KIN 292 1st Edition Lecture 17 These are the notes from Professor Starnes lecture of Clinical Human Physiology These come from the slideshows provided by the professor and include extra notes and explanations Highlighted or bolded information are things that I believe to be information that is important to look over multiple times The notes in red are my personal additions and quotes of Professor Starnes from the class lecture Outline of Last Lecture I 7 1 Overview of the Nervous System II 7 2 Cells of the Nervous System III 7 3 Establishment of the Resting Membrane Potential IV 7 4 Electrical Signaling Through Changes in Membrane Potential V 7 5 Maintaining Neural Stability Outline of Current Lecture I 8 1 Electrical Synapses II 8 2 Chemical Synapses III 8 3 Neural Integration IV 8 4 Presynaptic Modulation V 8 5 Neurotransmitters selected Structure Synthesis and Degradation Current Lecture Chemical synapses Most neurons communicate using this type Functional anatomy Presynaptic neuron Postsynaptic neuron These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Synaptic cleft 30 50 nm wide Unidirectional Usually synapse on dendrites axodendritic Some synapse on soma axosomatic or axons axoaxonic Active presynaptic neuron Depolarization by AP opens voltage gated Ca channels Ca signals vesicles to move toward membrane to fuse and undergo exocytosis of neurotransmitter NT Amount of NT release depends on Ca concentration Synaptic delay time from AP at terminal to change on postsynaptic Vm Approx 0 5 5 msec and almost entirely due to steps 2 and 3 4 fates of NT Step 4 6 7 8 7 Reuptake of some NT by reuptake molecules to remanufacture NT Postsynaptic Potential PSP Change in membrane potential in response to receptorneurotransmitter binding Magnitude of graded potential depends on amount of receptor neurotransmitter binding Excitatory postsynaptic potential EPSP o Depolarizes toward threshold potential o Most common neurotransmitter glutamate Inhibitory postsynaptic potential IPSP o Hyperpolarizes o Decreases likelihood of AP being generated o Most common neurotransmitter GABA Inhibitory Synapses Neurotransmitter opens K or Cl Channels Cl channels can also result in IPSP or membrane stabilization next slide Fast response K moves out IPSP Increased frequency of APs more NT released greater response The roles of chloride channels in inhibitory synapses For neurons actively transporting chlorideout of the cell Cli is low so when NT opens a Cl channel Cl goes in down its concentration gradient IPSP For neurons without active transport of chloride Chloride at equilibrium Thus when NT opens more channels no net movement occurs Same as b except NT2 binds to an excitatory synapse bringing in positive charge Clmoves in to counter or minimize depolarization thus stabilizing the membrane potential Considered an inhibitory action Example of convergence a neuron gets info from several sources next Divergence and convergence Refers to the amount of communication among neurons Part of neural integration Divergence Axons of neurons typically haveSeveral collaterals that communicate to severalOther neurons Convergence A neuron receives information from hundreds thousands of other neurons via axodendritic and axosomatic synapses Neural integration Synapses from many presynaptic neurons must summate to get the axon hillock to threshold potential Involves temporal and spatial summation to get to threshold for a single AP and to suprathreshold levels to achieve multiple APs from chap 7 8 4 Presynaptic Modulation The regulation of communication across a synapse o Axoaxonic synapses function as modulatory synapses Presynaptic facilitation E C enhances release from C Presynaptic inhibition With F H active H inhibits release from F 8 5 Neurotransmitters Structure Synthesis and Degradation The action of any chemical messenger does not depend on the messenger itself but rather on the signal transduction mechanism activated by the receptor once the messenger binds to it Acetylcholine synthesis action and degradation at cholinergic synapse o Synthesized inAxon terminal by choline acetyltransferase o Choline obtained through diet and undergoes reuptake after ACh degradation step 6 o Found in PNS and CNSMost abundant NT in PNS Acetylcholine Acetyl CoA choline acetylcholine CoA Synthesized in axon terminal Choline acetyl transferase CAT enzyme for synthesis o Breakdown Acetylcholine acetate choline Occurs in synaptic cleft Acetylcholinesterase AChE enzyme of degradation o Reuptake of choline for resynthesis of Ach The subsequent cellular action after Ach binding depends on which type of cholinergic receptor is on the postsynaptic neuron The action of any chemical messenger does not depend on the messenger itself but rather on the signal transduction mechanism activated by the receptor once the messenger binds to it Nicotinic and muscarinic cholinergic receptors o Nicotinic Ionotropic channel with 2 ACh binding sites On skeletal muscle cells and other places Action is EPSP o Muscarinic Metabotropic Dominant cholinergic receptor in CNS and lesser role in PNS Action depends on which G protein sensitive channels and enzymes are on postsynaptic neuron o Named by drug binding Nicotine binds to nicotinic receptor Muscarine binds to muscarinic receptors but not vice versa Biogenic Amines o Derived from amino acids Catecholamines derived from tyrosine Dopamine Norepinephrine also called noradrenalin Epinephrine also called adrenalin Serotonin derived from tryptophan Histamine derived from histidine o Enzymes for degrading biogenic amines Monoamine oxidase MAO Catechol O methyltransferase COMT o Synthesis Cytosol of axon terminal Packaged into synaptic vesicles o Release Dopamine and norepinephrine are common in CNS Norepinephrine is also found in PNS Epinephrine comes from CNS but is more commonly released as a hormone by the adrenal medulla Epi norepi receptors adrenergic receptors covered in chap 11 Serotonin o CNS neurotransmitter Main location Brainstem o Functions Regulating sleep Emotions Histamine o CNS neurotransmitter Main location Hypothalamus o Functions Most widely known for paracrine actions in non neuronal cells during allergic reactions Clinical Connections 8 1 Treating Depression o Associated with biochemical changes in brain including deficiencies in serotonin and norepinephrine o Pharmacological treatments