BCMB 230 1st Edition Lecture 9 Outline of Last Lecture I.Overview of the Nervous SystemII.Motor DivisionIII.Sensory-specialized Muscle CellsIV.Cells in the Nervous SystemV.The PNS vs. the CNSVI.Membrane PotentialOutline of Current Lecture I.Review of Last LectureII.The Last Membrane PotentialIII.Neurotransmitter Storage and ReleaseCurrent LectureMembrane Potentials and NeurotransmittersI. Review of Last LectureResting potential-ready state not transmitting information, but needed to transmitRequires three things:-need Na+/K+ ATPase-creates a small charge-establishes gradients (more Na+ on outside, more K+ on inside)-differential permeability-membrane more permeable to K+ than Na+-more K+ leaves than Na+ enters (gives us more positive on the outside)-anions in cell-gives cell a negative charge (typical value of -70 mV)Graded potential-response to a stimulus (neurotransmitter, mechanical stimulus, voltage stimulus); occurs on the dendrite-stimulus changes permeability-open Na+ channels-causes depolarization which is excitatory-open K+ channels-causes hyperpolarization which is inhibitory-open Cl- channels-causes hyperpolarization which is inhibitory-a very temporary event, after they close we go back to resting potential, a process called repolarization (re-establishes the gradient)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.-decrimental propagation-electrical charge moves along membrane inside of cell via diffusion, weakens with distance; as it moves it gets smaller which dictates how far it goes-summation-when the effects of different graded potentials/stimuli are added over time;may make the graded potential last longer; if we increase the stimulus, we increase the size of the potential-temporal summation-same stimulus repeated -differential summation-different stimuli at the same time -excitatory post synaptic potential (EPSP)-inhibitory post synaptic potential (IPSP)-hyperpolarization; farther away from threshold to action potential-threshold potential-right size of the graded potential to get one action potential-subthreshold-below the required threshold; never see action potential, just repolarize-suprathreshold-above required threshold; get more than one action potentialII. The Last Membrane Potential (3rd out of 3)Action potential-potential moving along axon, getting information from one spot to another; electrical signal propagated by neurons and muscle cells-threshold stimulus opens voltage-gated Na+ channels and causes a wave of depolarization down the length of the axon-axon hillock-where the graded potential has the effect (right next to cell body); first section that gets acted on-travels along axon, depolarizes next section which opens up more Na+ channels which diffuses to the next section opening up even more Na+ channels and keeps moving down axon-as depolarization moves down axon, repolarization occurs in the previous sections in order to send another signal-when wave of depolarization reaches the end, it causes a neurotransmitter release (which is always excitatory) which can have an effect on either nerve or muscle which can be either excitatory or inhibitory-an all-or-none depolarization of membrane polarity—either occur maximally or do not occur at all-nondecrimental propagation-action potential is the same along the entire, doesn’t get smaller/weaker-refractory period-limits how often depolarization can happen--because it is depolarized,it cannot respond-absolute refractory period-a period when the membrane during the action potential will not produce a second action potential to a second stimulus, no matter howstrong the stimulus is; has to be turned back on before it can be turned off again-relative refractory period-interval after the absolute refractory period during which a second action potential can be produced, but only if the stimulus strength isconsiderably greater than usual; you can depolarize it again before you have to repolarize it-in order to speed up repolarization, decrease the refractory period-action potential propagation-the movement of an action potential along an axon-salutatory conduction-signal jumps from one node of Ranvier in the myelin sheath to the next, makes it faster-axon has myelin wrapped around it; can still occur when myelin is not present, however it will not happen as quicklyIII. Neurotransmitter Storage and ReleaseSynapse-the anatomically specialized junction between two neurons where one neuron alters the electrical and chemical activity of anotherPresynaptic neuron-a neuron that conducts a signal toward a synapsePostsynaptic neuron-a neuron conducting signals away from a synapseAction potential moves down to synaptic bulb and opens up some voltage-gated Ca2+ channels-calcium comes in and releases a neurotransmitter-neurotransmitter is now in space in between the cells, separating the pre- and post synaptic neurons, called the synaptic cleftFates of neurotransmitters (in the synaptic cleft)-happens through random movement, not decided(1) Bind to receptor on the post-synaptic membrane (diffuse across synaptic cleft, bind to membrane, and initiates graded potential)(2) Bind to receptor on the pre-synaptic membrane (initiates signal transduction; feedback-control system that helps to regulate neurotransmitter production or release)(3) Diffuse away (get lost-move out of synaptic cleft)(4) Bind to an enzyme-destroy the neurotransmitter (dead end)(5) Bind to a transporter on the pre-synaptic membrane (re-uptake)-release neurotransmitter and then pull it back into the cell that released itFactors That Determine Synaptic StrengthI. Presynaptic factorsA. Avilabity of neurotransmittera. Availability of precursor moleculesb. Amount (or activity) of the rate-limiting enzyme in the pathway for neurotransmitter synthesisB. Axon terminal membrane potentialC. Axon Terminal Ca2+D. Activation of membrane receptors on presynaptic terminala. Axo-axonic synapsesb. Autoreceptorsc. Other receptorsE. Certain drugs and disease, which act via the above mechanism A-DII. Postsynaptic factorsA. Immediate past history of electrical state of postsynaptic membrane (e.g., excitation or inhibition from temporal or spatial summation)B. Effects of other neurotransmitters of neromodulators acting on postsynaptic neuronC. Up- or down-regulation and desensitization of receptorsD. Certain drugs and diseasesIII. General factorsA. Area