chapter 8b
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Chapter 8b
Neurons: Cellular and Network Properties
Figure 8-20
Cell-to-Cell: A Chemical Synapse
• Chemical synapses use neurotransmitters; electrical synapses pass electrical signals.
Axon ofpresynaptic
neuron
Postsynaptic neuron
Axon terminal
Mitochondrion
Synapticvesicles
Synapticcleft
ReceptorsNeurotransmitter Postsynapticmembrane
Figure 8-21
Cell-to-Cell: Events at the Synapse and Exocytosis1
Voltage-gatedCa2+ channel
Postsynaptic cell
Dockingprotein
Synapticvesicle
Actionpotential
Axonterminal
Neurotransmittermolecules
Synapticcleft
Receptor
An action potential depolarizes the axon terminal.
The depolarization opens voltage-gated Ca2+
channels and Ca2+
enters the cell.
Calcium entry triggers exocytosis of synaptic vesicle contents.
Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell.
Neurotransmitter binding initiates a response in the postsynaptic cell.
Cellresponse
Ca2+
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5
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5
Cell-to-Cell: Neurocrines
• Seven classes by structure• Acetylcholine• Amines• Amino acids• Purines• Gases• Peptides• Lipids
Cell-to-Cell: Synthesis and Recycling of Acetylcholine at a Synapse
Figure 8-22
1Synapticvesicle
Acetylcholine
Acetylcholinesterase (AChE)
Choline
Axonterminal
Acetate
Mitochondrion
Postsynapticcell
Cholinergicreceptor
Enzyme
CoAAcetyl CoA
Acetylcholine (ACh) is made from choline and acetyl CoA.
In the synaptic cleft ACh is rapidlybroken down by the enzymeacetylcholinesterase.
Choline is transported back intothe axon terminal and is usedto make more ACh.
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Myasthenia gravis
Amines
• Derived from single amino acid• Tyrosine• Dopamine• Norepinephrine is secreted by noradrenergic
neurons• Epinephrine
• Others• Serotonin is made from tryptophan• Histamine is made from histadine
Amino Acids
• Glutamate: Excitatory CNS• Aspartate: Excitatory brain• GABA: Inhibitory brain• Glycine• Inhibitory spinal cord• May also be excitatory
Other Neurotransmitters
• Purines • AMP and ATP
• Gases • NO and CO
• Peptides• Substance P and opioid peptides
• Lipids • Eicosanoids
Receptors
• Cholinergic receptors• Nicotinic on skeletal muscle, in PNS and CNS• Monovalent cation channels Na+ and K+
• Muscarinic in CNS and Parsympathetic NS • Linked to G proteins to 2nd messengers
• Adrenergic Receptors• and • Linked to G proteins and 2nd messengers
• Glutaminergic• Excitatory in CNS• Metabotropic and Ionotropic
Cell-to-Cell: Postsynaptic Response
• Fast and slow responses in postsynaptic cells
Figure 8-23
Postsynaptic cell
Presynaptic axon terminal
Ion channels open
MoreNa+ in
More K+
out or Cl– in
EPSP = excitatory
depolarization
IPSP = inhibitory
hyperpolarization
Ion channels close
LessNa+ in
Less K+out
EPSP = excitatory
depolarization
Alters openstate of
ion channels
Activated secondmessenger pathway
Inactivepathway
Modifies existingproteins or regulates
synthesis of newproteins
Coordinatedintracellular
response
Rapid, short-actingfast synaptic potential Neurocrine
Slow synaptic potentialsand long-term effects
Chemically gated ion channel
G protein–coupledreceptor
Cell-to-Cell: Postsynaptic Response
Figure 8-23, step 1
Postsynaptic cell
Presynaptic axon terminal
Ion channels open
MoreNa+ in
More K+
out or Cl– in
EPSP = excitatory
depolarization
IPSP = inhibitory
hyperpolarization
Rapid, short-actingfast synaptic potential Neurocrine
Chemically gated ion channel
G protein–coupledreceptor
Cell-to-Cell: Postsynaptic Response
Figure 8-23, steps 1–2
Postsynaptic cell
Presynaptic axon terminal
Ion channels open
MoreNa+ in
More K+
out or Cl– in
EPSP = excitatory
depolarization
IPSP = inhibitory
hyperpolarization
Rapid, short-actingfast synaptic potential Neurocrine
Slow synaptic potentialsand long-term effects
Chemically gated ion channel
G protein–coupledreceptor
Cell-to-Cell: Postsynaptic Response
Figure 8-23, steps 1–3
Postsynaptic cell
Presynaptic axon terminal
Ion channels open
MoreNa+ in
More K+
out or Cl– in
EPSP = excitatory
depolarization
IPSP = inhibitory
hyperpolarization
Alters openstate of
ion channels
Activated secondmessenger pathway
Inactivepathway
Rapid, short-actingfast synaptic potential Neurocrine
Slow synaptic potentialsand long-term effects
Chemically gated ion channel
G protein–coupledreceptor
Cell-to-Cell: Postsynaptic Response
Figure 8-23, steps 1–4
Postsynaptic cell
Presynaptic axon terminal
Ion channels open
MoreNa+ in
More K+
out or Cl– in
EPSP = excitatory
depolarization
IPSP = inhibitory
hyperpolarization
Ion channels close
LessNa+ in
Less K+out
Alters openstate of
ion channels
Activated secondmessenger pathway
Inactivepathway
Rapid, short-actingfast synaptic potential Neurocrine
Slow synaptic potentialsand long-term effects
Chemically gated ion channel
G protein–coupledreceptor
Cell-to-Cell: Postsynaptic Response
Figure 8-23, steps 1–5
Postsynaptic cell
Presynaptic axon terminal
Ion channels open
MoreNa+ in
More K+
out or Cl– in
EPSP = excitatory
depolarization
IPSP = inhibitory
hyperpolarization
Ion channels close
LessNa+ in
Less K+out
EPSP = excitatory
depolarization
Alters openstate of
ion channels
Activated secondmessenger pathway
Inactivepathway
Rapid, short-actingfast synaptic potential Neurocrine
Slow synaptic potentialsand long-term effects
Chemically gated ion channel
G protein–coupledreceptor
Cell-to-Cell: Postsynaptic Response
Figure 8-23, steps 1–6
Postsynaptic cell
Presynaptic axon terminal
Ion channels open
MoreNa+ in
More K+
out or Cl– in
EPSP = excitatory
depolarization
IPSP = inhibitory
hyperpolarization
Ion channels close
LessNa+ in
Less K+out
EPSP = excitatory
depolarization
Alters openstate of
ion channels
Activated secondmessenger pathway
Inactivepathway
Modifies existingproteins or regulates
synthesis of newproteins
Coordinatedintracellular
response
Rapid, short-actingfast synaptic potential Neurocrine
Slow synaptic potentialsand long-term effects
Chemically gated ion channel
G protein–coupledreceptor
Cell-to-Cell: Inactivation of Neurotransmitters
Figure 8-24
Synapticvesicle
Postsynaptic cell
Enzyme
Axon terminal of
presynaptic cell
Glialcell
Bloodvessel
Neurotransmitters can be returnedto axon terminals for reuse or transported into glial cells.
Enzymes inactivate neurotransmitters.
Neurotransmitters can diffuseout of the synaptic cleft.
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Rapid termination of NTs
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