1. Synaptic Transmission Classical –Mediated by Neurotransmitter Gated Ion Channel aka ionotropic receptors Neuromodulatory –Mediated by Metabotropic Receptors Both cause a post-synaptic potential, ie a change in the Membrane potential of the post-synaptic plasma membrane The psp can be depolarizing or hyperpolarizing

2. Synaptic Potentials and Their Integration EPSP: excitatory post-synaptic potential IPSP: inhibitory post-synaptic potential Temporal Summation Spatial Summation

3. Classical Neurotransmission Effects due to direct gating of ion channel Direct postsynaptic effects last for tens of milliseconds No secondary effects Postsynaptic electrical effects are fast and strong

4. Neuromuscular Junction is always excitatory is one for one 1 AP in presynaptic MN= 1 AP in post-synaptic muscle NMJ caused by release of 200 synaptic vesicles In the rest of the NS, it is not 1 for 1, the psp is so small that an AP is not always triggered at the hillock AP can cause release of 1 synaptic vesicle

5. Excitatory Transmission Synaptic transmission that causes depolarization of the postsynaptic neuron Increases the probability that the post synaptic neuron will fire an action potential Increases amount of neurotransmitter released from post synaptic neuron by presynaptic facilitation

7. Excitatory Post-synaptic Potential = EPSP Depolarization of the post-synaptic membrane caused by the neurotransmitter brings the membrane potential close to the threshold for firing an action potential Can increase sodium or calcium permeability or can be caused by decreasing potassium permeability

9. Inhibitory Transmission Synaptic transmission that causes transient hyperpolarization of the postsynaptic neuron Decreases the probability that the post synaptic neuron will fire an action potential This is called an inhibitory post-synaptic potential ipsp

10. I.P.S.P. Caused by increase in potassium permeability similar to the undershoot of the action potential Increase in chloride permeability If E Cl =V r then no change in V r will be observed, however an epsp would be smaller if the Cl permeability is still high

14. Neuronal Integration Summing of all ipsp and epsp to determine if threshold has been met for AP generation Based on temporal summation –Time constant Based on spatial summation –Space constant

16. Temporal Summation Rapid firing from a single presynaptic input leads to repeated post-synaptic potentials in a short period of time Causes repeated depolarization of membrane without time to go back to resting state Allows a weak presynaptic input to generate an action potential in post synaptic neuron

18. Time Constant The amount of time that a psp will last at a given membrane location= tau tau=membrane resistance x membrane capacitance Time it takes for constant applied voltage to build up to 63% of its final value

19. Temporal Summation Neurons with membranes that have long time constants show more temporal summation for conduction of psp Typical values are 10 msec Membrane resistance is reflected by number of open channels and channel density

20. Membrane Capacitance

21. Spatial Summation The simultaneous firing of multiple individual presynaptic neurons to one post- synaptic neuron. The post-synaptic effects sum and can bring the post synaptic membrane closer or further away from threshold.

23. Length constant Distance that a psp can spread along the membrane= lambda Lambda= resistance of membrane/resistance of cytoplasm Distance along a neurite at which a constant applied voltage will decay to 37% of its original value. Common value is 100-300 um to mm. The greater the membrane resistance, ie no channels the longer the psp travels

26. Synaptic Integration Look at Geometry of Inputs and the liklihood that any synapse will lead to an action potential in the axon of the post- synaptic neuron

31. PreSynaptic Inhibition and Facilitation Requires 3 synapses The middle synapse can be active or inactive

34. Types of CNS Synapses Axodendritic Axosomatic Axoaxonic Dendrodendritic

37. Functional/Structural Synapse Classification Gray’s Type I –Post-synaptic membrane is thicker than pre-synaptic –Asymmetrical –Excitatory Gray’s Type II –Symmetrical synapse, pre & post-synaptic densities are similar thickness –Inhibitory