1 Learning Objectives: Explain how neurons communicate stimulus intensity Explain how action potentials are conducted along the axon Describe the significance of myelination QUIZ/TEST REVIEW NOTES SECTION 7 NEUROPHYSIOLOGY [THE SYNAPSE AND PHARMACOLOGY] 1. THE SYNAPSE a. Defined - Region where an axon terminal meets its target cell - Number of synapses is not fixed - Single neuron can have up to 10,000 synapses b. Components of a synapse 1. Presynaptic Neuron - The neuron that delivers the signal to the synapse - Contains many small synaptic vesicles and large mitochondria 2. Synaptic Cleft - Space between pre/pos synaptic neuron where neurotransmitters are found E.C.F. 3. Postsynaptic Cell - Cell that receives signals from the Presynaptic neuron - May be neurons or non-neuronal cells c. Electrical Synapse 1. Definition - Pass an electrical signal or current directly from cytoplasm of one cell to another through gap junctions - Occur mainly in CNS neurons 2. Functionality - Found in glial cells, cardiac muscle, smooth muscle - Advantage: Rapid conduction of signals from cell to cell that synchronizes activity within network of cells d. Chemical Synapse 1. Definition - Use neurotransmitters to carry information from one cell to the next - Electrical signal of presynaptic cell is converted into chemical signal that crosses synaptic cleft between presynaptic neuron and target - Chemical neurotransmitter transmission either initiates an electrical response or actives a second messenger pathway
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Learning Objectives:
Explain how neurons
communicate stimulus intensity
Explain how action potentials are
conducted along the axon
Describe the significance of
myelination QUIZ/TEST REVIEW NOTES
SECTION 7 NEUROPHYSIOLOGY
[THE SYNAPSE AND PHARMACOLOGY]
1. THE SYNAPSE a. Defined - Region where an axon terminal meets its target cell
- Number of synapses is not fixed
- Single neuron can have up to 10,000 synapses
b. Components of a synapse 1. Presynaptic Neuron - The neuron that delivers the signal to the synapse
- Contains many small synaptic vesicles and large mitochondria
2. Synaptic Cleft
- Space between pre/pos synaptic neuron where neurotransmitters are found E.C.F.
3. Postsynaptic Cell
- Cell that receives signals from the Presynaptic neuron
- May be neurons or non-neuronal cells
c. Electrical Synapse 1. Definition
- Pass an electrical signal or current directly from cytoplasm of one cell to another
through gap junctions
- Occur mainly in CNS neurons
2. Functionality
- Found in glial cells, cardiac muscle, smooth muscle
- Advantage: Rapid conduction of signals from cell to cell that synchronizes activity
within network of cells
d. Chemical Synapse 1. Definition
- Use neurotransmitters to carry information from one cell to the next
- Electrical signal of presynaptic cell is converted into chemical signal that crosses
synaptic cleft between presynaptic neuron and target
- Chemical neurotransmitter transmission either initiates an electrical response or actives
a second messenger pathway
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2. SYNAPTIC TRANSMISSION
a. Arrival of the action potential - When depolarization of action potential reach axon terminal, the change in membrane potential
sets off sequence of events
- Axon terminal membrane has voltage-gated Ca2+ channels that open in response to
depolarization
- Calcium ions more concentrated in E.C.F. than in the cytosol and move into the cell
b. Exocytosis of Neurotransmitter - The binding of Ca2+ to regulatory proteins in the I.C.F. initiates exocytosis
- Membrane of the synaptic vesicle fuses with cell membrane with aid of multiple membrane
proteins
- Fused area opens and NT inside synaptic vesicle are released into synaptic cleft
Kiss-and-Run Pathway
> Synaptic vesicles fuse to presynaptic membrane at complex called the
fusion pore
> Fusion opens small channel that is just large enough for NT to pass
> Instead of vesicle now fusing with cell membrane it backs off and
returns to I.C.F. cytoplasm
c. Post-synaptic response - NT molecules diffuse across synaptic cleft to bind with membrane receptors on postsynaptic cell,
which will initiate a postsynaptic cell response
- Chemical neurotransmitter transmission either initiates an electrical response or actives a second
messenger pathway
d. Multiple Receptors on Post Synaptic Neuron 1. Definition
- All neurotransmitters have one or more receptors types to bind except nitric oxide
2. Receptor subtypes
- Receptors subtypes allows one neurotransmitter to have different effects in different
tissues
- Subtypes distinguished by combinations of letter and number subscripts
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3. N.T. Receptor Categories
- Ligand Gated Ion Channels: Simplest chemical receptor gate that opens/closes thus
altering ion concentrations
[Ionotropic receptors: alter ion channel function]
[Linked to fast synaptic potentials]
- G Protein-Coupled Receptors (GPCR): Linked to second messenger systems
[Metabotropic receptors: Exert actions through second messenger system/some
open or close ion channels]
[Linked to slow synaptic potentials]
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4. Basic Receptor Groups
(a) Cholinergic Receptors [mainly ACh NT receptors]