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.