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78 Cards in this Set

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T/F There is a sensory part to the autonomic division
False it is strictly an involuntary motor division controlled by hypothalamus that innervate glands, smooth muscle and cardiac muscle. Our internal environment's stability depends largely on the ANS for homeostasis.
What are the comparisons between the somatic and autonomic nervous systems?
Similarities: both somatic and autonomic nervous System have motor fibers. Differences: 1)differ in effectors 2) efferent pathways 3) target organ responses to neurotransmitters release. Somatic motor: cell bodies are located in the cord in the CNS,have no ganglia, 1 neuron chain-a single motor neuron forms the effernt pathway from CNS to the effectors (skeletal muscles) in the PNS. The axons fo the somatic motor neurons are myelinated w/schwann cells (salt. conduction). Autonomic (motor) thinner fibers & slower conduction than somatic motor, a 2-neuron chain, preganglionic & postganglionic neurons. Preganglionic neuron- cell bodies found in brain or spinal cord (CNS). The first neuron whose axon synapses w/cell body of 2nd neuron. lightly myelinated by Schwann cells;thin fibers. Post ganglionic neuron is the 2nd neuron of the ANS chain; cell bodies located in ganglion; extends to effectors (cardiac or smooth muscle & glands) ganglia is motor, NOT sensory ganglia. Postganglionic axons are unmyelinated & even thinner than preganglionic.
Describe parasympathetic and sympathetic divisions of the Autonomic Nervous System
SYMPATHETIC DIVSION: mobilizes (prepares) body for activity; called flight or fight response. PARASYMPATHETIC: promotes maintenance of functions, conserves body energy. Both divisions serve the same visceral organs (effectors: smooth&cardiac&glands) that are both controlled by the ANS/involuntary. They share DUEL INNERVATION: whatever one division does, the other does opposite. On or off. One division can stimulate glands to secrete & muscle to contract. the other division can inhibit. Provides counterbalance/antagonism between the 2 divisions. All effector organs are innervated by BOTH sym/parasymp. nerves. Example: Innervate erector pilli muscles in skin and blood vessels.
Para sympathetic
Preganglion is long and post is short. Ganglion on target organ synapses w/cell body in the organ. Has 2 outflows-through brain stem or spinal area, that's it. Called craniosacral outflow-characteristic of parasympathetic system.
Describe Cranial Outflow in ANS
Cranial Outflow: Preganglionic fibers run in the cranial nerves III, VII, IX, X. Cell bodies are located in associated motr-cranial nerve nuclei in brain stem. Oculomotor Nerve III-moves eyes left and right as part of conscious/somatic motor control. Autonomic fibers are also involved w/in the motor neurons. Parasympathetic fibers innervate the pupils & lens of the eye=constriction of pupils controlled by cranial nerve III. Facial Nerve VII: has mostly somatic motro components, but are autonomic too. 5 branches of facial nerves: of the five, one branch involving parasympathetic fibers stimulates lacrimal glands (tears) & nasal mucosa (runny nose)(not completely auto/cuz we can cry voluntarily also. Another branch goes to salivary glands (think french fries and salivate) thought triggers action. Glossopharyngeal nerves IX: parasympathetic innervation of salivary glands. Vagus Nerve X: 90% of all preganglionic parasympathetic fibers are in the vagus nerves-the majority of cranial outflow. AKA major parasympathetic cranial outflow and because the vagus nerves innervate so many organs they form autonomic plexuses around organs like liver, gallbladder, stomach, kidneys and pancreas.
Cranial nerve 9 Glosso pharangeal in ANS
It is also salivary.
T/F 90% of all preganglionic parasympathetic fibers are in one nerve
True: cranial nerve 10: Vagus nerve forms plexuses. Called major parasymapthetic outflow. Forms autonomic plexuses that innervates the organs.
What else is turned off in addition to digestion?
Reproduction
What is distinctive of T1-L2 in sympathetic
Most go to spinal ganglion. come out at same level of cord or different level and go to collateral ganglion
Where can you find splanchnic nerves
In both parasympathetic and sympathetic.
Where are collateral ganglion found?
In sympathetic of ANS
Why is the para and sym wired the way it is?
The cell bodies of pregangl are found in T1-L2, but the chain gang supercede these spots, but don't all have cell bodies, so they don't have white rami in these supersisions they are only located from t1-L2. This why it has ability for post ganglion to travel up. The fibers that bypass the chain ganglion going to the collateral nerve all form splanchic nerves and all turn something off.
What is the only neuron that does not release acetylcholine?
The sympathetic postganglionic nerve releases norepinephrine and is called an andrenergic neuron.
What are neurons called that release acetylcholine?
They are called cholinergic neurons. They have nicotinic and muscarinic receptors
Describe visceral reflexes.
Have the same parts as somatic reflex arcs. 1-receptor. 2-sensory neuron (a visceral sensory fiber of the CNs; cell body in dorsal root ganglia) 3-integration center-interpretation, 4-motor neuron (preganglionic neuron) 5-effector (postganglionic neruon travels to synapse w/ganglion of effector) Involve autonomic reflexes. A 2-neuron (pregang/postgang system. A tag-teaming system.
What is in charge of overall integration of the ANS autonomic nervous system
The hypothalamus is the boss-controls the divisions of the ANS. Gets input from the limbic system (emotional brain) and cerebral cortex (frontal lobe). Can shut things down and you get stomach aches or high blood pressure. Also can release certain hormones. Hypothalamus connects thoughts with autonomic function. Next levels are Reticular formation of brainstem-regulating pupil size respiration, heart blood pressure, swallowing, etc.; and the spinal cord-urination,defecation, eretion and ejaculation.
Describe sympathetic system outflow
Called thoracolumbar outflow, from T1-L2or 3. Pregangl. nerves are short goes to symp. chain ganglion located on left or right side of cord, post gangl longer. Sympathetic division is more complex. It innervates more organs and some glands and arrector pili muscles that require autonomic innervation.
Do pre or post ganglions release Ach and Nor
Ach is released by pre and nor is released by post
Name the three tunics of the eye
Fibrous Tunic-sclera & cornea; Vascular Tunic-choroid, ciliary body, iris; Sensory Tunic-retina- outerpigmented & inner-neural
What parts make up the Anterior Segment?
Anterior Chamber & Posterior Chamber
What are the 2 main parts of the eye classified as
Anterior segment and Posterior segment
Describe the Anterior Segment
One of 2 segments, the anterior segment has 2 chambers:anterior chamber and posterior chamber. The anterior segment is a cavity between cornea and posterior of the lens. The iris is the structure that divides the anterior segment into the 2 chambers. The anterior chamber between the cornea and iris, opens up and lets light through (pupil) to posterior chamber. Posterior chamber between the iris and the lens encompasses the lens and the space around the lens. Aqueous humor, a clear fluid blood filtrate like blood plasma, fills the entire anterior segment. Aqueous humor is made in the ciliary body of the posterior chamber (of the anterior segment) It flows into post chamber>>>then the fluid goes through the pupil to anterior chamber>>>drains into venous blood via the canal of schlemm, a venous channel that encircles the eye; aqueous humor supplies nutrients and O2 to the cornea (cornea is avascular) when it leaks via channel, venous sinus, waste products & CO2 leave w/ aq. humor. If Canal of Schlemm becomes plugged you get glaucoma due to build up of pressure, causing blindness.
Describe the fibrous tunic:sclera & cornea
Outer most layer of they eye, includes 1) whites of the eye called Sclera-it is white and avascular, function: tough connective tissue coat, provides attachment sites for ocular muscles, sclera continues to tough fibrous shapes eyeball 2) crystal clear Cornea that has no blood vessels either (avascular)forms area which allows light to pass into eye and is a major part of the refraction of light bending.
Describe Vascular Tunic
Involves 3 parts: Choroid, Ciliary body & Iris. 1) Choroid is red, highly vascularized, deep to cornea, darker in color because it holds melanocytes and it absorbs light, advantage-light won't scatter because it is absorbed. brings nutrients to all eye layers. Remember that the choroid is incomplete encountering the optic disc/nerve creating a blind spot. 2)Ciliary body anterior part of choroid is rings of muscle w/ projections called ciliary processes or bumps that project outside of ciliary body. Attached to these processes are suspensory ligaments which attach ciliary body to lens- which allows lens to change shape. 3) Anterior to this is the Iris. Iris is colored muscles, the color of our eyes is colored muscles that contract or relax allowing light or restricting light. Iris has to do w/light. Constrict is contraction and Relax is dilation. The center of the iris is the pupil allowing light to enter the eye. The iris regulates the amount of light entering the eye via constriction/contraction(parasympathetic) and dilation/relaxation (sympathetic).
Describe the Sensory Tunic
Aka Retina is innermost eye covering (tunic) outer and inner layer. The outer is pigmented and the inner layer is neural. Outer pigmented layer is one layer of cells deep, next to choroid. The pigmented cells (like the choroid) absorb light, have a variety of different pigments to absorb the light-prevents scatter of light. The neural layer is all the other layers of the retina. 3 types of Neural cells: 1) Photoreceptor cells-two types :rods,cones; 2) Bipolar cells; 3) Ganglion cells. The axons of the ganglion cells are what make up the optic nerve that exits via optic disc (blind spot-an area of neural layer of the retina where the optic nerve (ganglion cell axons) exits the eyeball. There are no photoreceptors located @ the blind spot. Location of where central artery & vein enter the eye. We still see in our blind spot cuz our brain tells we are...) The eye is a sensory structure
Are there photoreceptors where the optic nerve exits the eye?
No, that's why our brain fills in something to be there when it isn't. This is why we have a blind spot (called optic disc), but our brain wants to fill it in.
What kind of potential occurs in eye
Light is detected and causes a Generator impulses in cones and rods, graded potential in bipolar, and then finally at ganglionic hillock through optic nerve (made of ganglionic axons) is action potential.
Where is the vascularity located
Coming in w/optic nerve is the central aretery and vein of the retina. Because of this vasucular entrance it causes a blind spot called the optic disc, it's a weak area because of lack of sclera reinforcements.
What are the fluids of the eye
Anterior segment is filled with aqueous humor-watery, made in the ciliary body, enters posterior chamber of anterior segments through pupil through anterior chamber and out canal of schlemm. What is in it? nutrients and oxygen, this is how the cornea (avascular) is able to get some nutrients. When the canals empty-they release CO2 and waste, If the canals of schlemm get plugged you have glaucoma. Vitreous humor fills posterior segment, like jello, helps maintain firm structure of eye so it doesn't collapse.
What is the lens made of?
Fibers-from epithelial cells of mitosis in cornea-that helps hold lens together. New lens fibers are continuously added to the lens enlarging it over our lifetime-making it more dense as we age, & our lens becomes less elastic lens won't bulge which is needed to see closely-impairing our ability to focus light properly. Why we need bifocals later in life.
Backof the eye is called?
Fundus (aka back of eye), back of retina, blood vessels, optic disc, macula lutea,
Describe the physiology of the eye in regards to light.
Eyes collect and focus on visible light found on the electromagnetic spectrum. Visible light is found in the lambda wavelenth=hump to hump. Depending on where you are on the wave is another color. Cones will key in on different lengths. Light travels as a wave or a photon.
What are the different shapes of lens
convex and concave. Convex is bulged in middle our eyes are convex. bottom of image is reverted to top in back, and top of image is inverted bottom. It is also inverted from left to right. Concave?
Explain distant vision and the lens
Images are focused on the macula lutea. The shape of the lens is what foucses it on the back of the eye. Our eyes are best adapted for distant vision. Far point or our normal unaccommodated vision @ a distance; is the distance beyond which no accommodation is needed to focus, (lens remains relaxed & doesn't change shape); average far point is beyond 20 ft & up to 20ft. When the lens is relaxed it is in an elongated/relaxed/convex/normal shape. Lens is relaxed @ far point @ beyond 20 feet for the normal emmetropic eye. Relaxation means the ciliary muscles are allowing the lens to flatten in distant vision; when ciliary muscles are relaxed in far point and beyond, the lens pulls down & is actually in a stretched (not bulged) position. The lens is also at its lowest refractory power when it is relaxed (distant/farpoint). Relaxation of lens is due to increase sympathetic input/decrease in parasymptathetic inputs.
Why does the eye have to refract, bulge or accommodate?
When you are closer than 20 ft. The light is reflecting outward the eye has to take the light and bend it more or refract it and bulge it causing refraction. When you are closer than 20 ft-otherwise vision is blurred
What is it called when you can no longer accommodate?
Presbyopia
What is it meant by no longer able to converge eyes?
near point
Describe the Posterior Segment
Includes vitreous humor is posterior to lens, the ball of the eye.
Color blindness could be a result of
dull cones or not enough
T/F We are able to see color at night
False, at night everything is black and white straight on, but if you look at it w/the rods then you might be able to tell.
3 things happen when you are closer than far point
1) accomodation 2) pupils constrict -illiminating extra refractive light 3 )convergence of eyeballs which can happen at about 4 inches.
What the 3 anomalies of the eye and their corrections?
1) myopia-called nearsighted (see close, but blurry far away)-happens because eyeball is too long-the retina isn't where it should be, so what is focused ends up blurred. It is corrected by a concave (manmade) lens that diverges/spreads out the light waves since they have to travel farther to reach the retina-match up at retina to focus-though these type of glasses make the eyes look smaller. Also lasik surgery can correct myopia by putting cuts in cornea to rearrange the curvature of how light is refracted=focus properly. 2)Hyperopia-called "far-sighted" (can see far away, but not close up). Occurs as a result of an eyeball that is too short or a lens that is too flat; light waves focus beyond the retina=blurred vision. Corrected by a convex (manmade) lens which converges/refracts light so it comes together to focus on closer objects. Glasses w/ convex lenses make eyes look big "coke bottle" 3) Astigmatism-unequal curvature of the lens or cornea that leads to blurred vision, a refractory problem-corrected by either concave or convex lens, but lens is not smooth-it is distorted/bubbled in an opposite way to compensate for the unequal curvature of the lens/cornea.
What happens when you are far sighted
Lens is too flat and light focuses on retina and correction is a convex lens you can see far away. Eyeball is too short or lens is too flat. Person wears convex lens that makes their eyes look bigger.
Astigmatism
unequal curbature of lens of cornea a bubbled lens is the correction
Define the term phototransduction
Once light is focused on the retina, the photoreceptors get to work. Photo transduction is the process by which light energy is converted into a graded receptor potential.
How do we stimulate light reception.
Step 1
Trying to generate at generator potential. Initiation of transduction. ligt comes down, retinol is in 11scis conformation, detaches opsin changes shape and transducin can now bind onto alltrans retinol. Once it binds w/alltrans transducin changes shape and binds to phosphodiespherase. Once PDE releases cGMp to be realsesd and casues NaCa to change shape.
Step 2 light reception.
Rember light shuts down sodium, but in the dark sodium is free flowing, and causes depolarization ca channels open and neurotransmitter called glutamate is released which is and inhibitary ipsp in the bipolar neuron, preventing bipolar from releasing its neurotransmitter which inactivates the ganglion from transmitting epsp. This process is called dark current becasue it is in the dark-a current is generated. But when light strikes-bleaching-channel closes, sodium does not flow in, stays outside, but potassium is free flowing-hyperpolarization, no releases of transmitter ipsp- the removal of glutamate is what kicks off spontaneous of bipolar cell releasing normal acetylcholine, to fire a generator potential-received in brain-brain says i'm seeing something.
What are visual pathways?
Back of each eye-there is a right portion and left portion of each eye. Left portion is right, rt portion is left. Only fiber tracts located medially will cross, the lateral never cross. Right eye sees the left field, Left eye sees the left field
What is difference between predator and prey in how they see.
Predator-binocular, prey needs peripheral to see panaoramically to run.
Is hearing our primary or secondary sense?
Secondary, visual is primary
What is the ANS?
The ANS is the autonomic nervous system. It is the motor division of the peripheral nervous system under automatic/involuntary control; governed by the boss-the hypothalamus. Its functions are: shunting blood-redistributing blood to areas of need: ex. blood gets shunted to skeletal muscles when running (vigorous activity). It also controls blood pressure & digestion.
Describe the role and components of the sympathetic division
Turns things on. The fight or flight system; turns on anything to prepare for fight/flight. Increases heart rate, causes rapid breathing (get more O2); blood gets shunted from skin & digestive viscera (during exercise etc.) to the the brain and skeletal muscles; bronchial tubes in lungs dilate (get more O2) glucose floods the blood from the liver (giving extra nrg). Turns things on EXCEPT-it can slow digestion and turn off reproductive activity during fight/flight. When sympathetic is at word we feel: pounding of heart;dry mouth; deep breathing; cold, sweaty skin; dilated pupils. Sympathetic div. has 2 neruons: 1)preganglionic (short, slightly myelinated by Schwann saltatory cells). The cell bodies of the preganglionic neruons are found in lateral horn of spinal cord @ level of T1-L2 aka thoracolumbar region of the spinal cord; preganglionic transmit faster than postganglionic. 2) postganglionic neuron - long, non-mylenated, (continuous conduction; slower) synapses w/preganglionic neruon on a ganglion (location of postganglionic cell bodies. Cell bodies are found on the sympathetic chain ganglion or on collateral ganglion. EXCEPTION: is adrenal gland which is involved in fight/flight. Preganglionic cell body in spinal cord; postganglionic cell body is not located in ganglion, but ont eh adreanal gland itself=preganglionic neuron synapses with the gland itself.
Explain the role of the parasympathetic division
The resting/digesting system-turns things off EXCEPT-turns digestion on. Turns things off to allow body to rest /slow down; keeps body nrg use as slow as possible so body can digest & eliminate urine & feces. When parasymp is at work blood pressure and heart rate are regulated at low normal levels; pupil constrict;GI tract is actively digesting food-happens when relaxing after a meal. The parasymp div. neurons come from the brain (cranial nerves I II III IV) & sacral spinal cord s2-S4) aka craniosacral. Preganglionic neruon is long, axons travel long distances to synapse w/the postganglionic neuron near target organ. Cell bodies are in brain and spinal cord. Postganglionic neuron is short is located on target organ called the intramural/terminal ganglion;( is imbedded on wall of target organ). Pre & post neurons synapse on the intramural ganglion.
Explain the Thoracolumbar division
It is a sympathetic division, which is more complex, innervates more organs, supplies visceral organs & some visceral sturctures (glands & smooth muscles) like sweat glands & arrector pili muscles that require autonomic innervation. Preganglionic neruon cell bodies all arise from T1-L2 or L3 outflow is called thoracolumbar. Preganglionic axons leave the cord via the ventral root through spinal nerve-through branch of ventral ramus & enter the sympathetic trunk (chain ganglia) via the white ramus communicans.
Where are the white rami communicans found?
They are only found in T1-L2 (not found above T1 level. where preganglionic neurons flow from; why preganglionic neurons go up to effector organs.
When preganglionic neurons bypass synapsing in the trunk ganglia and travel to the through the trunk & out-what nerves do they form?
Splanchnic nerves (thoracic,lumbar, adn sacral) to then synapse on collateral ganglion.
Where are most collateral ganglia located?
On the aorta.
What is the function of splanchnic nerves?
They are mylenated and turn off Guts & reproduction;other organs may be turned on depending on fight/flight.
Which divisions do the thoracolumbar outflow and craniosacral outflow correspond?
Thoracolumbar outflow corresponds with the sympathetic division and the Craniosacral division corresponds with the parasympathetic division.
Explain the craniosacral outflow.
The preganglionic fibers come from opposite ends of the CNS: brain stem&spinal cord=cranialsacral division. (note-2 outflows are characteristic of para. pregang. axons extend from the CNS (long axons) & synapse w/ganglion called intramural/terminal ganglion ont eh surface of the target organ. A.)Cranial outflow: pregang fibers run in the cranial nerves III, VII, IX, X. Cell bodies are located in assocatied motor-cranial nervve nuclei in brain stem.
Describe splanchnic nerves, location and function
Splanchnic nerves are found in parasympathetic and sympathetic divisions of the ANS. In parasympathetic splanchnic nerves come from axons that run through ventral roots and ventral rami forming splanchnic nerves that innervate genitalia, bladder, ureters, small intestinea rectum (aka pelvic viscera) In the sympathetic division splanchnic nerves are preganglionic neurons that have bypassed synapsing in the trunk ganglia and travel through the trunk and out to collateral ganglion where splanchnic nerves synapse and turn OFF guts and reproduction (normally they turn things on) most collateral ganglia are located in the aorta.
Describe Sacral Outflow
Involves S2-S4
Neurons in lateral gray matter of spinal cord segments. Axons of these neurons run in ventral roots out ventral rami and branch off to form splanchnic nerves going to genitalia, bladder, ureters, sm. intestine, and rectum.
Describe the Posterior Segment
A cavity posterior region behind the lens, not divided into other areas, filled w/vitreous humor: clear, jello like gel that helps maintain the firm structure of the eye (protects eye from collapsing, keeps retina in place too)
Explain the flow of light through the cells of the neural layer
1st: light hits the axons of the ganglion cells>>>travels past bipolar cells>>>to rods (which detect black & white) & cones (detect color) where the light is detected (then goes in reverse to exit optic nerve). Light travels into the eye to reach macula lutea (oval area @ posterior pole of the eye), contains mostly cones. The center dimple of the macula lutea is called the fovea centralis; contains only cones; anything needing to be veiwed critically w/detail, color vision is focused on the fovea. Outward form the macula (peripherally) density of cones decreases & rods increase =peripheral vision is mostly black and white.
Explain the vascularity of the neural layer of the retina
The blood supply for the outer layer contains photoreceptors-nutrients from choroid, and the inner areas of the neural retina are supplied by the central artery and central vein of the retina which enter and exit via the optic nerve.
Explain the Extrinsic Eye Muscles
The movement of each eyeball is controlled by 6 ocular muscles:4rectus;2oblique.
1)lateral retus moves eye laterally, 2)medial rectus moves eye medially,
3)superior rectus elevates eye & turns it medially, 4) inferior rectus depresses eye & turns it medially.
Obliques: 1)inferior oblique elevates eye & turns it laterally, 2) superior oblique-depresses eye & turns it laterally.
How are the extrinsic eye muscles innervted?
All the extrinsic eye muscles are innervated by ocularmotor nerve III except for lateral rectus (Abducens VI), and Superior oblique (trochlear nerve IV). Eye muscles are most precisely rapidly controlled sk. muscles in the body.
Explain the difference between specific and non-specific vision.
Specific refined vision: happens when every cone synapses w/a bipolar cell that in turn synapses w/a ganglion cell. Color is more specific in vision due to specificity of the cones. In non-refined (non-specific) vision 4 rods wynapse with only 1 or 2 bipolar cells that snyapse w/a ganglion cell. rods pick up the black & white & peripheral movements needed for peripheral vision; rods aren't as specific as cones.
Why don't we have color vision at night?
When we look at something straight on @ night we only see black & white (cones only capable of detecting bright light/color) If we look peripherally @ something using our rods, we can see it clearer @ night, rods are suited for dim light/black & white suited for night vision.
Explain how light is detected
Light is detected @ the end of rods & cones (photoreceptors); energy from light triggers a generator potential (type of graded ptnl/ionic musical chairs) that travels along the rods & cones that synapse w/bipolar cells. The impulse is transferred as a graded potential along the entire length of the bipolar cells that synapse with ganglion cells; this impulse transfers as graded potential along ganglion cell until it reaches the axon hillock where an Action potential is triggered. Action Potential impulse travels length of ganglion axons forming optic nerve.
How many times is the light refracted or bent as it comes into the eye?
3 X: 1)bent as light enters the cornea (different density), 2)as it enters the lens 3) and when it leaves the lens. They all move from 1 density to another.
Explain accommodation, refractive power.
Involves 1)accommodation (when lens changes shape, allowing light to refract or bend so eye can focus). Accommodation is to focus @ a distance lens than far point, the lens has to change shape. 2) Refractive power-the ability to bend light; a bulged lens (for close vision) has more refractive power than relaxed lens. To bulge lens (refract) the ciliary muscles contract, pulling up & inward creating a bulged lens. In close vision the parasympathetic NS stimulates the ciliary muscle to contract, creating the bulged lens using refractive power to focus close up.
Explain how close vision occurs
When objects move closer to you the light is diverged (reflected more outward/spread out) making it hard to focus; light needs to be refracted in so you can focus on the proper area (otherwise = get a blur at the back of the retina) in order to focus, refraction must increase which occurs via bulging of the lens (accommodation). 3 important things happen that allow us to see closer as we move closer to "far point" and inward. 1) accommodation, 2)pupil constriction, 3) convergence of the eyballs-medial rotation of the eyeballs by medial rectus muscles so that eyes can direct toward the object at hand. Near point is the closest point that we can focus clearly before blurring occurs; usually around 4" from the eyes; the most the lens can bulge (accommodate)
Describe photreceptors and their photochemistry
PHOTORECEPTORS called RODS (1 type, absorbs black & white, night vision, dim light) and CONES (3 types, each contains 1 of 3 pigments for vivid colors absorbed: red blue green) have their outer segment (region imbedded into the pigment layer of the retina) Within their outer segments are stacks of discs that contain PHOTOPIGMENTS. These photopigments change shape as they absorb light. The discs at the ends of the outer segment of rods & cones break down and fall off & are phagocytized by pigment cells (phagocytes) of the pigmented layer of the retina. The chemical components of photopigment cells are: RETINAL-a light absorbing molecule & OPSIN- a type of protein that affects the absorption spectrum of retinal. These two molecules combine to form the complex RHODOPSIN. Rods and cones both absorb light @ different wavelengths. PHOTOCHEMISTRY IN RODS: retinal & opsin combine in rods to make rhodopsin (absorbs @ 500 nm).The 11-cis isomer conformation of retinal is combined w/opsin in rhodopsin. When pigment is hit by light, retinal underegoes a conformational change=to all-trans isomer. Retinal is bleached. Rhodopsin is broken down into 2 parts as opsin detaches from retinal. The breakdown of rhodopsin into retinal & opsin=bleaching. Once the all-trans isomer of retinal detaches from opsin it is reconverted by enzymes into its 11-cis conformation. Rhodopsin is regerated when the 11-cis retinal rejoins to opsin
Explain Dark Phototransduction
In the DARK:1) Na+ flows in cuz light is not available to close the channel. Na+ depolarizes the membrane of phoreceptor(cGMP binds to the channels keeping them open=Na+ & Ca2+ influx) creaks a dark current. 2) Ca2+ channel open. 3) In the dark, neurotransmitters called glutamate are released @ the synapse between the photoreceptor & the bipolar cells. 4)Glutamate hyperpolarizes the bipolar cells creating an IPSP. 5) The IPSP inhibits the release of neruotransmitters 2 the bipolar cell terminal end. 6) No EPSP is transferred to the ganglion cell-inactive. 7) W/No transmission of EPSP on ganglion cell,there is no AP>>>seeing DARK>>>no info travels to the brain. Process is called dark current because a current is generated @ the photoreceptor cell, but ultimately dark current results in IPSP in bipolar cell.
Explain Light Phototransduction
IN THE LIGHT: 1)Photoreceptor is hyperpolarzied: bleaching or breakdown of rhodopsin eventually results in channels closing ( a breakdown of cGMP that keeps channels open in the dark) IN MORE DETAIL: a)light breaks retinal to its all-trans form (opsin detaches) & visual pigment is activated b) transducin (g-protein) is activated c) transducin activates phosphodiesterase (PDE-an enzyme that breaks down cGMP) the cation channels close leading to hyperpolarization of photorecptor. *Light makes the channel close.
2) Ca2+ channels closed @ synpase of photoreceptor & bipolar cell (K+ influx in inner segment=hyperpolarization that inhibits neurotransmitter release. No Na+ flows in, but K+ leaks out. 3)No glutamate (inhib neurotrans.) released so can't inhibit action. 4)In absence of IPSPs, the bipolar cells can depolarize 5) Releases neurotransmitter (excitatory) from synapse between bipolar & ganglion cells. 6)EPSP in ganglion cell. 7) AP is triggered @ axon hillock of ganglion cell>>propagates along the optic nerve>>brain sees something (depending on rods or cones as to what colors are seen by the brain)
Explain visual processing
Optic nerves exit the posterior eyes, the medial fiber tracts of each eye cross over to the opposite side (@ optic chiasma) the lateral tracts remain on the same side as the eye they came from. (enables both eyes to see both visual fields-even thought the left eye views right visual field & right eye views left visual field-there is overlapping of visual fields.
Explain binocular and panoramic vision
Binocular: eyes going forward, creates overlap of visual fields from each eye. Humans, cats, primates have binocular vision=predators. It is useful for depth perception. Panoramic vision: (eyes on sides of face, further apart) Eyes can see in 2 different directions=panoramic view field. Rabbits, pigeons, etc. have panoramic; prey. Useful for seeing movement in many directions; survival.