Chapter 8b
Neurons: Cellular
and Network
Properties
Cell-to-Cell: A Chemical Synapse
• Chemical synapses use
neurotransmitters;
electrical synapses
pass electrical signals.
Axon of
presynaptic
neuron
Mitochondrion
Axon terminal
Postsynaptic
neuron
Synaptic
vesicles
Synaptic
cleft
Neurotransmitter Receptors
Postsynaptic
membrane
Figure 8-20
Cell-to-Cell: Events at the Synapse and Exocytosis
1 An action potential
depolarizes the axon
terminal.
2 The depolarization opens
voltage-gated Ca2+
channels and Ca2+
enters the cell.
3 Calcium entry triggers
exocytosis of synaptic
vesicle contents.
Axon
terminal
Synaptic
vesicle
Neurotransmitter
molecules
Action
potential
4 Neurotransmitter diffuses
across the synaptic cleft
and binds with receptors
on the postsynaptic cell.
5 Neurotransmitter binding
initiates a response in
the postsynaptic cell.
1
3
Ca2+
Synaptic
cleft
Docking
protein
2
4
Receptor
Postsynaptic cell
Voltage-gated
Ca2+ channel
Cell
response
5
Figure 8-21
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
Mitochondrion
Axon
terminal
CoA
Acetyl CoA
Enzyme
Myasthenia gravis
Acetylcholine
1
Synaptic
vesicle
2 In the synaptic cleft ACh is rapidly
broken down by the enzyme
acetylcholinesterase.
3
Choline
Acetate
1 Acetylcholine (ACh) is made
from choline and acetyl CoA.
2
Cholinergic
receptor
Acetylcholinesterase (AChE)
Postsynaptic
cell
3 Choline is transported back into
the axon terminal and is used
to make more ACh.
Figure 8-22
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
Presynaptic axon
terminal
Rapid, short-acting
fast synaptic potential
Slow synaptic potentials
and long-term effects
Neurocrine
G protein–coupled
receptor
Chemically
gated ion channel
Postsynaptic
cell
Alters open
state of
ion channels
Ion channels open
More
Na+ in
EPSP =
excitatory
depolarization
Inactive
pathway
Activated second
messenger pathway
Ion channels close
More K+
out or
Cl– in
Less
Na+ in
IPSP =
inhibitory
hyperpolarization
Modifies existing
proteins or regulates
synthesis of new
proteins
Less K+
out
EPSP =
excitatory
depolarization
Coordinated
intracellular
response
Figure 8-23
Cell-to-Cell: Postsynaptic Response
Presynaptic axon
terminal
Rapid, short-acting
fast synaptic potential
Neurocrine
G protein–coupled
receptor
Chemically
gated ion channel
Postsynaptic
cell
Ion channels open
More
Na+ in
EPSP =
excitatory
depolarization
More K+
out or
Cl– in
IPSP =
inhibitory
hyperpolarization
Figure 8-23, step 1
Cell-to-Cell: Postsynaptic Response
Presynaptic axon
terminal
Rapid, short-acting
fast synaptic potential
Neurocrine
Slow synaptic potentials
and long-term effects
G protein–coupled
receptor
Chemically
gated ion channel
Postsynaptic
cell
Ion channels open
More
Na+ in
EPSP =
excitatory
depolarization
More K+
out or
Cl– in
IPSP =
inhibitory
hyperpolarization
Figure 8-23, steps 1–2
Cell-to-Cell: Postsynaptic Response
Presynaptic axon
terminal
Rapid, short-acting
fast synaptic potential
Slow synaptic potentials
and long-term effects
Neurocrine
G protein–coupled
receptor
Chemically
gated ion channel
Postsynaptic
cell
Alters open
state of
ion channels
Inactive
pathway
Activated second
messenger pathway
Ion channels open
More
Na+ in
EPSP =
excitatory
depolarization
More K+
out or
Cl– in
IPSP =
inhibitory
hyperpolarization
Figure 8-23, steps 1–3
Cell-to-Cell: Postsynaptic Response
Presynaptic axon
terminal
Rapid, short-acting
fast synaptic potential
Slow synaptic potentials
and long-term effects
Neurocrine
G protein–coupled
receptor
Chemically
gated ion channel
Postsynaptic
cell
Alters open
state of
ion channels
Ion channels open
More
Na+ in
EPSP =
excitatory
depolarization
Inactive
pathway
Activated second
messenger pathway
Ion channels close
More K+
out or
Cl– in
Less
Na+ in
Less K+
out
IPSP =
inhibitory
hyperpolarization
Figure 8-23, steps 1–4
Cell-to-Cell: Postsynaptic Response
Presynaptic axon
terminal
Rapid, short-acting
fast synaptic potential
Slow synaptic potentials
and long-term effects
Neurocrine
G protein–coupled
receptor
Chemically
gated ion channel
Postsynaptic
cell
Alters open
state of
ion channels
Ion channels open
More
Na+ in
EPSP =
excitatory
depolarization
Inactive
pathway
Activated second
messenger pathway
Ion channels close
More K+
out or
Cl– in
Less
Na+ in
IPSP =
inhibitory
hyperpolarization
Less K+
out
EPSP =
excitatory
depolarization
Figure 8-23, steps 1–5
Cell-to-Cell: Postsynaptic Response
Presynaptic axon
terminal
Rapid, short-acting
fast synaptic potential
Slow synaptic potentials
and long-term effects
Neurocrine
G protein–coupled
receptor
Chemically
gated ion channel
Postsynaptic
cell
Alters open
state of
ion channels
Ion channels open
More
Na+ in
EPSP =
excitatory
depolarization
Inactive
pathway
Activated second
messenger pathway
Ion channels close
More K+
out or
Cl– in
Less
Na+ in
IPSP =
inhibitory
hyperpolarization
Modifies existing
proteins or regulates
synthesis of new
proteins
Less K+
out
EPSP =
excitatory
depolarization
Coordinated
intracellular
response
Figure 8-23, steps 1–6
Cell-to-Cell: Inactivation of Neurotransmitters
1 Neurotransmitters can be returned
to axon terminals for reuse or
transported into glial cells.
Rapid termination of NTs
2 Enzymes inactivate
neurotransmitters.
3 Neurotransmitters can diffuse
out of the synaptic cleft.
Blood
vessel
Axon
terminal of
presynaptic cell
Synaptic
vesicle
3
Glial
cell
1
Enzyme
Postsynaptic cell
2
Figure 8-24