Week-2- Behavioral neuroscience
Week-2- Behavioral neuroscience PSYC 4183-001
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This 9 page Class Notes was uploaded by Celine Notetaker on Friday January 29, 2016. The Class Notes belongs to PSYC 4183-001 at University of Arkansas taught by Nathan Parks in Spring 2015. Since its upload, it has received 42 views. For similar materials see Behavioral Neuroscience in Psychlogy at University of Arkansas.
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Date Created: 01/29/16
Behavioral Neuroscience – Week 2 EXAMPLE QUESTION 1: Dopamine cannot pass from the circulatory system into the neural tissue of the central nervous system. What best explains this system? A. Astrocytes B. Schwann cells C. Oligodendrocytes D. Microglia E. Myelin ANSWER: A The blood brain barrier is often a big complication when trying to make a drug aimed towards the brain. Often a drug has to be modified with a “disguise” that can pass through the blood-brain barrier then change into a neurotransmitter once it is inside. EXAMPLE QUESTION 2: True or False- Damaged neurons exhibit axonal regrowth primarily in the CNS Answer: FALSE Neural Communication (continued…) Resting Potential At rest, the inside of a neuron maintains a negative charge relative to the outside resting potential For a typical neuron the resting potential is approximately -70 mV The resting potential results from an imbalance of charged ions between intracellular and extracellular space Four types of ions involved : A- , Na+, K+, and Cl- Cl- and Na+ ions are more concentrated outside the axon A- and K+ are more concentrated inside the axon Their roles: 1) Na+: the key to this whole process- excites i) It has a very low membrane permeability 2) K+ is there to balance out what sodium is doing (also critical) 3) Cl- dampens the activity of the cell so that it doesn’t get overexcited (return to neutral) or make a normal cell MORE negative = inhibition Diffusion, electrostatic forces and ion pumps play a role in maintaining the resting potential Na+ and Cl- want to ENTER the cell while A- and K+ want to LEAVE due to the rules of concentration gradients But what’s a concentration gradient? The rules of the concentration gradient explain the tendencies of solutes or ions to travel from high concentration areas to low concentration areas. The goal is to try to get everything EVENLY DISPERSED So, lets learn about a mechanism that aids these ions goals!!! The Na+/K+ pump : Constantly pumps Na+ out of the cell. b) This keeps extracellular Na+ concentrations high and, in turn, balances out out K+ concentrations e Na+ K+ is free to enter and leave the cell but NA+ cannot reenter once pumped out. Na+ channels are ordinarily closed to prevent entry of Na+ INTO the cell In order for Na+ to enter the cell there must be some sort of trigger to activate the Na+ channel Fun FACT: It is possible for a cell to die from being overexcited Graded potentials = Positive or negative membrane potentials (charges) that vary in magnitude. Accumulates charges until it reaches the optimal charge to activate an action potential o Occur LOCALLY in the dendrites and soma and degrade with time and distance o Induced by the release of neurotransmitter from another neuron’s axon 1. Excitatory Post-Synaptic Potentials (EPSPs): Increased intracellular positivity (depolarization Due to an influx of Na+ into dendrites through normally closed Na+ channels Caused by a neurotransmitter being released and opening that ion’s channel 2. Inhibitory Post-synaptic potentials (IPSPs): Increased intracellular negativity (hyperpolarization) Due to an influx of Cl- into the cell or an efflux of K+ out of the cell Graded potentials (EPSPs and IPSPs) SUMMATE The summation of graded potentials can be thought of as the accumulation of information from other neurons EPSPs and ISPs summate in time and space, it matters when and where it happens (1) Spacial Summation (a) Is EPSPs summate to a threshold of -60 mV at the axon hillock, an action potential will be generated (2) Temporal Summations (a) If graded potentials occur at a high enough frequency (one after the other) they can overlap and quickly summate to the threshold for an action potential. OUTPUT OF THE CELL IS THE summary OF ALL THE EPSPs AND IPSPs occurring around the cell EXAMPLE QUESTION #3 - True or False: An IPSP will increase a neurons internal positivity Answer: FALSE EXAMPLE QUESTION #4: True or False- An EPSP always changes the membrane potential by +5mv Answer: FALSE because it changes by different amounts EXAMPLE QUESTION #5: K+ exiting a neuron will lead to: A. Hyperpolarization B. Depolarization Answer: A Action potentials The electrical signal conducted along an axon by which information is transmitted from one place to another in the nervous system. -Once an action potential begins it cannot be inhibited. “All or none” Action potentials have been classically studied in the giant axon of the squid A.P. is a very large but very brief depolarization of the axon membrane o Begins at the axon hillock then regenerated down the length of the axon The action potential always takes on the same form and has the same amplitude. It is repeatedly replicated as it travels down the length of the axon o The Axon’s membrane is lined with voltage-gated Na+ channels and voltage gated K+ channels 1) If EPSP summates to -60mV at the axon hillock it creates a positive enough charge to begin the action potential i) It will also trigger the voltage-gated Na+ channels near it to open 2) Once opened, Na+ will rush in a) The Na+ rapidly depolarizes a local section of the axonal membrane i) Which causes more channels to open = CHAIN REACTION down the axon Myelin insulates the cell and allows it to travel a longer distance until it reaches the next point of unmyelinated axon where there are more channels. This SPEEDS up the action potential The basis of the AP is the rapid influx of Na+ through voltage–gated Na+ channels, followed shortly thereafter by an efflux of K+ through voltage-gated K+ channels The threshold for an AP to occur is -60mv Threshold of excitation Repolarization: Na+ channels become refractory which means no more Na+ enters the cell Hyperpolarization: This occurs because the membrane overshoots its resting value (-70 mv) and the accumulation of K+ ions outside the membrane create this temporary hyperpolarization. o The extra K+ ions soon diffuse through which allows the membrane to return to its resting potential Absolute refractory period- This is the time during which another stimulus given to the neuron, no matter how strong it is, will NOT lead to another action potential. The absolute refractory period takes about 12 ms. Refractory period of NA+ channels: Na+ influx induces a refractory state in voltage-gated Na+ channels. This refractory state keeps the Na+ channel closed for brief periods. + Thus, because Na channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials. Relative Refractory period: During the relative refractory period, the neuron can be excited with stimuli stronger than that needed to bring a resting neuron to threshold. The strength of the stimulus required is very high early in the relative refractory period and gradually becomes smaller throughout the relative refractory period Occurs as Na channels recover from inactivation and as K permeability returns to its resting level
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