Chapter 17: The Special Senses Muse Bio 2440 w12 Lecture #6 5/24/12

Comparison of General and Special Senses General Senses Special Senses Include somatic sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations. Scattered throughout the body. Simple structures. Include smell, taste, vision, hearing and equilibrium. Concentrated in specific locations in the head. Anatomically distinct structures. Complex neural pathway.

Olfaction: Sense of Smell Olfactory epithelium contains 10-100 million receptors. Olfactory receptor- a bipolar neuron with cilia called olfactory hairs. - Respond to chemical stimulation of an odorant molecule. Supporting cells- provide support and nourishment. Basal cells- replace olfactory receptors.

Olfactory Epithelium and Olfactory Receptors

Olfactory Epithelium and Olfactory Receptors continued…

Smell (Olfaction) Olfactory Pathways Arriving information reaches information centers without first synapsing in thalamus

Physiology of Olfaction Can detect about 10,000 different odors. Odorant binds to the receptor of an olfactory hair→ G-protein activation→ activation of adenylate cyclase→ production of cAMP→ opening of Na+ channels→ inflow of Na+ →generator potential→ nerve impulse through olfactory nerves→ olfactory bulbs→ olfactory tract→ primary olfactory area of the cerebral cortex.

Olfactory transduction

Summary of sense of smell Odorant molecule binds one of 10-100 million receptors. Conformational change in receptor interacts with G protein G protein activates adenylate cyclase to generate cAMP cAMP opens Na+ channels to initiate depolarization. Information on number of action potentials decoded by olfactory bulbs. Animals have greater numbers of receptors thus better sense of smell Usually 10,000 times greater.

Gustation: Sense of Taste Taste bud

Taste 15-11 11

Taste (Gustation) Gustatory Discrimination Primary taste sensations Sweet (sugars) Salty Sour (acids) Bitter (alkali) umami - savory (fat)

Taste (Gustation) Gustatory Discrimination Dissolved chemicals contact taste hairs Bind to receptor proteins of gustatory cell Salt and sour receptors Chemically gated ion channels Stimulation produces depolarization of cell Sweet, bitter, and umami stimuli G proteins: (proteins that bind GTP- secondary messengers) gustducins

Anatomy of Taste Buds and Papillae Taste bud- made of three types of epithelial cells: supporting cells, gustatory receptor cells and basal cells. About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore. Taste buds are found in the papillae. Three types of papillae: vallate (circumvallate), fungiform and foliate.

Physiology of Gustation Five types of taste: sour, sweet, bitter, salty and umami. Tastant dissolves in saliva → plasma membrane of gustatory hair→ receptor potential→ nerve impulse via cranial nerves VII, IX and X→ medulla→ thalamus→ primary gustatory area of the cerebral cortex.

Gustatory Pathway

Neuronal Pathways for Taste Chorda tympani (part of VII): carry sensations from anterior one-third of tongue (except from circumvallate papillae Cranial nerve IX and X carry information from posterior one-third tongue, circumvallate papillae, superior pharynx, epiglottis. Information goes to medulla oblongata where decussation takes place and information projects from there to the thalamus. Then projects to taste area of cortex (extreme inferior end of the postcentral gyrus) 15-17 17

Specialist taste buds map to certain regions of tongue Maps differ somewhat , but generally

Actions of the Major Tastants 15-19 19

Vision or Sight Visible light: 400-700 nm.

Accessory Structures of the Eye Eyelids or palpebrae- Eyelashes and eyebrows- Extrinsic eye muscles-

Accessory Structures of the Eye

The Lacrimal Apparatus Tears from the lacrimal apparatus- lacrimal glands→ excretory lacrimal ducts→ lacrimal puncta→ lacrimal canals→ nasolacrimal sac→ nasolacrimal duct.

Anatomy of the Eyeball

The Eye Figure 17–4b The Sectional Anatomy of the Eye.

Wall of the Eyeball Three layers: Fibrous tunic- outer layer Sclera “white” of the eye Cornea-transparent coat Vascular tunic or uvea- middle layer Choroid Ciliary body consists of ciliary processes and ciliary muscle Iris lens (alpha crystalin protein) Retina- inner layer Optic disc Macula lutea- fovea centralis

Responses of the Pupil to Light Pupil is an opening in the center of the iris. Contraction of the circular muscles of the iris causes constriction of the pupil. Contraction of the radial muscles causes dilation of the pupil.

Interior of the Eyeball Lens- lack blood vessels, consists of a capsule with proteins (crystallins) in layers; transparent. Lens divides the eyeball into two cavities: anterior and posterior. Anterior cavity- further divided into anterior and posterior chambers. Both are filled with aqueous humor. Posterior cavity (vitreous chamber)-filled with vitreous body.

Cavities of the Eyeball

Refraction of Light Rays Refraction is the bending of light rays. The cornea and lens refract light rays. Most refraction done at corneal level - repair with corneal re-mapping (keratotomy)

Accommodation and the Near Point of Vision Increase in the curvature of the lens for near vision is called accommodation. Near point of vision is the minimum distance from the eye that an object can be clearly focused.

Refraction Abnormalities and their Correction Nearsightedness (myopia)- close objects seen clearly. Image is focused in front of the retina. Correction- use of concave lens. Farsightedness (hyperopia)- distant objects seen clearly. Image is focused behind the retina. Correction- use of convex (magnifyer) lens.

Most scientists

The Eye Most cones in fovea Figure 17–6c Photograph of the Retina as Seen through the Pupil.

Retina 15-35 35

Rods and Cones Cones- three types: red, green and blue. Named after the shapes of their outer segments. Rod- (more sensitive to light, but no color ) Cones- three types: red, green and blue. Outer segment- contains photopigments. Transduction of light energy into receptor potential occurs here. Inner segment- contains the nucleus, Golgi complex and mitochondria.

Structure of Rod and Cone Photoreceptors Back of eye Front of eye

Photoreceptors 15-38 38

Photopigments Two parts: opsin (four types, three in the cones and one in the rod) and retinal (light absorbing part). Rhodopsin- photopigment in rods. Cone photopigments- three types. (one for each color) Absorption of light by a photopigment → structural changes.

Bleaching and Regeneration of Photopigment

Rod disc in outer segment Colorless products Disc membrane cis- retinal opsin Cis-retinal binds to opsin (regeneration) Isomerization of retinal Light trans- Retinal isomerase converts trans- to cis-retinal Trans-retinal separates from opsin (bleaching) Rhodopsin molecule Colored photopigment (rhodopsin) 1 2 3 4 Rod disc in outer segment Colorless products Disc membrane cis- retinal opsin Isomerization of retinal Light trans- Retinal isomerase converts trans- to cis-retinal Trans-retinal separates from opsin (bleaching) Rhodopsin molecule Colored photopigment (rhodopsin) 1 2 3 Rod disc in outer segment Disc membrane cis- retinal opsin Isomerization of retinal Light trans- Trans-retinal separates from opsin (bleaching) Rhodopsin molecule Colored photopigment (rhodopsin) 1 2 Rod disc in outer segment Disc membrane cis- retinal opsin Isomerization of retinal Light Rhodopsin molecule Colored photopigment (rhodopsin) 1

15-42 42

Bleaching and Regeneration of Photopigment Isomerization: In darkness, retinal has a bent shape called cis-retinal. Absorption of photon causes straightening of the retinal (trans-retinal). Bleaching: trans-retinal separates from opsin. Regeneration: trans-retinal→ cis-retinal.

Light and Dark Adaptation Light adaptation: Dark → light. Faster. Dark adaptation: Light →dark. Slow. Cones regenerate rapidly whereas rhodopsin regenerates more slowly.

Operation of Rod Photoreceptors

Rods Bipolar photoreceptor cells; black and white vision. Found over most of retina, but not in fovea. More sensitive to light than cones. Protein rhodopsin changes shape when struck by light; and eventually separates into its two components: opsin and retinal Retinal can be converted to Vitamin A from which it was originally derived. In absence of light, opsin and retinal recombine to form rhodopsin. Rods are unusual sensory cells: when not stimulated they are hyperpolarized. Light causes them to depolarize. Depolarization of rods causes depolarization of bipolar cells causing depolarization of ganglion cells Light and dark adaptation: adjustment of eyes to changes in light. Happens because of changes in amount of available rhodopsin. 15-46 46

Color Blindness and Night Blindness Color blindness- inherited inability to distinguish between certain colors. Result from the absence of one of the three types of cones. Most common type: red-green color blindness. Night blindness or Nyctalopia- vitamin A deficiency.

Cones Bipolar receptor cells. Responsible for color vision and visual acuity. Numerous in fovea and macula lutea; fewer over rest of retina. As light intensity decreases so does our ability to see color. Visual pigment is iodopsin: three types that respond to blue, red and green light Overlap in response to light, thus interpretations of gradation of color possible: several millions 15-48 48

Processing of Visual Input Receptor potential in rods and cones→ graded potentials in bipolar neurons and horizontal cells→ nerve impulses in ganglion cells→ optic nerve→ optic chiasm→ optic tract→ thalamus→ primary visual area of cerebral cortex in occipital lobe.

Visual Pathway

1 2 4 5 3 1 2 3 4 5 6 1 2 4 3 1 2 3 1 2 1 Visual field of left eye Temporal half right eye Nasal Midbrain Left eye retina Optic radiations Left eye and its pathways tract Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Right eye Right eye and its pathways Nasal retina 1 2 4 5 3 Visual field of left eye Temporal half right eye Nasal Midbrain Left eye retina Optic radiations Left eye and its pathways tract Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Right eye Right eye and its pathways Nasal retina 1 2 3 4 5 6 Visual field of left eye Temporal half right eye Nasal Midbrain Left eye retina Optic radiations Left eye and its pathways tract Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Right eye Right eye and its pathways Nasal retina 1 2 4 3 Visual field of left eye Temporal half right eye Nasal Midbrain Left eye retina Optic radiations Left eye and its pathways Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Right eye Right eye and its pathways Nasal retina 1 2 3 Visual field of left eye Temporal half right eye Nasal Midbrain Left eye retina Optic radiations Left eye and its pathways Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Right eye Right eye and its pathways Nasal retina 1 2 Visual field of left eye Temporal half right eye Nasal Midbrain Left eye retina Optic radiations Left eye and its pathways Primary visual area of cerebral cortex (area 17) in occipital lobe Lateral geniculate nucleus of the thalamus Right eye Right eye and its pathways Nasal retina 1

Neuronal Pathways 15-52 52

Anatomy of the Ear Three main regions: External (outer) ear- auricle or pinna, external auditory canal, and tympanic membrane. Ceruminous glands- Middle ear- auditory ossicles: malleus, incus and stapes. Auditory (eustachian) tube. Internal (inner) ear- Labyrinth: bony and membranous. Bony labyrinth- perilymph and membranous labyrinth- endolymph. Oval window and round window- membranous regions.

Anatomy of the Ear

The Middle Ear and the Auditory Ossicles

The Internal Ear

The Internal Ear Three parts: the semicircular canals, the vestibule (both contain receptors for equilibrium) and the cochlea (contains receptors for hearing). Semicircular canals: anterior, posterior and lateral. Ampulla- Vestibule consists of two sacs: utricle and saccule.

Semicircular Canals, Vestibule and Cochlea

Semicircular Canals, Vestibule and Cochlea

Sprial organ Tectorial membrane Basilar membrane Inner phalangeal cells Outer phalangeal cells Inner hair cell Outer hair cells 60

Cochlea Snail-shaped. Section through the cochlea shows three channels: cochlear duct, scala vestibuli and scala tympani. Helicotrema Vestibular membrane Basilar membrane Spiral organ or Organ of Corti- hair cells.

Physiology of Hearing Audible sound range: 20-20,000 Hz. Sound waves→ auricle→ external auditory canal→ tympanic membrane→ malleus→ incus→ stapes→ oval window→ perilymph of the scala vestibuli→ vestibular membrane→ endolymph in the cochlear duct→ basilar membrane →hair cells against tectorial membrane → bending of hair cell stereocilia→ receptor potential→ nerve impulse. Sound wave → scala tympani→ round window. Be able to trace sound thru ear

Events in the Stimulation of Auditory Receptors

Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 8 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 7 8 9 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 6 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 5 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1 2 3 4 Scala vestibuli Cochlear duct (contains endolymph) tympani Perilymph Basilar membrane Cochlea Sound waves Helicotrema Stapes vibrating in oval window Malleus Incus External auditory canal Tympanic Secondary tympanic membrane vibrating in round window Auditory tube Vestibular membrane Middle ear Tectorial membrane Spiral organ (organ of Corti) 1

The Ear end Response map high low Figure 17–30 Frequency Discrimination. Response map high low

Effect of Sound Waves on Points Along the Basilar Membrane 15-66 66

Opening of K+ Channels 15-67 67

The Auditory Pathway

Physiology of Equilibrium Two types of equilibrium: Static- maintenance of the body position relative to the force of gravity. Dynamic- maintenance of body position (mainly head) in response to rotational acceleration and deceleration. Receptors for equilibrium are hair cells in the utricle, saccule and semicircular canals and are collectively called vestibular apparatus.

Location and Structure of Receptors in the Maculae

Otolithic Organs: Saccule and Utricle Macula- small thickened regions within the saccule and utricle. Sensory structures for static equilibrium. Also detect linear acceleration and deceleration. Contain hair cells and supporting cells. Stereocilia and kinocilium together called hair bundle. Otolithic membrane rests on the hair cells and contain otoliths.

Static Labyrinth Utricle has macula oriented parallel to base of skull Saccula has macula oriented perpendicular to base of skull Macula: specialized epithelium of supporting columnar cells and hair cells with numerous stereocilia (microvilli) and one cilium (kinocilium) embedded in gelatinous mass weighted by otoliths Gelatinous mass moves in response to gravity bending hair cells and initiating action potentials Otoliths stimulate hair cells with varying frequencies Patterns of stimulation translated by brain into specific information about head position or acceleration 15-72 72

Physiology of Equilibrium continued Tilting of the head forward→ sliding of the otolithic membrane bending the hair bundles→ receptor potential→ vestibular branch of the vestibulocochlear nerve.

Location and Structure of the Semicircular Ducts

Semicircular Ducts Crista, a small elevation in the ampulla contain hair cells and supporting cells. Cupula, a mass of gelatinous material covering the crista. Head movement→ semicircular ducts and hair cells move with it→ hair bundles bend→ receptor potential→ nerve impulses→ vestibular branch of the vestibulocochlear nerve.

Cupula in Still Position versus Rotation

Kinetic Labyrinth Three semicircular canals filled with endolymph: transverse plane, coronal plane, sagittal plane Base of each expanded into ampulla with sensory epithelium (crista ampullaris) Cupula suspended over crista hair cells. Acts as a float displaced by fluid movements within semicircular canals Displacement of the cupula is most intense when the rate of head movement changes, thus this system detects changes in the rate of movement rather than movement alone. 15-77 77

Equilibrium Pathway Hair cells of utricle, saccule and semicircular ducts→ Vestibular branch of the vestibulocochlear nerve →brain stem → cerebellum and thalamus→ cerebral cortex.

End of lesson