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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
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