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Anatomy Final Exam Review

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Anatomy and Physiology
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Anatomy Final Exam ReviewPhysiology of the Nervous System resemblance NeurophysiologyNeurons are highly irritable When an impulse is generated a response called an action potential is firedVoltage Measure of potential energy generated by separated charge Volts or millivolts 1mV0001 VCurrent Flow of electrical charge from one point to another Resistance Hindrance to charge flow provided by substances through which the current must pass Substances with high electrical resistance are called insulators and those with low resistance are called conductorsOhms Law Relationship between voltage current and resistance Current is directly proportional to voltage No net current flow between points that have the same potential Current is inversely related to resistanceoCurrent IVoltage VResistance RRole of Membrane Ion ChannelsIon channels are large proteins often with several subunits whose amino acid chains snake back and forth across the membrane Chemically gated channels open when the appropriate chemical bindsVoltagegates channels open and close in response to changes in the membrane potentialMechanically gated channels open in response to physical deformation of the receptorWhen gated ion channels are open ions diffuse quickly across the membrane following their electrochemical gradients creating electrical currents and voltage changes Ions move along chemical concentration gradients when they diffuse from an area of high concentration to an area of low concentration and along electrical gradients when they move toward an area of opposite electrical charges Electrochemical gradient Resting Membrane PotentialPotential difference in a resting neuron Membrane is said to be polarizedValue of the resting membrane potential varies from 40 mV to 90 mVResting membrane potential is generated by differences in the ionic makeup of the intracellular and extracellular fluid Extracellular fluid positive charges of sodium and other cations are balanced by chloride ions Negatively charged anionic proteins help to balance the positive charges of intracellular cations Potassium ions diffuse out of the cell along their concentration gradient K flowing out of the cell caused the cell to become more negative insideAt resting membrane potential the negative interior of the cell is due to much greater diffusion of K out of the cell than Na diffusion into the cell ATPdriven sodiumpotassium pumps first ejects three Na from the cell and then transports two K back into the cell stabilizes the resting membrane potential Signals are produced by a change in membrane potential graded potentials which are usually incoming signals operating over short distances and action potentials which are longdistance signals of axons Depolarization Reduction in membrane potential Inside of the membrane becomes less negative Hyperpolarization Occurs when the membrane potential increasesGraded Potentials Shortlives localized changed in membrane potential that can be either depolarizations or hyperpolarizationsStronger stimulus the more the voltage changes and the farther the current flowsReceptor of a sensory neuron is excited by some form of energy heat light is called a receptor potentialStimulus is a neurotransmitter released by another neuron is called a postsynaptic potential Current flow on both sides of the membrane between the depolarized active membrane area and the adjacent polarized resting areas Inside the cell positive ions K move away from the depolarized areaPositive ions on the outer membrane face are moving towards the region of reversed membrane polarity depolarized regionInside becomes less negative and the outside becomes less positive Action PotentialsPrinciple way neurons send signals over long distances Transition from local graded potential to action potential takes place in the axon hillockChanged in membrane permeability resulting from the opening and closing of voltagegated ion channels all induced by depolarization of the axon membrane 1Resting state Voltagegated channels closedNa channel has two gates voltage sensitive activation gate that is closed at rest and responds to depolarization by opening and an inactivation gate that blocks the channel once its openDepolarization open and then inactivated sodium channels2Depolarizing phase Increase in Na permeability and reversal of membrane potential
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