1. Communication between neurons
(chemical)

2. Action potential

3. Saltatory conduction Passive current is much faster within myelin
(speed of conduction can range from 1 to 100 meters/sec
2. Na/K pumps only in the nodes (saves energy)

5. Action potential – super-threshold depolarization in nearby regions
Saltatory conduction
Action potential – super-threshold depolarization in nearby regions
Opens Na+ channels

6. Action potentials in a non-mylinated neuron
Relatively slow
Consumes 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 law
The strength of the signal = frequency of Action potentials
NOT magnitude of potential

9. Decreases with distance
Passive conductance (graded potentials)
Decreases with distance
Rate of decrease depends on properties of axon (like diameter)

10. Graded Potential vs. Action potential
All or none: fixed magnitude
Larger for stronger triggers
Strength
Active
Does not decay. Saltatory conduction
Unidirectional (from soma to axon)
Passive
Decays with distance from source
Multi directional
conduction

11. The synapse Presynaptic neuron vs. Postsynaptic neuron
The junction between the terminal button of one neuron
and the membrane of another neuron (~20 nm)
Presynaptic neuron vs. Postsynaptic neuron

12. Types of synaptic connections
Axo-dendritic
Axo-somatic
Axo-axonic

13. Terminal button (structure)

14. The action potential has reached the terminal button. Now what?
Voltage dependent calcium (Ca2+) channels
Action potential -> depolarization.
Opens Ca2+ ion channels
Without Ca2+ - there will be no release of neurotransmitter

15. Each action potential  release of a fixed # of vesicles
Exocytosis - Followed by recycling

17. Exocytosis

18. Stages in the process of neurotransmitter release:
Docking vesicles containing neurotransmitters
An action-potential arrives, and causes voltage-gated Calcium-channels to open (Ca2+ enters the cell)
Ca2+ causes fusion of the vesicles with the cell membrane
Neurotransmitter 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 receptors
Open/close neurotransmitter-dependent channels:
1) Direct
2) Indirect

20. Post-synaptic receptors

21. How does it affect the cell?
Post-synaptic Potential
Excitatory postsynaptic potential - depolarization
Inhibitory postsynaptic potential - hyperpolarization

22. Excitatory Post-Synaptic Potential (EPSP)

23. Inhibitory Post-Synaptic Potential (IPSP)

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 !!!

25. Post-synaptic integration

26. Neural integration
Axon hillock
Summation by time
Summation by space

27. A single cell can receive synaptic input from up to ~100,000 !!!
Purkinje cell in cerebellum
150,000!! contacts

28. Neurotransmitter binds to postsynaptic receptors
and can Influence neurotransmitter-dependent channels:
1) Direct
2) Indirect

29. neurotransmitter-dependent channels
1. Ionotropic Receptor
2. Metabotropic Receptors

30. neurotransmitter-dependent channels
1. Ionotropic receptor
2. Metabotropic Receptors

31. Inotropic Metabotropic
Fast effect
Only opens transmitter dependent channels
Slow effect
may open/close transmitter dependent channels

32. Sensory neuron Motor neuron Action potential Receptor potential
Synaptic potential
Action potential

33. Enzymatic deactivation Diffusion
Removal of neurotransmitter from the synapse
Reuptake
Enzymatic deactivation
Diffusion

34. Regulation of neurotransmitter release
Autoreceptors (pre-synaptic)
Usually inhibitory effect
Presynaptic facilitation/inhibition
Axoaxonic synapse

35. Important notes:
IPSP does NOT necessarily mean inhibition of behavior
Auto-receptors are pre-synaptic receptors that respond to the neurotransmitter the same cell released. They do not open ion channels on the post-synaptic cell
Axo-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 released
Facilitation=> increase in the amount of neurotransmitter released.