Special Senses 15-02 PDF

PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky The Special Senses Part B 15 Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb Copyright © 2004 Pears...

PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky The Special Senses Part B 15 Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Inner Chambers and Fluids ▪ The lens separates the internal eye into anterior and posterior segments ▪ The posterior segment is filled with a clear gel called vitreous humor that: ▪ Transmits light ▪ Supports the posterior surface of the lens ▪ Holds the neural retina firmly against the pigmented layer Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Anterior Segment ▪ Composed of two chambers ▪ Anterior – between the cornea and the iris ▪ Posterior – between the iris and the lens ▪ Aqueous humor ▪ A plasma like fluid that fills the anterior segment ▪ Drains via the canal of Schlemm ▪ Supports, nourishes, and removes wastes Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Anterior Segment Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.12  Lens ▪ A biconvex, transparent, flexible, avascular structure that: ▪ Allows precise focusing of light onto the retina ▪ With age, the lens becomes more compact and dense and loses its elasticity Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Refraction and Lenses ▪ When light passes from one transparent medium to another its speed changes and it refracts (bends) ▪ Light passing through a convex lens (as in the eye) is bent so that the rays converge to a focal point Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Focusing Light on the Retina ▪ Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, and the neural layer of the retina to the photoreceptors Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Focusing for Distant Vision ▪ Light from a distance needs little adjustment for proper focusing ▪ Far point of vision – the distance beyond which the lens does not need to change shape to focus (20 ft.) Figure 15.17a Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Focusing for Close Vision ▪ Close vision requires: ▪ Accommodation – changing the lens shape by ciliary muscles to increase refractory power ▪ Constriction – the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye ▪ Convergence – medial rotation of the eyeballs toward the object being viewed Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Photoreception: Functional Anatomy of Photoreceptors ▪ Photoreception – process by which the eye detects light energy ▪ Rods and cones contain visual pigments (photopigments) ▪ Arranged in a stack of disk-like infoldings of the plasma membrane that change shape as they absorb light Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Rods ▪ Functional characteristics ▪ Sensitive to dim light and best suited for night vision ▪ Absorb all wavelengths of visible light ▪ Sum of visual input from many rods feeds into a single ganglion cell ▪ Results in fuzzy and indistinct images Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Cones ▪ Functional characteristics ▪ Need bright light for activation (have low sensitivity) ▪ Have pigments that furnish a vividly colored view ▪ Each cone synapses with a single ganglion cell ▪ Vision is detailed and has high resolution Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Cones and Rods Figure 15.10a Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  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 ear functions in both hearing and equilibrium ▪ Receptors for hearing and balance: ▪ Respond to separate stimuli ▪ Are activated independently Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  The Ear: Hearing and Balance Figure 15.25a Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Outer Ear ▪ The auricle (pinna) is composed of: ▪ The helix (rim) ▪ The lobule (earlobe) ▪ External auditory canal ▪ Short, curved tube Tympanic membrane (eardrum) ▪ Thin connective tissue membrane that vibrates in response to sound ▪ Transfers sound energy to the middle ear ossicles ▪ Boundary between outer and middle ears Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Middle Ear (Tympanic Cavity) ▪ Ossicles The tympanic cavity contains three small bones: the malleus, incus, and stapes ▪ Transmit vibratory motion of the eardrum to the oval window ▪ Pharyngotympanic tube – connects the middle ear to the nasopharynx ▪ Equalizes pressure in the middle ear cavity with the external air pressure Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Middle Ear (Tympanic Cavity) Figure 15.25b Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Inner Ear ▪ Bony labyrinth ▪ Tortuous channels worming their way through the temporal bone ▪ Contains the vestibule, the cochlea, and the semicircular canals ▪ Filled with perilymph Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Inner Ear Figure 15.27 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  The Vestibule ▪ The central egg-shaped cavity of the bony labyrinth ▪ Suspended in its perilymph are two sacs: the saccule and utricle ▪ The saccule extends into the cochlea ▪ The utricle extends into the semicircular canals ▪ These sacs: ▪ House equilibrium receptors called maculae ▪ Respond to gravity and changes in the position of the head Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Anatomy of Maculae ▪ Maculae are the sensory receptors for static equilibrium ▪ Contain supporting cells and hair cells that respond to vertical and horizontal movement Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Anatomy of Maculae Figure 15.35 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  The Semicircular Canals ▪ Three canals that each define two-thirds of a circle and lie in the three planes of space ▪ Membranous semicircular ducts line each canal and communicate with the utricle ▪ The ampulla is the swollen end of each canal and it houses equilibrium receptors in a region called the crista ampullaris ▪ These receptors respond to angular movements of the head Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Crista Ampullaris and Dynamic Equilibrium Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 15.37b  Mechanisms of Equilibrium and Orientation ▪ Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule ▪ Maintain our orientation and balance in space ▪ Vestibular receptors monitor static equilibrium ▪ Semicircular canal receptors monitor dynamic equilibrium Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Crista Ampullaris and Dynamic Equilibrium ▪ The crista ampullaris (or crista): ▪ Is the receptor for dynamic equilibrium ▪ Is located in the ampulla of each semicircular canal ▪ Responds to angular 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 © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  The Cochlea ▪ A spiral, conical, bony chamber that: ▪ Extends from the anterior vestibule ▪ Contains the cochlear duct, which ends at the cochlear apex ▪ Contains the organ of Corti (hearing receptor) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  The Cochlea ▪ The cochlea is divided into three chambers: ▪ Scala vestibuli ▪ Scala media ▪ Scala tympani Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  The Cochlea ▪ The scala tympani terminates at the round window ▪ The scalas tympani and vestibuli: ▪ Are filled with perilymph The scala media is filled with endolymph Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  The Cochlea ▪ The “floor” of the cochlear duct is composed of: ▪ The bony spiral lamina ▪ The basilar membrane, which supports the organ of Corti ▪ The cochlear branch of nerve VIII runs from the organ of Corti to the brain Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  The Cochlea Figure 15.28 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Transmission of Sound to the Inner Ear ▪ The route of sound to the inner ear follows this pathway: ▪ Outer ear – pinna, auditory canal, eardrum ▪ Middle ear – malleus, incus, and stapes to the oval window ▪ Inner ear – scalas vestibuli and tympani to the cochlear duct ▪ Stimulation of the organ of Corti ▪ Generation of impulses in the cochlear nerve Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Excitation of Hair Cells in the Organ of Corti Figure 15.28c Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Simplified Auditory Pathways Figure 15.34 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings