Bio Notes February 5

Bio Notes February 5 - Bio Notes February 5, 2009 Synapses

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Bio Notes February 5, 2009 Synapses Junctions between 2 neurons o Or between a neuron and effector (muscle cell) Presynaptic neuron o A neuron that terminates at a specific synapse Postsynaptic neuron o A neuron that begins at that synapse Synaptic transmission o Most synapses are chemical o Action potential continues down the axon but cant jump gap at end of axon o Therefore pre and post synaptic neurons separated by synaptic cleft- signal carried by neurotransmitters o Action potential reaches synaptic terminals at the end of the Presynaptic neuron o Ca2+ channels open in membrane letting Ca2+ from ECM (extracellular matrix) enter the Presynaptic terminal o Calcium ions cause synaptic vesicles to fuse with Presynaptic membrane releasing neurotransmitter into synaptic cleft o Neurotransmitter diffuses across the synaptic cleft combines with specific receptors on a postsynaptic neuron o Specific ion channels open or close. When depolarization reaches threshold level an action potential is generated o Neurotransmitter binds with receptor. Ligand-gated channel opens, resulting in depolarization (occurs allowing sodium through sodium channels- when sodium enters the neuron). When you depolarize you make the membrane more positive Right after depolarization occurs the neuron repolarizes Potassium gates open allowing potassium in Neurotransmitters Acetylcholine o Triggers contraction of skeletal muscle o Cells releasing acetylcholine are called cholinergic neurons Biogenic Amines o Norepinephrine, serotonin, dopamine Important in regulating mood (deficiency= ADD) Dopamine is also important in motor function Some amino acids o Glutamate (excitatory neurotransmitter in brain) o Gamma aminobutyric acid (GABA) (widespread inhibitory neurotransmitter) Neuropeptides (opioids) o Endorphins Bind to opioid receptors, block pain signals o Enkephalins
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Modulate effects of other neurotransmitters Nitric Oxide (NO) o Laughing gas o Gaseous neurotransmitter o Retrograde messenger Transmits signals from postsynaptic neuron to Presynaptic neuron Opposite direction from other neurotransmitters Neurotransmitter Receptors Proteins form Ligand-gated ion channels o E.g. acetylcholine receptor: permitting passage of Na+ and K+ Others work through a second messenger such as camp o E.g. serotonin: activates a kinase phosphorylation that closes K+ channels Postsynaptic Neurons Postsynaptic neuron must re-polarize to perpetuate an action potential Excess neurotransmitter must be inactivated o Enzyme inactivation o Or reuptake of excess neurotransmitter into vesicles which
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Bio Notes February 5 - Bio Notes February 5, 2009 Synapses

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