SPECIAL SENSES

Making Sense of The World

Sensation• relationship

between physical energies in the environment & psychological experience of those energies

• to perceive & detect physical energies & encode them into neural signals

Basic Senses• Sight• Hearing• Touch• Smell• Taste• also • Pain• Pressure• Temperature• Joint position• Muscle sense• Movement

SENSES• systems that translate outside information

into activity in nervous system• gather information by detecting energies• environment contains many different forms

of energies

Receptors• detect only the energies have receptor

for• restricted awareness• receptor cells transduce or change physical

energy into a signal brain can understand

Transduction • conversion of physical energies

into language of brain• receptor cells convert physical

energies into neural impulses which travel to cerebral cortex to be decoded

• all sense signals except smell go to relay station-thalamus

• from there to primary sensory areas in cerebrum-different for each sense

• here they are modified and sent on to higher regions of brain

Olfaction• sense of smell• chemical sense• air borne chemicals detected• oldest sense• all organisms have some type of chemical sense• major senses in most animals• help locate food, recognize trails & territories identify kin

& find receptive mates• social insects send & receive intricate chemical signals

which tell them where to go and how to behave• social behavior of most animals is controlled by

chemical signals• olfactory receptor area in German Shepherd-72X bigger

than in humans

Olfactory System• humans are able to distinguish 10,000 smells• detected in paired olfactory organs in nasal

cavity by specialized receptor cells found in olfactory epithelium-olfactory receptor neurons

Olfactory System• olfactory organs posses 2 layers• olfactory epithelium• lamina propria• olfactory epithelium covers inferior cribifrom plate, superior perpendicular

plate & superior nasal conchae of ethmoid bone• covered by mucus which contains olfactory receptors• lamina propria-comprised of areolar tissue, blood vessels, nerves &

olfactory or Bowman’s glands– produce secretions that bathe surface of olfactory receptors

Olfactory System• 10 – 100 million olfactory receptors• modified bipolar neurons• have terminal enlargements or

knobs which project above epithelial surface

• from each 8-20 olfactory cilia extend into mucus

• contain smell receptors• cilia project from knob & lie parallel

to epithelia surface• exposes considerable surface area

to dissolved compounds• at other end of receptor cell, axons

project to olfactory bulb• 10-100 axons form into bundles,

penetrate cribriform plate terminate in olfactory bulb

• stem cells allow neurons to regenerate

Olfaction• refers to breathing in chemicals• Inhaletake in chemicals or odorants

– chemicals that stimulate olfactory receptors

• must be small enough to be volatile to vaporize, reach the nose & dissolve in mucus to stimulate olfactory receptors

• at olfactory organswater & lipid soluble materials diffuse into mucus

OLFACTION• dissolved chemicals interact with receptors-

odorant binding proteins• 4 odorant molecules will activate an olfactory

receptoractivates adenylate cyclaseconverts ATPcAMPopens Na channels in membrane local depolarizationdepolarization large enough action potential in axon conveyed to CNS

Olfactory Pathways• axons of receptors extend through

olfactory foramina in cribiform plate to form right & left olfactory nerves

• terminate in brain in the olfactory bulbsaxons of bulbs extend posteriorlyform olfactory tract projects to primary olfactory cortex located at inferior & medial surface of the temporal lobe

• projects to hypothalamus & amygdala

• parts of limbic system• amygdale associate experiences

with smellsproducing emotion• projections are sent to thalamus

and to frontal cortex-recognition

Olfactory Discrimination• can recognize 2000-4000

chemical stimuli• several primary smells for which

thousands of receptors are needed

• 1) ethereal2) camphoraceous3) musky4) floral5) minty6) pungent7) putrid

• 1% of genes are needed to make receptor proteins to recognize smells

• no distinct receptor for each detectable odor

Gustation• chemical sense• chemicals are taken into the body & dissolved in

oral cavity• drives appetite• protects from poisons

– bitter & sour tastes produce aversive, avoidance reactions

– most poisons are bitter– off food goes sour or has an acidic taste

Taste Discrimination• 5 primary sensations• Sweet• Salty• Sour• Bitter• Umami

– MSG– taste of beef, chicken

broth & parmesan cheese• taste combined with smell

gives flavor– when nose is blocked

foods seem bland or tasteless

Anatomy of Gustation • receptor-taste bud• 10,000• tongue, soft palate,

pharynx & epiglottis• survives about 10 days• Consists of: • taste receptors or

gustatory cells • basal or stem cells• supporting cells

Anatomy of Gustation • Supporting cells• surrounds about 50

gustatory receptors cells in each taste bud

• one single long micovillus (gustatory hair) projects from each gustatory receptor cell to surface through taste pore

• Basal cells– stem cells– found in periphery of taste

buds

Anatomy of Gustation • gustatory receptors

– embedded in specializations of surrounding epithelium called papillae

• three types contain taste buds

• vallate• fungiform papillae• folliate

PapillaeTypes• Vallate or circumvallate papillae

– have 100 taste buds– back of tongue

• Fungiform papillae– possess 5 taste buds– over entire tongue

• Folliate– lateral margins– taste buds degenerate in early

childhoog• Filiform papillae

– no taste buds– Tactile receptors– provide friction sensations

•

Gustatory Transduction• dissolved

chemicals contact taste hairs

• bind to receptor proteins on gustatory cell

• causes series of chemical reactions producingaction potential

Gustatory Transduction• different tastes involve different receptor

mechanisms• salt receptorsdepolarize after Na

channels open• sweet receptors depolarize after K

channels open

Gustatory Transduction

Gustatory Pathways• Taste is monitored by cranial

nerves VII-facial– picks up sensation from

anterior 2/3rds of tongue• IX-glossopharyngeal

– covers posterior 1/3rd of tongue• X-vagus

– receives information from epiglottis

• axons from these nerves synapse on nucleus solitarius in medulla oblongata

• axons of postsynaptic neurons enter medial lemniscus & synapse in thalamus

• then project to gustatory cortex conscious perception

• here information is correlated with other sensory data such as texture, peppery, hot

Vision• primary sense in humans

• sensory organs-eyes

Accessory Eye Structures• Eyelids or palpebrae

– continuations of skin– blink continually to keep surfaces lubricated & things out of eyes

• Palpebral fissure– gap separating free margins of upper & lower eyelids

• Medial & Lateral canthus– where eyelids are connected

• Eyelashes– keep foreign materials out

Medial CanthusLateral

Canthus

Accessory Eye Structures• Tarsal glands

– sebaceous glands associated with eyelashes at inner margin

– secrete lipids to keep eyelids from sticking together • Lacrimal Caruncle

– medial canthus – makes a thick, gritty secretion often found in eyes after

sleeping

ACCESSORY STRUCTURES• Palpebral conjunctiva

– epithelium covers inner surface of eye

• Ocular conjunctiva– covers anterior surface

–extends to edges of cornea• transparent part of outer fibrous layer

ACCESSORY STRUCTURES-Lacrimal Apparatus• produces, distributes & removes tears

– tears reduce friction, remove debris, prevent bacterial infections & provide nutrients and O2 to eye

• consists of– lacrimal gland– lacrimal canaliculi– lacrimal sac– nasolacrimal duct

• lacrimal gland produces key ingredients and most of volume • tears accumulate at medial canthus or lacrimal lake• lacrimal puncta drains lakeempties into lacrimal caniliculilacrimal

sacnasolacrimal duct nasolacrimal canalnasal cavity

THE EYE• irregular spheroid• three layers or tunics• outer fibrous tunic• intermediate vascular tunic• inner neural tunic• two hollow cavities• posterior, vitreous chamber

– contains gelatinous vitreous body

– helps stabilize shape of eye

• anterior chamber– filled with aqueous humor– functions to retain shape of

eyeball

Fibrous Tunic• sclera & cornea• Functions: • mechanical support• physical protection• attachment site-extrinsic eye muscles• housing of focusing structures• Sclera• white of eye• site for insertion of 6 extrinsic eye

muscles• contains blood vessels & nerves• Cornea-continuous with sclera• cornea & lens comprise-refractive

system• focuses light on retina

– where photosensitive pigments are found

Vascular Tunic-Uvea• site of attachment for

intrinsic eye muscles• provides route for

blood & lymph• regulates amount of

light entering eye• secretes & reabsorbs

aqueous humor• controls shape of lens• Parts: • iris• cilliary body• choroid

THE IRIS• consists of pigment cells &

2 layers of smooth muscle• contraction of muscle

produces change in diameter of pupil– central opening in iris

• controlled by ANS• bright light causes

constriction via consensual light reflex– parasympathic pathway

• dim light causes dilatation via pupillary reflex– sympathetic pathway

Cilliary Body• thicken area at

periphery of eye

• iris is attached to it

• composed of cilliary muscles

CHOROID• separates

fibrous & neural tunics

Neural Tunic-Retina• light sensitive• thin, pigmented outer

layer• sheet of melanin

containing cells• thick, inner layer-

contains light receptors • begins visual pathway• consists of three layers

Retina Layers• Photoreceptor

layer

• Bipolar cell layer

• Ganglion cell layer

The Retina• Third layer

– light energy converted into neural activity• contains specialized photoreceptor cells-rods & cone• transduce light wavelengths into information the brain understands

• Second layer– bipolar cells– magnifies image

• First layer– ganglion cells– further adjust image– axons form optic nerve

Retina• if eyes simply transferred

stimuli from retina to brainimages would be blurry

• images are sharpened by sending information from photoreceptor cells back through first 2 layers of retina

• Bipolar cells connect photoreceptors to retinal ganglion cells

• axons from ganglion cells form optic nerve

Third Layer• light energy is converted into

neural activity• contains specialized

photoreceptor cells-rods & cones

• rods cannot see color– more sensitive than cones– sensitive enough to respond to

a single photon of light– basic unit of light

• create coarse, gray image• adequate for seeing in poor or

dim light• can make out shapes fairly well• colors are completely absent• no color vision in dim light

RODS & CONES• 18X more rods than cones

• approximately 125 million rods

• 6 million cones

• arranged to produce best possible combination of night & day vision

Cones• color vision• operate in bright

light• Three types• Blue• Red• Green• experience of color

is due to combination of these three cones

Cones• concentrated in

macula leutea• center is fovea

centralis• site of highest

visual acuity or resolution

THE LENS• transparent structure

located behind pupil in cavity of eyeball

• consists of concentric layers of cells, filled with crystallins– transparent proteins

responsible for clarity of lens & for focusing

Focusing• requires the cornea & lens• light is refracted or bent as it

passes from one medium to another with different density

• greatest amount of refraction occurs as light passes from air to cornea

• more refraction occurs as light passes from aqueous humor to lens

• lens provides extra refraction needed to focus light from object to focal point– specific point of interaction in

retina• distance between center of lens &

focal point is focal length or distance

PhotoPathway Horizontal cells extend across outer

part of retina at level of synapses between photoreceptor & bipolar cells

Amacrine cells found where ganglion cells synapse with bipolar cells

Light energy must pass through both ganglion & bipolar cells to get to photoreceptor cells where light energy is converted into neural signals which activates bipolar cells

One cone converges on one bipolar cell preserves precise information,

provides high acuity and fine detail 1000 or more rods funnel information

onto one bipolar cell increases original illumination &

activates ganglion cells

OPTIC NERVE Axons from 1 X 106 ganglion

cells converge on optic disc circular region medial to

fovea origin of optic nerve penetrates wall of eye at area

known as blind spot no photoreceptors

forms optic nerve which partially crosses at optic chiasm

continues on to thalamus from there to other areas of

cortex all at the same time

Refraction• light rays reflected by

object enter eye through cornea

• light proceeds through pupil– size controlled by

iris• behind pupillens

focuses light rays into an inverted image onto retina at back of eye

Refraction• lens focuses image on

photoreceptors by changing shape– accommmoation

• shape of lens is determined by tone of ciliary muscles

• shape determined by tone of cilliary muscles

Accommodation• cilliary muscles relax for far

vision– zonular fibers are pulled

taut lens is under tension & flat

• cilliary muscle contract for near vision – releases zonular fibers

from tensionlens assumes a natural, rounder & more refractive state• rounder shape

increases refractive power of lens

Errors of Refraction• Presbyopia

– lens thickensbecomes harder won't accommodate

– seen in almost all people over the age of 40

• Myopia-near sightedness

– eyeball is too long

Errors of Refraction• Hypermetropia-

far-sightedness

–eyeball is too short

• Astigmatism

–lens or cornea not smoothly spherical

Image Formation• Final stage-

constriction of pupil

• pupil constricts hole narrows

• due to the circular muscles of iris

Photoreception• Photoreceptors detect photons of light

– basic unit of visible light• light is radiant energy or electromagnetic radiation

– comes in waves– referred to by wavelengths

• wavelengths eyes detect are found in visible part of spectrum• can detect these because possess receptors excited by

wavelengths between 400-700nm

LIGHT• 2 physical characteristics of light determine sensory experience of it• Wavelength

– distance of one wave peak to next– each wavelength is sensed as a color

• Amplitude– indicates amount of energy– determines intensity of light

• large amplitude makes for bright color • small amplitude makes dull color

Photoreceptors• have outer segment containing

discs• shape of outer segment provides

name of photoreceptor• Rods

– each disc is independent entity– outer segment forms elongate

cylinder• Cones

– discs are infoldings of cell membrane

– outer segment tapers to tip– outer segment is connected to

inner by narrow stalk• outer segments of both contain

photopigment– absorbs light

PHOTOPIGMENTS• one in rods• one in each of 3 cones• derivatives of rhodopsin or

visual purple• consists of• protein-opsin-bound to light

sensitive chromophore-retinal-made from vitamin A

• Retinal-common to all photopigments– attaches to different

opsins in cones– opsin determines

wavelength of light that can be absorbed by retinal

Photoreception• photon strikes part of

rhodopsin molecule• absorbed by visual pigment• retinal has 2 possible

configurations• cis & trans forms

– normally retinal is in cis form

• once light is absorbedcis formtrans formtriggers chain of enzymatic steps

Steps in Photoreception

• Step 1: Isomerization

• Photon of light absorbed

• Opsin is activated• cis formtrans

form

Step 2-Photoreception• Bleaching• trans retinal

separates from opsin

• Photopigment looks colorless

Step 3-PhotoreceptionRegenerationTrans retinal

transforms back to the cis form

Cis-retinal can bind to opsin

Photopigment is functional again

Color Deficiency• Humans can discriminate 7X106 colors• some have difficulty with color perception• color deficient• 1 out of 50 individuals• gene responsible is sex-linked• deficiency seen more in males than in females

– 8% of males & 0.05%• color deficient usually lacks either red or green opsin• have difficulty distinguishing red from green (both appear

the same)• can’t color blend• Vision is said to be di- instead of tri-chromatic

Depth Perception• have binocular vision• when looking at an object

a representation comes from both retinas

• foveas are about 5-7.5 cm apart

• visual fields for each eye slightly different

• occipital cortex receives both of these images & fuses them into one picture

• fusing confers perception of depth

• Convergence

Visual Processing• axons from all ganglion

cellsoptic disc• optic nerves reach

diencephalon & incompletely cross over at optic chiasm

• From there ½ the fibers lateral geniculate nucleus on same side of brain

• ½ the fibers continue to opposite lateral geniculate nucleus

• From there image proceeds to occipital cortex via projection fibers

The Ear • three anatomical

areas• External

– collects sound waves & directs them toward middle ear

• Middle – consists of a

chamber in temporal bone

• Inner – contains sensory

organs for hearing & equilibrium

External Ear• composed of pinna

– cartilaginous auricle– surrounds

• external auditory canal– channels sound waves

through auditory canal to• eardrum or tympanic

membrane– thin, semi transparent

membrane separates external from middle ear

• ceruminous glands• secrete cerumen

– waxy substance– needed for protection– helps keep foreign objects

out of ear– helps slow infections

Middle Ear• filled with air• communicates with nasopharynx

through auditory or eustachian tube– equalization of pressures

• contains auditory ossicles– 3 tiny bones

• malleus• incus• stapes• malleus attaches to tympanic

membrane• stapes is bound to oval window

– opening in middle ear going to inner ear

• incus lies between malleus & stapes

Inner Ear• labyrinth• contains receptors for hearing &

equilibrium• Outer bony labyrinth encloses

an inner-membranous labyrinth• bony labyrinth consists of

vestibule, cochlea & semicircular canals

• filled with perilymph• fluid in membranous part is

endolymph• vestible comprised of

membranous sacs: saccule & utricle

• house receptors for gravity & linear acceleration perception

• semicircular canals– receptors in canals provide

information on head location• vestibule + semicircular canals

make up vestibular complex

Hearing Receptors• receptors for hearing are in

cochlea– spiral shaped bony

chamber• divided into thee channels• cochlear duct, scala vestibuli

& scala tympani• the vestibular membrane

separates the cochlear duct from the scala vestibuli

• the basilar membrane separates cochlear duct form scala tympani

• Resting on basilar membrane is spiral organ or organ or Corti

Hearing Receptors• sensory receptors are hair

cells– on basilar membrane– 16 X 106 hair cells found

in two groups• one-inner group arranged

in a row• outer group arranged in

three rows• free surface of each hair

cell contains 40-80 stereocilia– similar to long microvilli

• tectorial membrane covers the hair cells

Audition• detection of sound• stimulus is sound waves

– from compression & rarefaction of air-or alternating air pressure• distance between pressure peaks is wavelength• frequency determines pitch

– measured in terms of cycles or waves per second called hertz-Hz– humans detect sounds in frequency range from 20 to 20,000Hz

• longer waves produce lower frequencies & lower pitches• shorter wavelengths make higher frequencies & higher pitches• amplitude determines loudness • greater amplitude louder a sound

Sound• measured in decibels• 0 decibels=absolute

threshold• 10 decibels indicates 10X

increase• normal conversation-

around 60 decibels• passing train-about 100• above 80 damages hair

cells• uncomfortable at 120• painful above 140

Transduction of Sound• when we speak vocal cords

vibrate molecules of air movebump into one another producing waves of compressed, expanded air

• ears detect these waves & transduce them into nerve impulsesbrain decodes as sound

• sound waves enter via external earcontinue on to tympanic membrane

• air molecules under pressure cause tympanic membrane to vibrate

Transduction of Sound• movement of tympanic membrane

displaces auditory ossicles• first malleus vibrates• handle of malleus strikes incus

causing it to vibrate• vibrating incus moves stapes• vibrates oval window• total force transferred to oval

window– because window is much

smaller force per unit area increases 15-20X.

• vibrations of oval window produce pressure waves that vibrate perilymph in vestibular duct

• these waves distort basilar membrane on way to round window of tympanic duct

• location of maximum distortion varies with frequency

Frequency Coding • basilar membrane is narrow and stiff at window end• wide and flexible at apical end• topographical difference results in different regions

vibrating at different frequencies• end near stapes (window end) vibrates at high

frequencies• apical end vibrates at low frequencies

Transduction of Sound• pressure waves continue

into endolymph inside cochlear duct

• pressure waves in endolymph cause basilar membrane to vibrate which moves the hair cells of spiral organ against tectorial membrane

• leads to bending of stereocillia & generation of nerve impulse

Transduction of Sound

Auditory Pathways• bending of hair cells opens potassium

channels • Produces depolarizing potential • opens calcium channels• causes neurotransmitter vesicles

(probably glutamate) release• generates nerve impulse• impulses pass along axons of forming

cochlear branch of vestibulocochlear nerve (VIII)

• axons synapse with neurons in cochlear nucleus in medulla

• some axons cross over & ascend in lateral meniscus & terminate in inferior colliculi in midbrain

• other axons form cochlear nuclei • end in superior olivary nucleus in pons

Localization of Sounds• requires binaural fusion• brain compares information received from each ear• ears are about 6 inches apart• makes for intensity differences & time lags to brain• very small but allow for stereophonic or 3-

dimensional hearing• auditory system can detect minute differences• time difference of 0.000027 seconds is all that is

needed to be able to identify direction from which 2 sounds are coming

• localization is quite accurate unless sound is located directly ahead, behind, overhead or beneath ears-equidistant from both

Hair Cells• 16,000 hair cells• extremely

vulnerable• overexposure to

loud noises, disease, heredity or aging most humans will lose 40% of hearing by age 65

• once destroyed hair cells cannot regenerate

Equilibrium• vestibular sense

• sensation provided by vestibular complex

• Two types

• Static

• Dynamic

Static & Dynamic Equilibrium• Static

– maintenance of position of body (mainly head) relative to force of gravity

– know where head is when it is tilted

• Dynamic– maintenance of body

position (mainly head) in response to sudden movements, such as rotational deceleration or acceleration

– know where head is if it moves quickly

Vestibular Sense Receptors

• Vestibular apparatus

• Saccule

• Utricle

• Semicircular ducts

Saccule & Utricle• Otolithic organs

• walls contain macula

• houses receptors for equilibrium

• contains two types of cells

• 1) hair cells-sensory receptors 2) supporting cells

Saccule & Utricle• hair cells of utricle & saccule have 40-80

stereocillia of grduated height & one kinocillium• Longer than longest stereocilia• steorcillia are connected by tip inks• Together sterocilia and kinocillium are-hair

bundle

Saccule & Utricle• supporting cells

secrete a gelatin like glycoprotein layer called otolithic membrane

• rests on hair cells• layer of dense calcium

carbonate crystals called otoliths extend over surface of otolithic membrane

Equilibrium• when head is upright

statoconia sit on top of macula– weight presses down

• when head is tiltedstatoconia shift to sidedistorting hair cells

• sends information to CNS that head is no longer level

Semicircular Ducts • contain receptors which respond to rotational head movements-

dynamic equilibrium• anterior, posterior & lateral semicircular ducts are continuous with

utricle• each semicircular duct has an ampulla-expanded region containing

hair cells• hair cells attached to wall of ampulla form crista• each crista consists of hair and supporting cells• covering the cells is a gelatinous structure- cupula

Vestibular Sense• when head is rotatedendolymph

movespushes cupula distorts processes of receptor

• gluid movement in one directionstimulates hair cells

• movement in other directioninhibits hair cells

Vestibular Sense & Equilibrium• Hair cells of vestible & semicircular

ducts are monitored by sensory neurons-vestibular ganglia

• Branches form cranial nerve 8- vestibulocochlear nerve

– innervates vestibular nuclei located between pons & medulla

• nuclei send information to cranial nerves: III, IV, VI and XI-involved with eye, head and neck movements

• information is then sent down vestibulospinal tracts of spinal cord adjusts peripheral muscle tone & complements reflexive movements of head & neck

• nuclei also connect with cerebellum to coordinate movement

• one spins very fast & stops abruptly, liquid cannot return to normalfeel dizzy

• Neural connections are also made with ANSdigestive system partnausea.