Chapter 17Chapter 17 Sense OrgansSense Organs

General sensesTasteTasteSmellSmell

HearingHearingEquilibriumEquilibrium

VisionVision

The general sensesThe general senses Refers to the senses that are relatively simple in Refers to the senses that are relatively simple in

structure and physiology (touch, pressure, etc).structure and physiology (touch, pressure, etc). Their receptors tend to have a structure that is Their receptors tend to have a structure that is

specialized to detect a specific stimulus.specialized to detect a specific stimulus. They may so simple as to be simple nerve They may so simple as to be simple nerve

dendrites.dendrites. Unencapsulated receptorsUnencapsulated receptors are sensory dendrites are sensory dendrites

that lack a connective tissue wrapping (e.g. free that lack a connective tissue wrapping (e.g. free nerve endings, Merkels discs and hair nerve endings, Merkels discs and hair receptors).receptors).

Encapsulated receptorsEncapsulated receptors are dendrites with a are dendrites with a glial cell wrap or connective tissue covering (e.g. glial cell wrap or connective tissue covering (e.g. Meissners corpuscles, Pacinian corpuscles Meissners corpuscles, Pacinian corpuscles muscle spindles).muscle spindles).

Receptor Classification based on origin of stimulus

1.1. Exteroceptors-Exteroceptors- receptors sensitive to receptors sensitive to changes outside of body. Are found on or changes outside of body. Are found on or near the body surface: pain, pressure, near the body surface: pain, pressure, touch, temperature and special sense touch, temperature and special sense organs (eye, ear, nose, mouth).organs (eye, ear, nose, mouth).

2.2. Interoceptors- Interoceptors- visceroceptors receive visceroceptors receive stimuli from viscera; stretch, stimuli from viscera; stretch, temperature, chemical, taste.temperature, chemical, taste.

3.3. Proprioceptors-Proprioceptors- located in skeletal located in skeletal muscles, joints, tendons, and ligaments; muscles, joints, tendons, and ligaments; perceive stretch in these organsperceive stretch in these organs

ProprioceptorsProprioceptors

EncapsulatedEncapsulated receptors that receptors that monitor stretch monitor stretch in muscles and in muscles and tendons.tendons.

Ex. Muscle Ex. Muscle spindlesspindles

Extrafusal Extrafusal fibersfibers

IntrafusalIntrafusal

Classified by Stimulus Classified by Stimulus ModalityModality

1.1. Mechanoreceptors- respond to Mechanoreceptors- respond to mechanical forces: touch, pressure, mechanical forces: touch, pressure, stretch, vibration, and itch.stretch, vibration, and itch.

2.2. Thermoreceptors- respond to Thermoreceptors- respond to temperature changestemperature changes

3.3. Chemoreceptors- respond to chemicals Chemoreceptors- respond to chemicals in solution and blood chemistry.in solution and blood chemistry.

4.4. Photoreceptors- respond to changes in Photoreceptors- respond to changes in light-eyelight-eye

5.5. Nociceptors- respond to pain and Nociceptors- respond to pain and harmful stimuli leading to pain.harmful stimuli leading to pain.

Classification by Structure1.1. Free nerve endings- Free nerve endings- are found in all are found in all

tissues of body; especially abundant in tissues of body; especially abundant in epithelial and connective tissue.epithelial and connective tissue.

- respond to pain, temperature, itch and - respond to pain, temperature, itch and light pressurelight pressure

Ex.- Merckels discs, hair follicle receptorsEx.- Merckels discs, hair follicle receptors

2.2. Encapsulated nerve endings- Encapsulated nerve endings- enclosed enclosed in a capsule of connective tissue; vary in a capsule of connective tissue; vary in shape and distribution.in shape and distribution.

Ex.- Meissner’s, Pacinian and Ruffini’s Ex.- Meissner’s, Pacinian and Ruffini’s corpusclescorpuscles

Taste “Gustation”Taste “Gustation” Taste receptors are in taste buds- Taste receptors are in taste buds-

chemoreceptorschemoreceptors

Occur on tongue, palate, cheeks, pharynx and Occur on tongue, palate, cheeks, pharynx and epiglottis as papillae.epiglottis as papillae.- Tongue has 4 types of papillae: a). Filoform; b). Tongue has 4 types of papillae: a). Filoform; b).

Foliate; c). Fungiform and d). Circumvallate.Foliate; c). Fungiform and d). Circumvallate.- In adults last 2 types function in taste on surface of In adults last 2 types function in taste on surface of

tongue:tongue:- Fungiform papillae widely distributed on tongueFungiform papillae widely distributed on tongue- Circumvallate papillae form a “V” at back of tongueCircumvallate papillae form a “V” at back of tongue- Filoform papillae do not sense taste, but the texture of Filoform papillae do not sense taste, but the texture of

foods.foods.

Taste bud = 50-100 epithelial cells consisting of Taste bud = 50-100 epithelial cells consisting of supporting, basal and gustatory cellssupporting, basal and gustatory cells

Taste budsTaste buds

TastesTastes There are five tastes that we can There are five tastes that we can

discriminate when presented to the tongue discriminate when presented to the tongue and mouthand mouth

- Sweet- Sweet- Sour- Sour- BitterBitter- SaltySalty- UmamiUmami

Taste is perceived by taste receptors than Taste is perceived by taste receptors than relayed to brain via: CN VII (Facial), IX relayed to brain via: CN VII (Facial), IX (Glossopharyngeal) and X (Vagus) nerves.(Glossopharyngeal) and X (Vagus) nerves.

Taste is highly dependent on smell for full Taste is highly dependent on smell for full perception of the odor, without smell we lose perception of the odor, without smell we lose much of our taste.much of our taste.

Taste pathways to CNSTaste pathways to CNSvia cranial nervesvia cranial nerves

VIIVII = ant 2/3 tongue = ant 2/3 tongue

IXIX = post 1/3 tongue = post 1/3 tongue

and pharynxand pharynx

XX = pharynx and = pharynx and

epiglottis epiglottis

Smell “Olfaction”Smell “Olfaction” ChemoreceptorsChemoreceptors located in superior nasal concha and located in superior nasal concha and

septum in the olfactory epithelium (nasal mucosa). ~ 5 septum in the olfactory epithelium (nasal mucosa). ~ 5 sq. cm.sq. cm.

Olfactory epithelium is pseudostratified columnarOlfactory epithelium is pseudostratified columnar Odors must be in liquid state to be perceived, thus Odors must be in liquid state to be perceived, thus

they mix with mucus prior to be sensed by receptors.they mix with mucus prior to be sensed by receptors. ~ 10,000 different odor molecules and ~ 1,000 ~ 10,000 different odor molecules and ~ 1,000

different receptor types. Average human can detect different receptor types. Average human can detect 2,000 - 4,000 odors.2,000 - 4,000 odors.

Olfactory receptor cells are bipolar and in cribriform Olfactory receptor cells are bipolar and in cribriform plate of ethmoid bone. plate of ethmoid bone.

Olfactory nerve dendrites have olfactory cilia that bind Olfactory nerve dendrites have olfactory cilia that bind the odors to them. The odor is relayed to the olfactory the odors to them. The odor is relayed to the olfactory nerve axon which synapses with the mitral cell nerve axon which synapses with the mitral cell dendrites of the olfactory bulb → brain. dendrites of the olfactory bulb → brain.

Smell is perceived in the limbic system, hypothalamus Smell is perceived in the limbic system, hypothalamus and olfactory cortex (areas 28 & 34) of the piriform and olfactory cortex (areas 28 & 34) of the piriform lobe.lobe.

Olfactory pathwayOlfactory pathway

Hearing and EquilibriumHearing and Equilibrium Is mediated through the structures of the Is mediated through the structures of the

inner ear.inner ear. These structures are all embedded in the These structures are all embedded in the

temporal bones of the craniumtemporal bones of the cranium Hearing involves the perception of sound Hearing involves the perception of sound

waves entering the external auditory canal waves entering the external auditory canal which is received by the middle ear and which is received by the middle ear and relayed to the inner ear where it is then relayed to the inner ear where it is then registered in the cochlea.registered in the cochlea.

Equilibrium is maintained and perceived by Equilibrium is maintained and perceived by the structures in the semi-circular canals of the structures in the semi-circular canals of the inner ear.the inner ear.

Outer ear anatomyOuter ear anatomy

Pinna – auricle covered with skin and Pinna – auricle covered with skin and made of elastic cartilage; helix and lobulemade of elastic cartilage; helix and lobule

External auditory meatus- ear canal lined External auditory meatus- ear canal lined with skin and ceruminous glands passes with skin and ceruminous glands passes through temporal bonethrough temporal bone

Tympanic membrane – “ear drum” Tympanic membrane – “ear drum” separates outer ear from middle ear and separates outer ear from middle ear and is innervated with sensory fibers from is innervated with sensory fibers from trigeminal and vagus nerves. Responds to trigeminal and vagus nerves. Responds to air vibrations or sound waves and air vibrations or sound waves and transfers energy to middle ear ossicles.transfers energy to middle ear ossicles.

Hearing and EquilibriumHearing and Equilibrium

Middle ear anatomyMiddle ear anatomy Three middle ear ossicles joined together:Three middle ear ossicles joined together: Malleus – looks like a hammer attaches to tympanic Malleus – looks like a hammer attaches to tympanic

membrane and connected to the incus.membrane and connected to the incus. Incus - Looks like an anvil and connected to the Incus - Looks like an anvil and connected to the

stapes.stapes. Stapes- looks like a stirrup – footplate attaches to Stapes- looks like a stirrup – footplate attaches to

oval window of inner ear where it creates oval window of inner ear where it creates ossicilations in the scala vestibuliossicilations in the scala vestibuli

Middle ear muscles: stapedius inserts on stapes; Middle ear muscles: stapedius inserts on stapes; tensor tympani inserts on malleus. Contract during tensor tympani inserts on malleus. Contract during loud noises and relieve tension on ossicles to loud noises and relieve tension on ossicles to protect inner ear.protect inner ear.

Eustachian tube connects middle ear to Eustachian tube connects middle ear to nasopharynx. nasopharynx.

Middle ear anatomyMiddle ear anatomy

Inner ear anatomyInner ear anatomy Housed in a maze of temporal bone Housed in a maze of temporal bone

passages called the bony labyrinth.passages called the bony labyrinth. Bony labyrinthBony labyrinth is filled with perilymph and is is filled with perilymph and is

lined with periosteum; perilymph is lined with periosteum; perilymph is continuous with CSFcontinuous with CSF Bony labyrinth consists of: Bony labyrinth consists of:

-a). vestibule, b). cochlea and c). semicircular -a). vestibule, b). cochlea and c). semicircular canalscanals

Membranous labyrinthMembranous labyrinth lines inside of bony lines inside of bony labyrinth. It is lined with epithelium and is labyrinth. It is lined with epithelium and is filled with endolymph filled with endolymph (high in Na+, K+).(high in Na+, K+). Consists of semicircular ducts, utricle and Consists of semicircular ducts, utricle and

saccule and the cochlear duct.saccule and the cochlear duct.

Inner ear anatomyInner ear anatomy

Structures of hearingStructures of hearing Cochlea –spiraling chamber of bony Cochlea –spiraling chamber of bony

labyrinth. Looks like a snails shell, and labyrinth. Looks like a snails shell, and spirals around modiolus.spirals around modiolus. Lined with a membranous labyrinth with 3 Lined with a membranous labyrinth with 3

separate chambers:separate chambers: Scala vestibuliScala vestibuli –filled with perilymph abuts oval –filled with perilymph abuts oval

window.window. Cochlear ductCochlear duct –filled with endolymph and contains –filled with endolymph and contains

organ of Cortiorgan of Corti Scala tympaniScala tympani –filled with perilymph abuts round –filled with perilymph abuts round

window.window.

Scala vestibuli an scala tympani are joined by Scala vestibuli an scala tympani are joined by heliocotrema at the apex of cochlea.heliocotrema at the apex of cochlea.

Organ of CortiOrgan of Corti

Structures of hearingStructures of hearing

Innervation from CN-VIIIInnervation from CN-VIII

Cochlear portion of VIIICochlear portion of VIIIpathway to CNS for pathway to CNS for hearing.hearing.

Structures of equilibriumStructures of equilibrium Vestibule houses the saccule and utricle Vestibule houses the saccule and utricle

which each contain a macculae that are which each contain a macculae that are receptor cells for head position when the receptor cells for head position when the head is still = static equilibrium. They also head is still = static equilibrium. They also monitor head movements in a straight line = monitor head movements in a straight line = linear acceleration.linear acceleration.

Semicircular canals are lined with a Semicircular canals are lined with a membranous semicircular duct.membranous semicircular duct. Ampulla is bulge at each end of canal and inside Ampulla is bulge at each end of canal and inside

is the membranous ampulla which contains a is the membranous ampulla which contains a crista ampullaris.crista ampullaris.

These receptors detect head rotation or angular These receptors detect head rotation or angular rotation.rotation.

Macculae Macculae structurestructure

In utricle andIn utricle and

saccule. Respond saccule. Respond to: to:

- Static - Static equilibriumequilibrium

- Linear - Linear acceleration acceleration

Structures of equilibriumStructures of equilibrium

Semicircular canals are lined with a Semicircular canals are lined with a membranous semicircular duct.membranous semicircular duct. Ampullae is bulge at each end of Ampullae is bulge at each end of

semicircular canals.semicircular canals. Membranous ampullae contains a crista Membranous ampullae contains a crista

ampullaris.ampullaris. These receptors detect head rotation or These receptors detect head rotation or

angular rotation and dynamic equilibrium.angular rotation and dynamic equilibrium.

Semicircular Semicircular ductsducts

with ampullae and with ampullae and CristaCrista

Ampullaris.Ampullaris.

Respond to:Respond to:

-Detect angular -Detect angular rotationrotation

-Dynamic -Dynamic equilibriumequilibrium

The Eye and VisionThe Eye and Vision

Visual receptors account for ~ 70% of all Visual receptors account for ~ 70% of all sensory input in the body. 40% of the sensory input in the body. 40% of the cerebral cortex in involved in processing cerebral cortex in involved in processing visual perception.visual perception.

Eye balls are the sense organs for visionEye balls are the sense organs for vision Eye is a sphere ~ 1” in diameter and is Eye is a sphere ~ 1” in diameter and is

located in the orbital cavity of the skull located in the orbital cavity of the skull

Accessory structures of eyeAccessory structures of eye

EyebrowsEyebrows Eyelids with tarsal and ciliary glands.Eyelids with tarsal and ciliary glands. EyelashesEyelashes Lateral and medial canthus (angles at Lateral and medial canthus (angles at

corner of eyecorner of eye ConjunctivaConjunctiva Lacrimal apparatusLacrimal apparatus Extrinsic eye muscles (6)Extrinsic eye muscles (6)

Accessory structures of eyeAccessory structures of eye

Accessory structures of eyeAccessory structures of eye

Eye accessory structuresEye accessory structures Eyelids “palpebrae” protect eyes from Eyelids “palpebrae” protect eyes from

foreign objects and bright light.foreign objects and bright light.

- - Two lids separated by palpebral fissureTwo lids separated by palpebral fissure- Angle of eyes is canthus- medial and lateral Angle of eyes is canthus- medial and lateral

canthicanthi- Lacrimal caruncle is at median canthus Lacrimal caruncle is at median canthus - Levator palpebrae muscle raises and lowers Levator palpebrae muscle raises and lowers

eye lidseye lids- Tarsal glands in eyelids secrete oily substance Tarsal glands in eyelids secrete oily substance

that keeps eyes moist. Chalazionthat keeps eyes moist. Chalazion- Eyelashes on the margin of each lid help to Eyelashes on the margin of each lid help to

keep substances from entering eye; ciliary keep substances from entering eye; ciliary glands open into lash follicle. Sty glands open into lash follicle. Sty

Eye accessory structuresEye accessory structures ConjunctivaConjunctiva - transparent mucous membrane covering - transparent mucous membrane covering

inner surface of eyelids (palpebral conjunctiva) and inner surface of eyelids (palpebral conjunctiva) and anterior surface of eye (bulbar conjunctiva), but not the anterior surface of eye (bulbar conjunctiva), but not the cornea.cornea.-made up of stratified columnar epithelium with numerous -made up of stratified columnar epithelium with numerous

goblet cells that secrete mucous and keep eyeball and lids goblet cells that secrete mucous and keep eyeball and lids moist.moist.

-when eye is closed a slit-like space forms= conjunctival sac.-when eye is closed a slit-like space forms= conjunctival sac. Lacrimal apparatus Lacrimal apparatus keeps surface of eye moist with keeps surface of eye moist with

tears from lacrimal glands. From upper lateral position, tears from lacrimal glands. From upper lateral position, tears washover eyes when you blink eyes and move to tears washover eyes when you blink eyes and move to medial canthus to drain into lacrimal puncta → → medial canthus to drain into lacrimal puncta → → canaliculi → lacrimal sac and → nasolacrimal duct → canaliculi → lacrimal sac and → nasolacrimal duct → nasal cavity.nasal cavity.=- Lacrimal fluid “tears” contain mucus, antibodies and =- Lacrimal fluid “tears” contain mucus, antibodies and lysozymes that destroy bacteria.lysozymes that destroy bacteria.

Eye accessory structuresEye accessory structures Extrinsic eye muscles control all Extrinsic eye muscles control all

movements of eyeball in the socket.movements of eyeball in the socket. Six muscles:Six muscles:

Superior rectus: CN III- elevates eyeSuperior rectus: CN III- elevates eye Inferior rectus: CN III- depresses eyeInferior rectus: CN III- depresses eye Medail rectus: CN III- moves eye mediallyMedail rectus: CN III- moves eye medially Lateral rectus: CN VI- moves eye laterallyLateral rectus: CN VI- moves eye laterally Superior oblique: CN IV- depresses eye and Superior oblique: CN IV- depresses eye and

turns it laterallyturns it laterally Inferior oblique: CN III- elevates eye and Inferior oblique: CN III- elevates eye and

turns it laterallyturns it laterally

III- occulomotorIII- occulomotor; ; IV- trochlearIV- trochlear; ; VI- abducensVI- abducens

Extrinsic eye musclesExtrinsic eye muscles

Eye anatomyEye anatomy The eye is a sphere with a bulge (cornea) at the The eye is a sphere with a bulge (cornea) at the

front and a stem at the back (optic nerve). The front and a stem at the back (optic nerve). The outside is covered by a tough outer covering outside is covered by a tough outer covering called fibrous tunic.called fibrous tunic.

Consists of 3 tunics (fibrous, vascular and Consists of 3 tunics (fibrous, vascular and sensory) and 2 chambers (anterior and sensory) and 2 chambers (anterior and posterior) separated by a lens and iris.posterior) separated by a lens and iris. The anterior chamber is filled with aqueous humorThe anterior chamber is filled with aqueous humor Posterior chamber is filled with vitreous bodyPosterior chamber is filled with vitreous body

The visual receptor field (retina) occupies the The visual receptor field (retina) occupies the major portion of the posterior wall of the eye major portion of the posterior wall of the eye and light reaching the retina is regulated by and light reaching the retina is regulated by the iris.the iris.

Fibrous tunicFibrous tunic The fibrous tunic consists of the cornea and The fibrous tunic consists of the cornea and

sclera.sclera. CorneaCornea is avascular and transparent and allows is avascular and transparent and allows

light to pass through. It is made of 100’s of sheets light to pass through. It is made of 100’s of sheets of collagen fibers sandwiched between two layers of of collagen fibers sandwiched between two layers of epithelium. Highly innervated and sensitive to touch epithelium. Highly innervated and sensitive to touch or particles on it.or particles on it.

ScleraSclera is the white of the eye which protects, is the white of the eye which protects, shapes and serves as the anchor site for the shapes and serves as the anchor site for the extrinsic eye musclesextrinsic eye muscles

Limbus is junction between sclera and cornea- stem Limbus is junction between sclera and cornea- stem cells here between cornea and conjunctiva allow for cells here between cornea and conjunctiva allow for continual renewal of cornea.continual renewal of cornea.

Scleral venous sinus allows for drainage of aqueous Scleral venous sinus allows for drainage of aqueous humorhumor

Vascular tunicVascular tunic Consists of three parts: choroid, ciliary Consists of three parts: choroid, ciliary

body and iris.body and iris. ChoroidChoroid highly vascular dark brown pigmented highly vascular dark brown pigmented

layer that covers 5/6 of posterior chamber. layer that covers 5/6 of posterior chamber.

-Melanocytes produce melanin that accounts -Melanocytes produce melanin that accounts for dark brown color of choroid.for dark brown color of choroid.

Ciliary bodyCiliary body anterior to choroid consists of anterior to choroid consists of ciliary muscle (sm. m.), and the ciliary process. ciliary muscle (sm. m.), and the ciliary process. Radiating off of ciliary process are fine fibrils Radiating off of ciliary process are fine fibrils that attach to the iris and control its thickness.that attach to the iris and control its thickness.

IrisIris is the colored portion of the eye and is the colored portion of the eye and constricts and dilates to regulate the amount of constricts and dilates to regulate the amount of light entering into the eye.light entering into the eye.

Sensory tunic “Retina”Sensory tunic “Retina” Consists of two layers; thin pigmented layer Consists of two layers; thin pigmented layer

and a thick neural layerand a thick neural layer outer layerouter layer – pigmented layer – pigmented layer

- beginning of visual pathway to - beginning of visual pathway to brainbrain

inner layerinner layer – neural layer contains rods and cones – neural layer contains rods and cones

-layer where light rays are -layer where light rays are deciphered and converted into an impulse to be deciphered and converted into an impulse to be relayed to brain.relayed to brain.

- ganglion cells- synapse with bipolar cells and - ganglion cells- synapse with bipolar cells and make a 90 degree turn on retinal surface to go make a 90 degree turn on retinal surface to go into optic nerve.into optic nerve.- bipolar cells- synapse with rod and cone receptors to - bipolar cells- synapse with rod and cone receptors to

synapse with ganglion cells.synapse with ganglion cells.

Sensory tunicSensory tunic

- Rods= Blk/Whte- Rods= Blk/Whte

- Cones = Color - Cones = Color

Sensory tunicSensory tunic

Sensory tunic “Retina”Sensory tunic “Retina” optic disc (blind spot) – site where optic optic disc (blind spot) – site where optic

nerve exits eye ball.nerve exits eye ball. macula luteamacula lutea containing the containing the fovea fovea

centraliscentralis

-small flat yellowish spot in exact center -small flat yellowish spot in exact center of posterior eyeof posterior eye

-contains only CONES, and no bipolar -contains only CONES, and no bipolar or ganglion cells to scatter lightor ganglion cells to scatter light

- Macula lutea is the area of highest - Macula lutea is the area of highest visual acuityvisual acuity

Optic disc and Macula luteaOptic disc and Macula lutea

Optic discOptic disc

Fovea centralisFovea centralis

Macula luteaMacula lutea

The LENSThe LENS Defined: composed of proteins called crystallins Defined: composed of proteins called crystallins

arranged in layers much like an onion. It is arranged in layers much like an onion. It is completely transparent and lacks any blood completely transparent and lacks any blood vessels.vessels.

Attachments: Lens is enclosed in a clear Attachments: Lens is enclosed in a clear connective tissue capsule and is held in place connective tissue capsule and is held in place by encircling zonular fibers which attach it to by encircling zonular fibers which attach it to the ciliary processes.the ciliary processes.

Lens divides the eye into two cavities:Lens divides the eye into two cavities: anterior chamber – lies between the cornea and irisanterior chamber – lies between the cornea and iris

- is filled with aqueous humor a watery fluid that - is filled with aqueous humor a watery fluid that nourishes the lens and cornea.nourishes the lens and cornea.

posterior chamber – lies between the iris and in posterior chamber – lies between the iris and in front of the zonular fibers and lens.front of the zonular fibers and lens.

The PhotoreceptorsThe Photoreceptors RODSRODS- receptor for black and white light- receptor for black and white light

Location – (~ 250 million) in the Location – (~ 250 million) in the pigmented layer of the retinapigmented layer of the retina

Functions – low light and peripheral Functions – low light and peripheral vision receptorsvision receptors

CONESCONES- receptors for colored light- receptors for colored light Location – (~6 million) in the Location – (~6 million) in the

pigmented layer of retina and pigmented layer of retina and macula luteamacula lutea

Functions – operate in bright light Functions – operate in bright light and are high acuity color receptors.and are high acuity color receptors.

The PhotoreceptorsThe Photoreceptors

VisualVisualpathwaypathway