Chapter 10 Special Senses

Special Senses Touch Vision Hearing Smell Taste

Sensory Receptors Stimulated by changes in the environment Generalized in body Touch, pain, temperature and pressure (proprioceptors)

Sensory Receptors Specific receptors Taste buds of the tongue In the nose In the retina of the eye In the inner ear (organ of Corti)

The Eye Tender sphere about 1 inch (2.5 cm) in diameter Protected by orbital socket, eyebrows, eyelids, and eyelashes Lacrimal duct and glands

The Eye Oil glands Conjunctiva Stereoscopic vision The wall of the eye has three layers Sclera Choroid Retina

The Eye

Sclera Outer layer of the eye which is the white of the eye Fibrous capsule maintains shape and protects Extrinsic muscles

Extrinsic Muscles Superior rectus Inferior rectus Lateral rectus Medial rectus Inferior oblique

Cornea Circular clear area in front center of the sclerotic coat Transparency allows passage of light rays Five layers Very sensitive to pain and touch

Choroid Coat and the Iris Middle layer of the eye Blood vessels to nourish the eye Nonreflective pigment rendering it dark and opaque Circular opening called the pupil

Choroid Coat and the Iris Muscular layer surround the pupil called the iris Color of iris depends on the number and size of melanin pigment Intrinsic muscles Sphincter papillae (constricts pupil) Dilator papillae (dilates pupil)

Lens and Related Structures Crystalline structure located behind the iris and pupil Ciliary body Anterior chamber Aqueous humor Posterior chamber Vitreous humor

Retina Innermost, or third coat of the eye Images focus on the retina Optic nerve Cerebral cortex (occipital lobe)

Retina Rods and cones Macula lutea and fovea centralis Optic nerve or blind spot

Pathway of Vision Images in the light Cornea Pupil Lens Retina

Pathway of Vision Rods and cones Optic nerve Optic chiasma Optic tracts Occipital lobe of the brain for interpretation

Click Here to play Vision animation Animation – How We See Click Here to play Vision animation

Eye Disorders Conjunctivitis Glaucoma Cataracts Macular degeneration

Eye Disorders Detached retina Diabetic retinopathy Sty (hordeolum)

Eye Surgery Cataract surgery Detached retina surgery Phacoemulsification Extracapsular extraction Detached retina surgery Laser surgery and cryotherapy Pneumatic retinopexy Vitrectomy Scleral buckle

Eye Surgery Visual defects LASIK (laser-assisted in-situ keratomileusis) PRK (photorefractive keratectomy)

Eye Injuries Simple eye irritation Corneal abrasions and scarring Chemical or fragment eye irritations

Eyestrain Signs and symptoms Most common cause is a computer Dry eyes can also cause eyestrain Prevention

Vision Defects Night blindness Color blindness Presbyopia Hyperopia Myopia

Vision Defects Amblyopia Astigmatism Diplopia Strabismus

Effects of Aging – Eye Decreased ability to focus on fine detail Compromised accommodation Slower to adjust to changing light conditions Peripheral vision and depth perception decline Loss of visual acuity

The Ear Picks up sound waves and sends these impulses to the auditory center of the brain Auditory center in temporal area just above ears Receptor for hearing Organ of Corti Involved in equilibrium

Outer Ear Pinna Canal glands Tympanic membrane

Middle Ear Connects to pharynx (throat) via eustachian tube Hammer (malleus) Anvil (incus) Stirrup (stapes)

Inner Ear Cochlea Cochlear duct Organ of Corti Three semicircular canals

Pathway of Hearing Sound waves Pinna Auditory canal Tympanic membrane Ear ossicles

Pathway of Hearing Cochlea receptors Cochlear nerve Temporal lobe of the brain for interpretation

Click Here to play Hearing animation Animation – How We Hear Click Here to play Hearing animation

Pathway of Equilibrium Movement of head Stimulates equilibrium receptors in the semicircular and vestibule areas of the inner ear Vestibular nerve Cerebellum of the brain for interpretation

Loud Noise and Hearing Loss Hearing is both sensitive and fragile Damage done by loud noises Sound measured in decibels Prevention of damage

Ear Disorders Otitis media Otosclerosis Tinnitus Presbycusis Meniere’s disease

Types of Hearing Loss Conductive hearing loss Sensorineural damage

Effects of Aging – Hearing Tympanic membrane becomes fibrous Degeneration of ear bones, vestibular structure, cochlea, and organ of Corti Loss of hearing high-pitched frequencies Diminished ability to hear consonants Speech of others sounds garbled

Hearing Aids Behind the ear (BTE) In the ear (ITE) Canal aids Body aids

The Nose Smell accounts for about 90% of what we think of as taste Warms and moistens air breathed in Receptors Olfactory epithelium and bulbs Olfactory nerve Limbic system, thalamus, and frontal cortex

Disorders of the Nose Rhinitis Nasal polyps Deviated nasal septum

Effects of Aging – Smell Decreased in the number of olfactory neurons Decreased sense of smell affects appetite, social relationships, and detection of warning smells Senile rhinitis

The Tongue Tongue is a mass of muscle tissue Papillae Taste buds for sweet, sour, salty, and bitter Receptors in the taste buds send stimuli through three cranial nerves to the cerebral cortex for interpretation

Effects of Aging – Tasting Decrease in taste buds Increased amounts of salt, sweet, sour, and bitter needed to identify the food Impact of full upper dentures

Disorders of the Tongue Traumatic injury Hairiness Discoloration Infection Cancer Burning mouth syndrome