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Copyright © 2010 Pearson Education, Inc. Chapter 15 Special Senses
Copyright © 2010 Pearson Education, Inc. The Eye and Vision 70% of all sensory receptors are in the eye Nearly half of the cerebral cortex is involved in processing visual information! Most of the eye is protected by a cushion of fat and the bony orbit
Copyright © 2010 Pearson Education, Inc. Accessory Structures of the Eye Protect the eye and aid eye function Eyebrows Eyelids (palpebrae) Conjunctiva Lacrimal apparatus Extrinsic eye muscles
Copyright © 2010 Pearson Education, Inc. Conjunctiva Transparent membrane Palpebral conjunctiva lines the eyelids Bulbar conjunctiva covers the white of the eyes Produces a lubricating mucous secretion Lacrimal Apparatus Lacrimal gland and ducts that connect to nasal cavity
Copyright © 2010 Pearson Education, Inc. Extrinsic Eye Muscles Six straplike extrinsic eye muscles Four rectus muscles Names indicate the movements they promote Two oblique muscles move the eye in the vertical plane and rotate the eyeball
Copyright © 2010 Pearson Education, Inc. Structure of the Eyeball Wall of eyeball contains three layers Fibrous Vascular Sensory Internal cavity is filled with fluids called humors The lens separates the internal cavity into anterior and posterior segments (cavities)
Copyright © 2010 Pearson Education, Inc. Fibrous Layer Outermost layer; dense avascular connective tissue Two regions: Sclera Cornea
Copyright © 2010 Pearson Education, Inc. Vascular Layer (Uvea) Middle pigmented layer Three regions: Choroid Ciliary body Iris
Copyright © 2010 Pearson Education, Inc. Figure 15.5 Iris (two muscles) Sphincter pupillae Dilator pupillae Sphincter pupillae muscle contraction decreases pupil size. Dilator pupillae muscle contraction increases pupil size. Sympathetic +Parasympathetic +
Copyright © 2010 Pearson Education, Inc. Sensory Layer: Retina Delicate two-layered membrane Pigmented layer Outer layer Absorbs light and prevents its scattering Stores vitamin A Neural layer Photoreceptor: transduce light energy Cells that transmit and process signals
Copyright © 2010 Pearson Education, Inc. The Retina Ganglion cell axons Run along the inner surface of the retina Leave the eye as the optic nerve Optic disc (blind spot) Site where the optic nerve leaves the eye Lacks photoreceptors
Copyright © 2010 Pearson Education, Inc. Photoreceptors Rods More numerous at peripheral region of retina Operate in dim light Provide indistinct, fuzzy, non color peripheral vision Cones Found in the macula lutea; concentrated in the fovea centralis Operate in bright light Provide high-acuity color vision
Copyright © 2010 Pearson Education, Inc. Internal Chambers and Fluids The lens and ciliary zonule separate the anterior and posterior segments Posterior segment contains vitreous humor Anterior segment is composed of two chambers Anterior chamberbetween the cornea and the iris Posterior chamberbetween the iris and the lens
Copyright © 2010 Pearson Education, Inc. Eye Conditions Detached Retina The pigmented and neural layers separate May lead to permanent blindness Occurs from traumatic blows to the head or when the head is suddenly stopped Glaucoma Drainage of the aqueous humors is blocked Pressure builds upon the retina and optic nerve
Copyright © 2010 Pearson Education, Inc. Lens Biconvex, transparent, flexible, elastic, and avascular Allows precise focusing of light on the retina Lens becomes denser, more convex, and less elastic with age Cataracts (clouding of lens) occur as a consequence of aging, diabetes mellitus, heavy smoking, and frequent exposure to intense sunlight
Copyright © 2010 Pearson Education, Inc. Light Our eyes respond to visible light, a small portion of the electromagnetic spectrum Light: packets of energy called photons (quanta) that travel in a wavelike fashion Rods and cones respond to different wavelengths of the visible spectrum
Copyright © 2010 Pearson Education, Inc. Refraction and Lenses Refraction Bending of a light ray due to change in speed when light passes from one transparent medium to another Occurs when light meets the surface of a different medium at an oblique angle
Copyright © 2010 Pearson Education, Inc. Focusing Light on the Retina Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, neural layer of retina, photoreceptors Light is refracted At the cornea Entering the lens Leaving the lens Change in lens curvature allows for fine focusing of an image
Copyright © 2010 Pearson Education, Inc. Focusing for Distant Vision Light rays from distant objects are nearly parallel at the eye and need little refraction beyond what occurs in the at-rest eye Far point of vision: the distance beyond which no change in lens shape is needed for focusing; 20 feet for emmetropic (normal) eye Ciliary muscles are relaxed Lens is stretched flat by tension in the ciliary zonule
Copyright © 2010 Pearson Education, Inc. Figure 15.13a Lens Inverted image Ciliary zonule Ciliary muscle Nearly parallel rays from distant object (a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Sympathetic activation
Copyright © 2010 Pearson Education, Inc. Focusing for Close Vision Close vision requires Accommodationchanging the lens shape by ciliary muscles to increase refractory power Presbyopialoss of accommodation over age 50 Constrictionthe accommodation pupillary reflex constricts the pupils to prevent the most divergent light rays from entering the eye Convergencemedial rotation of the eyeballs toward the object being viewed
Copyright © 2010 Pearson Education, Inc. Figure 15.13b Divergent rays from close object (b) Lens bulges for close vision. Parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge. Inverted image Parasympathetic activation
Copyright © 2010 Pearson Education, Inc. Vision Impairments Diplopia – double vision Due to the inability to focus on the image with both eyes Myopia – nearsightedness Ability to see up close but not far away Hyperopia – farsightedness Ability to see far away, but not up close Astygmatism - Unequal curvatures of the cornea or lens
Copyright © 2010 Pearson Education, Inc. Chemical Senses Taste and smell (olfaction) Their chemoreceptors respond to chemicals in aqueous solution
Copyright © 2010 Pearson Education, Inc. Sense of Smell The organ of smell olfactory epithelium in the roof of the nasal cavity Dissolved odorants bind to receptor proteins in the olfactory cilium membranes
Copyright © 2010 Pearson Education, Inc. Sense of Taste Receptor organs are taste buds Found on the tongue On the tops of fungiform papillae On the side walls of foliate papillae and circumvallate (vallate) papillae
Copyright © 2010 Pearson Education, Inc. Structure of a Taste Bud Flask shaped 50–100 epithelial cells: Basal cellsdynamic stem cells Gustatory cellstaste cells
Copyright © 2010 Pearson Education, Inc. Taste Sensations There are five basic taste sensations 1.Sweetsugars, saccharin, alcohol, and some amino acids 2.Sourhydrogen ions 3.Saltmetal ions 4.Bitteralkaloids such as quinine and nicotine 5.Umamiamino acids glutamate and aspartate
Copyright © 2010 Pearson Education, Inc. Physiology of Taste In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs Binding of the food chemical (tastant) Depolarizes the taste cell membrane, causing release of neurotransmitter Initiates a generator potential that elicits an action potential
Copyright © 2010 Pearson Education, Inc. Influence of Other Sensations on Taste Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors in the mouth also influence tastes Temperature and texture enhance or detract from taste
Copyright © 2010 Pearson Education, Inc. The Ear: Hearing and Balance Three parts of the ear 1.External (outer) ear 2.Middle ear (tympanic cavity) 3.Internal (inner) ear
Copyright © 2010 Pearson Education, Inc. The Ear: Hearing and Balance External ear and middle ear are involved with hearing Internal ear (labyrinth) functions in both hearing and equilibrium
Copyright © 2010 Pearson Education, Inc. External Ear The auricle (pinna) is composed of: Helix (rim) Lobule (earlobe) External acoustic meatus (auditory canal) Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands
Copyright © 2010 Pearson Education, Inc. External Ear Tympanic membrane (eardrum) Boundary between external and middle ears Connective tissue membrane that vibrates in response to sound Transfers sound energy to the bones of the middle ear
Copyright © 2010 Pearson Education, Inc. Middle Ear A small, air-filled, mucosa-lined cavity in the temporal bone Flanked laterally by the eardrum Flanked medially by bony wall containing the oval (vestibular) and round (cochlear) windows
Copyright © 2010 Pearson Education, Inc. Middle Ear Epitympanic recesssuperior portion of the middle ear Pharyngotympanic (auditory) tubeconnects the middle ear to the nasopharynx Equalizes pressure in the middle ear cavity with the external air pressure
Copyright © 2010 Pearson Education, Inc. Ear Ossicles Three small bones in tympanic cavity: the malleus, incus, and stapes Suspended by ligaments and joined by synovial joints Transmit vibratory motion of the eardrum to the oval window
Copyright © 2010 Pearson Education, Inc. Internal Ear Bony labyrinth Tortuous channels in the temporal bone Three parts: vestibule, semicircular canals, and cochlea Filled with perilymph Series of membranous sacs within the bony labyrinth Filled with a potassium-rich endolymph
Copyright © 2010 Pearson Education, Inc. Vestibule Central egg-shaped cavity of the bony labyrinth Contains two membranous sacs 1.Saccule 2.Utricle These sacs House equilibrium receptor regions (maculae) Respond to gravity and changes in the position of the head
Copyright © 2010 Pearson Education, Inc. The Cochlea A spiral, conical, bony chamber Extends from the vestibule Coils around a bony pillar (modiolus) Contains the cochlear duct, which houses the spiral organ (of Corti) the receptor organ for hearing
Copyright © 2010 Pearson Education, Inc. Properties of Sound Sound is A pressure disturbance (alternating areas of high and low pressure) produced by a vibrating object A sound wave Moves outward in all directions Is illustrated as an S-shaped curve or sine wave
Copyright © 2010 Pearson Education, Inc. Properties of Sound Waves Frequency The number of waves that pass a given point in a given time Wavelength The distance between two consecutive crests Amplitude The height of the crests
Copyright © 2010 Pearson Education, Inc. Properties of Sound Pitch Perception of different frequencies Normal range is from 20–20,000 Hz The higher the frequency, the higher the pitch Loudness Subjective interpretation of sound intensity Normal range is 0–120 decibels (dB)
Copyright © 2010 Pearson Education, Inc. Transmission of Sound to the Internal Ear Sound waves vibrate the tympanic membrane Ossicles vibrate and amplify the pressure at the oval window Pressure waves move through perilymph of the scala vestibuli
Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances of Hearing Conduction deafness Blocked sound conduction to the fluids of the internal ear Can result from impacted earwax, perforated eardrum, or otosclerosis of the ossicles Sensorineural deafness Damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells
Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances of Hearing Tinnitus: ringing or clicking sound in the ears in the absence of auditory stimuli Due to cochlear nerve degeneration, inflammation of middle or internal ears, side effects of aspirin Menieres syndrome: labyrinth disorder that affects the cochlea and the semicircular canals Causes vertigo, nausea, and vomiting
Copyright © 2010 Pearson Education, Inc. Equilibrium and Orientation Vestibular apparatus consists of the equilibrium receptors in the semicircular canals and vestibule Vestibular receptors monitor static equilibrium Semicircular canal receptors monitor dynamic equilibrium
Copyright © 2010 Pearson Education, Inc. Maculae Sensory receptors for static equilibrium Maculae in the utricle respond to horizontal movements and tilting the head side to side Maculae in the saccule respond to vertical movements
Copyright © 2010 Pearson Education, Inc. Crista Ampullaris (Crista) Sensory receptor for dynamic equilibrium One in the ampulla of each semicircular canal Major stimuli are rotatory movements Each crista has support cells and hair cells that extend into a gel-like mass called the cupula Dendrites of vestibular nerve fibers encircle the base of the hair cells
Copyright © 2010 Pearson Education, Inc. Figure 15.36a–b Fibers of vestibular nerve Hair bundle (kinocilium plus stereocilia) Hair cell Supporting cell Membranous labyrinth Crista ampullaris Crista ampullaris Endolymph Cupula (a) Anatomy of a crista ampullaris in a semicircular canal (b) Scanning electron micrograph of a crista ampullaris (200x)
Copyright © 2010 Pearson Education, Inc. Activating Crista Ampullaris Receptors Cristae respond to changes in velocity of rotatory movements of the head Bending of hairs in the cristae causes Depolarizations, and rapid impulses reach the brain at a faster rate
Copyright © 2010 Pearson Education, Inc. Activating Crista Ampullaris Receptors Bending of hairs in the opposite direction causes Hyperpolarizations, and fewer impulses reach the brain Thus the brain is informed of rotational movements of the head
Copyright © 2010 Pearson Education, Inc. Developmental Aspects Vision is not fully functional at birth Babies are hyperopic, see only gray tones, and eye movements are uncoordinated Depth perception and color vision is well developed by age five Emmetropic eyes are developed by year six With age The lens loses clarity, dilator muscles are less efficient, and visual acuity is drastically decreased by age 70
The Ear: Hearing and Balance The three parts of the ear are the inner, outer, and middle ear The outer and middle ear are involved with hearing The inner.
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