1. Synaptic Transmission Chapter 4 Pages 95-122

2. Chemical Synapses  Most synapses in the brain are chemical. Electronically coupled gap junction synapses occur in special circumstances (embryos, cardiac muscle) where close coordination needed.  Chemical synapses release a chemical into the synaptic cleft which transfers information (a neural signal) from one neuron to another.

4. How a Synapse Works  The presynaptic neuron experiences an action potential.  Presence of the action potential at the terminal button permits calcium (Ca ++ ) to enter the neuron via voltage-gated calcium channels.  Calcium triggers the release of neurotransmitter from synaptic vesicles.  Neurotransmitter crosses the synaptic cleft and opens ion channels in the post-synaptic neuron.

5. Ion Channels  Found in all cells throughout the body.  Open and close in response to signals. Selectively permeable to specific ions High rate of flow (conductance)  Resting channels – usually open  Gated channels – open and close Refractory period – temporarily cannot be opened

6. Control of Gating  Binding of neurotransmitters, hormones, or second messengers from within the cell.  Voltage-gated – responds to a change in the membrane potential.  Stretch or pressure gated – mechanical forces.  Phosphorylation – energy comes from a phosphate that binds with the channel. Dephosphorylation – removal of the phosphate.

7. Kinds of Receptors  All neurotransmitters bind and act at more than one kind of receptor.  Two main kinds of receptors: Ion channel receptors G-protein-coupled receptors

8. Effects of Drugs  Exogenous ligands – drugs that come from outside the body.  Endogenous ligands – naturally occurring  Agonist – binds with and opens a channel. Endogenous or exogenous (e.g., drug) Receptors are often named for their agonists  Antagonist – binds with and closes a channel. Reversible (curare) or irreversible (snake venom)

9. Three Kinds of Neurotransmitters  Amino acids – released from synaptic vesicles  Monoamines – released from synaptic vesicles  Peptides – larger molecules released from secretory granules.  There may be more substances that act as neurotransmitters

10. Amino Acids  Glutamate (Glu) – excitatory, widespread.  GABA – inhibitory, widespread.  Glycine (Gly) – inhibitory at some locations.  The poison Strychnine blocks GABA receptors interfering with inhibition so excitations overwhelm the brain.

11. Monoamines  Cholinergic – Acetylcholine (ACh), used by muscles  Catecholaminergic – regulate thinking, mood, synethesized from tyrosine: Dopamine (DA) Norepinephrine (Noradrenaline) (NE) Epinephrine (Adrenaline) – widespread  Serotonin (5-HT) – broken down by MAO LSD binds at 5-HT receptors.

12. Peptides  Formed by chains of amino acids.  Oxytocin – released during childbirth to regulate maternal behavior.  Vasopressin – regulates proper blood volume and salt concentration in body.  Opioids (endorphins) – naturally occurring painkillers Morphine binds with opioid receptors.