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SENSORY SYSTEM
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.

Eye
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
Ear
Auditory or acoustic sense (hearing) is the
primary function of the ear.
 Helps maintain equilibrium.
 Three parts of the ear

External
Middle
Inner
Figure -2 Structures of the Ear
Tongue
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.

Nose
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
Structures
Skin
• 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
Nociceptors
Assessment Techniques
 Sight




Ophthalmoscope
Visual acuity
Tonometer
Color blindness chart
 Hearing




Otoscope
Impedance testing
Rinne’s test
Weber's test
Disorders of the Sensory
System

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
(cont…)

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
(cont…)

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.
(cont…)

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.
(cont…)

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.
(cont…)

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.
(cont…)
 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.
(cont…)
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.