BCMB 230 1st Edition Lecture 9 Outline of Last Lecture I Overview of the Nervous System II Motor Division III Sensory specialized Muscle Cells IV Cells in the Nervous System V The PNS vs the CNS VI Membrane Potential Outline of Current Lecture I Review of Last Lecture II The Last Membrane Potential III Neurotransmitter Storage and Release Current Lecture Membrane Potentials and Neurotransmitters I Review of Last Lecture Resting potential ready state not transmitting information but needed to transmit Requires 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 potential II 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 how strong 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 is considerably 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 quickly III Neurotransmitter Storage and Release Synapse the anatomically specialized junction between two neurons where one neuron alters the electrical and chemical activity of another Presynaptic neuron a neuron that conducts a signal toward a synapse Postsynaptic neuron a neuron conducting signals away from a synapse Action potential moves down to synaptic bulb and opens up some voltage gated Ca2 channelscalcium 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 cleft Fates 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 feedbackcontrol 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 it Factors That Determine Synaptic Strength I Presynaptic factors A Avilabity of neurotransmitter a Availability of precursor molecules b Amount or activity of the rate limiting enzyme in the pathway for neurotransmitter synthesis B Axon terminal membrane potential C Axon Terminal Ca2 D Activation of membrane receptors on presynaptic terminal a Axo axonic synapses b Autoreceptors c Other receptors E Certain drugs and disease which act via the above mechanism A D II III Postsynaptic factors A 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 neuron C Up or down regulation and desensitization of receptors D Certain drugs and diseases General factors A Area of synaptic contact B Enzymatic destruction of neurotransmitter C Geometry of diffusion path D