Cell to cell communication in the
nervous system
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The synapse
Electrical synapse
Chemical synapse
Role of calcium
“neurocrines”
Receptors
Post-synaptic responses
Terminating synaptic neurotransmission
The synapse
• Presynaptic cell
• Synaptic cleft
• Postsynaptic cell
Electrical synapse
•Rapid
•Few cns neurons, glia
•Cardiac muscle
•Smooth muscle
Chemical synapse
•Releases neurotransmitter
•Synaptic vesicles
•Docking
The effect of calcium on
synaptic neurotransmission
•Action potential
•Voltage gated Ca++ channel
•Synaptic vesicle docking
•Neurotransmitter exocytosis
•Ligand/receptor binding on
postsynaptic cell.
Substances released by neurons
• paracrines
– Neurotransmitters (act at synapse) and
neuromodulators (act away from synapse)
– Neurohormones released into blood
• Autocrines, same signaling molecules act
on the cell that releases them
Examples of neurotransmitters
• Acetylcholine- neuromuscular jn and CNS
• Amino acids – glycine, glutamate, GABA
• amino acid derived amines – epinephrine,
norepinephrine, dopamine, serotonin
• Peptides – substance P, endorphins
• Purines - ATP
• Gases – nitric oxide
Multiple neurotransmitter receptors
• Ionotropic – ligand gated channels
• Metabotropic – ligands activate 2nd
messengers and/or G proteins that gate
the channel
Ionotropic
receptor
Metabotropic
receptor
Multiple neurotransmitter receptors:
subtypes
• Cholinergic –
nicotonic
(neuromuscular jn),
ligand gated
– Muscarinic, 5
subtypes, G protein
and 2nd messenger
linked
Adrenergic receptors
• Adrenergic – alpha and beta
– Linked to G proteins and 2nd messengers
– Alpha and beta are linked to different G
proteins and different 2nd messengers
Glutaminergic receptors
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Important in the CNS
Named for agonists
AMPA receptors – ligand gated
NMDA receptors – bind ligand (glutamate)
but channel opens during depolarization
Glutamate Receptors
NMDA receptor
AMPA receptor
Duration of post-synaptic response
• Fast synaptic potential, usually from
ionotropic receptors.
– A channel is opened
– Synaptic potential can be depolarizing or
hyperpolarizing
• Slow synaptic potential
– G proteins and 2nd messengers
– Slower and lasts longer
Neurotransmitter activity is quickly
terminated
• Acetylcholine is
broken down by
acetylcholinesterase
Neurotransmitter activity is
terminated
• Norepinephrine is actively transported
back to the pre-synaptic axon
• CNS neurotransmitters (amines, peptides,
amino acids) move into circulation or
transported to pre-synaptic terminal.
Nervous system
• Termination of neurotransmitter activity
• Integration of Neural Information Transfer
• Read ahead for chapter 10: Sensory
systems:
– general properties (pgs 282- 286)
– Chemoreception (pgs 295 – 298)
– The eye and vision (pgs 309 – 319)
Neurotransmitter activity is quickly
terminated
• Acetylcholine is
broken down by
acetylcholinesterase
Neurotransmitter activity is
terminated
• Norepinephrine is actively transported
back to the pre-synaptic axon
• CNS neurotransmitters (amines, peptides,
amino acids) move into circulation or
transported to pre-synaptic terminal.
The relationships between many
neurons
• Integration
• Information flows in the nervous system
What happens when there are many synaptic inputs ocurring?
Excitatory post-synaptic potential
• Synaptic junction
• Binding of neurotransmitter leads to
depolarization of the post-synaptic cell
• EPSP, excitatory post synaptic potential
Post-synaptic inhibition
• At a synaptic junction
• The binding of the neurotransmitter
causes hyperpolarization
• IPSP – inhibitory post synaptic potential
Post-synaptic inhibition
-At a synaptic junction
- The binding of the neurotransmitter causes hyperpolarization
- IPSP – inhibitory post synaptic potential
Three synaptic junctions, each release an excitatory neurotransmitter
Three synaptic junctions, 2 are stimulatory, 1 is inhibitory.
Stimuli are very far apart in time. Stimuli don’t occur often.
Subthreshold stimuli arrive
At the trigger zone within a
Short period of time.
Synaptic Modulation at the axon terminal