Copyright 2003 by Mosby, Inc. All rights reserved. CHAPTER 19 SENSORY SYSTEM.

Copyright 2003 by Mosby, Inc. All rights reserved.

CHAPTER 19

SENSORY SYSTEM


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 19-1 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 19-3 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 19-5 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


Disorders of the Sensory System (continued)

• 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



• 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



• 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



• 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



• 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



• 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

Copyright 2003 by Mosby, Inc. All rights reserved. CHAPTER 19 SENSORY SYSTEM.

Documents

Transcript of Copyright 2003 by Mosby, Inc. All rights reserved. CHAPTER 19 SENSORY SYSTEM.