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

Disorders of the Sensory System (continued)

• 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

Disorders of the Sensory System (continued)

• 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

Disorders of the Sensory System (continued)

• 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

Disorders of the Sensory System (continued)

• 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

Disorders of the Sensory System (continued)

• 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

Disorders of the Sensory System (continued)

• 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