Chapter 16: Chapter 16:

The Special SensesThe Special Senses

1.1. Describe the structures of Describe the structures of the Special Sensesthe Special Senses

2.2. Explain the pathways of Explain the pathways of sound in the ear and light in sound in the ear and light in the eye the eye

3.3. Identify, describe, and Identify, describe, and discuss the receptors and discuss the receptors and neural pathways involved in neural pathways involved in each of the five special each of the five special senses senses

Chapter objectives:Chapter objectives:

1.1. TasteTaste2.2. SmellSmell3.3. SightSight4.4. HearingHearing5.5. Touch (Chapt 14)Touch (Chapt 14)

Chemical SensesChemical Senses

Chemoreceptors in Chemoreceptors in Taste BudsTaste Buds– Mostly in papillae on the tongueMostly in papillae on the tongue

Circumvallate, fungiformCircumvallate, fungiform Each has groups of Each has groups of gustatory gustatory

cellscells Sweet, Sour, Salt, Bitter, UmamiSweet, Sour, Salt, Bitter, Umami CN VII and IX to medulla oblongataCN VII and IX to medulla oblongata

The Chemical Senses: The Chemical Senses: 1. Taste1. Taste

The Chemical Senses: The Chemical Senses: 1. Taste1. Taste

The Chemical Senses: The Chemical Senses: 2. Smell2. Smell

Olfactory EpitheliumOlfactory Epithelium– Receptors in pseudostratified Receptors in pseudostratified

epithelium in nasal conchae epithelium in nasal conchae and septumand septum

Filaments from OE protrude Filaments from OE protrude through the Cribriform Platethrough the Cribriform Plate– CN I runs to the Olfactory CN I runs to the Olfactory

Bulb, and to the olfactory Bulb, and to the olfactory cortex of the cerebrumcortex of the cerebrum

Factoids:Factoids:Most dominant senseMost dominant sense

70% of the body’s receptors 70% of the body’s receptors are in the eyesare in the eyes40% of cortex dedicated to 40% of cortex dedicated to visual processingvisual processingMost metabolically active Most metabolically active tissuetissue

Only site where CNS can be Only site where CNS can be seenseenMedical careers:Medical careers:

OpticianOpticianOptometristOptometristOphthalmologistOphthalmologist

Vision (Eye and Accessories)Vision (Eye and Accessories)

Dissected ViewDissected View

Continuation of skinContinuation of skin

EyelashesEyelashes

Tarsal Plate of Hyaline C.Tarsal Plate of Hyaline C.

Tarsal (Meibomian) glands Tarsal (Meibomian) glands on on inner margin of lidinner margin of lid– The oily portion of the tear filmThe oily portion of the tear film– Swollen gland = chalazionSwollen gland = chalazion

Conjunctiva Conjunctiva (= mucous membrane)(= mucous membrane)– Palpebral or BulbarPalpebral or Bulbar– Over cornea very thin (5-7 cells Over cornea very thin (5-7 cells

thick)thick)– Conjunctivitis (pink eye)Conjunctivitis (pink eye) ChalazionChalazion

Palpebrae = EyelidsPalpebrae = Eyelids

Lacrimal ApparatusLacrimal Apparatus

Lacrimal gland Lacrimal gland with several ducts - with several ducts - superior and lateral to eyesuperior and lateral to eye

– Secretion contains Secretion contains water, water, lysozyme, Ab, mucus lysozyme, Ab, mucus

Lacrimal puncta Lacrimal puncta (superior and (superior and inferior) - holes next to the medial inferior) - holes next to the medial canthus to drain tearscanthus to drain tears

Nasolacrimal duct - empties to nasal Nasolacrimal duct - empties to nasal cavitycavity

Extrinsic Eye Muscles Extrinsic Eye Muscles

4 recti4 recti

– Lateral (CN XI), Lateral (CN XI), medial, superior, medial, superior, inferiorinferior

2 oblique2 oblique

– Superior (CN IV), Superior (CN IV), inferiorinferior

Innervation?Innervation?

– III, IV, VIIII, IV, VI

Eyeball

anteriorcavity

3 tunics:

Learn all of this chart!

The Three Layers (tunics):The Three Layers (tunics):

1.1. Fibrous Tunic (tough outer Fibrous Tunic (tough outer layer)layer)

1.1. sclera sclera - white part of fibrous - white part of fibrous tunictunic

2.2. corneacornea - transparent anterior part- transparent anterior part

1.1. Avascular: nutrition via Avascular: nutrition via diffusiondiffusion

2.2. pain receptorspain receptors

3.3. limbuslimbus - boundary between - boundary between the abovethe above

The Three Layers (tunics):

1.1. Vascular Tunic (= Uvea)Vascular Tunic (= Uvea)1.1. choroid choroid ––

1.1. heavily vascularheavily vascular2.2. posterior aspectposterior aspect

2.2. irisiris with with pupilpupil – inner – inner3.3. sphincter and outer radial sphincter and outer radial

musclesmuscles4.4. ciliary body ciliary body – (ciliary m.) – (ciliary m.)

attached toattached to5.5. Radial suspensory ligaments Radial suspensory ligaments

(ciliary zonule)(ciliary zonule)1.1. regulates focus of lensregulates focus of lens

The Three Layers (tunics): 3) 3) The Sensory TunicThe Sensory TunicAKA Nervous Tunic, retinaAKA Nervous Tunic, retina

Outer layer pigmented - inner layer Outer layer pigmented - inner layer photoreceptors 10photoreceptors 1066

a) rods - black/white vision, dim a) rods - black/white vision, dim lightlight

b) cones - color vision, intense b) cones - color vision, intense lightlight

Bipolar cells - synapse with rods and conesBipolar cells - synapse with rods and cones

Ganglion cells - synapse with bipolar cellsGanglion cells - synapse with bipolar cells

Ora serrata - anterior edge of retinaOra serrata - anterior edge of retina

Macula lutea – fovea centralis - all cones, best Macula lutea – fovea centralis - all cones, best visionvision

Optic disc – blind spot, where optic nerve exits Optic disc – blind spot, where optic nerve exits eyeeye

Optic nerve (CN II)Optic nerve (CN II)

Eye Fundus: Eye Fundus: clinical significance ?clinical significance ?

Age Related Macular Degeneration

RetinaRetina

RetinaRetina

•PhotoreceptorsPhotoreceptors•Infolding membranes Infolding membranes contain photopigmentscontain photopigments

•RodsRods•Most numerousMost numerous•Non-acute visionNon-acute vision

•ConesCones•Concentrated in maculaConcentrated in macula•Color vision –red, green Color vision –red, green blueblue

Fig 16.10

Chambers of the EyeChambers of the Eye

Posterior SegmentPosterior Segment

– Vitreous HumorVitreous Humor

Anterior Segment—filled with Anterior Segment—filled with aqueous humoraqueous humor

– Anterior chamber = between Anterior chamber = between iris and corneairis and cornea

– Posterior Chamber = Posterior Chamber = between lens and irisbetween lens and iris

Posterior cavity with Posterior cavity with vitreous humorvitreous humor

Vision Terminology Vision Terminology p 494p 494

Emmetropia = Normal visionEmmetropia = Normal vision Hyperopia = FarsightednessHyperopia = Farsightedness Myopia = NearsightednessMyopia = Nearsightedness Presbyopia = Poor close-up vision with Presbyopia = Poor close-up vision with

agingaging Astigmatism = Abnormal shape of the Astigmatism = Abnormal shape of the

surface of the lens and/or corneasurface of the lens and/or cornea Cataract = abnormal crystallization of the Cataract = abnormal crystallization of the

lens, common in diabetes, injury, hereditylens, common in diabetes, injury, heredity Amblyopia = Poor vision in a normal eye Amblyopia = Poor vision in a normal eye

(CNS defect)(CNS defect)

Visual PathwayOptic chiasma - optic nerves partially Optic chiasma - optic nerves partially cross (right side of the field of each eye cross (right side of the field of each eye combining and going to the lateral combining and going to the lateral geniculate on the right, those from the geniculate on the right, those from the left to the left) left to the left)

To superior colliculus and thalamus To superior colliculus and thalamus and visual cortex in occipital lobeand visual cortex in occipital lobe

The EarThe Ear

HearingHearingBalance (equilibrium)Balance (equilibrium)CN VIIICN VIII

1.1. External earExternal ear2.2. Middle earMiddle ear3.3. Inner earInner ear

1. External Ear1. External Ear

Auricle or PinnaAuricle or Pinna– Elastic CartilageElastic Cartilage

External ear canalExternal ear canal– Through the acoustic Through the acoustic

meatusmeatus– Ceruminous glandsCeruminous glands– In what bone??In what bone??

2. Middle Ear2. Middle Ear

•Tympanic membraneTympanic membrane

•Three Auditory OssiclesThree Auditory Ossicles

•Incus, Malleus StapesIncus, Malleus Stapes

•Transmit Vibrations to Transmit Vibrations to Inner EarInner Ear

•Eustachian Tube Eustachian Tube = Auditory = Auditory Tube = Pharyngotympanic Tube = Pharyngotympanic TubeTube

Otitis media

3. Inner Ear3. Inner Ear

Structure of cochlea: Structure of cochlea: 2.5 turns of ducts2.5 turns of ducts

Organ of CortiOrgan of CortiBasilar membrane on which sit hair cells with stereociliaBasilar membrane on which sit hair cells with stereocilia

Tectorial membrane above the hair cellsTectorial membrane above the hair cells

Sound causes hair cells to bounce and touch tectorial membrane causing Sound causes hair cells to bounce and touch tectorial membrane causing transductiontransduction

Vestibular ComplexVestibular Complex

•VestibuleVestibule•Saccule Saccule •UtricleUtricle•Static equilibriumStatic equilibrium

•Three Three semicircular canals semicircular canals with ampullae (mutually with ampullae (mutually perpendicular)perpendicular)

•Linear accelerationLinear acceleration

Each has a Each has a macula with macula with receptorsreceptors

Two Receptor Organs of vestibuleTwo Receptor Organs of vestibule

•Two Maculae Two Maculae •or: macula of saccule or: macula of saccule plus macula of utricleplus macula of utricle•Vertical and horizontal Vertical and horizontal orientationorientation•Contain otoliths that Contain otoliths that move according to gravitymove according to gravity•Hair cells conduct Hair cells conduct impulse to CN VIIIimpulse to CN VIII

Semicircular Canals Semicircular Canals

•Oriented perpendicularOriented perpendicular•AnteriorAnterior•PosteriorPosterior•LateralLateral

•Each has an ampullaEach has an ampulla•Crista ampullaris Crista ampullaris bendsbends

Auditory Pathway Auditory Pathway

To inferior colliculus of To inferior colliculus of opposite side of midbrainopposite side of midbrain

To thalamusTo thalamus

To auditory cortex To auditory cortex

Cochlear branch of CN VIIICochlear branch of CN VIII

To cochlear To cochlear nucleus of nucleus of medullamedulla