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ALS 2304, Week 8: Sense Physiology

by: Mara DePena

ALS 2304, Week 8: Sense Physiology ALS 2304

Mara DePena
Virginia Tech
GPA 3.62

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About this Document

These notes cover the first week of sense physiology. They go over smell, taste, and sight and the physiology of each sense.
Animal Physiology and Anatomy
Dr. Cline
Class Notes
sense, Physiology, smell, taste, sight, camp, ip3, EAR, eyes, mouth, tongue, tastebuds
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This 8 page Class Notes was uploaded by Mara DePena on Sunday March 20, 2016. The Class Notes belongs to ALS 2304 at Virginia Polytechnic Institute and State University taught by Dr. Cline in Spring 2016. Since its upload, it has received 10 views. For similar materials see Animal Physiology and Anatomy in Agricultural & Resource Econ at Virginia Polytechnic Institute and State University.

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Date Created: 03/20/16
SENSE PHYSIOLOGY SCENARIO FOR THE EXAM There is a pig at a feed trough. The trough is empty. A farmer comes and approaches the trough at a 45-degree angle, downwind so the pig smells it. The pig then hears and sees feed poured into the trough. The pig beings to eat and goes through the digestive system. He will tell us if the odorant molecule’s signal is transduced via cAMP or IP 3 SMELL  The first thing that has to happen for you to smell something is that an odorant molecule needs to be released into the air. Small chemistries remain airborne longer than large ones.  The odorant molecule has to be inhaled through the nasal cavity.  At the groove of the nasal cavity around the sinuses is the olfactory epithelium.  Sinuses- Refinement of the voice or the sound the animal makes. Warm the air before It goes down into the lungs. Cells were gases exchange on the lung could freeze otherwise.  Cells of the Olfactory Membrane o Modified neurons, with dendrites with ends called olfactory hairs. These are very sensitive dendrites. These dendrite are hanging free with mucus. o Mucus traps the odorant molecule and bring it in proximity to olfactory hair.  Too little or too much can hurt your sense of smell. With a runny nose, olfactory molecules can’t diffuse far enough to reach your olfactory hair.  Signal transduction via cAMP o Odorant molecule diffuses through mucus and binds to g-coupled receptor. o G olfctivates adenylyl cyclase and activates a calcium and sodium channel to propagate an EPSP. This EPSP is twice the magnitude of a normal sodium one. Calcium also opens up a chlorine channel and kick chlorine, which is in high concentration, out of the dendrite. o The EPSP further intensifies. o Action potential fires and goes up the soma. The neurotransmitter is released at the axon terminal.  Signal transduction via IP 3 o Odorant comes in, binds to receptor, releases Gaq, activates phospholipase C which activated IP an3 activated calcium channels. Calcium open chlorine channels and chlorine leaves the cell. o Generates an EPSP, which is weaker than the last.  There are thousands of odorant receptors. Odorant molecules bind to different receptors at different strengths. In order to illustrate the different strengths, action potentials are propagated at different frequencies.  In a real world diagram, you would show both cAMP and IP occur3ing at the same time at different frequencies, because you always smell more than one molecule.  Glomeruli in the olfactory bulbs are ganglions that olfactory receptors synapse on. There is a synapse onto second order neurons called mitral cells. These go in a westerly direction toward the thalamus.  The mitral cells go into different areas.  If a smell reminds you of something, it means the mitral cell ran through the hippocampus, which is in charge of memory. This used to give an evolutionary advantage, so you could recognize the smell of danger.  There is not a distinct region of the brain where the sense of smell is processed. This is probably the most complicated sense you have, as it activates a lot of parts of the brain.  Rodents rely on their sense of smell because they do not see well, so they have an extraordinary sense of smell wired into their brains from evolution.  There are two smells wired in our circuitry that make us run the other way. o The smell of feces- warning of bacteria and human pathogens o Decaying human flesh- threshold of detection is so low, and the smell is so potent it is very easy to detect  Adaptation and Odor Thresholds o You adapt to most smells relatively rapidly. o Low threshold to trigger action potentials that trigger smells  Only a few molecules need to be present  Bloodhounds and other species have even lower thresholds TASTE  On the surface of the tongue are crips or little holes. Taste buds are located on the walls of these crips. This somewhat protects them from abrasion.  Chemistry diffuses away from the food through saliva and goes into the crip. Advantage of the taste buds being in these crips is that the gustatory molecules are held in proximity to the taste buds for a longer time.  A taste bud is made up of several cells. Each one of these individual cells has the ability to respond to a different taste chemistry. Each one of these cells is nothing more than a modified neuron. Their axons aren’t very long, but they drop neurotransmitters onto the next neuron in circuit, which carries information away. Microvilli are fingerlike receptors that are modified dendrites that come up of the top of these cells.  Complete adaptation within 5 minutes. You won’t taste it anymore because action potentials will stop.  Taste thresholds vary considerably. Most sensitive to bitter (poisons) and least sensitive to salty and sweet.  Taste Sensations o Sweet  Sugars, some amino acids o Salt  Metal ions o Sour  Hydrogen ions o Bitter  Alkaloids, nicotine o Metal/umami  Anion form of glutamic acid (in protein rich foods)  Gustatory Pathway o Taste buds located on tongue. Several cranial nerves (three) drive it to the nucleus on the solitary tract (NTS) in medulla oblongata. Best friends with the dorsal motor nucleus of the vagus nerve, as they are side by side. o Through the NTS, the signal goes to the pons, and then to the thalamus, which decides if it is worthy of further processing or not. If it is, it is sent in the lateral direction and sent to the gustatory cortex. When neurons in this cortex fire, the neuron perceives this taste.  Influence of Other Sensations on Taste o Sense of taste is actually 80% smell. o As you chew the food, odorant molecules are released. They go backwards through the pharynx and up into the nasal cavity. This is more important to the sense of taste than the taste buds. o Taste is not good in high altitudes because there aren’t many air molecules. o Thermoreceptors, mechanoreceptors, nociceptors also influence tastes.  Mechanoreceptors- Sense the texture.  Thermoreceptors- Sense the temperature. (ex: Melted versus frozen ice cream.)  Nociceptors/Pain receptors- Nococin binds to pain receptors. (ex: Peppers) o Sight also influences taste. SIGHT  You see a red pen because it absorbs all wavelengths of light and reflects red. Light reflects in all directions.  If you see a pen from closer, the light hits it an an angle. If you see it from afar, the light rays are parallel.  Eyelids- Protect and lubricate the eye. Move debris on your eye out of the way.  Tarsal glands- Oily secretions to keep lids from sticking together.  Conjunctiva- Pink eye.  Eyelashes and eyebrows- Help protect from foreign objects, perspiration, and sunlight.  Retina- Where the photoreceptors are. Back of the eye.  The cornea and the lens bend the light, with the cornea bending the most. o If light strikes the cornea right in the middle, the light goes straight through. o If light hits the cornea at an angle, it bends. o All of the rays of light fall on a distinct focal point on the retina. o Light bends more if the object is closer. The image is not in focus because all of the light does not come to a focal point. The lens will then change shape to make the light fall on the retina.  Humans are the only species that cry from emotion.  Lacrimal glands in the lacrimal apparatus produce tears. These are meant to remove debris from the eye.  Extraocular muscles o Muscles in the eye itself. o Hold eye in orbit and move around eyes in orbit. o Six muscles attached to each eye.  Iris o In front of the retina. Regulates intensity of light by allowing more or less light to enter the eye. o Regulation of amount of light that goes into the eye. o Comprised of two muscles arranged in different directions. o Section of circular muscles arranged in a sphincter. When they contract, they reduce the amount of light striking the retina.  Parasympathetic nervous system is wired to these. o Outside of these circular muscles are radial muscles. When they contract, they increase the amount of light striking the retina by pulling the circular muscles.  Sympathetic nervous system is wired to these, so pupils are large when stressed.  Retina o Very very thin, extremely sensitive o Pigmented epithelium (very back of retina)  Nonvisual portion  Absorbs stray light and keeps image clear  Acts like a mirror and reflects the light back; increases night vision.  Why cat and deer eyes glow at night.  Red eye in photos means more developed pigmented epithelium. o Rods and cones, then horizontal cells, bipolar cells, amacrine cells, then ganglion cells. In humans you work backwards until you reach the rods/cones. In animals you reach the rods and cones, and then the pigmented epithelium, and then the rods and cones again.  Rods (rod shaped)  Very dim levels of light  Shades of gray  120 million rod cells  Discriminate shape and movement  Distributed along periphery  Photoreceptors o Rods contain rhodopsin (night vision). Highest concentration when eye is in the dark. o Made of opsin and retinal.  When retinal is in the trans form it is a linear molecule. This version exists in the light.  When retinal is in the cis form it is bent. This version exists in the dark. o Photons of light strike the rod and what they change is retinal, from cis to trans. Trans separates from opsin. This is called bleaching. o Isomerase returns cis to trans.  Phototransduction o Isomerase and vitamin a put retinal back in the cis form to associate it with opsin. o Opsin is an enzyme, and retinal is an inhibitory subunit on it. o Once opsin is activated, it activates transdusin which activates phosphodiesterase. It takes a molecule of cyclic GMP and changes it into GMP. This prevents cyclic GMP from letting sodium flow down its concentration gradient. With cGMP, sodium causes EPSPs which causes a release of neurotransmitter (glutamate) which is released in the dark. o Absence of stimulus (light) causes release og glutamate.  Cones (cone shaped)  Sharp, color vision  6 million  Highest collection of cones in back middle of retina  3 proteins for color vision, allowing for absorption of 3 different wavelengths of light o Horizontal cells, bipolar cells, and amacrine cells make the image crisper. o Axons of ganglion cells form optic nerve o 3 layers of neurons (outgrowth of brain)  Photoreceptor layer  Bipolar neuron layer  Ganglion neuron layer  Major Processes of Image Formation o Refraction of light (when light bends)  By cornea and lens  Light rays must fall upon the retina o Accommodation of the lens  Lens changes shape so light is focused on the retina  Lens gets fatter when you are looking at something close up o Constriction of the pupil  Regulation of light intensity  Refraction by Cornea and Lens o When the image falls on the retina at the focal point, the image is upside down. o The brain flips the image. o It is thought that when a baby is first born, the brain doesn’t do this. Part of the baby’s flailing around is teaching the brain to teach the image to flip right side up.  Central Pathways of Vision (proceeds in this order) o Optic nerve o Optic chiasm- Where the two optic nerves cross. The medial retina crosses to the other side of the brain and follows the pathway back. It is processed on the opposite visual area (opposite side of the body). The lateral retina stays on the same side of the brain.  Something is processed on both sides of the brain if it is directly in front  Something in the left field of vision is processed on the right and vice versa  For the diagram, the pig sees the farmer and processes the image on the opposite side of the brain. If the diagram says the farmer is right in front of the pig, it is processed on both. o Optic tract o Optic radiation o Lateral geniculate nucleus of thalamus o Area 17- Visual region of the brain. HEARING  Auricle- Outside of ear. Funnels sound waves into external auditory canal.  Earwax- Insecticide. Keeps bugs from nesting in ears.  Eardrum/tympanic membrane- Attached to malleus, incus, and stapes, the three smallest bones in the body. Vibrates at exact same frequency as sounds you are hearing. The three bones are basically lever systems which increase force. They amplify the vibrations.  Cochlea- Where hearing starts. Filled with fluid. Fluids are incompressible. The stapes plunges on it. This causes a wave. o Has a top tube and a bottom tube. The stapes is attached to the top tube. The fluid in the cochlea moves back and forth at the frequency of the stapes. o Channel in between upper and lower channel is full of fluid and also vibrates back and forth. In this inner channel are little hair cells that stick up. These hair cells are all different lengths. Frequency is a function of length. At different frequencies, different hairs move back and forth violently. If one hair cell starts moving back and forth violently with wide swings, the door opens and closes. The door is a sodium channel. When it swings open it causes and EPSP on the top of the hair cell. The EPSP is not continuous. It alternates. The hair cells beside it are stimulated randomly. Gates somewhat open and cause low level EPSPs all the time. The brain knows you are hearing whichever circuit is undulating widely, from full to no action potentials. o If an animal is subjected to an intense sound for a very long frequency of time, the hair cells are super stimulated and the animal can go deaf and the hair cells break off. Hair cells do not come back. o Dogs have much shorter and much longer hair cells, and that is why they can hear things we can’t.  The perception of sound is dependent upon sound wave frequency.  High frequency sound- Sound waves hit ear and make it vibrate back and forth very very frequently. Do not wrap around an obstruction very well. The animal can tell the origin of the sound by which eardrum is vibrating back and forth with more force.  Low frequency sound- Wrap around an obstruction very well. Travel much slower. There is a delay between the two eardrums. The brain can tell which eardrum was stimulated first and the brain then rationalizes that the sound is coming from that direction.  You actually can’t tell if a sound is coming from in front of or behind you. You use other cues.  Vestibular apparatus o Semicircular canals- Big ring-like structures full of fluid. Orientated into three dimensional dimensions. Fluid keeps spinning if you twirl in circles, and when you stop and it keeps spinning, you get dizzy. This is called vertigo. o Cupula- Little flap that sticks up into semicircular canal. Bends with movement in one direction. It either goes up really high in action potential frequencies or stops.


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