5 Action potential – super-threshold depolarization in nearby regions Saltatory conductionAction potential – super-threshold depolarization in nearby regionsOpens Na+ channels
6 Action potentials in a non-mylinated neuron Relatively slowConsumes more energy (need more channels along the membrane)
7 Action potentials characteristics (regardless of myelin): All or none (always same shape and size)Does not diminish with distance (or splits along the axon) until it reaches the terminal buttons that form synapses with the target neuron
8 The Action Potential is All or None So how can we differentiate btw strong and weak stimulations?The rate lawThe strength of the signal = frequency of Action potentialsNOT magnitude of potential
9 Decreases with distance Passive conductance (graded potentials)Decreases with distanceRate of decrease depends on properties of axon (like diameter)
10 Graded Potential vs. Action potential All or none: fixed magnitudeLarger for stronger triggersStrengthActiveDoes not decay. Saltatory conductionUnidirectional (from soma to axon)PassiveDecays with distance from sourceMulti directionalconduction
11 The synapse Presynaptic neuron vs. Postsynaptic neuron The junction between the terminal button of one neuronand the membrane of another neuron (~20 nm)Presynaptic neuron vs. Postsynaptic neuron
12 Types of synaptic connections Axo-dendriticAxo-somaticAxo-axonic
14 The action potential has reached the terminal button. Now what? Voltage dependent calcium (Ca2+) channelsAction potential -> depolarization.Opens Ca2+ ion channelsWithout Ca2+ - there will be no release of neurotransmitter
15 Each action potential release of a fixed # of vesicles Exocytosis - Followed by recycling
18 Stages in the process of neurotransmitter release: Docking vesicles containing neurotransmittersAn action-potential arrives, and causes voltage-gated Calcium-channels to open (Ca2+ enters the cell)Ca2+ causes fusion of the vesicles with the cell membraneNeurotransmitter in vesicle is expelled (exocytosis)Vesicle membrane either fuses with cell membrane or closes back inside the cell
19 Now that we have neurotransmitters in the synapse….. Neurotransmitters bind to postsynaptic receptorsOpen/close neurotransmitter-dependent channels:1) Direct2) Indirect
24 What determines whether the post-synaptic potential is Excitatory or Inhibitory is NOT the neurotransmitter !!!The same neurotransmitter can have an IPSP or EPSP effect on the target neuron.The ultimate effect depends on the target RECEPTOR and the channels it open !!!
35 Important notes:IPSP does NOT necessarily mean inhibition of behaviorAuto-receptors are pre-synaptic receptors that respond to the neurotransmitter the same cell released. They do not open ion channels on the post-synaptic cellAxo-dendritic and Axo-somatic synapses cause either IPSP or EPSP. Axo-Axonic synapses can regulate the amount of neurotransmitter that will be released.Inihibition => reduction in the amount of neurotransmitter eventually releasedFacilitation=> increase in the amount of neurotransmitter released.