Cell to cell communication in the nervous system 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 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 spatial summation

Three synaptic junctions, 2 are stimulatory, 1 is inhibitory. spatial summation

Stimuli are very far apart in time. Stimuli don’t occur often.

Temporal Summation Subthreshold stimuli arrive At the trigger zone within a Short period of time.

Synaptic Modulation at the axon terminal