From Chapter 8
Action & Graded Potentials
(review Interactive Physiology)
& the Synapse
Outline

Detailed look at an action potential

Synapses



Electrical versus chemical synapses
Review of important neurotransmitter of PNS
Note: this chapter contains additional
information on some CNS neurotransmitters
which I have not emphasized
A simple flow chart of electrical
events

Graded potentials

Action potentials

Neurotransmitter
release
Graded potentials decrease in strength as
they spread out from the point of origin
The Action Potential
Action Potential: depolarization
step-by-step
Repolarization
SUMMARY
Refractory Periods
 Absolute


Na+ channels are inactive
K+ channels are open
 Relative


Some Na+ channels reset
Some K+ open
Quiz Question:
What 2 factors contribute to the
interruption of the positive
feedback loop?
Answers:

Closing of Na+ channels

Opening of “slow” K+ channels
What are two factors related to
the neuron that might contribute
to the speed of an action
potential?
Answers:
 Diameter
 Myelination
Blocking an Action Potential:
 Local


Anesthetics
Procaine (Novocaine)
Lidocaine (Xylocaine)
NO ACTION POTENTIAL
NO SENSORY PERCEPTION
Blocks Na+ channels
2. Types of Synapses
Synapses
 Chemical:
 Electrical:
via neurotransmitters
via gap junctions
Chemical Synapse
Cholinergic Chemical Synapse

Neurotransmittor:


Acetylcholine
Receptors:


Nicotinic
Muscarinic
Cholinergic Receptors

Nictotinic


Only Excitatory
Found: neuromuscular junctions

Muscarinic


disorder
Myastenia Gravis
Excitatory or Inhibitory
Found in CNS, heart
Adrenergic Chemical Synapse

Neurotransmitter:

Norepinephrine

Receptors:
 Alpha
 Beta

How does Norepinephrine
“breakdown?
ADRENERGIC

Alpha-1
Excitatory
 Found in: Smooth muscle
contracts blood vessels
 Found in CNS

Beta 1
Excitatory
 Found in the heart
 Increases heart rate
 Dilates blood vessels
of skeletal muscle
How
does Norepinephrine “breakdown?
Monoamine Oxidase=MAO
mitochondrial enzyme breaks down
norepinephrine; dopamine; serotonin
Note: Synaptic Potentials
may be classified as depending upon the effect of
the neurotransmitter:
 Excitatory
Postsynaptic Potential (EPSP)
or
 Inhibitory
Postsynaptic Potential (IPSP)
Summary:
Post synaptic cell varied response
The end!