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