Sense of Hearing and Equilibrium and Sight PPT #2 Senses Hearing and Equilibrium hearing a response to vibrating air molecules equilibrium the sense of motion, body orientation, and balance both senses reside in the inner ear, a maze of fluidfilled passages and sensory cells fluid is set in motion and how the sensory cells convert this motion into an informative pattern of action potentials 16-2 The Nature of Sound sound any audible vibration of molecules a vibrating object pushes on air molecules in turn push on other air molecules air molecules hitting eardrum cause it to vibration Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ossicles: Stapes Incus Malleus Helix Semicircular ducts
Inner ear 16-3 Pitch and Loudness Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Threshold of pain 120 Music 80 Speech 60 40 20 20,000 10,000 Figure 16.9 5,000 2,000
500 200 100 1,000 All sound Threshold of hearing 20 0 50 Loudness (decibels) 100 Frequency (hertz) pitch our sense of whether a sound is high or low
determined by the frequency - cycles/sec cps or hertz, Hz human hearing range is 20 Hz - 20,000 Hz (cycles/sec) speech is 1500-5000 where hearing is most sensitive hearing loss with age is 250 to 2,050 Hz loudness the perception of sound energy, intensity, or amplitude of the vibration expressed in decibels (dB) prolonged exposure to sounds > 90dB can cause damage Can you hear me now????? Try thishttp:// onlinetonegenerator.com/hearingtest.html 16-4 Anatomy of Ear ear has three sections outer, middle, and inner ear first two are concerned only with the transmission of sound to the inner ear inner ear vibrations converted to nerve signals
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ossicles: Stapes Incus Malleus Helix Semicircular ducts Oval window Vestibular nerve Cochlear nerve Vestibule Auricle Cochlea Round window Tympanic membrane Tympanic cavity Auditory canal
Tensor tympani muscle Auditory tube Lobule Figure 16.11 Outer ear Middle ear Inner ear 16-6 Outer Ear Only two structures Actual ear that we see is the pinna Opens to a tube called auditory cannal Both are designed to collect logitudinal compression and rarefaction waves Anatomy of Middle Ear
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ossicles: Stapes Incus Malleus Helix Semicircular ducts Oval window Vestibular nerve Cochlear nerve Vestibule Auricle Cochlea Round window Tympanic membrane Auditory canal Tympanic cavity Tensor tympani muscle
Auditory tube Lobule Outer ear Middle ear Inner ear Figure 16.11 16-8 Middle Ear middle ear - located in the air-filled tympanic cavity in temporal bone tympanic membrane (eardrum) closes the inner end of the auditory canal separates it from the middle ear vibrates freely in response to sound innervated by sensory branches of the vagus and trigeminal nerves highly sensitive to pain tympanic cavity contains auditory ossicles auditory (eustachian) tube connects middle ear cavity to nasopharynx equalizes air pressure on both sides of tympanic membrane
normally flattened and closed and swallowing and yawning opens it allows throat infections to spread to the middle ear auditory ossicles bones3 smallest in your body malleus - attached to inner surface of tympanic membrane incus - articulates in between malleus and stapes stapes - footplate rests on oval window inner ear begins 16-9 Middle-Ear Infection Otitis media (middle ear infection) is common in children auditory tube is short and horizontal infections easily spread from throat to tympanic cavity and mastoid air cells 16-10 Anatomy of Inner Ear Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Temporal bone Figure 16.12a (a)
16-11 Inner (Internal) Ear bony labyrinth - passageways in temporal bone membranous labyrinth - fleshy tubes lining the bony labyrinth filled with endolymph - similar to intracellular fluid floating in perilymph - similar to cerebrospinal fluid Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endolymphatic sac Temporal bone Dura mater Semicircular ducts: Anterior Figure 16.12c Posterior Scala vestibuli
Lateral Scala tympani Semicircular canal Cochlear duct Ampulla Vestibule: Saccule Utricle Tympanic membrane (c) Stapes in oval window Secondary tympanic membrane in round window 16-12 Inner Ear Actual
center where sound waves are processed Has fluid filled chambers called semicircular canals, responsible for spatial orientation The cochlea is the hearing center Connected to auditory nerve, which relays info to auditory complex in cerebrum Details of Inner Ear Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 16.12b Vestibule: Saccule Cochlea Utricle Spiral ganglion of cochlea Ampullae
Cochlear nerve Facial nerve Vestibular nerve Semicircular ducts: Anterior Vestibular ganglion Lateral Posterior Endolymphatic sac (b) labyrinth - vestibule and three semicircular ducts cochlea - organ of hearing 2.5 coils around an screwlike axis of spongy bone, the modiolus threads of the screw form a spiral platform that supports the fleshy tube of the cochlea 16-14 Physiology of Hearing - Middle Ear tympanic membrane and tympanic space ossicles and their muscles have a protective
function lessen the transfer of energy to the inner ear middle ear muscles also help to coordinate speech with hearing dampens the sound of your own speech 16-15 Stimulation of Cochlear Hair Cells vibration of ossicles causes vibration of basilar membrane under hair cells as often as 20,000 times per second hair cells move with basilar membrane https://www.youtube.com/watch?v=0jyxhozq89g Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outer ear Middle ear Inner ear Stapes Oval window Incus
deafness hearing loss conductive deafness - conditions interfere with transmission of vibrations to inner ear damaged tympanic membrane, otitis media, blockage of auditory canal, and otosclerosis otosclerosis - fusion of auditory ossicles that prevents their free vibration sensorineural (nerve) deafness - death of hair cells or any nervous system elements concerned with hearing factory workers, musicians and construction workers 16-17 Innervation of Internal Ear Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 16.12b Vestibule: Saccule Cochlea Utricle Spiral ganglion
of cochlea Ampullae Cochlear nerve Facial nerve Vestibular nerve Semicircular ducts: Anterior Vestibular ganglion Lateral Posterior Endolymphatic sac (b) vestibular ganglia - visible lump in vestibular nerve spiral ganglia - buried in modiolus of cochlea 16-18 Auditory Projection Pathway sensory fibers begin at the bases of the hair cells
somas form the spiral ganglion around the modiolus axons lead away from the cochlea as the cochlear nerve joins with the vestibular nerve to form the vestibulocochlear nerve, Cranial Nerve VIII each ear sends nerve fibers to both sides of the pons..end in cochlear nuclei 16-19 Auditory Projection Pathway fibers ascend to the inferior colliculi of the midbrain helps to locate the origin of the sound, processes fluctuation in pitch, and mediate the startle response and rapid head turning in response to loud noise third-order neurons begin in the inferior colliculi and lead to the thalamus fourth-order neurons complete the pathway from thalamus to primary auditory complex involves four neurons instead of three unlike most sensory pathways primary auditory cortex lies in the superior margin of the temporal lobe site of conscious perception of sound 16-20
Auditory Pathway Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Primary auditory cortex Auditory reflex (head turning) Neck muscles Medial geniculate nucleus of thalamus Temporal lobe of cerebrum Inferior colliculus of midbrain Superior olivary nucleus of pons Cranial nerves
V3 and VII Tensor tympani and stapedius muscles Cochlea Cochlear tuning Tympanic reflex Cochlear nuclei of pons Cranial nerve VIII (a) Figure 16.18a 16-21 Auditory Processing Centers Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thalamus Figure 16.18b Primary auditory cortex Inferior colliculus Superior olivary
nucleus Cochlear nucleus Cranial nerve VIII (b) Medulla oblongata Cochlea 16-22 Equilibrium equilibrium coordination, balance, and orientation in threedimensional space vestibular apparatus constitutes receptors for equilibrium three semicircular ducts detect only angular acceleration two chambers anterior saccule and posterior utricle responsible for static equilibrium and linear acceleration static equilibrium the perception of the orientation of the head when the body is stationary dynamic equilibrium - perception of motion or acceleration linear acceleration - change in velocity in a straight line (elevator) angular acceleration - change in rate of rotation (car turns a corner)
https://www.youtube.com/watch?v=YMIMvBa8XGs 16-23 Sense of sight Conjunctiva Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Frontal bone Levator palpebrae superioris muscle Orbicularis oculi muscle Superior rectus muscle Figure 16.23a Tarsal plate Tarsal glands Cornea Conjunctiva Lateral rectus muscle
Inferior rectus muscle (a) conjunctiva a transparent mucous membrane that lines eyelids and covers anterior surface of eyeball, except cornea richly innervated and vascular (heals quickly) secretes a thin mucous film that prevents the eyeball from drying 16-25 Anatomy of the Eyeball Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sclera Ora serrata Choroid Ciliary body Retina Macula lutea Suspensory ligament Fovea centralis Optic disc
(blind spot) Iris Cornea Optic nerve Pupil Lens Central artery and vein of retina Anterior chamber Posterior chamber Hyaloid canal Figure 16.25 Vitreous body three principal components of the eyeball three layers (tunics) that form the wall of the eyeball
optical component admits and focuses light neural component the retina and optic nerve 16-26 Tunics(Layers) of the Eyeball tunica fibrosa outer fibrous layer sclera dense, collagenous white of the eye cornea - transparent area of sclera that admits light into eye tunica vasculosa (uvea) middle vascular layer choroid highly vascular, deeply pigmented layer behind retina ciliary body extension of choroid that forms a muscular ring around lens supports lens and iris secretes aqueous humor iris - colored diaphragm controlling size of pupil, its central opening melanin in chromatophores of iris - brown or black eye color reduced melanin blue, green, or gray color tunica interna - retina and beginning of optic nerve 16-27 Optical Components transparent elements that admit light rays, refract (bend)
them, and focus images on the retina cornea transparent cover on anterior surface of eyeball aqueous humor serous fluid posterior to cornea, anterior to lens produced and reabsorbed at same rate lens lens fibers flattened, tightly compressed, transparent cells that form lens changes shape to help focus light 16-28 Aqueous Humor Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cornea Anterior chamber Scleral venous sinus Ciliary body: Ciliary process Iris Posterior
chamber Lens Ciliary muscle Vitreous body Figure 16.26 released by ciliary body into posterior chamber, passes through pupil into anterior chamber reabsorbed into canal of Schlemm 16-29 Neural Components Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Lisa Klancher Figure 16.28a 16-30 Neural Components includes retina and optic nerve
retina - made of neurons and photo receptors forms as an outgrowth of the diencephalon attached to the rest of the eye only at optic disc and at ora serrata (optic blinnd spot)!! pressed against rear of eyeball by vitreous humor detached retina causes blurry areas in field of vision and leads to blindness examine retina with opthalmoscope macula lutea patch of cells on visual axis of eye fovea centralis pit in center of macula lutea blood vessels of the retina 16-31 Ophthalmoscopic Exam of Eye Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Arteriole Venule Fovea centralis Macula lutea Optic disc Figure 16.28b
(b) macula lutea - cells on visual axis of eye (3 mm) fovea centralis - center of macula; finely detailed images due to packed receptor cells direct evaluation of blood vessels 16-32 Test for Blind Spot Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 16.29 optic disk - blind spot optic nerve exits posterior surface of eyeball no receptor cells at that location blind spot - use test illustration above close eye, stare at X and red dot disappears visual filling - brain fills in green bar across blind spot area 16-33 Formation of an Image light passes through lens to form tiny inverted image on retina
conversion of light energy into action potentials occurs in the retina neural components of the retina from the rear of the eye forward photoreceptor cells absorb light and generate a chemical or electrical signal rods, cones, and certain ganglion cells only rods and cones produce visual images bipolar cells synapse with rods and cones and are first-order neurons of the visual pathway ganglion cells largest neurons in the retina and are the secondorder neurons of the visual pathway 16-34 Generating Visual Signals Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Rhodopsin absorbs no light 1 Rhodopsin absorbs light Rod cell Figure 16.38
2 Rod cell releases glutamate 3 Bipolar cell inhibited 2 Glutamate secretion ceases Bipolar cell 3 Bipolar cell no longer inhibited 4 Bipolar cell releases neurotransmitter 4 No synaptic activity here Ganglion cell 5 No signal in optic nerve fiber 5 Signal in optic nerve fiber
(a) In the dark (b) In the light 16-35 Photoreceptor Cells light absorbing cells derived from same stem cells as ependymal cells of the brain Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rod Cone rod cells (night - scotopic vision or monochromatic vision) Outer segment cone cells (color, photopic, or day vision) Inner
segment Stalk Cell body Mitochondria Nucleus Synaptic vesicles (b) Figure 16.35b 16-36 Generating Optic Nerve Signals in dark, rods steadily release the neurotransmitter, glutamate from basal end of cell when rods absorb light, glutamate secretion ceases
bipolar cells sensitive to these on and off pulses of glutamate secretion some bipolar cells inhibited by glutamate and excited when secretion stops these cells excited by rising light intensities other bipolar cells are excited by glutamate and respond when light intensity drops when bipolar cells detect fluctuations in light intensity, they stimulate ganglion cells directly or indirectly ganglion cells are the only retinal cells that produce action potentials ganglion cells respond to the bipolar cells with rising and falling firing frequencies via optic nerve, these changes provide visual signals to the brain 16-37 Visual Projection Pathway
bipolar cells of retina are first-order neurons retinal ganglion cells are second-order neurons whose axons form optic nerve two optic nerves combine to form optic chiasm half the fibers cross over to the opposite sides of the brain to form optic tracts right cerebral hemisphere sees objects in the left visual field because their images fall on the right half of each retina each side of brain sees what is on the side where it has motor control over limbs 16-38 Visual Projection Pathway Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Uncrossed (ipsilateral) fiber Crossed (contralateral) fiber Optic radiation Right eye Fixation
point Occipital lobe (visual cortex) Left eye Optic nerve Optic chiasm Pretectal nucleus Optic tract Figure 16.43 Lateral geniculate nucleus of thalamus Superior colliculus
16-39 Visual Information Processing primary visual cortex is connected by association tracts to visual association areas in parietal and temporal lobes which process retinal data from occipital lobes object location, motion, color, shape, boundaries store visual memories (recognize printed words) 16-40 Innervation of Extrinsic Eye Muscles Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Trochlear nerve (IV) Abducens nerve (VI) Levator palpebrae superioris muscle Superior oblique muscle Superior rectus muscle
Medial rectus muscle Lateral rectus muscle Oculomotor nerve (III) Inferior rectus muscle Figure 16.24c Inferior oblique muscle (c) Frontal view superior, inferior, medial and lateral rectus muscles move the eye up, down, medially & laterally superior and inferior oblique mm. turn the twelve oclock pole of each eye toward or away from the nose orbital fat surrounds sides and back of eye, cushions eye and allows free movement, protects blood vessels, and nerves 16-41 Extrinsic Eyes Muscles
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Trochlea Trochlea Optic nerve Muscles: Superior oblique Superior oblique tendon Muscles: Superior oblique Superior rectus Medial rectus Lateral rectus Medial rectus Muscles: Superior rectus Lateral rectus Inferior rectus Inferior oblique
Levator palpebrae superioris (cut) Inferior rectus (a) Lateral view Figure 16.24a (b) Superior view Figure 16.24b 6 muscles attached to exterior surface of eyeball superior, inferior, lateral, and medial rectus muscles, superior and inferior oblique muscles innervated by cranial nerves III, IV and VI 16-42
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