Psyc 4640 1st Edition Lecture 3 Current Lecture Blood brain barrier lets more chemicals in brain keeps others out Protects Composed of endothelial cells Line capillary and ventricle walls so tightly that not much can get through Covalent and fat soluble molecules can get to brain easily Heroin is fat soluble morphine is not Glucose active transport system needs oxygen Area postremia vomit reflex area Weak area of BBB that allows stuff in and allows you to get rid of it quickly BBB can be broken down by radiation infections and high blood pressure Neuron activity Concentration gradient when talking about ions crossing a membrane high a low Results in homeostasis Na K Cl Electrical gradient charges attract like charges repel Neuronal membrane has selective permeability Deals w ions Require voltage dependent gates In absence of outside influence the neuron is slightly negative inside the cell due to uneven distribution of ions It s resting potential energy in absence of stimulus is 70 millivolts Sodium Potassium pump At rest Cl and K gates are slightly open but Na gates are very tightly closed The pump kicks Na out for K at a 3 2 ratio Requires energy Explosive system At rest you have more K inside and Na outside K electrical gradient wants it inside the cell opposite of what the gradient wants Na electrical gradient wants it inside same as gradient Certain events make RP more negative Hyperpolarizes neuron and it is less likely to respond Making cell more positive depolarizes it You ve reached the threshold 55 Mv An action potential occurs Na gates open slightly and the ion pours in Electric and gradients push it in It reaches zero and becomes positive inside neuron Around peak K gates open K begins rushing out Competing gradients cause Na gates to close and K flows out Membrane become hyperpolarized With the help of the Na K pump and closing of K gates somehow the neuron gets back to its resting potential Neuron does not immediately refire because of its absolute refractory period where no amount of stimulus can make it fire again Relative refractory period a lot of energy can make it fire again Axons w o myelin sheath Action potential occurs travels along down axon and a new action potential occurs at every point along the axon Travels via propagation As strong at end as beginning Action potentials start at axon hillock Size and shape of APs are same no matter what caused them Intensity of stimulus doesn t matter All or none law Flow of ions is critical to proper neuronal functioning EX Novacane blocks Na gates No action potentials No pain inflammation EX Scorpion venom opens Na gates and closes K gates Constant depolarization Axons w myelin sheath Only see action potentials occurring at Nodes of Ranvier Not propagation Saltatory conduction Just jumps from each N of R Speedier transmission Multiple sclerosis MS causes destruction of myelin and oligodendrocytes Myelinated cells do not just begin working like unmyelinated cells after the sheath has deteriorated Neurons w o axons Graded potentials do decay over time and space unlike action potentials All or none law does not apply Distance affects transmission Axonal transmission only goes in one direction Axon hillock to terminal bulbs Graded potentials are not one way streets For local neurons ACTION POTENTIAL HANDOUT 1 The neuron s resting potential is 70mV the charge is slightly negative inside the cell relative to outside the cell 2 At rest Na s concentration and electrical gradients are driving it into the cell but its gates are closed 3 At rest K s concentration gradient is driving it out of the cell and its electrical gradient is driving it into the cell but its gates are closed 4 Once threshold is reached 55mV an action potential occurs Na gates open wide and Na rushes into the cell the charge overshooting 0 so that the cell becomes positively charged inside This causes Na s electrical gradient to now drive it OUT of the cell this opposition of gradients closes the Na gates 5 At about the peak of the action potential K gates open and now its concentration and electrical gradients its positive inside now are driving it out of the cell so much so that it eventuates in hyperpolarization of the membrane 6 Eventually things right themselves with some help from the Na K pump and the neuron returns to its resting potential 7 The neuron can t immediately refire because of its refractory period 8 Recall all or none law once that threshold 55mV is reached the intensity of the stimulus is irrelevant it may be the or the pattern of neurons firing 9 On neurons without myelin information travels down the axon via Propagation