Principles of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyPrinciples of Animal PhysiologyNeuronal PhysiologyIntroductionPrinciples of Animal PhysiologyNeuronal PhysiologyIntroduction▪ Two types of cells use the membrane potential▸ Membrane potential undergo rapid, transient changes▸ These fluctuations serve as signaling mechanisms▪ Cells that produce electrical signals when stimulated are called Excitable Tissues. These are:▸ Nerve cells▸ Muscle cellsPrinciples of Animal PhysiologyNeuronal PhysiologyIntroduction▪ Excitable tissues▸ Nerve cells - Neurons♦ Receive, process, initiate and transmit messages♦ Short & long distance communication♦ Coordinate activities between cells▸ Muscle cells♦ Contraction & force generation♦ Will be dealt with in detail laterPrinciples of Animal PhysiologyNeuronal Physiology▪ Terminology▸ Normal, unpolarized, equlibrium♦ No diggerence in polarity, charge or concentration▸ Polarized♦ Differences in charge (+ or -) across membrane♦ Membrane potential not 0 mV▸ Resting Membrane Potential♦ Membrane potential of the cell at rest▸ Depolarization♦ Membrane potential becomes less negative than resting level▸ Repolarization♦Membrane potential returnig to resting levelIntroductionPrinciples of Animal PhysiologyNeuronal Physiology▪ Terminology - changes in membrane potentialIntroductionPrinciples of Animal PhysiologyNeuronal PhysiologyIntroduction▪ Electrical signals via movement of ions across plasma membrane▸ Changes in membrane potential cause by changes in ion movement across plasma membrane▸ Changes in ion movement caused by changes in permeability of the membrane▸ Changes in permeability cause by a triggering event(stimulus)Principles of Animal PhysiologyNeuronal PhysiologyIntroduction▪ Stimulus may be caused by:▸ Sound waves stimulating nerve endings▸ A change in the electrical field in neural endings▸ An interaction of a ligand with a receptor▸ Spontaneous change in potential cause by leak channelsPrinciples of Animal PhysiologyNeuronal Physiology▪ Two types of channels▸ Leak channels (nongated channels)♦ Remain open ▸ Gated channels♦ Open and close in response to some triggering event♦ At least 3 kinds– Voltage-gated ion channels– Chemically (ligand) gated channels– Mechanically gated channels– Respond to stretch or other mechanical deformation▸ There are two basic electrical signals generated by the movement of ions across the membraneIntroductionPrinciples of Animal PhysiologyNeuronal Physiology▪ Graded potentials - local changes in membrane potential that occur in varying grades or degrees of magnitude or strength.▸ Amplitude directly related to level of stimulus▸ Amplitude inversely related with distance▸ Local event♦ Active area▸ Begins at a point where ions enter ECF▸ Duration directly related to duration of stimulus▸ Different graded potential can be added - Summed▸Graded potentials can travel to Trigger zoneGraded PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Magnitude and duration of graded potentialsGraded PotentialsPrinciples of Animal PhysiologyNeuronal PhysiologyGraded PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Current flow during graded potentialGraded PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Current loss and decrement of graded potentialGraded PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Graded potentials▸ Decremental - gradually decreases from initial site▸ Passive conduction▸ Electronic conduction▸ Nonspiking or local circuit▸ Limited signaling distance▸ Types of graded potentials♦ Postsynaptic potentials♦ Receptor potentials♦ End-plate potentials♦ Pacemaker potentialsGraded PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Summation of graded potentialGraded PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Stereotypical response in membrane potential to a threshold level stimulus▸ Brief rapid change▸ Large change in membrane potential▸ Membrane potential reverses▸ Conducted throughout the membrane▸ Conducted over long distances▸ Nondecrimental conduction▸ Stable durationAction PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Components/characteristics▸ Resting Membrane Potential▸ Depolarizing stimulus▸ Threshold▸ Rapid Na+entry (depolarization)▸ Isopotential▸ Overshoot▸ Repolarization (K+moves out)▸ Undershoot (after-hyperpolarization)▸ Absolute refractory periodAction PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Changes to voltage-gated sodium and potassium channels during an APAction PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Positive-feedback cycleAction PotentialsPrinciples of Animal PhysiologyNeuronal Physiology▪ Ionic movememnts responsible for