BIO 330 Cell Biology
Lecture Outline
Spring 2011
Chapter 13: Signal Transduction in Neurons
I. Overview of the Neuron
II. Resting Membrane Potential
A. Concentration gradients
Potassium
Sodium
Chloride and other counterions
Leakage
Na+/K+ pump
B. Electrical terminology
Electrical potential (voltage): The tendency of separated charges to flow back toward
each other
Current: when separated charges are actually flowing
C. Equilibrium membrane potential
Nernst equation allows us to calculate the Vm based on concentration gradients
D. Combined effects of several ions on Vm
Goldman equation uses concentration gradients and the permeability of the membrane
to each ion to determine Vm
III. Electrical Excitability and the Action Potential
A. Action potential
Reversal of Vm polarity following a slight depolarization
Due to voltage-gated ion channels
Local event; propagated throughout the length of the axon
B. Phases of an AP
Subthreshold depolarization
Depolarizing phase
Repolarizing phase
Hyperpolarizing phase (undershoot)
Refractory period (absolute vs. relative)
C. AP propagation
Passive spread of depolarization (dendrites and soma)
Can lose strength over distance
AP (axons)
Maintains strength of signal due to repeated propagation
New AP is triggered due to passive spread of depolarization
Myelin sheaths increase rate of AP propagation by allowing passive spread of
depolarization to occur over long distances
Saltatory conduction
BIO 330 Cell Biology
Lecture Outline
Spring 2011
IV. Synaptic Transmission
A. Synapse terminology
Presynaptic neuron
Postsynaptic neuron
Synpase
Synaptic cleft
B. Electrical synapses
Gap junctions
C. Chemical synapses
1. Electrical signal must be converted to chemical signal to cross synaptic cleft, then
reconverted into a new electrical signal in the postsynaptic cell
2. Neurotransmitters
Excitatory vs. inhibitory
Criteria
Elicit appropriate response in postsynaptic cell
Occur naturally in presynaptic cell
Released at appropriate time following stimulus of presynaptic neuron
Classes
Acetylcholine
Catecholamines
Amino acids & derivatives
Neuropeptides
Release of neurotransmitters
Trigger: high intracellular calcium (voltage-gated Ca2+ channels)
Neurosecretory vesicles dock & fuse as described last week!
Some neurotoxins work by preventing neurotransmitter release
3. Neurotransmitter receptors on postsynaptic neurons
ACh receptors
Nicotinic vs. muscarinic
nAchR is excitatory by opening sodium channels
GABA receptors
Inhibitory by opening chloride channels
4. Neurotransmitter inactivation
Neurotransmitter reuptake
Degradation
Acetylcholinesterase
V. Integration of Nerve Signals
A. Postsynaptic potentials (PSP)
Excitatory (EPSP) vs. inhibitory (IPSP)
B. Summation
Temporal vs. spatial