Chapter 17: The Special Senses Flashcards
Olfactory Epithelium
Occupies the superior part of the nasal cavity, covering the inferior surface of the cribriform plate and extending along the superior nasal concha.
Consists of 3 kinds of cells: olfactory receptor cells, supporting cells, basal cells.
Olfactory Receptor Cells
First order neurons of the olfactory pathway. Each cell is a bipolar neuron with an exposed, knob shaped dendrite and axon projecting through the crib form plate that ends in the olfactory bulb.
Olfactory Cilia
Sites of olfactory transduction.
Olfactory Receptor
Found within olfactory cilia plasma membrane.
Proteins that detect inhaled chemicals.
Odorants
Chemical that bind to and stimulate the olfactory receptors in the olfactory cilia.
Supporting cells
Columnar epithelial cells of the mucous membrane lining the nose.
Provide physical support, nourishment and electrical insulation for the olfactory receptor cells. Helps detoxify chemicals that come in contact with the olfactory epithelium.
Olfactory Glands
Or bowman’s glands
Found within the connective tissue that supports the olfactory epithelium. Produces mucus that is carried to the surface of the epithelium ducts.
Olfactory Transduction
Olfactory Nerve (I) innervate olfactory receptors cells responsible for transduction.
Binding of an odorant molecule to an olfactory receptors proteins activates the G proteins and ardently Cyclades, resulting in production of cAMP.
CMAP opens cation channels Na+ and Ca2+ ions entering the olfacotry receptors.
Results in depolarization to generate an action potentials.
Olfaction
Special sense : smell
Low threshold, only a few molecules needed to smell an odor.
Adaptation
Decreasing sensitivity
Happens rapidly with olfaction.
Gestation
Taste, chemical sense.
Simpler than olfaction.
Has 5 primary tastes: salty (sodium), sour (hydrogen), sweet (sugars) bitter (guinine, caffeine, morphine), umami (meaty or savory).
Taste Bud
Oval body consisting of 3 kinds of epithelial cels
1. Supporting cells (surrounds 50 % of gustatory cells)
2. Gustatory cells
3. Basal cells (stem cells found at periphery of taste bud)
Gustatory Microvilli
Project from each gustatory receptor cell to the external surface through taste pore.
Taste Pore
Opening in the taste bud.
Papillae
Elevations on the tongue where taste buds are found. Increase surface areas and provides the ruff texture on surface of tongue.
3 Types of Taste Buds
- Vallate Papillae: 12 large, circular or form inverted V shaped row at back of tongue. House 100-300 taste buds.
- Fungiform Papillae: mushroom shaped elevations scattered over entree surface of tongue. Contain 5 tastes buds each.
- Foliate Papillae: located in small trenches on the lateral margins of tongue. Most taste buds degenerate in early childhood.
Filiform Papillae
Found on entire surface of the tongue. Pointed, threadlike structures contain tactile receptors but no taste buds.
Increases friction between tongue and food, making it easy to move food in oral cavity.
Tastants
Must dissolve in salvia before making contact with gustatory cells.
Chemicals that stimulate gustatory receptor cells.
The receptor potential arises differently for different tastants.
Na+ in salty foods causes depolarization, increases neurotransmitter when entering gustatory receptor cells.
Other tastants responsible for sweet, bitter, umami do not enter gustatory cells.
Taste Threshold and Adaption
Threshold for taste varies for each primary tastes.
Threshold for bitter substances, (guanine) is the lowest.
Complete adaptation to taste occurs in 1-5 mins of continuous stimulation.
Accessory Structures of the Eye
Includes: eye lids, eyelashes, eyebrows, lacrimal apparatus, extrinsic eye muscles.
Eye Lids
Or palpebrae
Shade the eyes during sleep
protect eyes from excessive light and foreign objects
Spread lubricating secretions over the eyeballs.
Levator Palpebrae Superioris Muscle
Superior region of eyelid and is more moveable than the lower.
This muscles will twitch and is harmless.
Palpebral Fissure
Space between the upper and lower eyelids that exposes the eye ball.
Lateral Commissure
Angles of the eye lids. Narrower and closer to temporal bone.
Medical Commissure
Angles of the eyelid. Broader and nearer the nasal bone.
Lacrimal Caruncle
Reddish elevation in the medial commissure. Contains sebaceous oil glands and sedoriferous sweat glands.
Tarsal Plate
Is a thick fold of connective tissue that gives form and support to the eyelids.
Tarsal Glands
Or Meibomian glands
A row of elongated modified sebaceous glands, secretes a fluid that keep eyelids from adhering to each other,
em-bedded in each tarsal plate.
Conjunctiva
A thin protective membrane composed of nonkeratinized stratified squamous epi with numerous globes cells that is supported by areolar CT.
Palpebral Conjunctiva
Lines the inner eye aspect of the eyelids
Bulbar Conjunctiva
Passes from the eyelids into the surface of the eyeball where it covers the sclera but not the cornea.
Bloodshot eyes occur here by the dilation and congestion of the blood vessels.
Eyelashes
Project from the border of each eyelid
Eyebrows
Arch transversely above the eyelids, help protect the eyeballs from foreign objects, perspiration and direct rays of the sun.
Sebaceous Ciliary Glands
Sebaceous glands at the base of the hair follicles of the eyelashes. Releases a lubrication fluid into the follicles.
Infection of this areas is known as a sty.
Lacrimation
Process of producing tears
Sequence of flow of tears
1. Lacrimal gland
2. Excretory lacrimal ducts
3. Superior or inferior lacrimal canaliculi
4. Nascolacrimal duct
5. Nasal cavity
Lacrimal Apparatus
Is a group of structures that produces and drains lacrimal fluid.
Lacrimal Fluid
Tears
Consists of salts, some mucus and lysozyme.
Protects, cleans, lubricated and moistens the eye ball.
Lacrimal Gland
Size and shape of an almond, secretes lacrimal fluid into ducts.
Excretory Lacrimal Ducts
Lacrimal fluid drains into this duct about 6-12 ducts at a time. Empties tears onto the surface of the conjunctiva of upper lid.
Lacrimal Puncta
Two small openings in the eyeball where tear pass into two ducts known as superior and inferior lacrimal canaliculi.
Lysozyme
Protective bacterial enzyme in lacrimal fluid.
Periorbital Fat
Surrounds the eye and extrinsic eye muscle in the orbit.
There are 6 extrinsic eye muscles.
Eyeball
Measures 2.5 cm. Only the anterior 1/6 is exposed.
Consists of 3 layers:
1. Fibrous tunic
2. Vascular tunic
3. Retina inner tunic
Fibrous Tunic
Superficial layer of the eyeball. Consists of anterior cornea and posterior sclera.
Cornea
Transparent curved coat that covers the colored iris. The curve helps focus light onto the retina.
Admits and retracts light.
Sclera
The white of the eye. Provides shape and protects inner parts of the eye.
Layer of dense CT made up of collagen fibers and fibroblasts. Covers entire eyeball except the cornea.
Sclera Venous Sinus
Or canal of Schlemm
Opening at the junction cation of the sclera and corneas. Fluid known as aqueous humor drains into this sinus.
Vascular Tunic
Is the middle layer of the eyeball.
Composed of 3 parts:
1. Choroid
2. Ciliary body
3. Iris
Choroid
Highly vascularized, posterior portion vascular tunic.
Lines internal surface of sclera.
Contains blood supply and melanocytes that produce pigment melanin. Causes layer to be dark to absorb stray light to prevent scattering of light in the eyeball.
Ciliary Body
Anterior portion of vascular tunic. Extends from oral serrata to junction of sclera and cornea.
Contains melanin producing melanocytes and contains ciliary processes and ciliary muscles.
Secretes aqueous humor.
Alters shape of lens for near or far vision.
Ora Serrata
Jagged anterior margin of the retina.
Ciliary Processes
Protrusion or folds on the internal surface of the ciliary body. Contains blood capillaries that secret aqueous humor.
Zonular Fibers
Extends from the ciliary process, attached to the lens.
Consists of thin, hallow fibrils that resemble elastic CT fibers.
Ciliary Muscle
Circular ban of smooth muscle. Contraction of this muscle changes the tightness of the zonular fibers, which alters the shape of the lens adapting it to near or far vision.
Iris
(Rainbow)
Colored portion of the eyeball. Shaped like a flattened donut.
Suspended between the cornea and the lens and is attached to the outer margin to the ciliary processes.
Function: regulates the amount of light entering the eyeball through pupil.
Pupil
The hole in the center of the iris. Appears black due to seeing the back of the iris.
Appears red when direct light hits it due to blood vessels.
Circular Muscle
Or sphincter papillae. When stimulated by parasympathetic fibers of nerve III by bright light, causing a decrease in the size of the pupil (constriction).
Radial Muslces
Or Dilator papillae
In Dim light this muscle is stimulated and the iris contracts cause an increase in pupil size.
Retina
Third and inner layer of the eyeball. Lines the posterior three quarters of the eyeball.
Beginning of the visual pathway.
Received light and converts it into receptors potential and nerve impulses.
Output to the brain via axons of ganglion cells, forms optic nerve II.
Optic Disc
Where optic nerve II exits the eyeball.
Also know as “the blind spot” because it does not contain rods or cones.
Central Retinal Artery
Bundles with optic nerve.
Branch of ophthalmic artery.
Nourishes the anterior surface of the retina.
Central Retinal Vein
Drains blood from the retina through the optic disc.
Pigmented Layer of Retina
Sheet of melanin containing epi cells located between the choroid and the neural part of the retina.
Melanin is the pigmented layer, helps absorb stray light rays.
Neural (sensory) Layer
The multilayered outgrowth of the brain that processes visual data extensively before sending nerve impulses into axons that form the optic nerve.
3 Distinct Layers of Retinal Neurons
- Photoreceptors cell layer
- Biopolar cell layer
- Ganglion cell layer
There’s layers are separated by two zones: outer and inner synaptic layers
Horizontal Cells and Amacrine Cells
Both present in bipolar cell layer of the retina.
These cells form laterally directed neural circuits that modify the signals being transmitted along the pathway from photoreceptors to biopolar cells to ganglion cells.
Rods
Allows us to see in dim lights. Do not provide color vision, in dim light we only see black, white and shades of gray.
Cones
Stimulated by bright lights. Produce color vision.
3 Types of Cones in the Retina
- Blue cones: sensitive to blue light
- Green cones: sensitive to green light
- Red cones: sensitive to red light
Color vision results from stimulation of various combinations of these 3 types of cones.
Macula Lutea
Small, flat spot or yellow spot in the exact center of the posterior portion of the retina, at the visual axis of the eye.
Fovea Centralis
A small depression in the center of the macula lutea. Contains on cones.
Also contains biopolar and ganlion cells. These scatter light and do not cover the cones. This causes the fovea contrails to be the area of highest acuity (resolution of vision).
Lens
Found behind the pupil and iris within the cavity of the eyeball.
Refracts light.
Crystalline
Proteins within the cells of the lens.
Arranged in layers like an onion, make up the refractive media of the lens, transparent and lack blood vessels.
Anterior Cavity of the Lens
Space anterior to the lens.
Consists of 2 chambers-
1. Anterior chamber: between cornea and iris
2. Posterior chamber: lies behind the iris, in front of the zonular fibers and lens.
Filled with aqueous humor, helps maintain shape of eye ball and supplies O2 and nutrients to lens and cornea.
Aqueous Humor
A transparent watery fluid that nourished the lens and the cornea.
Continually filters out of blood capillaries in the ciliary process of the ciliary body and enters the posterior chamber. Flows forward between iris and lens, through pupil the into the anterior chamber.
Vitreous Chamber
Larger posterior cavity of the eyeball. Lies between the lens and the retina.
Contains vitreous body that helps maintain shape of eye ball.
Keeps retina attached to choroid.
Vitreous Body
Lies within the vitreous chamber.
A Transparent jellylike substance that holds the retina flush against the choroid. This gives the retina an even surface for the receptor of clear images.
Vitreal Floaters
Collections of debris that may cast a showdown in the retina. Creates an apperance of speaks that dart in and out of the filed of vision.
Common in older individuals and are harmless.
Hyaloid Canal
Narrow channel that is inconspicuous in adults. Runs through the vitreous body from the optic disc to the posterior aspect of the lens.
Intraocular Pressure
Pressure in the eye that maintains the eyeball shape. Produced mainly by the aqueous humor and partly by vitreous body.
Image Formation
- Refraction or blinding of light by the lens and cornea
- Accommodation, the change in shape of the lens
- Constriction or narrowing of the pupil.
Refraction of Light
Light rays traveling through a transparent substance like air then passes through a second transparent substance with a different density such as water, the ray bend at the junction between the 2 substances.
Refraction
Bending of light rays
75% of total refraction occurs at the cornea. Remaining 25% is at the lens to focus power and near and distance objects.
Images Focused on the Retina
Are inverted (upside down). Also undergo right to left reversal.
Convex
Surface that curses outward, like a ball. Lens will refract incoming light rays towards each other so they will eventually intersect.
Concave
Surface of a lens curves inward, like inside a hallow ball. Light rays will refract away from each other.
Accommodation
Increase in the curvature of the lens for near vision.
When the eye is focusing on a close object, the lens becomes more curved, causing greater refraction of the light rays.
Near Point of Vision
Is the minimum distance from the eye that an object can be clearly focused with maximum accommodation. About 10 cm in young adult.
Emmetropic Eye
The normal eye. Can sufficiently refract light rays from an object 6 m away so that a clear image is forced on the retina.
People who lack this ability have a refraction abnormality.
Myopia
Or nearsightedness
Occurs when the eyeball is too long relative to the focusing power of the cornea and lens or when the lens is thicker than normal. The image converges in from of the retina.
Can only see close objects clearly.
Hyperopia
Or farsightedness or hypemetropia.
The eyeball length is short relative to the focusing power of the cornea and lens, or the lens is thinner than normal. The image converges behind the retina.
Can see distance objects clearly.
Astigmatism
Where the cornea or the lens has an irregular curvature. As a result part of the image are out of focus and thus vision is blurred or distorted.
Constriction of the Pupil
Is the narrowing of the diameter of the hole through which light enters the eye due to the contraction of the circular muscles of the iris.
Binocular Vision
Both eyes focus on only one set of objects. This features allows the perception of depth and appreciation of the 3 dimensional nature of objects.
Convergence
Refers to the medial movement of the 2 eyeballs so that both are directed towards the object being viewed.
Rod and Cone Photorecptors Structure
Inner segments contain metabolic machinery for synthesis of photopigments and production of ATP.
Photopigments are integral proteins that are embedded into the membrane discs or folds of the outer segments.
Outer segments contains the cell nucleus, Golgi complex and many mitochondria.
Transduction of Light Energy
Transduction of light energy into a receptor potential occurs in the outer segment of both the rods and cones.
Photopigments
Or visual pigment
A colored protein that undergoes structural changes when it absorbs light in the outer segments of a photoreceptor.
Rhodopsin
Single type of photopigment in rods.
Cone Photopigments
3 different pigments are present in the retina. One in each 3 types of cones (blue, green and red cones).
Color vision results from different colors of light activating the different cone photopigments.
Retinal
One photopigment associated with vision.
A derivative of vitamin A, formed from carotene. Is the light absorbing part of all visual photopigments.
Carotene
Planet pigments that gives carrots their organge color.
Opsin
Glycoprotein
One of the photopigment associated with vision.
Light Adaption
Occurs when your visual system adjusts in seconds to the bright environment by decreasing its sensitivity.
Dark Adaptation
When you enter a darkened room, the visual system undergoes the darker adaption. Sensitivity increases slowly over minutes.
Phototransduction
Is the process by which light energy causes a hyper polarizing that is converted into a receptor outer potential in the outer segments of a photoreceptor. This decreases releases an inhibitory neurotransmitter glutamate.
Hearing
Is the ability to perceive sounds.
Anatomy of the Ear
3 main regions
1. External ear
2. Middle ear
3. Internal ear
External Ear
Collects sounds waves and channels them inward.
Consists of;
1. Auricle: flap of elastic cartilage shaped like the flared end of a trumpet and covered by skin.
Helix: rim of auricle. Lobule: inferior portion.
2. External Auditory Canal: curved tube about 2.5 cm long. Lies in temporal bone and leads to ear drum.
3. Tympanic membrane (eardrum): thin, semitransparent portion. Covered by epidermis, lined by simple cuboidal epi. Between these layers is CT composed of collagen, elastic fivers and fibroblasts.
Ceruminous Glands
Few specialized hairs and sweat glands
Found near the exterior opening, contain in the external auditory canal.
Secretes cerumen (earwax).
Hairs and wax prevent dust and foreign objects from entering ear.
Middle Ear
Is a small, air filled cavity in the petrous portion of the temporal bone that is lined by epithelium.
Auditory Ossicles
3 of the smallest bones in the body.
1. Malleus: attaches to the internal surface of the tympanic membrane. Malleus actuates with the body of the incus.
2. Incus: middle bone, articulates with head of stapes.
3. Stapes: the baser footplate, fits into the oval window.
Below the oval window in the round window which is enclosed by the secondary tympanic membrane.
Tensor Tympani
One of the tiny skeletal muscle that attach to the auditory ossicles.
This muscle is supplied by the mandibular branch of the Trigeminal V nerve. Limits movement and increases tension on the eardrum to prevent damage to the inner ear from loud noises.
Stapedius
One of the two skeletal muscles that attach to the auditory muscles. Smallest skeletal muscles in body.
Muscle that is supplied by the facilitator VII nerve.
Dampens large vibrations of the stapes dues to loud noises. Protects the oval window and decreases the sensitivity of hearing.
Auditory Tube
Or eustachian tube.
Opening in anterior wall leads to this tube. Consists of both bone and elastic cartilage. Connects the middle ear with the nasopharyngnx.
Inner Ear
Or labyrinth
Contains complicated series of canals.
2 main division:
1. Outer bony labyrinth: enclosures and inner membranous labyrinth.
2. Bony labyrinth: petrous portion of the temporal bone.
Bony Labyrinth
Lined with periosteum and contains perilymph (fluid). This fluid surrounds membranous labyrinth.
Divided into three ares;
1. Semicircular canals
2. Vestibule
3. Cochlea
Membranous Labyrinth
Series of epithelial spaces and tubes inside the bony labyrinth that have the same general form as the bony labyrinth.
House the receptors for hearing and equilibrium.
Contains endolymph. This fluid has high level of K+ as it plays a role in generation of auditory signals.
Vestibule
The oval central portion of the bony labyrinth. Consists of 2 sacs, (1)Utricle and (2) saccule which are connected by a small duct.
Semicircular Canals
Projects superiorly and posteriorly from the vestibule.
3 bony canals. Each lies approx. tight angles to the other 2.
Named based on positions: anterior, posterior and lateral canals.
Ampulla
Swollen enlargement at one end of each semicircular canals.
Semicircular Ducts
Portion of membranous labyrinth that lie inside the bony semicircular canals.
These structures connect with the utricle of the vestibule.
Vestibular Branch of Vestibulocochlear VIII Nerve
Consists of ampullary, uticular and saccular nerves. These nerves contain both first order sensory neurons and efferent neurons that synapse with receptors for equilibrium.
Vestibular Ganglia
Where cell bodies of sensory neuron are located in vestibular branch.
Cochlea
Anterior to the vestibule. Bony spiral canal that resembles a snail shell.
Makes almost 3 turns around a central bony core.
Divided into 3 channels
1. Cochlear duct
2. Scalia vestibuli
3. Scala tympani
Modiolus
Central bony core of cochlea
Cochlear Duct of the Cochlear
Or scala media
Is a continuation of the membranous labyrinth into the cochlea.
Filled with endolymph.
Scala Vestibuli of the Cochlea
Channel above the cochlear duct.
Ends at the narrow window.
Filled with perilymph.
Completely separated from the scala tympani by the cochlear duct.
Scala Tympani of the Cochlea
A channel below the cochlear duct.
Ends at the round window.
Filled with perilymph.
Completely separated from the scala vestibuli by the cochlear duct.
Helicotrema
Opening at the apex of the cochlea.
Membranes of the Cochlear
Vestibular membrane separates the cochlear duct from the scala vestibuli.
The basilar membrane separates the cochlear duct from the scala tympani.
Spiral Organ
Or organ of Corti
Rests on the basilar membrane.
Spiral organ that is a coiled sheet of epithelial cells, supporting cells and hair cells.
Hair Cells of the Ear
Site of transduction into sound waves.
16,000 hair cells. Receptors for hearing.
2 groups of hair cells
(1) inner hair cells: arranged in a single row (site of transduction)
(2) outer hair cells: arranged in 3 rows. ( 90% of these cells synapse with efferent neurons in the cochlear nerve)
Stereocilia
Located at the apical tip of each hair cell. Extend into the endolymph of the cochlear duct.
Long, hairlike microvilli arranges in several rows of graded height.
Tectorial Membrane
Flexible gelatinous membrane. Covers the hair cells of the spiral organ.
The ends of the stereocillia of the hair cells are embedded in the membrane.
Sound Waves
Alternating high and low pressure regions traveling in the same direction through some medium.
Pitch
Frequency of a sound vibration.
The larger the intensity of the vibration the louder is the sound.
Sound Measurement
Sound intensity is measured in units called decibels (dB).
Equilibrium
Detection of changes in balance.
Vestibular Apparatus
Receptor organs for equilibrium.
Includes: the utricle, saccule of the vestibule and semicircular ducts of the semicircular canals.
Otolithic Organs
2 types:
1. Utricle
2. Saccule
Macula
Small thicken region.
Attached to the inner walls of both the utricle and saccule.
The 2 maculae contain the receptors for the linear acceleration or deceleration and the position of the head tilt used by the equilibrium for balance.
Contains: hair cells and supporting cells.
Hair Bundle of the Ear
Collectively the stereoccilia and kinocillium.
Microvilli and cilium.
Otolithic Membrane
Found scatted amongst hair cells.
Thick, glycoproteins layer secreted by columnar supporting cells.
Otoliths
Layer of dense calcium carbonate crystals that extend over the entire surface of the Otolithic membrane.
Ampulla
Dilated portion of each semicircular duct.
Crista
Small elevation in the ampulla.
Each crista consists of a group of hair cells and supporting cells.
Cupula
Mass of gelatinous material, covers the crista.
Optic Tract Fibers
Terminate in the superior colliculi and control extrinsic eye muscles.
Ethmoid Bone
Contains crista galli and crib form plate
Facial Nerve (VII)
Parasympathetic neurons of this nerve innovates supporting cells of nasal epithelium and olfactory glands.
Damage to this nerve would cause: drooling, issues closing of the eye, picking of lips or smiling.
Visble Light
The part of the electromagnetic spectrum where light can be seen by the human eyes. The eyes can detect wavelength of light between 400nm and 700 nm.
Light at 400nm: violet
Light at 700nm: red
Electromagnetic Spectrum (Radiation)
Visible light: only light that can be seen by human eye
Gamma rays, x-rays, UV rays, infrared radiation, microwaves, radio waves.
Shape of Eye Ball
Fluid in the vitreous chamber and anterior cavity help maintain the shape of the eye.
Opsins
There are 3 different types of opsins in cones: red, blue, green
The opsin in rods is: rhodopsin
Different opsins cause the absorption of different wavelengths by the photopigment.
Found in the outer segment of a photoreceptor.
Primary Auditory Area
Located in the temporal lobe of the Cerebral Cortex and process sound awareness.
Vestibulospinal Tract
Recieves commands from the vestibular tract then down the spinal cord to skeletal muscles to help maintain equilibrium.
Auditory Pathway
- Cochlear nuclei
- Midbrain
- Thalamus
- Cerebral cortex
Cochlear Nuclei
Located in the medulla Oblongata of the brainstem.
Neurons within the cochlear branch of the Vestibulocochlear nerve synapse with neurons in the cochlear nuclei.
Isomerization
Where the cis to trans conversation of retinal when photopigments respond to light.
