Unit 2-Part 2 Action Potential PDF

Unit 2 Part 2-Action potential propagation p.179-193  Describing Changes in membrane potential Normal resting potential is approximately -70mV Depolarization: If the voltage increases relative to the resting membrane potential Hyperpolarization: If the voltage...

Unit 2 Part 2-Action potential propagation p.179-193  Describing Changes in membrane potential Normal resting potential is approximately -70mV Depolarization: If the voltage increases relative to the resting membrane potential Hyperpolarization: If the voltage decreases relative to the resting membrane potential Repolarization: restoration of resting  What causes changes in the membrane potential? Stimulus : any change in the environment of the cell May cause ion channels to open/close As a result ions will move in/out of the cell Membrane potential changes Resultant change is called either – A graded potential – An action potential  2 types of potentials Action potential Graded potential Large change in membrane Small change in membrane potential (to +30 mv) potential Set long distances along cell Strength dissipates as it moves membranes at full strength along cell membranes Our bodies version of a ‘message’ Is not a ‘message’ How our cells communicate Multiple graded potentials can be added together (summed) to produce an action potential  Graded potentials Stimuli cause voltage gated ion channels to open But, sometimes, we don’t get enough Na+ into the cell to get to a charge of + 30 mv (the action potential) If a change in charge occurs, but it’s not an action potential, it’s called a graded  Stimuli strength and size of graded potential GP are small changes in membrane potential (changes in the voltage across the membrane) A stronger stimulus produces a larger change in the voltage  GP are decremental GP dissipates as it moves away from area of stimulus  Graded potentials aka Postsynaptic potential (PSP) Change in membrane potential of post synaptic membrane Can be either an inhibitory postsynaptic potential (IPSP) or excitatory post synaptic potential (EPSP)  Excitatory and inhibitory neurotransmitters Excitatory Inhibitory neurotransmitter neurotransmitter Increases likelihood of an AP Decreases likelihood of an AP occurring on post synaptic neuron occurring on post synaptic neuron Leads to an excitatory post Leads to an inhibitory post synaptic synaptic potential (EPSP) potential (IPSP) Most abundant is Acetylcholine Most abundant in brain is GABA Acetylcholine works via opening GABA works via the opening of Cl- Na+ ion channels ion channels  Threshold & the development of an action potential For an AP to be generated, the membrane potential must depolarize to -55mv – threshold If the stimulus was strong enough to allow enough Na+ into the cell to bring the membrane potential from – 70 mv to -55 mv, an action potential will occur – Once the charge reaches -55mv, MORE Na+ gates open, and more Na+ is added Action potential Action potential Na+ K+ _+ Na+ K Leakage channels K K _ + 2K Na+ + K K + K+ A- _+ Na++ + K+ + + K K A- _+ Na+ 3Na+ + K+ + Na+ Na+ K Na+ + Voltage Na+ Leakage gated K+ channels channels Voltage gated Na+ Chemically channels gated Na+ channels Specialized channels exist on the cell membrane. Voltage-gated Na+ and K+ channels. As the name implies they only open/close when the membrane potential changes. Action potential sequence of events 1) Stimulus (eg. temperature, pressure, light, sound) causes alteration of resting membrane potential. (Chemically gated Na+ channels open). 2) If graded potential is strong enough to cause the membrane potential to reach threshold (-55mV), then voltage gated Na+ channels open and Na+ rushes into cell. 3) Membrane potential quickly climbs from -70 to +30 (action potential is generated) 4) Na+ channels close, and K+ open 5) Repolarization due to K+ exiting cell 6) K+ channels close slowly and membrane becomes hyperpolarised for short duration. Action potential-all or non principle Refractory Periods  Linking the AP to a nerve cell The previous slides on the generation of the AP apply mostly to neurons – They are the cells that are designed to detect stimuli, and then communicate with other cells Functional cell of the nervous system is called a neuron Integrati receptor effector ng centre Respons Stimulus e Details of the neuron Part Job Dendrites Detect stimuli Axon Develops and sends action potentials Cell body Nucleus Action potential propagation  Myelinated neurons Whitish, fatty covering of axons Associated with long, and large diameter nerve fibers. Form Nodes of Ranvier Myelinated fibers conduct impulses at a much faster rate than non-myelinated fibers. Signal decay Myelinated Fibers vs. Non Myelinated Fibers  of action potential through myelinated fiber Speed of nerve conduction