PSY 250 Lecture Notes - Lecture 4: Neurotransmitter Receptor, Exocytosis, Neuroplasticity
30 Jul 2018
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Lecture #4
3. Speed of axonal signal conduction depends on:
●(i) Axon diameter
●(ii) Myelination
●Consider axon as a pipe with pores,
●Unmyelinated axon: neurons not covered by myelin fibers
○slower
○loss potential because of NO insulation
○Action potential has to be generated in every little bit of the membrane → slower
●Myelinated axon: neurons covered by myelin fibers
○faster
○Saltatory conduction (Saltare = to skip or jump)
○Travels down to the end because it jumps
●Saltatory conduction speeds up transmission of action potential
○Action potential is reproduced only at the nodes of Ranvier
○Jumps from one node of ranvier to another node of ranvier
○Size and diameter of the myelin together determines the speed
○Examples:
■Mammalian motor neuron = 100 m/sec
■Squid motor neuron = 35 m/sec
■Unmyelinated sensory neuron = 1-10 m/sec
Figure: Unmyelinated axon vs. Myelinated Axon
4. Multiple Sclerosis
●A demyelinating condition in the CNS
●Diagnosis 20-40 years of age
●Disruption of neural signal transmission
●Oligal dendrocytes are big glial cells that cover the axon, act as myelin sheaths in the CNS
●When attacked you lose myelin for multiple cells, you lose neural transmission
●When myelin is removed, the signal will not survive → happens more in women
Q & A #3
1.In a myelinated axon, how would the action potential be affected if the nodes were much close together?
The action potential would be faster, however if you have too much myelin ad they're too far apart they
may not survive. If they’re too close together then it will slow things down because you have to make an
action potential again and again (almost like its unmyelinated).
2. How might it be affected if the nodes were much farther apart?
If they’re too far apart they may not survive.
IV. Synaptic Transmission - chemical transmission of signal from one neuron to another
IV.A. Synaptic structures
●Neurons communicate with an electrical signal which is within the neuron
●In between the neuron is chemical signal
1
●L dopa as a dopamine precursor because it can cross over the BBB and get into the nervous
system and treat the dopamine deficiency parkinson’s patients have
●Levodopa is a precursor it can become dopamine or other neurotransmitters (mostly dopamine)
●Must know synaptic structures, properties, receptors, and how drugs affect them in a certain way
1. What is a synapse?
●It is where one neuron communicates with another.
●Presynaptic neuron, synaptic cleft, postsynaptic neuron
●Action potential travels down
●Neurotransmitters will bind on to the receptors on the dendritic spine of the postsynaptic neuron,
will produce a biological effect → postsynaptic potential change; excitatory or inhibitory
●Chemical released is called "neurotransmitters"
●There are different types of synapses: E.g., axodendritic
○An axon terminal making synapse from a presynaptic neuron with a postsynaptic neuron
→ close to each other they make a synapse
●Also called neuroplasticity occurs with changes in synaptic organization
●Synapses are modifiable
○Can be enhanced when doing something relevant
○Can break apart when behavior is no longer useful
IV.B. Synaptic properties
1. Delayed transmission at the synapse
2. History of chemical transmission:
●Loewi's discovery
○In austria, won the nobel prize
○Studying frog’s heart, put two hearts in each jar that still had nerves attached to it
○How does signal get through if there are gaps?
○Connected a tube between the two jars, stimulated the nerve of one heart → the next heart
follows the donor’s heart speed
○Shows that neurons release chemicals called neurotransmitters which is only found in the
brain
○Acetylcholine (ACh) → first neurotransmitter discovered
●Neurons discharge chemicals!
3. Two kinds of synaptic transmission:
● (i) Excitatory synapses: can increase next neuron
● (ii) Inhibitory synapses: can inhibit next neuron
IV.C. Key Events at a Synapse:
When a train of action potential reaches axon terminal, a sequence of events follows.
1. Opening of Calcium ion channels
●Action potential opens Ca2+ channels (voltage-gated )
○Ca2+ influx
○Ca2+ causes vesicles to release their neurotransmitter
2
Document Summary
Lecture #4: speed of axonal signal conduction depends on: Consider axon as a pipe with pores, Unmyelinated axon: neurons not covered by myelin fibers. Action potential has to be generated in every little bit of the membrane slower. Myelinated axon: neurons covered by myelin fibers. Saltatory conduction (saltare = to skip or jump) Travels down to the end because it jumps. Saltatory conduction speeds up transmission of action potential. Action potential is reproduced only at the nodes of ranvier. Jumps from one node of ranvier to another node of ranvier. Size and diameter of the myelin together determines the speed. Figure: unmyelinated axon vs. myelinated axon: multiple sclerosis. Oligal dendrocytes are big glial cells that cover the axon, act as myelin sheaths in the cns. When attacked you lose myelin for multiple cells, you lose neural transmission. When myelin is removed, the signal will not survive happens more in women.
