Lecture 10 Lecture Outline:I Nervous Systema. Multi-neuron signalb. Electrical synapseII Chemical synapsea. Anatomy and typesb. Physiologyc. PharmacologyIII Neurotransmittersa. Acetylcholineb. Gamma amino butyric acidc. Neuropeptides d. Norepinephrine IV Modulation of synaptic transmissiona. Attenuation, enhanceb. Drug reactionsCurrent Lecture:Multi neuron signals:- Synapse: specialized region where a neuron transmits info to another cell- Presynaptic neuron: synapse sending the signal- Postsynaptic neuron: synapse receiving the signal- Electrical synapse: Direct flow of electrical signal from one cell directly to next cello short synaptic delay o possibility for two way transmission- Gap junction: membrane proteins that hold adjacent membranes together, allow flow of electrical signal- Chemical synapses: use of neurotransmitter to carry electrical signal from pre to post synaptic neurono Most abundant type of synapse in CNS and PNSo Axodendritic synapse: where axon connects to a dendrite, most abundant synapseo Axosomatic synapse: where axon connects directly to cell bodyo Axoaxonic synapse: where axon connects to another axono Each synapse contains only one type of neurotransmittero Synaptic vesicles: contain and release neurotransmittero Synaptic cleft: area where axon meets up with the postsynaptic location, areas do not touch Post-synaptic membrane is covered with chemically gated ion channels (Na, Cl, or K)o Physiology of chemical synapses: Electrical signal travels down axon which triggers electrical gated ion channel to allow diffusion of calcium into the axon. Calcium ions diffusing into the axon terminal causes the exocytosis of the synaptic vesicles releasing neurotransmitters Neurotransmitters diffuse through the axon terminal, through the synaptic cleft, and bind to the chemically gated ion channel on the membrane of the post synaptic neuronBio 312- Neurotransmitters will be recycled up into the axon terminal, destroyed by enzymes, or diffuse away from the synaptic cleft into the extracellular space- Acetylcholine: important neurotransmittero Acetylcholinesterase: enzyme embedded in postsynaptic membrane that destroys acetylcholine after it is used. Acetyl is disposed of, choline is taken back up Gated ion channel opens and allows ions to flow through and the continuation of the action potentialo Two way transmission is impossible, much longer synaptic delay than electrical synapseo Pharmacology of chemical synapse:  Agonist drug: mimics/imitates the effects of a naturally occurring neurotransmitter.- Causes channels to open Antagonist drug: chemical that binds to receptor but does not cause it to open- Keeps channels from opening Cholinesterase inhibitor: stops acetylcholinesterase from working, causing buildup of acetylcholine in synaptic cleft, and causes a prolonged and heightened effect- Excitatory synapse: triggers the opening of certain type of chemically gated ion channels, causing small depolarizationo Excitatory postsynaptic potential (EPSP): small depolarization that increases likelihood of action potential reaching its threshold Graded potential that travels decrementally in all directions to axon hillocks - Inhibitory synapse: triggers the opening of certain type chemically gated ion channel, causing small hyperpolarizationo Inhibitory postsynaptic potential (IPSP): hyperpolarization of postsynaptic membrane, somewhat inhibiting action potential being able to reach threshold Graded potentials that travel decrementally from point of origin in all directions to axon hillocks- Duration of IPSP and EPSP is determined by how long neurotransmitter stays in synaptic cleft, until destroyed or diffuse out.- The type of postsynaptic response (EPSP or IPSP) produced by a given NT depends on the type of chemically gated channel associated with the NT receptor, causing hyper or depolarization.- The same neurotransmitter can be inhibitory in some places and excitatory in others depending on what kind of gated ion channel it effects.- Signal transduction at chemical synapse can be either simple (1 step) or complex (requiring several steps to open)- Synaptic integration: a postsynaptic neuron receives hundreds of synaptic inputs (convergence)o Some are excitatory, some inhibitoryo Postsynaptic neuron must integrate potentially conflicting incoming signalso AP’s not initiated on dendrites or cell body because of the lack of ion channels on these membraneso AP’s are triggered on the axon hillock whenever net depolarization reaches the threshold because this areacontains enough of and the right type of gated ion channelso Single EPSP reaching axon hillock insufficient to reach threshold potential, requires summation of EPSPsoccurring near simultaneouslyo Facilitation: membrane is partially depolarized but not yet to thresholdo No summation: multiple stimuli separated in time cause EPSPs that do not add together or cause APo Temporal summation: 2 (or more) excitatory stimuli close in time at same synapse causing EPSPs to add togethero Spatial summation: 2 or more near simultaneous stimuli at different locations causing EPSPs to add together Can have spatial summation of EPSPs and IPSPs which can cancel each other outNeurotransmitters: about 50 have been discovered- Acetylcholine: Near muscular junction between nerve cells and muscle cells ; excitatoryo In ANS mostly excitatory for smooth muscle cells, inhibitory to hearto In CNS both excitatory and inhibitoryo Some medicines for Alzheimer’s patients increase Acetylcholine- Gamma amino butyric acid (GABA)o Found in CNS; inhibitory (opens Cl- channels)o One of the most prevalent NTs in braino Valium (agonist)works by binding to GABA receptors and inhibits pathways that produce anxiety- Neuropeptides: short chains of amino acids, endorphins and enkephalinso Found in brain and spinal cordo Help block perception of paino Implicated in “runner’s high”o Morphine mimics effects of endogenous opiates- Norepinephrine (NE): important neurotransmitter in CNS and sympathetic NSo Both excitatory and inhibitoryo In brain, functions in emotions and feelings of well beingo Stimulates heart and blood vesselso Cocaine blocks re-uptake of NE (and others) which can lead to over stimulation of heartModulation of synaptic transmission: transmission of signals across synapses can be either attenuated or enhanced- Attenuated: changed so that a potential