A&P II Lecture: Chapter 15

important terms - taken from lecture

special senses

smell, taste, vision, hearing, & vestibular sensation

transduction

the conversion of stimuli into electrical signals that can be interpreted by the CNS

olfactory epithelium

in superior nasal cavity; penetrates ethmoid bone at cribriform plate

what are the 3 types of cells in the olfactory epithelium

olfactory neurons, basal cells, supporting cells

what are the 3 anatomical structures of the olfactory epithelium?

olfactory nerve (CN I), olfactory bulb, olfactory tract

odorants

detected by olfactory neurons; chemical stimuli are transduced to electrical signals which are transmitted to regions of the brain for identification

step 1 in activation of olfactory receptors

binding of an odorant to its receptor activates G-protein

step 2 in activation of olfactory receptors

activated G-protein triggers enzyme adenylate cyclase to convert ATP into cyclic AMP (cAMP)

step 3 in activation of olfactory receptors

cAMP opens ion channels that allow sodium & calcium ions to enter cell; causes depolarization & action potential generation if threshold is reached

step 1 of olfactory pathway

axons of olfactory neurons (olfactory nerve) carry olfactory stimuli to olfactory bulb in CNS & synapse w dendrites of mitral cells in olfactory bulb

step 2 of olfactory pathway

olfactory tract that travels between olfactory bulb & primary olfactory cortex in temporal for awareness & identification of odor (no synapse in thalamus)

step 3 of olfactory pathway

hypothalamus & components of limbic system receive info from the primary olfactory cortex, which evokes emotional & visceral responses to odors

step 4 of olfactory pathway

integration of frontal lobe

anosmia

lack of olfaction

hyposmia

reduced olfactory sensitivity

gustatory sense/taste

involves chemoreceptors that are stimulated by various chemicals (also olfactory chemoreceptors, thermoreceptors, & nociceptors)

taste buds

small clusters of specialized receptor cells and supporting cells scattered about tongue and other surfaces of oral cavity

papillae

rounded projections that cover the tongue

vallate (circumvallate) papillae

largest; contains 100s of taste buds

fungiform papillae

mushroom-shaped; contain only a few taste buds

foliate papillae

sides of tongue; only contain taste buds in childhood

filiform papillae

long, thin cylinders scattered across tongue; contain sensory nerve endings that detect food texture and temperature

gustatory (taste) cells

specialized epithelial cells with microvilli that project into a small opening on papilla surface; CN VII, IX, X

taste pore

small opening on papilla surface

basal cells (gustation)

stem cells that continuously differentiate into new gustatory cells

supporting cells (gustation)

surround and physically support gustatory cells but have no role in taste sensation

5 taste sensations/receptors

sweet, sour, salty, bitter, umami

sweet tastes

elicited by simple sugars; glucose & fructose; can cause accidental poisoning; G-protein

sour tastes

produced by hydrogen ions such as citric acid found in lemon juice; H+ leak channel

salty tastes

elicited by presence of metal ions such as sodium and potassium ions; Na+/K+ leak channel

bitter flavors

produced by nitrogen-containing compounds; commonly found in poisonous substances; G-protein

umami (savory) taste

taste associated with meat or broth; produced by glutamate or other amino acids; G-protein

taste receptors

classified by substance they detect, with only one type of receptor associated with an individual gustatory cell

activation of taste receptors

substance must first dissolve in saliva before it can reach a taste bud where it may be detected as a gustatory stimulus

step 1 in activation of taste receptors

chemical dissolves in saliva and changes in ion movements depolarize the gustatory cell’s plasma membrane (Gradients Core Principle)

step 2 in activation of taste receptors

Depolarization of membrane opens voltage-gated calcium ion channels, and calcium ions enter cell

step 3 in activation of taste receptors

Calcium ions trigger release of neurotransmitters; produce an action potential in axon of sensory neuron

step 1 of the gustatory pathway

axons of the facial, glossopharyngeal & vagus nerves carry taste stimuli from the tongue into the CNS

step 2 of the gustatory pathway

axons of these 3 nerves terminate in the solitary nucleus in the medulla oblongata by synapsing on central sensory neurons

step 3 of the gustatory pathway

axons from the solitary nucleus synapse on neurons in the thalamus, which then send the taste signals to the primary gustatory cortex in the parietal lobe

strabismus

“lazy eye”; – disorder present at birth where eyeballs are not properly aligned with one another; leads to diplopia (double vision)

fibrous layer of eyeball

outermost layer

sclera

white part of eye; made of irregularly arranged collagen fibers that allow it tt maintain its shape

cornea

continuous with sclera anteriorly but is translucent instead of opaque due to parallel arrangement of its collagen fibers; avascular; allows light to pass into eyeball

vascular layer of eyeball

middle layer

choroid

contains capillaries and a pigment that minimizes scattering of incoming light rays

ciliary body

ring of smooth muscle that surrounds lens

suspensory ligaments

connect ciliary body to lens which allows for contraction and relaxation; changes shape of lens to focus light

iris

colored region of anterior eye; amount of pigment melanin determines iris color

lens

slightly flattened sphere found behind pupil and iris; focuses light on retina from objects near eye

lens fibers

lack nuclei making them translucent} ;cataracts-clouded lens

pupil

opening found in center of iris through which light enters eyeball

neural layer of eyeball

innermost layer

pigmented epithelium

absorbs and reduces scattering of light

photoreceptor cells

found in retina detect and transduce light stimuli into electrical signals

fovea centralis

central region of macula; contains a large number of photoreceptor cones; allows for detailed vision and ability to focus on an object

macula lutea

yellowish region of retina; contains a large number of photoreceptors

optic disc

location where optic nerve exits from retina; does not contain photoreceptors; called blind spot

posterior cavity/segment

larger cavity found behind lens; filled with a gelatinous material called vitreous humor

anterior cavity/segment

in front of lens and ciliary body; filled with aqueous humor; divided into two chambers

aqueous humor

watery fluid secreted by ciliary body and drained by scleral venous sinus

posterior chamber of anterior cavity

between lens and iris

anterior chamber of anterior cavity

between iris and cornea

glaucoma

overproduction or inadequate drainage of aqueous humor

visible light

range of wavelengths that human eye can detect as a range of particular colors

color of shorter wavelengths

blue & violet

color of longer wavelengths

red

refraction

light rays are bent as they pass through water or eye structures

convex lens

surface that bulges outward in its middle region; causes light rays to converge or focus as they pass through

concave lens

thicker on edge and is depressed in its middle region; causes light rays to diverge or spread out (unfocused)

accommodation

(CN III) ciliary body contracts and lens thickens bringing more refraction so more light rays are focused on retina for close vision

pupillary constriction

parasympathetic response reduces scattering of light; objects appear more focused (CN III)

convergence

(CN III) eyeballs move more medially to direct light rays on to photoreceptor-dense region of fovea

emmetropic vision

ciliary body relaxes & flattens the lens for distant vision

hyperopia

eyeball is too short

myopia

eyeball is too long

cones

photoreceptors that function best in bright light for processing high-resolution color vision

rods

photoreceptors that do not detect colors; instead, rods are most sensitive in low light and as component of peripheral vision

layers of retina from deep to superficial - transduction

photoreceptors, bipolar, ganglion

photoreceptors

rods and cones; adjacent to outer pigmented epithelial layer of retiina

bipolar cells

neurons that communicate with retinal ganglion cells

ganglion cells

in most anterior region of retina; axons form optic nerve (CN II)

horizontal cells & amacrine cells

cells involved in image processing

rhodopsin

composed of protein opsin and pigment retinal derived from vitamin A (rods)

iodopsin

composed of retinal and the protein photopsin (cones)

step 1 of photoreceptor cells reacting in the dark

opsin and cis-retinal combine to form rhodopsin in rod; G- protein complex transducin and phosphodiesterase enzyme (PDE) are inactive

step 2 of photoreceptor cells reacting in the dark

sodum ion channels in plasma membrane are opened by second messenger cyclic guanosine monophosphate (cGMP); sodium ions flow down concentration gradient into cell and depolarize cell

step 1 of photoreceptor cells reacting in the light

retinal is converted to trans-retinal and separates from opsin

step 2 of photoreceptor cells reacting in the light

transducin and phosphodiesterase (PDE) are activated

step 3 of photoreceptor cells reacting in the light

Na+ channels close and photoreceptor hyperpolarizes

step 1 of image processing by the retina (in the dark)

photoreceptor depolarizes and releases glutamate onto bipolar cells

step 2 of image processing by the retina (in the dark)

glutamate inhibits bipolar cell and reduces its release of neurotransmitters

step 3 of image processing by the retina (in the dark)

ganglion cell does not produce an action potential; no signals are sent to brain via optic nerve

step 1 of image processing by the retina (in the light)

light hyperpolarizes photoreceptor, and it stops releasing glutamate

step 2 of image processing by the retina (in the light)

bipolar cell is freed from inhibition and depolarizes, releasing neurotransmitter onto ganglion cells

step 3 of image processing by the retina (in the light)

ganglion cell produces action potentials that are sent to brain via optic nerve

step 1 of the visual pathway

the retina of each eye detects visual stimuli from portion of the right and left visual fields

step 2 of the visual pathway

some visual stimuli cross at the optic chiasma so that all stimuli from the right visual field are processed by the left hemisphere and stimuli from the left visual field by the right hemisphere

step 3 of the visual pathway

visual stimuli travel from the thalamus to the primary visual cortex in the medial portion of the occipital lobe

visual pathway for the nasal visual field

images are projected on the contralateral temporal retina upside down and reversed