Special Senses

• General Sense

is touch

• Special Senses are taste, smell, hearing,

and vision

TASTE SENSATION

• Sensory receptors are called

chemoreceptors or taste buds

• Taste buds are located within the filiform

*fungiform or *circumvallate (vallate)

papillae *Contain most of the taste buds

– Filiform – scattered across tongue in V

formations

– Fungiform – scattered across tongue surface;

most abundant at tip and sides

– Vallate – largest and least numerous (7-12);

found as an inverted V at the back of the tongue

TASTE SENSATION

TASTE SENSATION

• Gustatory cells with

gustatory hairs are the

receptor cells

• Basal cells divide and

differentiate into new

gustatory and supporting

cells

– Average life span of a

taste bud 7-10 days

There are four

basic taste

sensations:

sweet, sour,

bitter, salty

and *umami

TASTE SENSATION

Sweet Sour Bitter Salty

sugars acids nicotine metal ions

saccharin caffeine

alcohols quinine

amino acids aspirin

lead salts

• Most taste buds will respond to

a combination of taste qualities

TASTE SENSATION

TASTE SENSATION

• Also found in the mouth:

– Thermoreceptors – for sensing

temperature

– Nociceptors – for sensing pain

– Mechanoreceptors - for

sensing pressure and distortion

OLFACTORY SENSATION

• olfactory epithelium – organ of sense on the roof of the

nasal cavity

• life span is 60 days (neurons)

• cells include: olfactory receptor cells, supporting cells and

basal cells

• mucus continually produced

OLFACTORY SENSATION

The Pathway of Smell

•olfactory cilia of the olfactory receptor cells

captures and dissolves odor molecules

•a mechanism is set into motion to depolarize the

olfactory receptor cell and the message is sent

through the neurons axon and transmitted to

the mitral cells (2nd order neurons) through the

glomeruli (each glomerulus receives only one

type of odor signal)

•mitral cells clean up and amplify the signal to

transmit it to the brain

OLFACTORY SENSATION

OLFACTORY SENSATION

HEARING SENSATION

• External Ear

• Middle Ear – small, air filled cavity

– its borders include the eardrum (tympanic membrane) and a bony wall

• the bony wall has 2 openings: oval or vestibular window & round or cochlear window

– superior border is the epitympanic recess

– auditory (pharnogotympanic or Eustachian) tube links the middle ear with the nasopharynx – functions to equalize air pressure across the tympanic membrane

– houses the ossicles: malleus (hammer), incus (anvil), stapes (stirrup)

• vibration from the eardrum is transmitted by the ossicles to the inner ear through the oval window

• 2 skeletal muscles (tensor tympani & stapedius) control the amount of vibration transmitted

HEARING SENSATION

HEARING SENSATION

Can you hear this?

HEARING SENSATION

• Internal Ear or Labyrinth

– located behind the eye socket in the

temporal bone

– 2 major divisions

• Membranous Labyrinth

– a continuous series of membranous sacs & ducts

contained in the osseous labyrinth

– filled with endolymph

HEARING SENSATION

• Internal Ear or Labyrinth

• Osseous Labyrinth

– a system of canals through the temporal bone

– Filled with perilymph

3 regions

– Cochlea

» houses the spiral organ of Corti, receptor for hearing

– Vestibule

» contains 2 membranous labyrinth sacs (utricle and

saccule) containing equilibrium receptor regions

(maculae)* which responds to gravity and helps to

determine head positioning & linear acceleration

– Semicircular Canals (anterior, posterior, lateral)

» a semicircular duct is contained in each canal and

communicates with the utricle

» the ampulla (enlarged swelling of the duct end)

contains an equilibrium receptor site (crista

ampullaris) that responds to angular movements

HEARING SENSATION

HEARING SENSATION

HEARING SENSATION

STRUCTURE OF VISION

Accessory Structures

* eyebrows – shade & sweat protection

* palpebrae – protection

* conjunctiva – mucous membrane lining the eye

* lacrimal apparatus – secretes tears

* extrinsic eye muscles – movement of the eye

STRUCTURE OF VISION

STRUCTURE OF VISION

The eye wall has three coats or tunics

Fibrous tunic – outermost layer, made of dense

avascular connective tissue with two

regions: sclera and cornea

• Sclera - “white of the eye”

tough, tendon-like

functions: protection, shapes the eye, and

anchors extrinsic eye muscles

• Cornea

transparent (parallel collagen fibers)

covered by stratified squamous epithelium

highly innervated

- covered with epithelium

STRUCTURE OF VISION

Vascular Tunic or Uvea – middle coat of the

eyeball

three regions: choroids, ciliary body, iris

• choroid - brown, highly vascularized membrane

providing nutrients to all eye tunics

• ciliary body - consists of interlacing smooth

muscles called ciliary muscles that control

lens shape; posterior, ciliary processes

secrete aqueous humor to fill anterior cavity;

suspensory ligament (zonule) holds the lens

in place

• iris - colored part of the eye, has a round

central opening called the pupil, has 2 layers

of smooth muscle to vary pupil size

•Eye color and pattern (sticky elastic fibers)

STRUCTURE OF VISION

Sensory Tunic (Retina) - 2 layered innermost tunic

(pigmented layer and neural layer)

•Pigmented layer – external single cell layer

•Neural layer (retina) – internal layer containing 3

neuron types: photoreceptors, bipolar cells,

and ganglion cells

2 types of photoreceptors: rods and cones

rods – dim light, peripheral vision receptors

- more numerous

cones – high light, color vision receptors

- concentrated in the fovea centralis in

the macula lutea

-Optic disc- optic nerve exits the eye creating a

blind spot

STRUCTURE OF VISION

Internal Chambers & Fluids

Anterior Segment –

2 parts: anterior & posterior chamber

Anterior chamber – b/t cornea and iris

Posterior chamber – b/t iris and lens

*filled with aqueous humor circulating from

ciliary processes to the scleral venous sinus

Posterior Segment –

*filled with vitreous humor

functions:

transmit light

support the lens and retina

maintains intraocular pressure aiding

muscle movement

STRUCTURE OF VISION

Lens

avascular, biconvex structure that can flex to

focus light; held by the zonule or suspensory

ligament

STRUCTURE OF VISION

Mechanics of Vision

Light and Optics

• Eyes respond to visible light (400 nm-700 nm)

– Red wavelengths are longest with lowest energy

– Violet wavelengths are shortest with highest energy

• Reflection

– Occurs when light bounces (reflects) off a surface

• Refraction

– Occurs when light is bent as it travels from one

medium to another

– The lens of the eye bends light rays so they

converge on the photoceptors of the retina

Mechanics of Vision

Focusing of light

• Pathway of Light

– Air Cornea Aqueous Humor Lens

Vitreous Humor Neural Layer photoceptors

• Bending of Light

– Bent once through the cornea (most refraction)

– Bent entering and leaving the lens

Mechanics of Vision

Focusing for Distant Vision

• Ciliary muscles are completely relaxed

• Lens is stretched as thin as possible

Mechanics of Vision

Focusing for Close Vision

• Lens Accommodation

– Ciliary muscles contract

– Lens bulges giving shorter focal length

– Near-point of vision – closest point on which we can

focus clearly; maximum lens bulge

• Pupil Constriction

– Limits blurred vision by prohibiting the most divergent

light rays from entering the eye

– Called the Accommodation Pupillary Reflex

• Eyeball Convergence

– Medial rotation of the eyeballs toward the object being

viewed

Mechanics of Vision

• Myopia

– Distant objects are focused in front of

the retina

– Can see close objects but distant

objects are blurred

• Hyperopia

– Distant objects are focused behind the

retina

– Can see distant objects but close

objects are blurred

• Presbyopia

– Loss of accomodation; old person

vision

Mechanics of Vision

• Astigmatism

– Blurred vision is a result of light not focusing as a

point but instead as lines

– Unequal curvatures of the lens

• Nyctalopia

– Night blindness

– Rod function decreases; caused by vitamin A

deficiency

• Stereoscopic Vision

– Smaller total visual field but provides depth

perception

Photoreceptor Cells • Rods

– “regenerate” in morning with first light

– Sensitive, best for night vision and peripheral vision

– Absorb all wavelengths of light by perceived in gray tones

– Information is summated resulting in fuzzier vision

– Deep purple pigment, Rhodopsin

• Cones

– “regenerate” at night with darkness

– Need to be activated by bright light

– Contain pigments that give a colored view of the world

– Each cone has its own neuron to the ganglion and to the

visual centers of the brain

– Pigments are (Photopsin) retinal and opsin (red,green,blue)

Color Blindness

Lack of one or more cone types

3 types of cones

short (S) wavelength cones (blue)

medium (M) wavelength cones (green)

long (L) wavelength cones (red)

Mechanics of Vision

How do you see the world?

Light and Dark Adaptation

• Light Adaptation occurs as we move from dim light to

bright light

– Both rods and cones are stimulated and we see only

white light; large amounts of photopigments breakdown

– To adapt, retinal sensitivity decreases

– The cones take over within 60 seconds and improve

vision in 5-10 minutes

• Dark Adaptation occurs as we move from bright light to

dim light

– Cones stop functioning

– Rod pigments were bleached by the bright light

– Rhodopsin begins to accumulate