Olfactory neurons in the olfactory epithelium (10 million)
Axons of bipolar neurons extend through cribriform plate to the olfactory bulb. Dendrites extend to the epithelial surface of the olfactory recess and enlarge into olfactory vesicles.
Odorants bind to chemoreceptor molecules, Depolarize and initiate action potentials in neurons, Low threshold for odor detection
Binds to a chemoreceptor on the olfactory hair membrane and causes depolarization of the membrane and initiates action potentials in the olfactory neurons.
Seven primary odors
1) camphoraceous, 2) musky, 3) floral, 4) pepperminty, 5) ethereal, 6) pungent, and 7)putrid. More than one type of odorant can stimulate a receptor.
Most have very poor replication abilities, but are constantly being replaced. The entire epithelium, including the neurosensory cells, are replaced about every two months. Replaced by a proliferation of basal cells in the olfactory epithelium.
Bundles of unmyelinated axons extend through approximately 20 olfactory foramina in the cribriform plate from each nasal cavity. Collectively these bundles are the olfactory nerves, (cranial nerve I). The olfactory neuron bundles synapse with mitral cells and/or tufted cells. These cells relay information via the olfactory tracts and synapse with association neurons in the olfactory bulb. The association neurons also receive information from nerve cell processes that enter the olfactory bulb from the brain. Thus association neurons can modify olfactory information before it leaves the olfactory bulb. The olfactory tract terminates in the olfactory cortex. It is the only major sensation that goes directly to the cerebral cortex without first passing through the thalamus.
Lateral olfactory area
located in the temporal lobe. More specifically within the lateral fissure of the cerebrum. Responsible for the conscious perception of smell
Medial olfactory area
responsible for the visceral and emotional reactions to odors, with connections to the limbic system, and subsequently to the hypothalamus
Intermediate olfactory area
located along the nerve tract to the olfactory bulb and is involved in the modulation of sensory information and accommodation
(about 10,000) mostly located on the papillae, but are also found on the lips, throat, and palate, and more so in children. Each consists of about 50 gustatory cells that are continuously replaced, each cell lasting about 10 days
filament shaped. no taste buds but most numerous on the surface of the tongue. provide rough surface for food to be manipulated more easily
Histology of taste buds
Sensory cells of each taste bud consist of about 50 taste (gustatory) cells. Nonsensory cells are basal cells and supporting cells
Function of taste buds
Receptors on hairs detect dissolved substances called tastants. These taste cells have no axons so cannot generate action potentials, but instead release neurotransmitters which cause associated sensory neurons to depolarize.
Factors that Affect Taste
texture, temperature of food, combination, adaptation occurs within 1-5 min, variation of thresholds, olfactory sensations, appetite
The Chorda tympani
crosses tympanic membrane but it is really actually involved in TASTE!! Not hearing
Eye, Accessory structures (Eyebrows, eyelids, eyelashes, tear glands that lubricate and protect eyes from sunlight and damaging particles), Optic nerve (II) (Tracts and Pathways), Eyes respond to light and initiate afferent action potentials
are double or triple rows of hairs along the free edges of the eyelids (palpebrae) that help protect the eyes.
are modified sweat glands that lubricate the lashes. The plugging or inflammation of one of these glands = sty
Meibomian or tarsal glands
produce sebum which lubricates the palpebrae and restrains tears from overflowing the margins of the eyelids. A blockage or infection is referred to as a chalazion, or a meibomian cyst.
thin transparent mucous membranes that cover the inner surface of the eyelid and the anterior surface of the eye.
is an irritation or infection of the conjunctiva. Acute contagious conjunctivitis caused by bacteria is commonly called "pinkeye."
are located in the lateral corners of the orbit and lubricate the eye. Most of the fluid evaporates, but excess fluid is collected in the lacrimal canaliculi which connects to the nasal cavity.
Three coats or tunics. Fibrous: Consists of sclera and cornea. Vascular: Consists of choroid, ciliary body, iris. Nervous: Consists of retina
White outer layer, maintains shape, protects internal structures, provides muscle attachment point, continuous with cornea.
Allows light to enter eye and bends and refracts it as part of focusing. Avascular and transparent due to proteoglycans small collagen fibers, and low water content.
Inner. Contains neurons sensitive to light. Contains 120 photoreceptor cells called rods and 6 or 7 million cones. Center of posterior retina has a macula, at the center of this is the fovea centralis where light is focused. Portion with greatest visual acuity because photoreceptor cells are more tightly packed. Optic disc is medial to macula.
Anterior & Posterior compartments
Aqueous humor circulated via the canal of Schlemm. Helps maintain intraocular pressure
Vitreous or Postremal compartments
Vitreous humor, thicker and not as rapidly turned over and exchanged. Helps maintain eyeball shape and intraocular pressure. Holds lens and retina in place
Functions of the eye
like a camera in some respects, iris allows light into eye, then cornea, lens, humors focus light onto retina, light striking retina is converted into action potentials relayed to brain
Portion of electromagnetic spectrum detected by human eye: 400-700 nm. Each color is a different wavelength
Light striking a convex surface. As they converge they cross and a focal point occurs (focusing)
Far point of vision
The distance at which the lens does not have to thicken for focusing to occur - 20 feet or more from the eye.
Near point of vision
The closest distance at which the eye can focus. Things closer start to blur. This point is usually 2-3 inches for children and up to 60 inches for 80 year olds. (Accommodation, Pupil constriction, Convergence)
120 million rods in the retina. Photoreceptor portion of each rod contains 700 double layered membranous disks containing rhodopsin.
6-7 million in the retina. Vital for color vision & visual acuity. Use iodopsin visual pigment. As light decreases, fewer cone cells respond to dim light.
Degeneration of accommodation, corrected by reading glasses; regular sight problems with age
Can result in complete blindness; a hole or tear in retina allowing fluid to accumulate between neural and pigmented layers
Increased intraocular pressure by inhibition of aqueous humor circulation (causing build up)
Hearing; terminates at eardrum or tympanic membrane. Includes auricle or pinna (elastic cartilage covered by skin) and the external acoustic meatus.
Hearing; air filled space that contains auditory ossicles. Auditory, pharyngotympanic, or eustachian tube, and oval window.
External Acoustic Meatus
Part of external ear. Lined with hairs and ceruminous glands that produce cerumen (earwax)
Auditory or pharyngotympanic (eustachian) tube
Part of middle ear. Passage way that opens into pharynx, equalizes pressure.
Part of inner ear that is bony and contains membranous labyrinth (outer surface covered with perilymphatic cells)
Fills the space between the membranous and bony labyrinths. Similar to cerebrospinal fluid, high concentrations of Na+ & low concentrations of K+.
Of the vestibule. Evaluates position of head relative to gravity, Detects linear acceleration and deceleration. Utricle and saccule.
Patch of epithelium on utricle and saccule. Consists of support cells & hair cells which contain many microvilli called stereocilia and one kinocilium embedded in gelatinous mass containing otoliths
The base of each semicircular canal. Contains crista ampullaris, cupula, which is displaced by fluid movements within the semicircular canals which bend the hairs and initiates action potentials.
Dysfunction caused by lack of normal stimulation from the vestibule and semicircular canals
Aging effects on special senses
Slight loss in ability to detect odors, Decreased sense of taste, Lenses of eyes lose flexibility, Development of cataracts, macular degeneration, glaucoma, diabetic retinopathy, Decline in visual acuity and color perception, Decrease in hearing and balance
Area in the retina, at the center of which is the fovea centralis: Area of greatest visual acuity.
At the center of the macula in the retina. Contains 35,000 cones and no rods so it contributes to visual acuity.