BIOL 1108 Edition 2nd Lecture 13 Outline of Last Lecture I Learning Objectives II In The News III Negative Feedback IV Homeostasis V Thermoregulation VI Abiotic vs Biotic Factors Outline of Current Lecture I Learning Objectives II In The News III Electrical Signals IV Resting Potential to Action Potential V Action Potential Propagation Current Lecture I Learning Objectives 1 Describe the range of vertebrate nervous systems 2 Describe information processing 3 Identify neuron structure and function 4 Describe the basis of membrane potential 5 Be able to describe what an action potential is including depolarization hyperpolarization 6 Describe how an electrical signal moves 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 II III down an axon from one neuron to the next 7 Apply what you ve learned to real world situations In The News In what ways does our understanding of giraffes not measure up Maternal Behavior mourning over died offspring social groups like elephants Male Behavior show sexual features depending on the presence of other males Fighting necking sexual selection evolution Circulatory system thick blood vessels to avoid fainting Ecological impacts seed distributers Physiology testosterone androgen fluctuates based on sexual activity o Body temperature averages around 38 degrees endothermic Electrical Signals a TOPHAT Which has more vertebrae a giraffe or a mouse i They are the same all animals have 7 vertebrae b Anatomy of a Neuron The functional unit of the nervous system is the neuron Dendrites receives the signals Cell body contains organelles Axon Hillock signals are generated Myelin sheath Schwan Cell insulation and increase speed Node of Ranvier gap helps signals leap down the axon Axon transmits signal from cell to cell Axon Terminal connects cell to dendrites of another cell c Membrane Potential The charged difference or voltage mV between the inside and outside of the axon Two factors that influences membrane potential is ion concentration diffusion and electrical force The negative charge inside the axon is built up through active transport o Resting potential when no signals are being sent at all is between 60 mV and 80 mV Why is the axon resting membrane potential 70 mV There are more potassium channels than there are sodium channels So potassium is going to leave the cell and sodium is going into the cell The net movement of potassium out of cell positive charges leave cell negative net loss Sodium in the outside also is positive and remains on the outside creating a positive gradient Number of sodium and potassium attempt to balance through diffusion More diffusion out than in the cell Using ATP as energy to transport sodium out and the potassium in the cell d TOPHAT At which phase does depolarization first occur i B At graded potential e TOPHAT An action potential is triggered when the membrane potential reaches i 55 mV f Equilibrium Potential Eion When the electrical gradient opposes the concentration gradient Calculated using the Nernst Equation o Eion 62 mV log ion concentration outside ion concentration inside o EK 90 mV o ENa 60 mV Depends on the concentration gradient IV Resting Potential to Action Potential Action Potential includes o Depolarization what happens to the membrane potential with increased permeability to Na o Hyperpolarization what happens to the membrane potential with increased permeability to K How is an action potential generated in an axon o Some voltage gated channels allowing sodium to pass through until threshold is reach and then all of the channels are open o Allows a rush of sodium to come into the cell o Then after it reaches a threshold graded potential all of the sodium voltage gated channels open o Action potential occurs at the maximum of membrane potential V Sodium channels begin to close and potassium channels being to open Action Potential Propagation a Speed based on i Size of the axon ii Myelin sheath The more myelinated and bigger the axon the faster the speed of the signal Myelination has a greater effect in speed than the size of an axon b Structure i Myelin sheath insulate signals by preventing anything Na or K from moving in and out the axon Gaps create another action potential c TOPHAT QUESTION In a neuron signal transmission speed is affected MOST by which structure i Myelin sheath d Signal Movement Between Neurons i Electric Synapses connected to another neuron ii Chemical Synapses more common via neurotransmitter a Axon action potential reaches the end of the synapses and then triggers Ca2 voltage gated channel to open b Channels neurotransmitters fill synaptic vesicles c Synaptic Cleft neurotransmitters pass through the gap into ligand gated ion channels of the other axon s postsynaptic membrane 5 Groups of Neurotransmitters o Acetylcholine muscle stimulation memory formation learning o Amino Acids long term memory o Biogenic Amines sleep mood attention learning Used for nervous system disorders and treatments o Neuropeptides pain reception o Gases Nitric oxide local regulators Carbon monoxide hypothalmic hormone release intestine smoot h muslce plasma membrane hyperpolarization e Post Synaptic Responses i Excitatory Post Synaptic Potential EPSP a Depolarization occurs triggering active potential Na inside the membrane ii Inhibitory Post Synaptic Potential IPSP a K is greater than Na inside the membrane weak response iii The membrane potential in the postsynaptic neuron change with an EPSP vs an IPSP by a Spatial Summation occurs when several EPSPs arrive at the axon hillock simultaneously b Temporal Summation means that postsynaptic potentials created at the same synapse in rapid succession can be summed When EPSP and IPSP simultaneously occur the signals cancel each other out f TOPHAT QUESTION Electrical signals are kept moving in one direction down an axon by i Potassium leaving the cell rapidly when voltage gated potassium channels are open keeps signal from going backward Initiation of action potential Na enters rapidly when voltage Na channels are open g Nervous System Disorders