test day

its test day. so, im not really learning anything new, just memorizing and reviewing. so, please take the time to go to this website and "sign a cast." it takes less than 30 seconds and someone will donate $5 to a kid who needs a surgery.
http://www.helpcurenow.org/site/c.nvI1IeNYJyE/b.4137607/k.9A91/Sign_a_Cast.htm

thanks!

alcohol poll and dysdiadochokinesis

i'm a little surprised at the poll results. some have quite a bit of alcohol experience(zero order kinetics), some have none (i have no idea or first order kinetics), and others are just plain alcoholics (mmm... alcohol). it turns out, as emily so expertly pointed out that alcohol is a mixed order or dose dependent. when a drugs elimiation is mediated predominantly by metabolism, its elimination will tend to follow first order kinetics when concentrations are well below the Km of the metabolic enzymes, but will follow zero order kinetics at high doses that greatly exceed the Km of the metabolic enzymes due to saturation of the metabolic pathways. alcohol is one such drug.

so congrats to those of you who voted, you're all a little wrong, and all sort of correct. just remember... "you don't booze, you don't win. you booze you win. you don't booze you don't race you don't win, you booze you race you win."

dysdiadochokinesis: the ability to preform rapidly alternating movements. this is impared in cerebellar damage. so whatever you do this fine weekend, don't damage your cerebellum!

smooth pursuit... not just a nickname for a girl i know...

first let me say that its almost midnight and im still at school studying, and i have to say that medical school is perhaps the coolest thing that i have ever done and i feel so privlaged to be here. let me tell you what i have learned today.

smooth pursuit: this refers to the eyes tracking an object slowly across your visual field. the ability comes for the occipital lobe. however, it is impossibe to do this unless you are following an object. try it. start at the corner of the ceiling and try to slowly move your eyes to the other corner. your eyes will jump from spot to spot. now follow your finger, its a smooth movement. clinical application: this is how you tell if a schizophrenic person is really seeing something, if they can smoothly track it with their eyes. crazy, huh?
btw, the fast movement of your eyes is controlled by the frontal lobe of the brain.

random fact: men have a 1:2 chance of getting some form of cancer anywhere in the body during their lifetime. guys, look at your roomate/cubicalmate/playmate (oh, wait...) and chances are either you or they will develop cancer. most likely cancer? prostate, 1:6 chance.

tonight i was walking across the atrium of the school and tripped, but didn't fall. at first i blushed and hoped that no one saw. then i just realized that i knew the pathway that fired to keep me upright. my semicircular canals sent a signal to the vestibulochocler nerve (Crainial Nerve VIII) to my cerebellum through the inferior cerebellar peducle to the flocculonodular lobe, then to the fastigial nucleus, then out to the vestibular nuclei then down the spinal cord thru the lateral and medial vestibulospinal tract to my arms and legs to respond to keep me from falling. and it all took place in less than a second without me even thinking about what i was doing. amazing!

thank God we have such amazing and complex systems. i really am in awe of the body im struggling to learn about.

what to look forward to tomorrow? dysdiadochokinesia. (it really is a word, i promise)

hijacking viruses

many diseases are characterized by the lack of something, perhaps an enzyme. or sometimes it is benificial to provide a growth factor. in these cases, it would be benificial to add a gene to a cells DNA. but how? well, some really smart people realized thats what viruses do, so why not hijack them and make them work for us? so they did. there are 5 kinds of viruses we use.
1)adenovirus- most commonly used; infects respiratory epithelium,
disadvantages- very immunogenic (causes immune reaction), infection only lasts a few months
2)adeno-associated virus - infects many cell types, no immune response
disadvantage- hard to harvest to any large number
3)retrovirus - used to treat immune deficiencies, generated in high titer
disadvantage- only integrates into dividing cells, and the site of intigration is unpredictable so it could insert anywhere and cause cancer!
4) lentivirus - virus associated with HIV, infects all cells, gene expression lasts for years
disadvantage - site of integration unpredictable
5) herpesvirus - (yes, as in herpes the STD), infects neurons
disadv. - large and dificult to use

once you insert a gene via a virus, it is always there, you can never get it out. so, hope you don't screw up! what they started doing is inserting a progene, meaning you have to give a drug or something to make that gene active. when you don't want the gene to be expressed anymore, then you stop taking the drug. kind of eliminates the purpose of inserting the gene in the first place (so you don't have to remember to take your drug) but it still has its advantages.

amazing drug that keeps on giving!

i still can't get over how cool this one is... so some really smart people realized that our cells secrete a molecule we decided to call "nerve growth factor" (NGF). they then thought, well, if it does what it's called, then why don't we use it to treat neuronal degenerative diseases? so they did. how did they deliver it? the took a really long needle and injected it into the lateral ventricles! that is in the very center of your brain! they had to go through the skull, through the brain and sinuses and meningies and all that menusha with a needle! unbelieveable. turns out the patients all developed debilitating neuropathies, so they stopped the trial. but not done yet. they are currently back at it, but delievering it a diferent way.
round 2: they are implanting genetically engineered fibroblasts (special type of cell) that secrete NGF into the forebrain! awesome right? thats like putting a drug into the sight of action that just keeps on giving! so far, they are having great success at improving cognitive function in diseases such as alzheimer's.

there are some pretty awesome other techinques they are using or developing, but i have to go learn about them right now. more later...

alcohol

in pharm drugs fall in to two classes of kinetics. first order or zero order. it deals with their clearance, or how fast the drug is eliminated from the body. first order kinetics is what almost all drugs are. first order drugs are cleared with a constant half-life. this means that they are concentration dependent. the more drug present, the faster it will be cleared. zero-order kinetics means that the drug clearance is constant. it does not have a constant half life. so if you have a huge amount of that drug in your system, it will be eliminated from the body at the same rate is if you had just a little. the drug metabolism pathways are saturated.

I'm going to make this post interactive. take my poll. from your experience with drinking, do you think alcohol is first order or zero order?

stroke

when someone has a stroke in the right brain, they have left sided symptoms. this is because the motor neurons cross to the other side in the lower medulla. the top of the face, such as your forehead does not experience these symptoms however, because the motor neurons that control these muscles come from both sides. cool huh?