Special Senses

Special Senses

Utilize distinct receptor cells as receptors

Chemical senses

Taste (gustation)Smell (olfaction)

Taste Taste buds.

• Most are on the tongue.• Papillae.

–Filiform - rough, conical shape, few taste buds

–Fungiform – scattered; most numerous on sides and tips

–Circumvallate –largest; least numerous; back of tongue

Structure of a taste bud.

Supporting cells – form bulk, insulate Receptor (Gustatory or Taste) cells –

contain gustatory hairs that extend through surface

Basal cells - stem cells that divide giving rise to new gustatory cells

Taste sensation Sour – stimulated by acids Sweet – stimulated by sugars,

alcohols, some amino acids Bitter – stimulated by bases Salty – stimulated by metal ions

Sensitivity of the taste buds in different locations.

Anterior tongue is more sensitive to sweet and salty substances

Posterior tongue is more sensitive to bitter substances.

Lateral tongue is more sensitive to sour substances.

Physiology of taste. Chemical comes in contact with gustatory

hair cells on receptor cells. Depolarization of taste cells results in

generation of action potentials in associated sensory neurons.

Relayed to the gustatory cortex. Other sensations

• Taste is 80% smell• Affected by temperature; texture; heat

Smell Localization and structure of olfactory

receptors Detects chemicals in solution Olfactory epithelium - Contains the

olfactory receptors and is located in the roof of the nasal cavity.

Structure of olfactory receptors.

Supporting cells – Basal cells – Olfactory receptor cells –

Specificity of the olfactory receptors –

Can distinguish 10,000 chemicals Not clearly understood May be 1000 odorant binding proteins

that act in combinations

Activation of olfactory receptors.

Chemical comes in contact with the olfactory hair cells on the receptor cells.

Depolarization of the receptor cells results in the generation of action potentials.

Homeostatic imbalances of the chemical senses

Anosmias – without smell Uncinate fits – temporary distortions

of smell due to brain damage, psychological disorders, or even seizures

Vision Accessory structures of the eye

• Eyebrows

• Eyelids “palpebrae”

–Canthi – angles of the eyelids

–Epicanthic fold – found in Asians

–Lacrimal Caruncle – fleshy elevation found at medial canthus

• Meibomian glands – Modified sebaceous glands in eyelid

•Infection of these called Chalazion

• Ciliary glands – between hair follicles of eyelashes

•Infection of these called a Sty

• Conjunctiva – mucus membrane covering eye (infection called conjunctivitis or pinkeye

Accessory Structures of Eye Lacrimal apparatus

• Lacrimal glands – secrete tears

• Lacrimal secretions – contains mucus, antibodies, & lysosozyme–Cleanses, protects, & lubricates

eye

Extrinsic eye muscles

Medial rectus – Superior rectus - Lateral rectus - Inferior rectus - Superior oblique - Inferior oblique –

Structures of the eyeball

Fibrous tunic (coat) – outermost layer

–Sclera – whites of the eye

–Cornea – clear portion in front of eye

Vascular tunic (coat) – middle layer (uvea)

–Choroid – vascular brown membrane

–Ciliary body – encircles lens forming the:

• Ciliary muscles – control lens shape

• Ciliary processes - contain capillaries that secrete fluid

• Suspensory ligaments –

–Iris – colored portion

–Pupil – opening in iris

Sensory tunic (Retina) – innermost layer

–Pigmented layer – absorbs light

–Neural layer – contains photorecptor cells

–Cells of the retina.

• Ganglionic cells – generate action potentials

• Bipolar cells – transfer energy from receptors to ganglionic cells

• Photoreceptors - sensitive to light

• Rods – dim-light, no color, and peripheral vision• Cones – bright light, color vision• Macula lutea – “yellow spot” directly behind

pupil• Fovea centralis – minute pit in center of macula

lutea• Contains cones only• Macular degeneration - linked to nutritional

deficiencies• Optic disc (blindspot) – location of junction with

optic nerve

Internal chambers and fluids

Posterior segment - behind lens• Vitreous humor - clear gel

Anterior segment - in front of lens

–Anterior chamber - in front of iris

–Posterior chamber - between iris and lens

–Aqueous humor - clear liquid filling anterior segment

–Scleral venous sinus (Canal of Schlemm) - drains aqueous humor back into veins; located at corneal / scleral junction

–Glaucoma - elevated pressure of the aqueous humor

Lens Biconvex; transparent; held in place by

suspensory ligaments Lens epithelium - outer covering Lens fibers - inner bulk of lens

• made of folded proteins called crystallins Cataracts - clouding of the lens

• Age related hardening and thickening; diabetes; inadequate delivery of nutrition to lens

Physiology of vision

Photons - packets of light Wavelength

• Electromagnetic spectrum - all wavelengths

• Visible spectrum - 400-700 nanometers

–nanometer = 1 billionth of a meter

• Color - reflection of different wavelengths

–Red, Orange, Yellow, Green, Blue, Indigo, Violet

Refraction and lenses

Reflection - light bounces off a surface Refraction - light bends as it passes through

one substance to another with a different density

Lens - a transparent material curved at one or both surfaces• Convex - thicker in the center; light converges

• Concave - thicker at the edges; light spreads

Focusing of light on the retina.

•Light is refracted three times–Cornea

–Entering the lens

–Exiting the lens

Focusing for distance vision.

Eye are fixed (preset) on an object 20 feet or more away.

Ciliary muscles are completely relaxed.

Lens is stretched as thin as it can get.

Focusing for close vision.

Accommodation of the lens.–Ciliary muscles contract.

–Lens bulges.

Constriction of the pupils - Convergence of the eyeballs -

Homeostatic imbalances of refraction.

Myopia - Nearsightedness• Eyeball is too long

• Image is focused in front of retina Hyperopia - Farsightedness

• Eyeball is too short

• Image is focused behind the retina Astigmatism - caused by unequal

curvature in different parts of the lens

Photoreception.

Functional anatomy of the photoreceptors• Outer segment.

• Inner segment

The chemistry of visual pigments.

Retinal - a light absorbing pigment • made from vitamin A

• combines with opsonins forming–Rhodopsin - “purple” visual pigment of Rods

–Light stimulation separates retinal from the opsins

–Retinal will be re-joined with the opsins to regenerate rhodopsin later

Different types of opsins in cones. 3 Different types of Cones

• Blue - absorbs blue wavelengths best

• Green - absorbs green wavelengths best

• Red - absorbs red wavelengths best Cone wavelengths overlap Stimulation of various cones in different

amounts creates different shading and coloration

Color blindness -

Sex-linked, genetic trait Lack specific types of cones,

usually red or green

Light transduction in photoreceptors.

Generation of electrical current Photoreceptors depolarize in dark and

hyperpolarize in light Produce graded potentials (local) Action potentials produced by Ganglion

cells

Light and dark adaptation -

Light adaptation - from dark to light (5-10 minutes)

Dark adaptation - from light to dark (20-30 minutes)

Binocular vision and stereopsis

Anterior placement of eyes results in greater depth perception or three-dimensional vision

Hearing and balance

Structure of the ear• Outer (External) ear.

–Auricle (pinna)

–External auditory canal (meatus)• Ceruminous glands - wax glands

–Tympanic membrane - “eardrum”• boundary between outer and middle ear

Middle ear (Tympanic cavity) Mastoid antrum - canal leading to mastoid

process Pharyngotympanic (auditory or eustachian)

tube - equalizes pressure on eardrum Ear ossicles.

• Malleus (hammer) -

• Incus (anvil) -

• Stapes (stirrup) -

• Ear muscles: Tensor tympani & Stapedius

Inner (Internal) ear

Bony (Osseous) labyrinth.• Cochlea - “snail” ; hearing

• Semicircular canals - balance

• Vestibule - central cavity Membranous labyrinth.

• Perilymph - surrounds membrane structures

• Endolymph - fills membrane structures

Vestibule

Saccule - smaller sac nearer cochlea

Utricle - larger sac nearer semicircular canals

Maculae - receptors for balance and head position

Semicircular canals. anterior, posterior, lateral

Semicircular ducts - connect canals to utricle

Ampulla - swollen base of canals; houses:• Crista ampullaris - receptors for

head movement

Mechanisms of equilibrium

Static equilibrium = head position Maculae - receptors for static equilibrium

• Supporting cells contain hair cells embedded in gel-like otolithic membrane

–Otoliths -crystals that make membrane heavier, increase inertia

–Utricle’s macula is horizontal for linear acceleration stimuli -

–Saccule’s macula is vertical and responds to vertical movements

Dynamic equilibrium.

Crista ampullaris -- located in the ampulla • Supporting cells -

• Hair cells -

• Cupula - gelled mass resembling a pointed cap

Responds to rotational stimuli -

Cochlea.

Modiolus - • bony pillar at center

Cochlear duct - • wedge-shaped duct

containing Organ of Corti

• Organ of Corti - receptor for hearing

Scalas “chambers”

• Scala vestibuli - connects to vestibule at oval window

• Scala media = cochlear duct

• Scala tympani - connects to vestibule at round window

Vestibular membrane - roof of cochlear duct

Basilar membrane - floor of cochlear duct

Sound and mechanisms of hearing Properties of sound.

• Frequency - measured in hertz

• Amplitude - measured in decibels (dB) -

–logarithmic (exponents of ten)

–0 dB = hearing threshold

–50 dB = normal conversation

–90 dB = danger zone

–120 dB = Rock concert

–130 dB = Pain threshold

Transmission of sound to the inner ear - Vibrations transferred from air to

tympanic membrane to malleus, incus, stapes, to oval window, to cochlear fluid causing resonance of the basilar membrane -

Basilar membrane contains fibers of different lengths that resonate to different frequencies from high to low

Excitation of hair cells in the organ of Corti.

• Organ of Corti - rests atop the basilar membrane

• contains approx. 16,000 cochlear hair cells

Auditory processing. Perception of pitch - specific hairs in specific

sections of basilar membrane identify pitch Detection of loudness - some hair cells for a

certain frequency require stronger stimulation; more stimulation = more hair cells = louder perception

Localization of sound -identified by timing and intensity

Homeostatic imbalances of hearing. Deafness.

• Conduction deafness - –possible causes include: ear wax, perforated

eardrum, inflamation, otosclerosis • Sensineural deafness - nerve damage

Tinnitus - ringing in the ear Meniere's syndrome - attacks of dizziness, nausea,

caused by excess endolymph in the membranous labyrinth