© 2014 Pearson Education, Inc. PowerPoint ® Lecture Presentations prepared by Leslie Hendon University of Alabama, Birmingham 16 The Special Senses

© 2014 Pearson Education, Inc. I. The Special Senses A. Include: taste, smell, sight, hearing, and balance B. Special sensory receptors 1. localized - confined to the head region 2. receptors are distinct specialized receptor cells 3. are neuron-like epithelial cells or small peripheral neurons 4. transfer sensory info to other neurons via afferent pathways

© 2014 Pearson Education, Inc. II. Taste and Smell A. Taste (gustation) and Smell – (olfaction) B. Receptors are classified as chemoreceptors 1. respond to specific chemicals (shape of molecules) a. food dissolved in saliva b. airborne chemicals that dissolve in fluids of nasal mucosa C. Taste receptors - occur in taste buds 1. most are found on the surface of the tongue 2. located within tongue papillae (e.g. fungiform, villate, etc.)

© 2014 Pearson Education, Inc. D. Taste Buds - collection of 50–100 epithelial cells 1. contain two major cell types a. gustatory epithelial cells: supporting cells b. basal epithelial cells: gustatory cells 2. contain long microvilli - extend through a taste pore to surface 3. cells in taste buds replaced every 7–10 days E. Taste information reaches the cerebral cortex: 1. primarily through the facial (VII) and glossopharyngeal (IX) 2. some taste information through the vagus nerve (X)

© 2014 Pearson Education, Inc. Taste bud Taste fibers of cranial nerve Foliate papillae Fungiform papillae Vallate papilla

© 2014 Pearson Education, Inc. Facial nerve (VII) Glossopharyngeal nerve (IX) Vagus nerve (X) Three Cranial Nerves carry taste information

© 2014 Pearson Education, Inc. F. Olfactory receptors - part of the olfactory epithelium 1. olfactory epithelium is pseudostratified columnar a. olfactory sensory neurons b. located in olfactory epithelium c. ends in a knob from which olfactory cilia radiate d. olfactory cilia act as receptive structures for smell e. mucus captures and dissolves odor molecules

© 2014 Pearson Education, Inc. Olfactory epithelium Olfactory tract Olfactory bulb Olfactory tract (I) Olfactory epithelium Mucus Olfactory cilia Olfactory sensory neuron Olfactory axon Filaments of olfactory nerve Cribriform plate of ethmoid bone Olfactory bulb

© 2014 Pearson Education, Inc. G. Disorders of Chemical Senses 1. anosmia - absence of the sense of smell a. due to injury, colds, allergies, or zinc deficiency 2. uncinate fits - distortion of smells or olfactory hallucinations a. often result from irritation of olfactory pathways b. typically after brain surgery or head trauma

© 2014 Pearson Education, Inc. III. The Eye and Vision A. Vision - the dominant sense in humans 1. 70% of all sensory receptors are in the eyes 2. 40% of cortex involved in processing visual information 3. anterior one-sixth of the eye’s surface is visible

© 2014 Pearson Education, Inc. B. Accessory structures of the eye 1. eyebrows - coarse hairs on the superciliary arches 2. eyelids (palpebrae) - separated by the palpebral fissure 3. lacrimal caruncle - reddish elevation at the medial canthus 4. tarsal plates - connective tissue within the eyelids 5. tarsal glands - modified sebaceous glands

© 2014 Pearson Education, Inc. III. The Eye and Vision B. Accessory structures of the eye (cont’d) 6. conjunctiva - transparent mucous membrane 7. lacrimal apparatus - (tears) keeps the surface of the eye moist a. lacrimal gland - produces lacrimal fluid b. lacrimal sac - fluid empties into nasal cavity

© 2014 Pearson Education, Inc. Lateral view; some structures shown in sagittal section Conjunctival sac Eyelashes Palpebral fissure Tarsal glands Conjunctiva Tarsal plate Eyebrow

© 2014 Pearson Education, Inc. Lateral view; some structures shown in sagittal section

© 2014 Pearson Education, Inc. Lacrimal sac Lacrimal gland Excretory ducts of lacrimal glands Lacrimal punctum Nasolacrimal duct

© 2014 Pearson Education, Inc.

Extrinsic eye muscles Muscle Action Controlling cranial nerve Lateral rectus Medial rectus Superior rectus Inferior rectus Inferior oblique Superior oblique Moves eye laterally Moves eye medially Elevates eye and turns it medially Depresses eye and turns it medially Elevates eye and turns it laterally Depresses eye and turns it laterally VI (abducens) III (oculomotor) IV (trochlear)

© 2014 Pearson Education, Inc. Superior oblique muscle Superior rectus muscle Lateral rectus muscle Inferior oblique muscle Inferior rectus muscle Lateral view of the right eye

© 2014 Pearson Education, Inc. IV. Anatomy of the Eyeball A. Components of the eye 1. protect and support the photoreceptors (rods and cones) 2. gather, focus, and process light into precise images a. anterior pole - most anterior part of the eye b. posterior pole - most posterior part of the eye c. external walls - composed of three tunics d. internal cavity - contains fluids (humors)

© 2014 Pearson Education, Inc. WOW!!! Ciliary body Suspensory ligament Cornea Iris Pupil Anterior segment (contains aqueous humor) Lens Posterior segment (contains vitreous humor) Sclera Choroid Retina Fovea centralis Optic nerve Central artery and vein of the retina Optic disc (blind spot) Be patient!!!

© 2014 Pearson Education, Inc. B. Most external layer (tunic) of the eyeball 1. composed of two regions of connective tissue a. sclera - posterior five-sixths of the tunic ► “white” and opaque region ► provides shape and an anchor for eye muscles b. cornea—anterior one-sixth of the fibrous tunic ► contact lens rests on this surface

© 2014 Pearson Education, Inc. Cornea Lens Sclera Optic nerve

© 2014 Pearson Education, Inc.

C. The Vascular Layer (Tunic) – middle part of the eyeball 1. Choroid - vascular, darkly pigmented membrane a. forms posterior five-sixths of the vascular tunic b. brown color - from melanocytes 2. Ciliary body – thick ring of tissue, which encircles the lens a. composed of ciliary muscle b. suspensory ligament - circumference of the lens 3. Iris - visible colored part of the eye (brown, blue, green) a. attached to the ciliary body b. composed of smooth muscle c. Pupil—the round, central opening

© 2014 Pearson Education, Inc. Ciliary body Cornea Iris Pupil Lens Sclera Choroid Suspensory ligament Optic nerve

© 2014 Pearson Education, Inc.

Pupil dilation and constriction Sphincter pupillae muscle contracts: Pupil size decreases. Iris (two muscles) Sphincter pupillae Dilator pupillae Dilator pupillae muscle contracts: Pupil size increases. Parasympathetic  Sympathetic 

© 2014 Pearson Education, Inc. C. Retina (the Inner Layer) – light detecting layer of the eyeball 1. Composed of two layers a. pigmented layer - single layer of melanocytes b. neural layer - sheet of nervous tissue with 3 cell types path photoreceptors ► bipolar cells ► ganglion cells (form optic nerve II) 2. Photoreceptors – detect light and translate into nerve impulses a. rods – used in low light levels; do not detect color b. cones – used in normal light; can detect colors

© 2014 Pearson Education, Inc. Pathway of light Optic disc Neural layer of retina Pigmented layer of retina Choroid Sclera Optic nerve

© 2014 Pearson Education, Inc. Microscopic anatomy of the retina Photoreceptors Ganglion cells Axons of ganglion cells Bipolar cells Rod Cone Pathway of signal output Pathway of light Pigmented layer of retina Cells of the neural layer of the retina

© 2014 Pearson Education, Inc. Photomicrograph of retina Axons of ganglion cells Nuclei of bipolar cells Nuclei of rods and cones Pigmented layer of retina Choroid Microscopic anatomy of the retina

© 2014 Pearson Education, Inc. Photoreceptors – Rods and Cones Process of bipolar cell Inner fibers Rod cell body Cone cell body Synaptic terminals Rod cell body Nuclei Light Mitochondria Connecting cilia Outer fiber Apical microvillus Discs containing visual pigments Discs being phagocytized Pigment cell nucleus Basal lamina (border with choroid) Melanin granules Pigmented layer Outer segment Inner segment

© 2014 Pearson Education, Inc. Ciliary body Suspensory ligament Cornea Iris Pupil Lens Sclera Choroid Retina Optic nerve

© 2014 Pearson Education, Inc.

C. Retina (cont’d) 3. Other structures a. fovea centralis - only cones; region of highest acuity b. optic disc - blind spot = no photoreceptors in this area c. central artery and vein

© 2014 Pearson Education, Inc. Ciliary body Cornea Iris Pupil Lens Sclera Choroid Retina Fovea centralis Optic nerve Central artery and vein of the retina Optic disc (blind spot) Suspensory ligament

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Posterior wall of the right eye as seen with an ophthalmoscope Central artery and vein Optic disc Retina

© 2014 Pearson Education, Inc. V. Internal Chambers and Fluids A. The lens and ciliary zones divide the eye into two segments B. Posterior segment (cavity) 1. filled with vitreous humor - a clear, jellylike substance a. transmits light b. supports the posterior surface of the lens c. helps maintain intraocular pressure

© 2014 Pearson Education, Inc. C. Anterior segment (cavity) 1. filled with aqueous humor - a clear, jellylike substance a. Anterior chamber - between the cornea and iris b. Posterior chamber - between the iris and lens

© 2014 Pearson Education, Inc. CorneaLens Iris Lens Cornea Aqueous humor Anterior chamber Posterior chamber Sclera Ciliary muscle Ciliary processes Ciliary body Anterior segment Posterior segment 123 Vitreous humor

© 2014 Pearson Education, Inc. Ciliary body Suspensory ligament Cornea Iris Pupil Anterior pole Anterior segment (contains aqueous humor) Lens Posterior segment (contains vitreous humor) Sclera Choroid Retina Fovea centralis Posterior pole Optic nerve Central artery and vein of the retina Optic disc (blind spot)

© 2014 Pearson Education, Inc. The Parts of the Eyeball

© 2014 Pearson Education, Inc. IV. Visual Pathways A. Most visual information travels to the cerebral cortex 1. Occipital lobe (1 ◦ visual cortex) - responsible for “seeing” B. Pathway begins at the retina ► light activates photoreceptors ► photoreceptors signal bipolar cells ► bipolar cells signal ganglion cells ► axons of ganglion cells exit eye as the optic nerve

© 2014 Pearson Education, Inc. C. The path of visual information 1. axons of ganglion cells of retina form the optic nerves to 2. optic chiasma (fibers from medial aspect of retina cross over) to 3. lateral geniculate nucleus of the thalamus to 4. optic radiations to 5. primary visual cortex (occipital lobe) NOTE: axons from medial aspect of each retina cross to opposite side axons from lateral aspect of each retinal stay on the same side

© 2014 Pearson Education, Inc. Optic radiation Fixation point Optic chiasma Optic nerve Optic tract Lateral geniculate nucleus of thalamus Occipital lobe (primary visual cortex) Both eyes Right eyeLeft eye Right eye only Left eye only Crossed (contralateral) fiber

© 2014 Pearson Education, Inc. V. The Ear: Hearing and Equilibrium A. Ear - receptor organ for hearing and equilibrium B. Composed of three main regions 1. outer ear - functions in hearing 2. middle ear - functions in hearing 3. internal ear - functions in both hearing and equilibrium

© 2014 Pearson Education, Inc. C. Outer Ear 1. auricle (pinna) - helps direct sounds 2. external acoustic meatus a. hairs, sebaceous glands, and ceruminous glands 3. tympanic membrane (“ear drum”) a. boundary between the external and middle ear

© 2014 Pearson Education, Inc. Auricle (pinna) Helix Lobule External acoustic meatus Tympanic membrane Pharyngotympanic (auditory) tube External ear Middle ear Internal ear (labyrinth) The three regions of the ear

© 2014 Pearson Education, Inc. D. Middle Ear 1. tympanic cavity - small, air-filled space in temporal bone 2. medial wall is penetrated by a. oval window b. round window 3. pharyngotympanic tube (auditory tube) - links to pharynx 4. ear ossicles - smallest bones in the body a. malleus - attaches to the eardrum b. incus - between the malleus and stapes c. stapes - vibrates against the oval window 5. tensor tympani and stapedius a. two tiny skeletal muscles in the middle ear cavity

© 2014 Pearson Education, Inc. Middle and internal ear Oval window (deep to stapes) Auditory ossicles Malleus (hammer) Incus (anvil) Stapes (stirrup) Tympanic membrane Round window Semicircular canals Vestibule Vestibular nerve Cochlear nerve Cochlea Pharyngotympanic (auditory) tube

© 2014 Pearson Education, Inc. Pharyngotym- panic tube Tensor tympani muscle Tympanic membrane (medial view) Stapes Stapedius muscle IncusMalleus View Superior Lateral Anterior

© 2014 Pearson Education, Inc. E. Inner Ear 1. is also called the labyrinth 2. lies within the petrous part of the temporal bone 3. consisting of three parts a. semicircular canals b. vestibule c. cochlea

© 2014 Pearson Education, Inc. Middle and internal ear Oval window (deep to stapes) Entrance to mastoid antrum in the epitympanic recess Auditory ossicles Malleus (hammer) Incus (anvil) Stapes (stirrup) Tympanic membrane Round window Semicircular canals Vestibule Vestibular nerve Cochlear nerve Cochlea Pharyngotympanic (auditory) tube

© 2014 Pearson Education, Inc. Middle and internal ear

© 2014 Pearson Education, Inc. E. Inner Ear (cont’d) 4. membranous labyrinth a. filled with fluid called endolymph b. fits within the bony labyrinth (filled with parilymph) c. contains three membrane-walled sacs and ducts i. semicircular canals ii. utricle and saccule iii. cochlear duct

© 2014 Pearson Education, Inc. Vestibular nerve Cochlear nerve Saccule in vestibule Utricle in vestibule Semicircular canals Cochlea

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VI. The Cochlea A. A spiraling structure in the bony labyrinth B. Coils around a pillar of bone C. Has three different chambers 1. cochlear duct (scala media) - contains receptors for hearing a. vestibular membrane - the roof of the cochlear duct b. basilar membrane - the floor of the cochlear duct 2. scala vestibuli 3. scala tympani

© 2014 Pearson Education, Inc. The COCHLEA cut into a wedge. Cochlear nerve Scala tympani Cochlear duct Scala vestibuli

© 2014 Pearson Education, Inc. Vestibular membrane Tectorial membrane Basilar membrane Cochlear duct Scala vestibuli Scala tympani Cross-section through COCHLEA showing chambers and membranes Spiral organ (Organ of Corti )

© 2014 Pearson Education, Inc. D. Spiral organ (Organ of Corti) – contain receptors for hearing 1. hair cells (receptor cells for hearing) a. sit on the basilar membrane b. tectorial membrane sits on the stereocilia of the hair cells

© 2014 Pearson Education, Inc. Hair cells Tectorial membrane Basilar membrane Hairs (stereocilia) Fibers of cochlear nerve Microscopic view of the Spiral Organ (Organ of Corti)

© 2014 Pearson Education, Inc. The COCHLEA cut into a wedge. Cochlear nerve Scala tympani Cochlear duct Scala vestibuli 1 – (1000X)

© 2014 Pearson Education, Inc. Vestibular membrane Tectorial membrane Basilar membrane Cochlear duct Scala vestibuli Scala tympani Cross-section through COCHLEA showing chambers and membranes Spiral organ (Organ of Corti ) 2 – (5000X)

© 2014 Pearson Education, Inc. Hair cells Tectorial membrane Basilar membrane Hairs (stereocilia) Fibers of cochlear nerve Microscopic view of the Spiral Organ (Organ of Corti) 3 – (10,000X)

© 2014 Pearson Education, Inc. Helicotrema at apex Modiolus Cochlear nerve, division of the vestibulocochlear nerve (VIII) Spiral ganglion Osseous spiral lamina Vestibular membrane Cochlear duct (scala media) Vestibular membrane Tectorial membrane Stria vascularis Spiral organ Basilar membrane Osseous spiral lamina Spiral ganglion Cochlear duct ( scala media ; contains endolymph) Scala vestibuli (contains perilymph) Scala tympani (contains perilymph) Outer hair cells Tectorial membraneInner hair cell Basilar membrane Hairs (stereocilia) Supporting cells Afferent nerve fibers Fibers of cochlear nerve Inner hair cell Outer hair cell

© 2014 Pearson Education, Inc. VII. The Vestibule A. The organ for detecting linear movement and balance B. Lies medial to the middle ear C. Composed of two organs: 1. utricle – horizontal accelleration 2. saccule – vertical accelleration D. Macula – contains receptor cells called hair cells 1. synapse with the vestibular nerve 2. tips of hair cells are embedded in otolith membrane 3. contains crystals of calcium carbonate called otoliths

© 2014 Pearson Education, Inc. Maculae Temporal bone Saccule in vestibule Utricle in vestibule

© 2014 Pearson Education, Inc. Macula of utricle Macula of saccule Stereocilia OtolithsOtolith membrane Vestibular nerve fibers Hair cells Macula

© 2014 Pearson Education, Inc. Head uprightHead tilted Force of gravity Hair cell Otoliths Otolith membrane

© 2014 Pearson Education, Inc. VII. The Semicircular Canals A. Lie posterior and lateral to the vestibule at right angles B. One canal lies in each of the three dimensional planes (X,Y,Z) 1. anterior semicircular canal 2. posterior semicircular canal 3. lateral semicircular canal C. Semicircular duct – space within each canal D. Membranous ampulla – has a structure called a crista ampullaris 1. cristae contain receptor cells of angular acceleration 2. epithelium contains receptor hair cells

© 2014 Pearson Education, Inc. Semicircular canals with cristae ampularis Anterior Posterior Lateral Cristae ampullares in the membranous ampullae Temporal bone Semicircular ducts in semicircular canals

© 2014 Pearson Education, Inc. Crista ampullaris Fibers of vestibular nerve Membranous labyrinth Anatomy of a crista ampullaris in a semicircular canal Endolymph Supporting cell Hair cell Hair bundle (kinocilium plus stereocilia) Ampullary cupula Cristae ampularis

© 2014 Pearson Education, Inc. Section of ampulla, filled with endolymph Ampullary cupula Fibers of vestibular nerve Flow of endolymph At rest, the ampullary cupula stands upright. Movement of the ampullary cupula during rotational acceleration and deceleration During rotational acceleration, endolymph moves inside the semicircular canals in the direction opposite the rotation (it lags behind because of inertia). Endolymph flow bends the ampullary cupula and excites the hair cells. As rotational movement slows, endolymph keeps moving in the direction of the rotation, bending the ampullary cupula in the opposite direction from acceleration and inhibiting the hair cells.

© 2014 Pearson Education, Inc. VIII. Auditory Pathway A. The ascending auditory pathway ► cochlear nerve ► spiral ganglion of cochlear nerve ► cochlear nuclei ► medulla ► inferior colliculus ► medical geniculate nucleus of the thalamus ► primary auditory cortex (temporal lobe)

© 2014 Pearson Education, Inc. Medial geniculate nucleus of thalamus Primary auditory cortex in temporal lobe Inferior colliculus Lateral lemniscus Superior olivary nucleus (pons- medulla junction) Cochlear nuclei Midbrain Medulla Vestibulocochlear nerve Spiral ganglion of cochlear nerve Bipolar cell Spiral organ Vibrations