usually requires more than one EPSP The action potential All or none response

Usually requires more than one epsp the action

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usually requires more than one EPSP The action potential All-or-none response When threshold is reached the neuron “fires” and the AP either occurs or it doesn’t Through APs- message can be transmitted from one neuron to another
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When threshold is reached, voltage-activated ion channels are opened The ionic basis of Action Potentials When summation near the axon hillock results in the threshold of excitation (-65mV) being reached, voltage-activated Na+ channels open and sodium rushes in Remember, al forces were acting to move Na+ into the cell And now permeability isn’t an issue Membrane potential moves from -70mV to +50mV
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Rising Phase: Na+ moves membrane potential from -70mV to +50mV End of rising phase: after about 1 milisec, Na+ channels close Repolarization: concentration gradient and change in charge leads to efflux of K+ Hyperpolarization: channels close slowly –K+ efflux leads to membrane potential <-70mV Refractory Periods – after it fires, it goes into the refractory period where it cannot fire Prevent the backwards movement of Aps and limit the rate of firing (to 1000 times/sec!) ABSOLUTE impossible to initiate another action potential RELATIVE harder to initiate another action potential Only periods of VERY high thresholds will be enough to cause am AP Conduction in Myelinated Axons: Saltatory Conduction Passive conduction along each myelin segment to next node of Ranvier New action potential generated at each node Faster conduction than in unmyelinated axons – Saltatory conduction Neurotransmitter (NT) Release- EXOCYTOSIS AP arrives at axon terminal NT’s are released from vesicles into synapse NT’s act on next neuron Calcium enters the cell- this is the signal to dump the neurotransmitters into the cleft EXOCYTOSIS is mediated by CALCIUM Receptors Multiple receptor types for a given NT
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c.1.1. IONOTROPIC RECEPTORS  associated with ligand-activated ion channels - job to open or close ion channels – allowing them to come in or out c.1.2. METABOTROPIC RECEPTORS  associated with signal proteins and G proteins - can affect the actual functioning of the neurons - effects are much more varied Ionotropic Receptors NT binds associated ion channel opens or closes  PSP Na+ channels opened Na+ in  EPSP K+ channels opened  K+ out  IPSP Metabotropic Receptors Effects are slower, longer-lasting, more diffuse and more varied attach to G protein (can do other jobs) NT BINDS  G Protein breaks away  Ion Channel opening/closed & 2 nd messenger synthesized Reuptake, enzymatic Degradation and recycling As long as NT is in the synapse, it is “active” – activity must somehow be turned off Reuptake – “scoop up” and recycle NT – takes it back into the presynaptic button Enzymatic degradation – NT broken down by enzymes (break the NT apart in the cleft) Neurotransmitters Serotonin – mood, temperature regulation, aggression & sleep cycle Dopamine – motor function and reward (pleasure) Acetylcholine- memory and learning – muscle activation (PNS) cortical arousal (CNS)
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