Give an example from this chapter of the scientific method at work.
ALS 2304 SENSE PHYSIOLOGY (CONT.) 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 (stimulus proceeds in this order) o Retina 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 Optic radiation 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. EQUILIBRIUM (BALANCE) Vestibular apparatus- thickened regions called macula within the saccule and utricle. o Utricle senses horizontal acceleration (while standing). Forward and backward motion. o Saccule senses vertical acceleration (while standing). Up and down motion. o Otoliths- Calcium carbonate crystals that moves when you tip your head. o Semicircular canals- Big ring-like structures full of fluid. Orientated into three dimensional dimensions. Tell you about rotational changes in direction. 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. o Animal only has a sense of what’s happening in its head location, not anything else. DIGESTIVE PHYSIOLOGY DIGESTIVE SYSTEM Alimentary canal/GI Tract- Essentially a tube from your mouth to your butt. o Intrinsic controls Nerve plexuses near GI tract Short reflexes mediated by local enteric plexuses (gut brain) o Extrinsic controls- Central nervous system regulates what the gut brain is doing. It will either accelerate the process of digestion or turn it off. Long reflexes arising within or outside of the GI tract. Involve CNS centers and extrinsic autonomic nerves. Ingestion- Swallowing food. Propulsion- Moving food through the cancal. Mechanical digestion- Grinding of teeth on food, kneading around in stomach. Chemical digestion- Breakdown of food. Absorption- Nutrients are pulled from the food and dumped into the bloodstream. o Takes place along the walls. Defecation- Eliminating unused nutrients and waste products. ENTERIC NERVOUS SYSTEM Endocrine cells release hormones. Distension/stretching of the canal- Activates mechanoreceptors. Chemoreceptors respond to the amount of acid in the canal. They bind to food and look at the degree of digestion. Secretory cells found all throughout the alimentary canal secrete digestive enzymes, acids, and mucus into the lumen. Sensory cells branch out from the gut brain. Digestive process is automatic. If you put something in the oral cavity, it will automatically be digested if you cut away the autonomic nervous system. Parasympathetic nervous system enhances the digestive process. The sympathetic nervous system inhibits the digestive process. An automatic mechanism starts the digestive process. PERISTALSIS AND SEGMENTATION Peristaltic waves are beltlike contractions along that canal that squeeze food down the canal. Once triggered, they go all the way down the canal. Segmentation- Bands of alimentary canal that all spontaneously contrict at one point. o Maximum contact with walls of the canal to aid with process of absorption. HUNGER AND SATIETY Stretch receptors respond to distention. Pathway from small intestine to nucleus of solitary tract, from NTS to arcuate nucleus at the base of the hypothalamus. This nucleus is a collection of soma which acts as a relay center and doesn’t affect appetite on its own. In the arcuate nucleus are two important neuron types. o Neurons that secrete neuropeptide Y Activated by NTS when there is a lack of distension Causes hunger Activates PVN and lateral hypothalamus o Neurons that release POMC When duodenum stretches, sends a signal to the NTS which communicates with the arcuate nucleus and turns on POMC release. Causes satiety Activates DMN, VMN, and PVN If you eat a bunch of food really fast it takes time for it to go to the duodenum, which will fill slowly and turn off your appetite eventually. This is how you could gain weight. Eating too fast, you’ll feel way too full. Arcuate nucleus neurons: ventral medial nucleus, dorsal medial nucleus, paraventricular nucleus, lateral hypothalamic area. o Lateral hypothalamus- Activated, makes you feel hungry. o DMN, VMN- Makes you feel full. o PVN- Sometimes when it fires, the animal is hungry, other times the animal is satiated. ORAL CAVITY Where ingestion occurs. Digestion begins when food mixes with saliva, which has the very first digestive enzyme, salivary amaylase. It breaks down carbohydrates. Breaks glycogen down. Salivary reflex causes saliva to be secreted from the salivary gland. Flows from taste bud to NTS to superior salivatory nucleus, through nerve, to salivary gland to release saliva. If you smell food, you will salivate. Swallowing Buccal phase- When food is in the oral cavity and the tongue is moving it around. Tongue motion/phase is under conscious control. Pharyngeal-espohageal phase- Unconscious control. Tongue mashes food down through the esophagus. Peristaltic wave. Anything from here to the rectum is unconscious. o If you choke, that means food went into your trachea. The epiglottis covers your trachea to prevent this. o Wave reaches stomach. Cardiac/gastroesophageal sphincter is closed when food arrives. There is a circuit that runs forward that causes dilation. The food can then move down into the stomach. Distal pharyngeal esophagus phase o Acid reflux- Cardiac sphincter doesn’t close up, acid goes up into the esophagus. Stand up and gravity pulls the acid down. STOMACH Has three layers of muscle that help with contraction. When food is digested it is considered chyme. It is food mixed with HCl. Stomach lining o Gastric pit gives way to the gastric gland. Inside the gastric gland is the G-cell. Below that are mucus neck cells that secrete mucus. Below that are parietal cells that produce HCl and are found in the wall’s mucosa. Below that are chief cells that release pepsinogen. Pepsinogen- A zymogen. It is an inactive enzyme. It is the inactive form of pepsin. Pepsin breaks bonds between amino acids/breaks down proteins. Pepsin is activated from pepsinogen when it encounters HCl. The most important aspect of HCl is the activation of digestive enzymes. It is released as pepsinogen so the pepsin doesn’t digest the chief cell that secreted it. Stages of the digestive process: o Cephalic phase Cephalic means head. Brain is the major regulator during this phase. Animal sees food, tastes food, smells food, hear food- thinks about food. Those are initiators of the cephalic phase. They cause activation of the dorsal motor nucleus of the vagus nerve. Two pathways. First releases Ach onto parietal cell. Second releases GRP onto the G cell. The G cell then secretes gastrin which feeds back and causes the parietal cell to be further activated. The cell excretes protons which helps to make HCl. They do not always both occur at the same time. This is inhibited by increased sympathetic outflow, including stressful events and depression. o Gastric phase The stomach is the major regulator of the digestive process. Something in the stomach causes distension of the stomach wall. Everything in the cephalic phase continues to happen. Stretch receptors send information back up to the central system. They send them backwards through the vagus nerve to the vagal nucleus. The vagal nucleus then increases vagal outflow, increasing the frequency of Ach and GRP. This is known as a vagal-vagal reflex (information goes up and then back down.) If we cut the vagus nerve, info can’t go up or down, but the stomach can still release HCl and gastrin, because stretch receptors (local reflexes) can also release Ach. Much more HCl is secreted. o Intestinal phase The small intestine is the regulator of the digestive process. Most complicated phase. Satiety mechanism is a part- duodenum is distended, you feel fullz. Pyloric sphincter opens and injects the chyme into the duodenal lumen. This causes distension. Many hormones are released into local circulation. They feed back onto the stomach and onto the G cell and parietal cell. Some hormones stimulate and some inhibit. They either enhance or stop contractility of the stomach. HCls major function is to activate the zymogens. If the nutrients aren’t digested enough, hormones will be released that augment digestion. If stuff coming out is too digested, hormones will cause inhibition to stop the production of HCl. Too much HCl can burn the mucus layers. Need the right amount- enough to turn on digestive enzymes but to keep you from digesting yourself. o If you cut the vagus nerve, you will delay the digestive process slightly; the first stage wouldn’t occur. o These can all occur simultaneously. Parietal cell o Produces hydrochloric acid. o Chlorine comes through a chlorine channel while proton comes through a proton pump. Once these get into the nucleus they form HCl. o The cell cannot produce HCl in itself and exocytosis. It does not secrete HCl itself, it secretes Cl and H which are combined in the mucus. o As a hydrogen ion goes out, K goes in. Proton pump burns ATP. Potassium cycles. If it is turned on, everything else in the parietal cell happens (Downhill biochemical process). o Chlorine comes from capillary bed and enters cell through another antiporter. As soon as Chlorine goes in, HCO3 (bicarbonate) goes out and is picked up by the circulatory system. This buffers the blood against pH changes. Bicarbonate is formed when water diffuses into the cell and breaks into a hydroxyl group, liberating a proton. This proton goes through the pump. The hydroxyl group is not stable, so carbonic anhydrase takes the hydroxyl group and mashes it together with carbon dioxide. This forms the bicarbonate ion. Without this ion, the pump would not function. Sources of CO2 = Kreb’s cycle and air o Regulating HCl Go: Ach binds to muscarinic receptor, which also opens a calcium channel Gastrin binds to CCK receptor These are activated, liberating a Gaq and activating phospholipase C in the membrane. The phospholipase C takes PIP2 and liberates DAG and IP3. IP3 goes into the ER and causes the release of calcium which turns on the hydrogen pump. DAG activates PKC which also turns on the pump. Histamine- Binds receptor, liberates Gas which turns on AC, which activates cAMP, which activates PKA and turns on the proton pump . PKA is the major mechanism which turns on the pump. It turns it on to a much higher magnitude. Stop: Somatostatin comes in and binds to receptor, liberate Gai which turns down AC. At the same time, prostaglandin binds to its receptor and does the same. Inhibiting AC turns down PKA which turns down the proton pump. o Relation of parietal and enterochromaffin like (ECL) cells Vagus nerve arrives through gut brain, releases Ach on parietal cell. Gastrin binds to CCK receptor on ECL and parietal cell, encourages release of histamine on ECL cell. ECL cell hangs out near parietal cell. Branch of vagus nerve dumps Ach onto this ECL cell. ECL cell responds by producing and secreting histamine. Histamine is dumped into the extracellular space, which diffuses over and binds to the histamine receptor. This is the origin of the histamine that was mentioned previously. G cell, just south is the D cell. There is also a D cell to the right of the ECL cell. In different parts of the stomach. Both have access to what’s in the lumen of the stomach. Pick up chemistry of content of stomach. D cell picks up pH, G cell looks at chemistry of the food. GRP receptor on G cell causes it to secrete gastrin when bound. Gastrin goes into local circulation, feeds back and binds on CCK receptor which turns on the proton pump. Some of the gastrin also binds to the CCK receptor on the ECL cell and causes the release of more histamine. If we have undigested proteins in the lumen of the stomach, the G cell picks up on it, and in the absence of GRP this is a trigger for the G cell to secrete gastrin. D cell secretes somatostatin. This turns off the parietal cell. Low pH causes the release of somatostatin, because if pH is too low you can burn through your stomach. D cell is essentially the safety mechanism. Somatostatin inhibits the G cell, which slows down the release of gastrin, which slows the proton pump. Mucus cells o Bicarbonate in the mucus acts as a buffer against low pH environment of stomach o Mucus neck cells secrete bicarbonate in addition to the mucus Gastric contractile activity o Anytime something is in your stomach causing distension, this causes peristaltic waves in the stomach o Think of the stomach as a large pastry bag full of vomit… You are going to decorate your enemy’s birthday cake with vomit. This opening is tiny, so all of the vomit is not going to go out the hole. Most of it bubbles backwards. This is what happens with each peristaltic wave. Most of the chyme is injected backward as you go down. o With each wave that approaches the pyloris sphincter, the pyloris will dilate. ½-2 mils of chyme is injected into the duodenum with each wave. If it is not digested to the correct extent, the duodenum will increase the release of HCl and send a circuit back that will cause the pyloric sphincter to ignore the signal to open in the next peristaltic wave. The intestinal phase is critical in regulating the amount of HCl and the emptying rate of the stomach. Summary: Duodenum is in charge of the emptying rate of the stomach. o A stomach full of fat empties faster than a stomach full of protein, because pepsinogen -> pepsin is released onto protein to destroy the amino acids. o Diet the animal is on influences the rate at which it is released from the stomach. It affects gastric emptying rate by means of the duodenum. o What is going on when your stomach growls The thought of food turned on the cephalic phase of digestion, which turned on gastric contraction. The gases bubbling back causes rumbling. Peptic Ulcer Disease o Too much hydrochloric acid. Burns holes in the lining of the stomach. o Caffeine goes in and binds muscarinic receptor in absence of Ach. This tricks the system to release HCl, which starts working on the stomach lining itself. o You start to bleed into the stomach and digest your own blood. This triggers the G cell to release gastrin which increases the production of HCl. o This is a positive feedback system, and if you don’t break this the animal will destroy itself. o Our physiology did not evolve to drink coffee! If you eat something when you drink caffeine, you should be okay.