Ionic Mechanisms of Synaptic Excitation Synaptic transmission - PowerPoint PPT Presentation

Ionic Mechanisms of Synaptic Excitation � Synaptic transmission Synaptic input 1) Communication within the nervous system 2) A site of plasticity for learning and memory 3) A site of action for disease, psychoactive drugs Whimpy axon!

Crayfish NMJ as a model for human brain synapses Neuromuscular Innervation Uni-terminal Multi-terminal Uni-neuronal Poly-neuronal Excitation Only Inhibition Often no APs Mammals Arthropods See Synapse Tutorial on class web site for review

Crayfish NMJ preparation

Example Data

Map Muscle Innervation Patterns (Also better distinguish number of axons in nerve 3 ) Synaptic Integration See G-PRIME for example of- Muscle Innervation - Cross Correlation

EPSP trying to reach AP threshold Synaptic integration Axon Hillock Dendrite spatial and temporal

Space constant important Time constant important Spatial summation Temporal summation

Synaptic Inhibition Two flavors: Algebraic Summation Shunting How do they work?

Synaptic Inhibition Stimulation of inhibitory nerve blocks AP production

Presynaptic inhibition � Presynaptic inhibition � reduces transmitter � release �

Types of Chemical Synaptic Transmission direct, fast indirect, ~slow

Action Potentials can arise from subthreshold depolarizations if they are not spontaneous

Stimulate presynaptic axon

Steps in ionotropic chemical synaptic transmission

Excitation: Conductance increase (resistance decrease): Channels in membrane open Membrane potential goes towards Vrev (Equil. Pot)

Vrev = Eion Results if EPSP were due to only Na + or K +

Isyn= g ACh (V m -V rev ) (Vm-Vrev)= Driving force Depolarizing because of large Na driving force -60 mV

Conductance change due to multiple ions

Inhibition: Conductance increase (resistance decrease): Membrane potential goes towards Vrev (Equil. Pot)

Most common fast transmittters Proof of Neurotransmitter Identity?? Presence Action Release Pharmacological Congruence Synthetic/packaging machinery

Release of Transmitter Snake Neuromuscular Junction Model

EM section of NMJ Freeze-fracture of NMJ

Brain Synapse Few vesicles at each synaptic site