Neural Communication Signaling within a neuron

Postsynaptic Potentials n E m changes dendrites & soma n Excitatory: + n Inhibitory: - ~

Postsynaptic Potentials - PSPs n Chemically-gated ion channels n Graded Summation n Fast n Decremental ~

n Excitatory Postsynaptic Potential n Depolarization (+) E m becomes more positive n Na+ influx ~ EPSPs

-65mv - 70mvAT REST EmEm Time EPSP + - n *Depolarization more likely to fire ~ Record here +

-65mv - 70mvAT REST EmEm Time *Temporal Summation + - n Repeated stimulation n same synapse ~ +

-65mv - 70mvAT REST EmEm Time + - *Temporal Summation more depolarization +

-65mv - 70mvAT REST EmEm Time + - *Temporal Summation more depolarization +

-65mv - 70mvAT REST EmEm Time + - *Spatial Summation + n Multiple synapses +

n Inhibitory Postsynaptic Potential n similar to EPSPs EXCEPT opposite n hyperpolarization (-) l E m becomes more negative n K+ efflux ~ IPSPs

- 70mvAT REST EmEm Time IPSP + - n *Hyperpolarization less likely to fire also summate (max) -

EPSPs & IPSPs summate n CANCEL EACH OTHER n Net stimulation l *EPSPs + IPSPs = net effects ~

- 70mv EPSP IPSP +

ExcitatoryInhibitory DepolarizationHyperpolarization Na+ influxK+ efflux or Cl- influx more likely to fireless likely ~ EPSP IPSP

-70mV EPSP IPSP threshold toward threshold away from threshold

Action Potentials n Large and rapid change in membrane potential n electrically-gated channels n EPSPs l threshold potential n Occurs in axon triggered at axon hillock ~

AP Characteristics n Voltage-gated channels n All or none n Slow n Non-decremental n Self Propagated l regenerated ~

Time Depolarization Na+ influx C & E gradients drive Na+ into cell

Na+ K+ pos neg axon outside DEPOLARIZATION

Na+ K+ Na+ axon outside DEPOLARIZATION neg pos

Time Depolarization Na+ influx = 110 mV Amplitude - 70 mV to +40 mV

Time Repolarization K+ efflux

Na+ K+ Na+ axon outside REPOLARIZATION neg pos

Na+ axon outside K+ REPOLARIZATION pos neg

Time After- hyperpolarization

Na+ axon outside K+ AFTER-HYPERPOLARIZATION K+ pos neg

Refractory Period n after AP won’t fire again relative & absolute n Relative during after hyperpolarization requires greater depolarization ~

Absolute refractory period n Na+ channels deactivate will not trigger AP must reset n Ball & Chain Model ~

Na+ channel deactivation

Saltatory Conduction n Myelinated neurons l oligodendroglia & Schwann cells n Transmit long distances l APs relatively slow, regenerates l EPSPs - fast, decremental n Saltatory: combines both types of current l speed without loss of signal ~

Saltatory Conduction n Nodes of Ranvier l action potentials n Myelinated l like electricity through wire l decremental but triggers AP at next node l Safety factor - trigger AP across 5 nodes ~

Saltatory Conduction

Presynaptic Modulation n Modifying PSP by influencing presynaptic neuron n Presynaptic inhibition  amount of NT released n Presynaptic inhibition  amount of NT released n Effect on activity of postsynaptic neuron l depends on nature of synapse ~

Excitatory Synapse n A active n B more likely to fire n Add a 3d neuron ~ A B + Presynaptic Inhibition

Excitatory Synapse n axoaxonic synapse n C is inhibitory ~ A B + Presynaptic Inhibition C -

Excitatory Synapse A B + Presynaptic Inhibition C - n C active n less NT from A when active n B less likely to fire ~

A B Presynaptic Inhibition C - n C active n more NT from A when active n B more likely to fire ~ Inhibitory Synapse -

Excitatory Synapse A B + Presynaptic Facilitation C + n C active (excitatory) n more NT from A when active n B more likely to fire ~

A B Presynaptic Facilitation C - n C active n more NT from A when active n B even less likely to fire ~ Inhibitory Synapse - C +