Preeti Malik

Structure and Function

 Sensory system consists of receptors in specialized cells and organs that perceive changes in the internal and external environment

 The stimuli cause nerve impulses that are sent to the brain for interpretation

 Environmental stimuli are perceived with the senses of vision, hearing, touch, taste, position, and balance.


 The most important sensory organ because

90% of the information about the environment reaches the brain from the eyes.

 Movement of the eye is controlled by the extrinsic muscles.

 Only one fifth of the eye is actually exposed to the environment.

Figure - 1 Structures of the Eye


 Auditory or acoustic sense (hearing) is the primary function of the ear.

 Helps maintain equilibrium.

 Three parts of the ear




Figure -2 Structures of the Ear


 Taste, or the gustatory sense, is perceived by specialized cells located in papillae on the tongue called taste buds.

 Flavor is identified by smell as well as taste.


 Olfactory sense originates in olfactory receptor cells in the nose that immediately transmit impulses to the brain through the olfactory cranial nerves.

 Nasal cavity is divided into two sections by the septum.

 Olfactory receptor neurons are stimulated by chemicals (gases) in the air.

 Smells can reduce stress, affect blood pressure, recall memories, and aid in the sense of taste.

Figure -3 Nose and Surrounding



Senses of the skin perceive touch, pressure, temperature, and pain through five specialized cells located in the skin

Meissner's corpuscles

 Pacinian corpuscles

End-bulbs of Krause

Corpuscles of Ruffini


Assessment Techniques

 Sight


Visual acuity

 Tonometer

 Color blindness chart

 Hearing


Impedance testing

 Rinne’s test

Weber's test

Disorders of the Sensory


 Achromatism

Called color blindness, is a common inherited defect

 Amblyopia

◦ Also called “lazy eye,” is poor vision in one eye often resulting from better vision in the other eye during infancy or early childhood

 Anacusis

Hearing loss resulting from damage to neural tissues


 Astigmatism

A congenital defect causing imperfect curvature of the cornea resulting in blurred vision

 Cataract

Clouding of the lens that causes blurred or partial vision

 Conjunctivitis

Also called pink eye, is a bacterial or viral inflammation of the eyelid


 Diabetic retinopathy

Condition of damaged blood vessels in the retina caused by uncontrolled diabetes mellitus

 Diplopia

Or double vision, results from muscle imbalance or paralysis of an extraocular muscle

 Epistaxis

Nosebleed resulting from disease, trauma, or other conditions such as hypertension, leukemia, or rheumatic fever

Copyright 2003 by Mosby, Inc. All rights reserved.


 Glaucoma

An increase in the pressure inside the eye, caused by trauma or hereditary factors

 Hyperopia

Farsightedness resulting from a congenital deformity in the eye

 Macular degeneration

A slow or sudden painless loss of central vision

Copyright 2003 by Mosby, Inc. All rights reserved.


Meniere’s disease

A collection of fluid in the labyrinth of the ear leading to dizziness, ringing in the ear or tinnitus, pressure, and eventual deafness

 Myopia

Nearsightedness resulting from a congenital deformity in the eye

 Night blindness

Poor vision in dim light that results from a deficiency in the rods of the retina

Copyright 2003 by Mosby, Inc. All rights reserved.


 Otitis media

A middle ear bacterial or viral infection common in young children

 Presbyopia

A type of farsightedness related to aging

 Retinal detachment

Due to injury or uncontrolled diabetes mellitus

Copyright 2003 by Mosby, Inc. All rights reserved.


 Rhinitis

Inflammation of the lining of the nose caused by allergic reaction, viral infection, sinusitis, or chemical irritants

 Ruptured eardrum

Results from infection, an explosion, a blow to the head, or a sharp object inserted into the ear

 Sinusitis

A chronic or acute inflammation of the cranium

Copyright 2003 by Mosby, Inc. All rights reserved.


 Strabismus

A condition in which both eyes do not focus on the same point or direction

 Stye

Bacterial infection of the sebaceous glands of the eyelid

Copyright 2003 by Mosby, Inc. All rights reserved.

Issues and Innovations

 Visual correction by surgery

– Radial keratotomy

– Epikeratophakia

– Photorefractive keratectomy (laser surgery)

 Noise pollution

– Inner ear damage is permanent

– Loud music and phones can cause hearing loss

Copyright 2003 by Mosby, Inc. All rights reserved.