Special Senses

General Senses

• have receptors scattered throughout the body

• Nociceptors- free nerve endings that convey the sense of pain

• thermoreceptors- temperature sensitive

• mechanoreceptors- establish an action potential in response to physical deformation.

  • Tactile receptors- May measure “touch”

  • baroreceptors/pressoreceptors- mechanoreceptors might measure change in pressure

  • Proprioreceptors- sense of body position and motion

• senses can also be classified based on the location of stimulus

• exteroreceptors- receptors that respond to a stimulus outside the body such as touch or temperature

  • teloreceptors- detect change that occur away from the body

    • include eye and the ear

  • Interoceptors/enteroceptors/visceral receptors- detect changes within the body

Special senses

• receptors are localized in special, complex sensory structures

• chemical senses- receptors for these senses respond to specific molecular stimuli

  • olfaction, gustation, and “common chemical” sense

  • Common chemical- sense of chemical irritants

    • receptors found in mucous membranes of humans

    • respond to onion fumes, tear gas, and acid fumes

  • Olfaction- sense of smell

    • neurons from the nasal epithelium convey impulses through the cribriform plate of the ethmoid bone to the olfactory bulb

    • olfactory hairs (dendrites) are exposed to the surface of the nasal epithelium

    • mucus is secreted by glands in the epithelium to dissolve the substances we smell (odorants)

  • Gustation- sense of taste

    • receptors found on tongue, soft palate, and pharynx

    • Taste buds found on the tongue associated with papillae (small elevations) of the tongue

Papillae

• circumvallate/ vallate papillae- largest of the papillae

  • located at the very back of the tongue and form a “V” shape

• fungiform papillae- large bumps on the tongue

• filiform papilla- smallest papillae

  • when they get excessively long, a person is said to have a “hairy tongue”

  • people are instructed to scrub tongue with a toothbrush to wear papillae down

Circumvallate, fungiform, and foliate papillae are associated with taste buds. Filiform are not

• foliate papillae- posterior, lateral border of tongue is irregularly shaped in children

  • looks like edge of a leaf

  • as person gets older, tongue flattens and broadens, and this surface disappears

Primary tastes

• flavor comes from odor produced by food

• has specific receptors on the tongue

• more than sweet, salt, sour, and bitter

• chemical senses are especially prone to sensory adaptation

• sensory adaptation- decrease in the intensity of a sensation as time passes

  • strong smell but we then get nose blindness

The eye

• ophthalmology- study of structure, function, and diseases of the eye

• superciliary (supraorbital) ridge- ridge above eye/eyebrow

  • helps keep perspiration out of the eye

  • deflect overhead sunlight

• palpebrae- eyelids

  • protect eye and keep it moist

• palpebral fissure- space between the upper and lower palpebrae

• commissures- corners of the palpebral fissure

• medial commissure/ medial canthus- corner next to the nose

• lacrimal caruncle- small pink mass of tissue in medial canthus

• lateral commissure/lateral canthus- corner of the palpebral fissure that is away from the nose

• conjunctiva- mucous membrane that covers the visible surface of the eye and lines the underside of the eyes

• lacrimal glands- superior and lateral to the eye

  • produce tears that wash across the surface of the eye toward the medial commissure

  • helps to clean surface of eye and keep it moist

  • contain lysozyme (bactericide enzyme) that helps prevent bacterial infections

  • tears drain through nasolacrimal ducts into nasal cavity

    • why excess production of tears cause “sniffling”

Wall of eye

• fluid filled structure composed of 3 tunics/coat (layers) in the wall

• fibrous tunic- outermost layer of the eye is tough

  • composed of an anterior, transparent cornea and a posterior, white sclera

    • sclera “white of the eye”

• vascular tunic/uvea- middle layer of eye

  • iris- most anterior part of the eye that gives people different eye colors

  • pupil- opening in the iris that allows light to enter the internal part of the eye

  • Ciliary body- behind iris is muscular structure that is shaped like a donut

    • alters shape of the lens and allow the eyes to focus on objects that are different distances from the eye

  • lens- in hole of donut; focuses light on the back of the eye

  • Choroid- posterior part of the uvea

    • many blood vessels and supplies nutrients to the nervous, inner layer of the eye

  • Nervous tunic/retina- inner layer of the posterior portion of the eye

    • photoreceptors- nervous receptors sensitive to light

Ciliary body

• muscle shaped like a donut that can alter the shape of the lens

  • lens has natural tendency to become round, but is attached to ciliary body by suspensory ligaments

  • ligaments pull on lens and make it have a lesser curvature

• When look at distance object, lens is pulled into a relatively flat shape

  • as you move an object closer, tension of the ligaments is lessened and the lens becomes more round

  • new shape bends light to a greater degree and the image stays focused on the retina of the eye

  • accommodation- increasing curvature to maintain focus

• as we age, eye loses some of its elasticity and its ability to get as round

  • presbyopia- cant focus on near objects

    • why a person holds phone book or newspaper farther

Eye cavities

• lens and ciliary apparatus divide the inerior part of the eye into 2 cavities (segments)

• anterior cavity- front of lens

  • aqueous humor-filled with a thin, runny fluid

    • aqueous humor can flow from the posterior chamber through pupil to the anterior chamber

  • anterior chamber- anterior cavity is divided by iris into this in front of iris

  • posterior chamber- behind iris

Chamber and cavity are not the same!!!

• Posterior cavity/vitreous chamber- behind the lens.

  • vitreous humor/body- posterior cavity is filled with a thick, jelly-like substance

• glaucoma- pressure can build up in the eye if aqueous humor is produced faster than it is reabsorbed. increase in pressure within eye.

pigment

• pigment- some molecules absorb certain wavelengths (colors) of light

  • photopigments- pigment molecules that change structure when they absorb light.

    • said to be BLEACHED when their structure is altered.

    • altered protein initiates a nerve impulse

    • pigment has to be rejuvenated/returned to original form

    • photopigments of the eye are found in specialized photoreceptors in the retina of the eye

• Photoreceptors- have rods and cones

  • rods- more numerous

    • do not allow us to distinguish different colors, but do not require much light

  • cones- more important

    • allow us to distinguish different colors and form a sharper image

    • require more intense light, so rods are an important part of our vision in dim light

Rods

• photopsin- general term for visual pigment

• rhodopsin/visual purple- visual pigment in rods

  • absorbs light, is bleached,

  • molecules split into trans retinal (molecule) and opsin (protein)

  • this event initiates a nerve impulse

  • trans retinal- carotenoid which means that is relative to vitamin A.

  • Retinal isomerase- enzyme changes the shape of trans retinal

    • cis retinal- new molecule

    • spontaneously recombines with the opsin to reform rhodopsin

• Bright room= pigment in rods is bleached faster than it can be rejuvenated

• dark room= slowly see better as your rods become functional

Cones

• events in cone vision are similar to those in rod vision

• one of three different pigments.

• pigments absorb different wavelengths of light

  • so different wavelengths, colors, affect different cones

  • allows us to distinguish between different colors

• red, green, and blue

  • different pigments have different proteins associated with trans retinal.

  • if a person is missing one or more of the three pigments, he would be “color blind”

• reason cones are more important is the location of the cones in our retina.

  • macula lutea- lens focuses light on a part of our retina that has only cones

  • fovea centralis, central fovea, or central depression- depression in the macula lutea where the cones have the greatest concentration.

    • this area of the retina forms the sharpest image

Vision terms

• emmetropia- normal vision

• myopia- image is formed in front of the retina; “nearsighted”

• hyperopia (hypermetropia)- image is focused behind the retina; “farsighted”

• astigmatism- irregular curvature of the cornea or lens

Other terms with eye and vision

• optic disc- site on the retina where the optic nerve is attached

  • “blind spot”- no photoreceptors here

  • medial to the macula lutea

  • two reasons you do not have a “blank” are in your visual field

    • light that is striking the optic disc on one eye is striking the lateral part of the retina on the other eye. so light from that part of the visual field is striking photoreceptors

    • even when you close one eye, no blank area. because the brain fills in the area with an image of what it believes should be in that area.

• Snellen chart- tests visual acuity, or ability to form sharp image

  • 20/40- if lowest line you can read lists 40 feet for a person with normal vision

  • 20/25- see the line that lists 15 feet

• Ishihara chart- image with lots of color dots

  • person with normal color vision sees one word or image.

  • person who is color blind sees a different word or image

• miosis- pupil constriction

• mydriasis- pupil dilation

The outer ear

• pinna/auricle

  • part of ear on the sides of the head

• external auditory meatus-

  • pinna channels sound waves, like a funnel into these

  • cerumen(earwax)- canal has tiny hairs and this

  • tympanum, tympanic membrane, ear drum- EAM ends at a thin membrane

    • sound waves striking the tympanum cause it to vibrate

    • tympanum separates the outer ear and the middle ear

The middle ear

• middle ear/tympanic cavity- medial (deep) to the tympanic membrane

• auditory ossicles- there is a space with three tiny bones

  • malleus/hammer- most lateral of these bones

    • touches the tympanic membrane

  • incus/anvil- next ossicle

  • stapes/stirrup- most medial ossicle, smallest bone in the body

When tympanic membrane vibrates, causes malleus to vibrate

• malleus causes the incus to vibrate, and the incus makes the stapes vibrate

• vibrations of the stapes are transferred into the inner ear through OVAL WINDOW (opening)

Canal that connects the middle ear with the nasopharynx

• Eustachian tube, auditory tube, or pharyngotympanic tube

• passage allows air pressure to equalize on both sides of the tympanic membrane

  • why your ears “pop” when you swallow as you drive in the mountains or fly in an airplane

  • as external pressure changes when you change altitude, you need to alter the pressure in the middle ear to compensate

  • Auditory tube- passage is also a route taken by bacteria to cause otitis media (middle ear infections). Many children get this

Two muscles associated with middle ear

• tensor tympani & stapedius

  • when muscles contract, inhibit movement of ossicles

  • helps protect the delicate structures of the inner ear from loud noises

The inner ear/labrynth

• has osseous labrynth (outer bony) and an inner membranous labrynth

• perilymph- fluid between the bone and the membrane

  • chemically similar to the CSF

• Endolymph- inside membranous labrynth

  • chemically similar to intracellular fluid

• vestibule- middle, enlarged part of the inner ear

  • semicircular canals- 3 tubes above vestibule

  • cochlea- below vestibule; snail shaped

Inner ear responsible for much of our sense of balance and equilibrium. also responsible for hearing

Equilibrium in the ear

• vestibule and semicircular canals associated with the sense of equilibrium

  • utricle and saccule- vestibule of osseous labyrinth contains portions of the membrane labyrinth

  • macula- each of these parts of the membranous labyrinth has thickened wall

  • otolithic membrane- cells in the maculae have tiny hairs that extend into a thick, jelly-like mass

    • gravity causes otolithic membrane to bend the nerve hairs

    • if you tild head, these slide across the hairs

    • conveys a sense of the orientation of the head

  • Static equilibrium- sense of body position

dynamic equilibrium

• semicircular canals- bony loops of the inner ear

• semicircular ducts- membranous labyrinth within the canals

• 3 semicircular canals are located on three different planes

  • ampullae- there are swelling or enlargements at the base of each of the 3 duscts

  • cristae- thickenings in the ampullae

  • cupula- cells with nerve hairs in the cristae and hairs are covered with this gelatinous mass

• when head moves, inertia causes a current of fluid (endolymph) in a semicircular dict

  • current bends the nerve hairs

• since ducts are located on 3 different planes, direction of head movement determines which ampullae are affected

  • allows us to maintain equilibrium as the body is moving

Dynamic equilibrium- this equilibrium of motion

Sound waves

• sound waves converted into nervous impulses in the snail-shaped cochlea

• Illustration has cochlea unwound to see perilymph (gray shading) is in a passage that begins at the oval window

• oval window- where vibrations of the stapes creates waves in perilymph of inner ear

  • FENESTRA VESTIBULI/ FENESTRA OVALIS

• helicotrema- channel with perilymph goes around “end of snail”

• Fenestra cochlea/fenestra rotundum- comes back to the lower part of the vestibule where there is another opening covered by a membrane

• scala vestibuli- channel containing perilymph from the oval window to the helicotrema

• scala tympani- channel from helicotrema to the round window

Waves are created in the perilymph at the oval window and the waves are dissipated at the round window

• organ of Corti- spiral organ in the inner ear which has hair cells (stereo cilia) in a basilar membrane

  • tectorial membrane rests on the hair cells

  • waves in the perilymph create waves in the endolymph

  • waves cause basilar membrane to vibrate which pushes the nerve hairs into the tectorial membrane

    • creates nerve impulses

  • Pitch- wavelength of the sound waves determines which hairs on the organ of Corti get bent

    • louder sounds cause bigger waves, so more nerve hairs are stimulated