CH. 15 Learning Objectives

Describe olfactory neurons, and explain how airborne molecules can stimulate action potentials in olfactory nerves.

-Odors are perceived by OLFACTORY EPITHELIUM. -Cilia are OLFACTORY HAIRS of olfactory neuron. Odors must be dissolved into mucus to be detected. Odors attach to receptors and the cilia begin to DEPOLARIZE which initiate ACTION POTENTIALS in olfactory neurons. OLFACTORY EPITHELIUM is replaced as it wears down. This is a unique characteristic as most neuron cells ARE NOT replaceable.

Trace the pathway of the action potential to the taste area of the cerebral cortex.

-Sensory neurons synapse with axons that pass through cranial nerves VII, IX, and X and enter the ganglion of those nerves. -These axons then enter the brainstem and synapse with the tractus solitarius -axons from the nucleus of the trracrtius solitaries synapse with the axons in the thalamus -axons from the thalamus terminate in the taste area of the cortex

12. Describe the pathway an action potential will travel from the rods and cones to the visual cortex.

1. Rods and cones synapse with bi-polar cells that in turn synapse with ganglion cells 2. Ganglion cells converge at the optic disc then exit via the OPTIC NERVE to send visual impulses to the VISUAL CORTEX

Describe the chambers of the eye and the fluids they contain.

Anterior compartment: anterior to lens; filled with aqueous humor and includes: -Anterior chamber: between cornea and iris -Posterior chamber: between iris and lens Vitreous chamber: posterior to lens. Filled with jelly-like vitreous humor. This helps to: -Maintain Intraocular pressure -Hold lens and retina in place

List the accessory structures of the eye, and explain their functions.

EYEBROW: Keeps sweat out of eye/Shade EYELIDS: 5 layers of tissue that helps maintain shape of eyelid Palpebral fissure: space between eyelids. Canthi: located lateral and medial, where eyelids meet. Conjunctiva: thin transparent mucous membrane Palpebral conjunctiva: inner surface eyelids Bulbar conjunctiva: anterior surface of eye except over pupil More Eye Structures: Lacrimmal Appartus: prodded tears

Name the tunics of the eye, list the parts of each tunic, and describe the functions of each part.

FIBROUS TUNIC!!!! SCLERA: white outer structure maintains shape of eye and provides muscle attachment points Cornea: Allows light to enter eye as well as bending and refracting of it VASCULAR TUNIC!!!!! Iris: colored part of the eye. Controls light entering the pupil. Smooth muscle determines size of pupil. Ciliary Body: produces aqueous humor that fills anterior chamber Choroid: Supplies blood to the retina Retina: Converts received light into neural signals and sends them to the brain for vital recognition Ciliary body: produces aqueous humor that fills anterior chamber

EYE DISEASES

Myopia: Nearsightedness Focal point too near lens, image focused in front of retina Hyperopia: Farsightedness Image focused behind retina Presbyopia Degeneration of accommodation, corrected by reading glasses Astigmatism: Cornea or lens not uniformly curved Strabismus: Lack of parallelism of light paths through eyes Retinal detachment Can result in complete blindness Glaucoma Increased intraocular pressure by aqueous humor buildup Cataract Clouding of lens Macular degeneration Common in older people, loss in acute vision Diabetes; Dysfunction of peripheral circulation

Locate the areas of the brain where olfaction is processed. (this process does not go through the thalamus, it is the only major sense that does not)

Olfactory Bulb tracts in cribriform plate ——-> Olfactory Cortex (conscious perception of smell) ———> Medial Olfactory Area (emotional odor area) ———-> Intermediate Olfactory Area (info from medial area) ——-> Intermediate axons go to olfactory bulb and modulates activity of olfactory bulb axons.

Explain the differences between the rods and cones.

RODS: Photoreceptor cells that supply black and white vision. The protein Rhodopsin changes shape when hit by light Rods are SENSORY cells that light cause to HYPERPOLARIZE CONES: Are responsible for color vision and visual acuity. Visual pigment is constructed of IODOSPIN that responds to RED, BLUE, and GREEN light.

Describe the formation of an action potential in a taste cell for each type of tastants.

Salt: Sodium ions diffuse in Na+ channels and result in depolarization Sour (acid): H+ ions cause depolarization by, (1) enter direct through H+ channels (2) bind to gated K+ channels causing K+ to not leave the cell (3) They can open ligand gated channels for other positive charged ions. Sweet: Cause depolarization after binding to receptor cell by means of a G PROTEIN MECHANISM, this closes K+ ion channels and the channels close resulting in depolarization. Bitter: bind to receptor and depolarize through a G PROTEIN MECHANISM Umami: Amino acids like glutamate bind to receptor cell and depolarize through a G PROTEIN MECHANISM. CA2+ channels are opened and depolarization begins with influx of Ca2+

List the five major tastants. Relate the relationship of taste to smell.

Sour: Most sensitive receptors on lateral aspects of tongue Salty: Most sensitive receptors on tip of tongue (shares lowest sensitivity with sweet) Bitter: Most sensitive receptors on posterior aspect of tongue Sweet: Most sensitive receptors on tip of tongue (shares lowest sensitivity with salty) Umami: Scattered sensitivity caused by amino acids Taste has very rapid adaptation and the lowest threshold for the 5 tastings is bitterness of which many alkaloids contain and are poisonous.

Explain the processes involved in olfactory adaptation.

The Olfactory Bulb has branches called "Dendrites". The Dendrites contain "Cilia" which have odor receptors. An Action Potential is then sent to the Olfactory Bulb. Calcium Ions can send or stop impulses to the brain to the scent is no longer detected. An example of neural adaptation is to prevent the overloading the the neural system so other dangerous odors can be detected once one is deemed that it is not a threat.

Describe the structure of the retina, and explain how light stimulates action potentials in the optic nerves.

The retina is a thin layer of tissue that lines the back of the eye on the inside. It is located near the optic nerve. The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition. Exposure of the retina to light hyperpolarizes the rods and cones, The now-active bipolar cells in turn stimulate the ganglion cells, which send action potentials along their axons (which leave the eye through the optic nerve).

Relate the arrangement of the visual field to binocular vision and depth perception.

The right part of each visual field projects to the left side of the brain the left part of each visual field projects to the right side of the brain. Binocular vision: visual fields partially overlap yielding depth perception

Relate how images are focused on the retina.

Visual acuity of enhanced by isolating individual photo receptors which reduces light scattering. The image is left-right reversed and inverted in the retina.

Accommodation

the process by which the eye's lens changes shape to focus near or far objects on the retina