SENSORY SYSTEM Preeti Malik. Structure and Function Sensory system consists of receptors in specialized cells and organs that perceive changes in the

SENSORY SYSTEM

Preeti Malik

Structure and FunctionSensory 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

ExternalMiddleInner

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 corpusclesPacinian 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 visionCataract

◦ Clouding of the lens that causes blurred or partial vision

Conjunctivitis ◦ Also called pink eye, is a bacterial or viral

inflammation of the eyelid

Copyright 2003 by Mosby, Inc. All rights reserved.

(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


(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


(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 eyeNight blindness

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


(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


(cont…)

Rhinitis Inflammation of the lining of the nose caused by

allergic reaction, viral infection, sinusitis, or chemical irritants

Ruptured eardrumResults 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


(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


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

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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