Lecture on October 10th: Synapses (Continued)

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University of Massachusetts Amherst
Psychology & Brain Sciences
Lori Astheimer Best

Behavioral Neuroscience, Lecture on October 10th Direct synapses involve a direct connection between a presynaptic cell and a postsynaptic cell. Axodendritic synapses involve a presynaptic neuron connecting to the dendrites of the postsynaptic cell.  Need a direct connection to the dendritic spine or the smooth dendrite. Axosomatic synapses connects directly to the soma of the postsynaptic cell.  EPSPs and IPSPs have less distance to travel to the axon hillock. Axoaxonic synapses - presynaptic terminal button synapses directly onto the terminal button of another axon.  presynaptic facilitation and inhibition. Examples: > excitatory axoaxonic synapse + excitatory axodendritic synapse equals increased numbers of EPSPs. > excitatory axoaxonic synapse + inhibitory axodendritic neurons equals increased IPSPs. > inhibitory axoaxonic synapse + inhibitory axodendritic neurons equals a decreased number of IPSPs. Indirect synapses: instead of having terminal buttons, they have strings of terminal varicosities. Release neurotransmitter out through these.  “string of beads" release a constant flow of neurotransmitter. Neural circuits: Monosynaptic - spinal reflex that makes your knee jerk. Complex - thousands of neurons. Neurochemistry and Neuropharmacology: *Many drugs work by either mimicking or blocking neurotransmitter function. Receptors can work in a variety of ways. Most neurotransmitters can bind to several different types of receptors. (Both ionotropic and metabotropic). Agonists and Antagonists: Ligands are chemicals that bind to receptors.  neurotransmitters are ligands. An agonist is a ligand that initiates the normal effects of the receptor. An antagonist blocks the receptor from being activated. An inverse agonist initiates an effect that is the opposite of the normal function. (Think of metabotropic receptors). Neurotransmitters are "endogenous" ligands.  closely related to agonists. Criteria for neurotransmitters: 1) substance needs to exist in the presynaptic axon terminals. 2) needs to be synthesized in presynaptic cells. 3) needs to be released when action potentials reach axon terminals. 4) receptors for the substance need to exist on postsynaptic membrane. 5) when applied, substance produces changes in postsynaptic cell. 6) blocking substance release prevents changes in postsynaptic cell. Major classes of neurotransmitters: Acetylcholine (class of its own). Function, Central nervous system- important in learning and memory and you see a widespread loss in Alzhemimer's. Peripheral nervous system - somatic nervous system (controls voluntary skeletal muscle movement) acetylcholine controls ALL striated muscle mo
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