EXAM 4 CHAPTER 17

Define gustation.

Gustation is the sense of taste, provided by gustatory epithelial cells (taste receptors) responding to dissolved chemical stimuli.

If you completely dry the surface of your tongue and then place salt or sugar on it, you can't taste the substance. Why not?

Gustatory epithelial cells (taste receptors in taste buds) are sensitive only to molecules and ions that are in solution. If you dry the surface of your tongue, the salt ions or sugar molecules have no moisture in which to dissolve, so they will not stimulate the cells.

How would a blockage of the scleral venous sinus affect your vision?

If the scleral venous sinus (canal of Schlemm) were blocked, the aqueous humor could not drain, producing an eye condition called glaucoma. Accumulation of this fluid increases the pressure within the eye, distorting soft tissues and interfering with vision. If untreated, the condition would ultimately cause blindness.

Define olfaction.

Olfaction is the sense of smell; it involves olfactory sensory neurons in paired olfactory organs responding to airborne chemical stimuli.

Rods

PHOTORECEPTOR do not discriminate among colors of light, highly sensitive to light, they enable us to see in dimly lit rooms, at twilight, and in pale moonlight

Cones

PHOTORECEPTOR give us color vision, cones give us sharper, clearer images than rods do, but cones require more intense light, sharpness

As Sue enters a dimly lit room, most of the available light becomes focused on the fovea centralis of her eye. Will she be able to see very clearly?

Sue will likely be unable to see at all. The fovea centralis (fovea) contains only cones, which need high-intensity light to be stimulated. The dimly lit room contains light that is too weak to stimulate the cones.

Which layer of the eye would be affected first by inadequate tear production?

The conjunctiva would be the first layer of the eye affected by inadequate tear production. Drying of the conjunctiva would produce an irritated, scratchy feeling.

Define focal point.

The focal point is the point at which the light rays from an object intersect on the retina.

How does the lens change shape?

The lens is held in place by the ciliary zonule that originates at the ciliary body. Smooth muscle fibers in the ciliary body act like sphincter muscles. When the ciliary muscle contracts, the ciliary body moves toward the lens, thereby reducing the tension in the ciliary zonule. The elastic capsule then pulls the lens into a rounder shape that increases the refractive (bending) power of the lens.

Why don't you see a blank spot in your field of vision?

The reason is that involuntary eye movements keep the visual image moving and allow your brain to fill in the missing information.

VISON

VISON

When the lens of your eye is more rounded, are you looking at an object that is close to you or far from you?

When the lens becomes more rounded, you are looking at an object that is close to you.

Your grandfather can't understand why foods he used to enjoy just don't taste the same anymore. How would you explain this to him?

Your grandfather is experiencing the effects of several age-related gustatory and olfactory changes. The number of taste buds decreases dramatically after age 50, and those that remain are not as sensitive as they once were. In addition, the loss of olfactory sensory neurons contributes to the perception of fewer flavors in foods.

Lacrimal caruncle

a mass of soft tissue, contains glands producing the thick secretions that contribute to the gritty deposits that sometimes appear after a good night's sleep

Umami

a pleasant, savory taste imparted by the amino acid glutamate present in taste buds of the vallate papillae

Focal point

a specific point of intersection on the retina

Cornea

a transparent part of the outer fibrous layer of the eye, the cornea is covered by a very delicate squamous corneal epithelium, five to seven cells thick, that is continuous with the bulbar conjunctiva

Scotoma

abnormal blind spot

Salt and sour channels

activate chemically gated ion channels resulting in cell depolarization

Tarsal glands

along the inner margin of the lid are small, modified sebaceous glands secrete oil onto eyelashes, secrete a lipid-rich substance that helps keep the eyelids from sticking together

Vallate (vallum, wall) papillae

appear as an inverted "V" near the posterior margin of the tongue there are up to 12 vallate papillae, and each contains as many as 100 taste buds

Visual pigments

are derivatives of the compound rhodopsin, or visual purple, the visual pigment found in rods

Sweet, bitter, and umani receptors

are linked to G proteins called gustducins of which are protein complexes that use second messengers to produce their effects

Olfactory organs

are located in the nasal cavity on either side of the nasal septum, contain olfactory sensory neurons

Fungiform (fungus, mushroom) papillae

are scattered around the tongue with concentration along the tip and sides, each small fungiform papilla contains about 5 taste buds

Olfactory reception

begins with the binding of an odorant to a G protein-coupled receptor in the plasma membrane of an olfactory dendrite, this creates a depolarization called a generator potential, this potential leads to the generation of action potentials, which are then carried to the CNS by sensory afferent fibersGs

Three types of cones

blue cones, green cones, and red cones, each type has a different form of opsin and is sensitive to a different range of wavelengths, their sensitivities overlap, but each type is most sensitive to a specific portion of the visual spectrum red cones are the most abundant

Corneoscleral junction

border between cornea and sclera

Lingual papillae

bumps and projections on the tongue that are the sites of the taste buds FOUR TYPES

Intra-ocular pressure

can be measured in the anterior chamber, where the fluid pushes against the inner surface of the cornea

Horizontal and amacrine cells

can facilitate or inhibit communication between photoreceptors and ganglion cells, altering the sensitivity of the retina, these cells play an important role in the eye's adjustment to dim or brightly lit environments

Flavor

combination of taste and smell

Water receptors

concentrated in pharynx, provide information to hypothalamus for water balance regulation sensory output of these receptors is processed in the hypothalamus and affects several systems that affect water balance and the regulation of blood volume

Sclera

consists of a dense fibrous connective tissue containing both collagen and elastic fibers, this layer is thickest over the posterior surface of the eye, near the exit of the optic nerve cornea is structurally continuous with the sclera

Rhodopsin

consists of a protein, opsin, bound to the pigment retinal synthesized from vitamin A, all rods contain the same form of opsin, cones contain the same retinal pigment that rods do, but the retinal is attached to different forms of opsin

Fibrous layer

consists of the whitish sclera and the transparent cornea, the fibrous layer (1) supports and protects the eye, (2) serves as an attachment site for the extrinsic eye muscles, and (3) contains structures that assist in focusing

Cornea

consists primarily of a dense matrix containing multiple layers of collagen fibers, organized so as not to interfere with the passage of light no blood vessels but most sensitive part of the eye due to multiple free nerve endings

Taste buds

contains about 40-100 gustatory epithelial cells and many small stem cells called basal epithelial cells each gustatory epithelial cell extends microvilli, sometimes called taste hairs, into the surrounding fluids through the taste pore, a narrow opening, despite this relatively protected position, it's still a hard life: a typical gustatory epithelial cell survives for only about 10 days before it is replaced

Vascular layer

contains numerous blood vessels, lymphatic vessels, and the intrinsic (smooth) muscles of the eye, this middle layer (1) provides a route for blood vessels and lymphatics that supply the tissues of the eye; (2) regulates the amount of light that enters the eye; (3) secretes and reabsorbs the aqueous humor that circulates within the chambers of the eye; and (4) controls the shape of the lens, an essential part of the focusing process CHOROID, CILIARY BODY, IRIS

Pigmented layer of retina

contains pigment cells that support the functions of the photoreceptors, which are located in the neural layer of the retina absorbs light that passes through the neural layer, preventing light from bouncing (reflecting) back through the neural layer and producing visual "echoes"

Olfactory epithelium

contains the olfactory sensory neurons, supporting cells, and regenerative basal epithelial cells (stem cells) epithelium covers the inferior surface of the cribriform plate, the superior portion of the perpendicular plate, and the superior nasal conchae of the ethmoid, the second layer, the underlying lamina propria, consists of areolar tissue, numerous blood vessels, and nerves

Conjunctiva

covering the inner surfaces of the eyelids and the outer surface of the eyeball mucous membrane covered by a specialized stratified squamous epithelium

Palpebral conjunctiva

covers the INNER SURFACE of the eyelids

Astigmatism

defective curvature of the cornea or lens of the eye

Nasolacrimal duct

delivers tears to the nasal cavity on that side

Filiform (filum, thread) papillae

filiform papillae are found in the anterior two-thirds of the tongue running parallel to the midline groove, they do not contain taste buds, but they do provide an abrasive coat that creates friction to help move food around the mouth

Aqueous humor

fluid produced by the ciliary body and found in the anterior chamber and posterior chamber, maintains the shape of the eye Unlike the aqueous humor, the vitreous body is formed during development and is not replaced

Lens

focuses light onto retina provides the extra refraction needed to focus the light rays from an object toward a focal point

Tastes along the axis of the tongue

greatest sensitivity to salty-sweet anteriorly and sour-bitter posteriorly NO DIFFERENCE IN THE STRUCTURE OF TASTE BUDS

Macula

has no rods the highest concentration of cones occurs at the center of the macula, an area called the FOVEA CENTRALIS site of the sharpest color vision

Olfactory sensory neurons

highly modified nerve cells exposed tip of each sensory neuron forms a prominent dendritic bulb that projects beyond the epithelial surface the dendritic bulb is a base for up to 20 cilia-shaped dendrites that extend into the surrounding mucus, these dendrites lie parallel to the epithelial surface, exposing their considerable surface area to odorants

Lens fibers

highly specialized cells have lost their nuclei and other organelles, they are long and slender and are filled with transparent proteins called crystallins, these proteins give the lens both its clarity and its focusing power

Glaucoma

if aqueous humor cannot drain into the scleral venous sinus, intra-ocular pressure rises due to the continued production of aqueous humor, and glaucoma results

Looking at a dim star

in very dim light, cones cannot function, that is why you can't see a dim star if you stare directly at it, but you can see it if you shift your gaze to one side or the other, shifting your gaze moves the image of the star from the fovea centralis, where it does not provide enough light to stimulate the cones, to the periphery, where it can affect the more sensitive rods

Neural layer of retina

inner layers of the retina contain supporting cells and neurons that do preliminary processing and integration of visual information, the outermost part, closest to the pigmented layer of the retina, contains the photoreceptors, the cells that detect light

Near point of vison

inner limit of clear vision, is determined by the degree of elasticity in the lens

Lens

is a transparent, biconvex (outwardly curving) flexible disc that lies posterior to the cornea and is held in place by the ciliary zonule that originates on the ciliary body of the choroid the primary function of the lens is to focus the visual image on the photoreceptors, the lens does so by changing its shape

Accomodation

is the automatic adjustment of the eye to give us clear vision, during accommodation, the lens becomes rounder to focus the image of a nearby object on the retina, the lens becomes flatter to focus the image of a distant object on the retina

Disc shed

new discs containing visual pigment are continuously assembled at the base of the outer segment of both rods and cones, a completed disc then moves toward the tip of the segment, after about 10 days, the disc is shed in a small droplet of cytoplasm, ahe pigment cells absorb droplets with shed discs, break down the disc membrane's components, and reconvert the retinal to vitamin A, the pigment cells then store the vitamin A for later transfer to the photoreceptors

Foliate papillae

on side walls of tongue are found as a series of folds along the lateral margins with taste buds embedded in their surfaces

Bipolar neurons

one axon and one dendrite

Palpebral fissure

opening between eyelids

Optic disc

optic disc has no photoreceptors or other structures typical of the rest of the retina, because light striking the optic disc goes unnoticed, this area is commonly called the blind spot

Refraction

or bent, when it passes from one medium to another medium with a different density

Bulbar conjunctiva

or ocular conjunctiva, covers the ANTERIOR SURFACE of the eye

Eyelids

or palpebrae

Intrinsically photosensitive retinal ganglion cell (ipRGC)

photopigment in the ipRGC is melanopsin, these cells are known to respond to different levels of brightness and influence the body's 24-hour circadian rhythm (biological clock)

Lacrimal apparatus

produces, distributes, and removes tears the lacrimal apparatus of each eye consists of (1) a lacrimal gland with associated ducts, (2) paired lacrimal canaliculi, (3) a lacrimal sac, and (4) a nasolacrimal duct

Stimulus and cones

provide information about the wavelength of arriving photons, giving us the perception of color

Bleaching

rhodopsin is broken apart into retinal and opsin before recombining with opsin, the retinal must be enzymatically converted back to its original shape, this conversion requires energy in the form of ATP (adenosine triphosphate), and it takes time, then rhodopsin is regenerated by being recombined with opsin, bleaching and regeneration is a cyclical process contributes to the lingering visual impression you have after you see a camera's flash opsin is inactivated when bleaching occurs, and the breakdown of cGMP halts as a result, as other enzymes generate cGMP in the cytosol, the chemically gated sodium ion channels reopen

Stimulus and rods

rods provide the central nervous system with information about the presence or absence of photons, with little regard to their wavelength

Olfaction

sense of smell

Gustation

sense of taste

Where do these taste nerve takes this stimulus?

sensory afferent fibers carried by these cranial nerves synapse in the solitary nucleus of the medulla oblongata, axons of the postsynaptic neurons then enter the medial lemniscus, there, the neurons join axons that carry somatic sensory information on touch, pressure, and proprioception, after another synapse in the thalamus, the information is sent to the appropriate portions of the gustatory cortex of the insula

Visual acuity

sharpness of vision when visual acuity falls below 20/200, even with the help of glasses or contact lenses, the individual is considered to be legally blind

Gustatory pathways

starts with taste buds, which are innervated by cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus) (facial nerve innervates all the taste buds located on the anterior two-thirds of the tongue, from the tip to the line of vallate papillae, the glossopharyngeal nerve innervates the vallate papillae and the posterior one-third of the tongue, the vagus nerve innervates taste buds scattered on the surface of the epiglottis)

phenylthiocarbamide (PTC)

substance tastes bitter to some people, but is tasteless to others

Primary taste sensations

sweet, sour, salty, bitter, umami

Lacrimal gland

tear gland provides the key ingredients and most of the volume of the tears that bathe the conjunctival surfaces, the lacrimal secretions supply nutrients and oxygen to the corneal cells by diffusion, the lacrimal secretions are watery and slightly alkaline contain lysozyme

Olfactory cortex

temporal lobe interpretation

Ciliary body

the ciliary zonule (suspensory ligament) is the ring of fibers that attaches the lens to the ciliary processes, the connective tissue fibers hold the lens in place posterior to the iris and centered on the pupil, as a result, any light passing through the pupil also passes through the lens composed of ciliary muscle

Photoreception

the detection of light

Focal distance

the distance between the center of the lens and its focal point

Focal distance is determined by what factors?

the distance of the object from the lens, the closer an object is to the lens, the greater the focal distance the shape of the lens, the rounder the lens, the more refraction occurs, so, a very round lens has a shorter focal distance than a flatter one

Human eye refraction

the greatest amount of refraction occurs when light passes from the air into the corneal tissues, which have a density close to that of water, when you open your eyes under water, you cannot see clearly because refraction at the corneal surface has been largely eliminated, light passes unbent from one watery medium to another

Detached retina

the neural layer of the retina becomes separated from the pigmented layer resulting in the two parts of the retina are reattached, the photoreceptors will degenerate and vision will be lost

Gustatory epithelial cells

the receptor cell responsible for taste sensation, developed from support cells, taste buds are distributed over the superior surface of the tongue and adjacent portions of the pharynx and larynx

accessory structures of the eye

the superficial epithelium of the eye, as well as the structures involved with the production, secretion, and removal of tears

Olfactory glands

their secretions absorb water and form thick, pigmented mucus

Cateract

transparency of the lens depends on the crystallin proteins maintaining a precise combination of structural and biochemical characteristics, because these proteins are not renewed, any modifications they undergo over time can accumulate and result in the lens losing its transparency

Olfactory pathways

unlike in the other sensory systems, neural signals do not pass through the thalamus before reaching high cortical levels in the brain begins with afferent fibers leaving the olfactory epithelium that collect into 20 or more bundles, these bundles penetrate the cribriform plate of the ethmoid bone to reach the olfactory bulbs of the cerebrum, where the first synapse occurs, efferent fibers from nuclei elsewhere in the brain also innervate neurons of the olfactory bulbs axons leaving the olfactory bulb travel along the olfactory tract to the olfactory cortex of the cerebral hemispheres, the hypothalamus, and portions of the limbic system REACHES THE CEREBRAL CORTEX

Odorants

water-soluble and lipid-soluble substances a normal, relaxed inhalation carries a small sample (about 2 percent) of the inhaled air to the olfactory organs

Aging and taste

we begin life with more than 10,000 taste buds, but by the time we reach adulthood, the taste receptors on the pharynx, larynx, and epiglottis have decreased in number

Fovea

when you look directly at an object, its image falls on this portion of the retina, an imaginary line drawn from the center of that object through the center of the lens to the fovea centralis establishes the visual axis of the eye

Bleaching process

1) upon absorbing light, rentinal changes to a more linear shape (trans) and opsin is activated 2) opsin activation changes the Na+ permeability of the outer segment and this in turn, affects neurotransmitter release 3) this is detected by the bipolar neurons and ganglion cells, the location of the stimulus is detected in a specific area of the retina by the arriving photons 4) after absorption of the photon, rhodopsin begins to break down into retinal and opsin, BLEACING 5) The retinal is converted into its original shape, CIS, this conversion needs ATP 6) after the retinal has been converted, it can recombine with opsin to repeat the process sensitivity decreases as bleaching occurs

Our eyes are sensitive to wavelengths of

700-400 nm rainbow, visible light is also described as being made up of photons, small energy packets with characteristic wavelengths photons of red light carry the LEAST energy and have the LONGEST wavelength, photons from the violet portion of the spectrum contain the MOST energy and have the SHORTEST wavelength.

Amacrine cells are found where what other types of cells synapse? Horizontal cells are found where what other types of cells synapse?

Amacrine cells are found where bipolar cells synapse with ganglion cells. Horizontal cells are found where photoreceptors (rods and cones) synapse with bipolar cells.

Trace the olfactory pathway, beginning at the olfactory epithelium.

Axons from the olfactory epithelium collect into bundles that reach the olfactory bulb. In the olfactory pathway, axons leaving the olfactory bulb then travel along the olfactory tract to the olfactory cortex, hypothalamus, and portions of the limbic system.

When you first enter the A&P lab for dissection, you are very aware of the odor of preservatives. By the end of the lab period, the smell doesn't seem to be nearly as strong. Why?

By the end of the lab period, central adaptation has occurred. Inhibition of synapses along the olfactory pathway reduces the amount of information reaching the olfactory cortex, even though the olfactory neurons remain active.