PROPAGATION OF ACTION POTENTIAL 4 Understand the steps of action potential and how one leads to the next How is action potential started and propagated What ion enters first Through what type of channel does it enter What forces drive it inside Why does that channel close What channel opens next What ion moves through that channel What forces drive that At rest o lots of Na and Cl outside of neuron o lots of K inside the neuron o negatively charged proteins inside the cell o restin potential 70mV o maintained by semipermeable nature of the cell membrane and by the Na K pump action potential o Na channel causes voltage o occurs when axon hillock depolarizes to threshold 50mV Na rushes INTO cell pushed in by o opens Na channels concentration and electrical gradients positive 30mV o Na channel close K LEAVES cell pushed out by concentration o K channel opens and electrical gradients of the cell to change and actually become o Continues over and over again down the length of the axon Propagation transmission of an action potential down an axon by voltage gate ion channels and concentration gradients 5 Terms to know and understand polarized depolarization hyperpolarization repolarization resting potential and threshold What voltage is resting potential What voltage is threshold Where must threshold be reached for an action potential to occur Polarized inside of cell is negatively charged compared to outside of cell due to unequal distribution of ions 70mV Depolarization inside of cell becomes less negative 70mV o Caused by positive ions coming into cell Hyperpolarization inside of cell becomes more negative 70mV o K channels let more K out during action potential Repolarization inside of cell returns to polarized level from hyperpolarized level 70mV o Na K pump Resting Potential membrane is polarized 70mV o Maintained by semipermeable membrane Threshold critical level of depolarization that must be achieved to trigger an action potential 50mV o threshold must be reached at axon hillock 6 What is the sodium potassium pump What does it do What purpose does it serve Na K pump acts to maintain proper concentrations of Na and K o Needed for maintaining resting potential and for recovery from an action potential o 3 Na out for every 2 K in more positive on the outside 7 What is the purpose of myelin What happens at the nodes of Ranvier What is saltatory conduction Myelin provides insulation Voltage gated Na channels are concentrated at the Nodes of Ranvier o At some cases the action potential starts at the axon hillock in others it starts at the nodes of ranvier Salutatory conduction energy and speed o The jumping of action potentials from node to node o Provides rapid conduction of impulses o Conserves energy instead of admitting sodium ions at every point along the axon and then having to pump them out via sodium potassium pump a myelinated axon admits sodium only at its nodes o Timing of action potentials is often essential for coding so speed matters Auditory system and sound localization Opening of Na channels in chain reaction down axons o In myelinated axons action potential can jump down axon Faster Allows long distance rapid communication 8 What does it mean that an action potential is all or none Action potentials are generated in an all or none fashion o Most but not all neurons subthreshold depolarizations have no effect but once the threshold is crossed an action potential is generated o The rate frequency of action potentials depends on the magnitude and duration of the depolarizing stimulus o There is great variability in the firing frequency of neurons some can only fire a single action potential even to a sustained depolarization others can fire up to a limit of about 1000Hz 1 SYNAPTIC POTENTIAL Know the different parts of a synapse presynaptic cell postsynaptic cell synaptic cleft neurotransmitters receptors vesicles Presynaptic terminal 2 Know what happens at a synapse chemical transmission neuron synthesizes chemicals that serve as neurotransmitters synthesizes the smaller neurotransmitters in the axon terminals and neuropeptides in the cell body action potentials travel down the axon presynaptic terminal action potential enables Ca2 to enter cell calcium releases neurotransmitters from the terminals and into the synaptic cleft space between pre and post released molecules diffuse across teh cleft attach to receptors alter the activity of postsynaptic neuron neurotransmitter molecules separate from their receptors NT molescules may be taken back into the presynaptic neuron for recycling or they may diffuse away some postsynaptic cells send reverse messages to control the further release of NT by presynaptic cells some postsynaptic cells send reverse messages to control the further release of NT by presynaptic cellsNT molescules may be taken back into the presynaptic neuron for recycling or they may diffuse awayneurotransmitter molecules separate from their receptorsreleased molecules diffuse across teh cleft attach to receptors alter the activity of postsynaptic neuronaction potentials travel down the axonneuron synthesizes chemicals that serve as neurotransmitters 3 Understand different types of ion channels ligand and voltage gated Where are ligand gated channels located What is a ligand Voltage gated channel VGC Ligand gated channel LGC On the axon Open when cell reaches a certain At synapses Open when a ligand voltage Allows ions in or out o Changes voltage of cell neurotransmitter binds Allows ions through o Changes voltage of cell o May also start biochemical cascade within cell 4 What is an excitatory synapse What is an inhibitory synapse For each one what ion enters the cell What does that do to the cell Does it make an action potential more or less likely Excitatory synapse o Depolarization of the membrane of the postsynaptic cell o Decreases the negative charge within the cell o Na flow into neuron o Makes action potential more likely closer to the threshold Inhibitory synapse o Hyperpolarization of the membrane of the postsynaptic cell o Increases the negative charge within the cell o K leaves cell Cl enters cell o Makes action potential less likely further from the threshold 5 Know what EPSP and IPSP are How do these differ from an action potential Excitatory postsynaptic potential EPSP a graded depolarization resulting from the flow of Na into a neuron Inhibitory postsynaptic potential IPSP a temporary hyperpolarization of a membrane occurring when
View Full Document
Unlocking...