnel and leads to the ear drum. which protects the eardrum from shock and intrusion by external objects.

Ear drum

·              It is a cone shaped piece of skin.

·              It is very sensitive, even the slightest pressure variation will cause it to vibrate.

·              It is also separates the outer ear from the middle ear.

The middle ear

It transfer the energy of a sound wave by vibrating the three bones found there.

Ossicles:- smallest bone of the body. Ear bones are malleus, incus and stapes.

Eustacian tube

A tube that connects the middle ear to the back of the nose. It equalizes the pressure between the middle ear and the air outside.

The inner ear

It has two main parts.


This is a spiral that is covered in a stiff membrane. It contains thousands of hair cells attached to the end of the organ of the auditory nerve called organ of corti. These tiny hairs bend because of the vibrations caused by the sound waves.

The auditory nerve

The vibration from the hairs stimulated tiny nerve cells. The nerve cells then send signals along the auditory nerve to the brain.


Functions of Ear

Any source of sound sends vibrations or sound waves in to the air. These funnel through the ear opening, down the ear canal and strike eardrum acquiring in to vibrate. The vibrations become nerve impulses and transported to the brain, which interprets the impulses sound [music, voice, etc.]



Tongue is a muscular organ situated in the floor of the mouth. It is associated with the function of taste, speech, mastication, degurtition.

Parts of the tongue

·              Root

·              Tip

·              Body – it consists of two

·              Dorsum – oral part

·              Pharyngeal part

·              Posterior part

·               Inferior – inferior surface.

There are two groups of muscles of the tongue.

1. Four intrinsic - alter the shape of the tongue and not attached to the bone.

2. Four paired extrinsic muscles- change the position of the tongue and are anchored to the bone.

The tongue upper surface is covered by taste buds housed in numerous lingual papillae. It is responsible for taste.



The organ of smell is located in the middle of the face. The internal part of the nose lies above the roof of the mouth.

The nose consists of external nose and nasal cavity both are divided by the septum into right and left.

Functions of the nose

·               Respiration

·              Olfaction

1.           Nose is the first part of the upper respiratory tract.

2.           Warming and moistening of the inhaled air.

3.            Filter the air by removing particulates.


 It has olfactory receptor neuron and it is responsible for sense of smell.


The normal speech is produced with pressure from the lungs, this can be modified using airflow through the nose in a process called nasalization.


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12th Nursing : Chapter 1 : Human Anatomy and Physiology : Sensory system |

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