1. Action Potential
Action Potential
The All-or-none Principle

2. All-or-None A threshold must be overcome (between -60 mV and - 55 mV)
Will open voltage-regulated sodium channels
If less than -62 mV will produce a graded depolarization
The action potential is independent of the relative strength of the depolarizing stimulus
Like the pressure on the trigger of a gun: slight pressure gun does not fire, more pressure = gun fires

3. Generation of Action Potential

4. Generation of Action Potential
Depolarization to Threshold
Activation of Sodium Channels & Rapid Depolarization (this is positive feedback)
Inactivation of Sodium Channels & the Activation of Potassium Channels
Return to Normal Permeability

5. Action Potential Animations

6. Propagation of Action Potentials

7. Continuous Propagation
An action potential is propagated (moved) along an unmyelinated axon
Action potential moves at the same speed along the entire length of the axon
Moves at about 1 meter/second
Similar to dominoes falling

8. Saltatory Propagation
Myelinated axons allows the action potential to travel faster
Action potential travels only along the nodes
Node to node – skips the internodes
Faster and uses less energy

10. Synaptic Activity

11. General Properties
Electrical – the Presynaptic & Postsynaptic membranes are locked together at gap junctions, start action potential more quickly
Located int CNS & PNS but very rare
Few areas of the brain, the eye & ciliary ganglia of the PNS
Chemical – Presynaptic & Postsynaptic membranes do not touch, most abundant type
Several types of neurotransmitters

12. Cholinergic Synapses Release Acetylcholine (Ach)
Released at neuromuscular junctions
At many synapses in CNS
At all neuron-to-neuron synapses in PNS
At all neuromuscular and neuroglandular junctions within the parasympathetic division of the ANS

14. Other Neurotransmitters
Norepinephrine – in brain and ANS, has an excitatory, depolarizing effect on the postsynaptic membrane
Dreaming, learning, emotions, sleeping, controls body temp.
Dopamine – a CNS neurotransmitter, may be inhibitory or excitatory
inhibitory – imp. role in our precise control of movements
excitatory – cocaine inhibits the removal of dopamine from synapses in areas of the brain resulting in a “high”

15. Other Neurotransmitters
Serotonin – inadequate production can have widespread effects on a person’s attention & emotional state & may be responsible for many cases of severe chronic depression
Thought to be involved with regulation of sleep and wake patterns
Gamma aminobutyric (GABA) – inhibitory, in the CNS appears to reduce anxiety

16. Information Processing by Individual Neurons

17. Postsynaptic Potentials
Excitatory - a graded depolarization caused by the arrival of a neurotransmitter, affects only the area immediately surrounding the synapse
Inhibitory – a graded hyperpolarization of the postsynaptic membrane, a larger than usual stimuli would be needed to bring the membrane potential to threshold

18. Postsynaptic Potential
Summation – individual excitatory postsynaptic potentials combine which integrates the effects of all graded potentials
Facilitation – a neuron whose transmembrane potential shifts closer to threshold
the larger the degree of facilitation, the smaller is the additional stimulus needed to trigger an action potential