Exam 1 Review Exam 1 2 25 14 Advantages of multi cellularity Diffusion o SA Volume Ratio squared vs cubed Size Being able to eat things Main Being able to separate external environment from internal o Being able to control and regulate internal environment Evolved organ systems specialized cells Course will focus on organ systems that regulate internal environment homeostasis 4 Origins of cells Neurons Muscle Epithelial Connective Tissue Picture of you Exam 1 Review Exam 1 2 25 14 Primarily regulating composition of extracellular fluid This causes non changing intracellular fluid If we fool around with extracellular fluid cells may not be able to regulate intracellular fluid and then you re sick Plasma is the extracellular fluid in your blood No platelets etc Interstitial fluid Fluid outside of circulatory system Main component of extracellular fluid along with plasma Homeostasis Closed loop negative feedback 1 Measure sensory structure 2 Comparator with preset reference value brain 3 Send error signal to effector organ to regulate 4 Repeat Closed loop The output changes the input Negative feedback Eliminates the difference you observe between real value and desired Positive feedback Small disturbance increase in magnitude of perturbation Often destructive and sometimes lethal o Ex temperature goes up and keeps going up o Ex Hypertension Central Nervous System CNS Brain and spinal cord Exam 1 Review Exam 1 2 25 14 Peripheral Nervous System PNS Everything else Communicates with CNS We isolate cerebrospinal fluid CSF from blood Blood Brain Barrier glial cells astrocytes Creates permeability barrier for certain drugs Gases and hydrophobic molecules passively diffuse Hydrophobic molecules glucose amino acids need transporters Sensory afferent Pathway Somatic senses From touching and feeling Special senses Hear See Smell Taste Visceral senses Internal organs Efferent pathway Somatic Skeletal muscle Autonomic Cardiac muscle smooth muscle enteric nervous system GI Tract o Sympathetic Fright or flight o Parasympathetic Rest digest Exam 1 Review Exam 1 2 25 14 Nerve bundle of neurons Neuron Dendrites soma cell body axon axon terminals Exam 1 Review Exam 1 2 25 14 Microtubules carry vesicles down the axon One neuron receives input from 100 other neurons but our discussion will be simplified Exam 1 Review Exam 1 2 25 14 Achieve a concentration gradient through the Na K ATPase pump Trans membrane proteins serve as ion channels K has the highest permeability diffuses fastest o Most leak channels o If you block leak channels NO membrane potential Membrane potential is due to diffusion of ions Positive charge is leaving the cell inside becomes negative K out will never be equal to K in o Inside becomes negative and the concentration gradient o We can predict how negative the inside will become with the becomes opposed by the electrical gradient Nernst Equation Nernst Assume 37 degrees Celsius simplifies to 61 5log ratio of ions get mV V m Equilibrium potential When E ion V m NO net movement of ion If inside is more positive than outside moves out Vice versa Value at which concentration gradient of K out is equal and opposite to electrical gradient holding potassium in Sometimes Nernst equation with 58 constant instead of 61 5 20 Celsius due to the large squid axon on which the original experiments were done Magnitude of membrane potential is exclusive from magnitude 90 mV 70 mV Membrane potential more negative than 70 hyperpolarization Less negative Depolarization Returning to 70 from depolarization Repolarization Exam 1 Review Exam 1 2 25 14 Ohm s Law V I R V voltage I current R Resistance 1 R conductance g expression of permeability but not the same Current Voltage Conductance Conductance related to number of open channels Increase conductance of potassium hyperpolarization Chloride hyperpolarization Sodium depolarization K out depolarization o Potassium chloride Ca 2 is not permeable Permeability of an ion is proportional to that ion s contribution to membrane potential Calculate V m Goldman Constant Field Equation Gives accurate membrane potential Only ions with same valence Nernst Estimate by imputing most permeable ion K Exam 1 Review Exam 1 2 25 14 Relative permeability P K 0 03 Goldman Equation P Na 1 all other ions 1 Graded vary in duration Small depolarization or hyperpolarization on a portion of the Does not travel over the whole cell travels in both directions along Graded local potential membrane membrane Summation EPSP or IPSP Graded potentials caused by 1 Signal molecule strikes dendrite causes EPSP or IPSP 2 Some dendrites are specialized to physical parameters o Pressure stretch sensitive etc Deform channels graded potential Excitable cells all muscle cells all neurons Can conduct action potentials o Contain voltage gated channels Voltage gated channels are trans membrane proteins Made of amino acids with charged R group arms blocking channel Voltage change moves arm and unblocks membrane Require a certain voltage to change threshold Once gate is open stays open and then closes o While returning to original configuration another gate swings and temporarily blocks channel Gate inactivation Cannot reopen Critical feature of channel Voltage gated Na channel 4 domains of non polar amino acids in alpha helices Exam 1 Review Exam 1 2 25 14 Red dot on top loop moves to open channel at threshold IG inactivation gate blocks channel after certain amount of time Returns to original position Overall time period refractory period Can only depolarize as far as most positive ion equilibrium potential Na Action potential Na opens depolarization Na closes and inactivates repolarization K closes repolarization hyperpolarization K closes Effect on permeability of ions during AP Red AP Blue Na conductance Green K conductance o Blue and green explain red If you had less sodium action potential would have smaller amplitude Would have smaller equilibrium potential for sodium lower peak check this Exam 1 Review Exam 1 2 25 14 Exam 1 Review Exam 1 2 25 14 Action Potential All or none enters No summation o Refractory Period o Same amplitude and duration each time on given neuron o Same number of sodium channels same amount of sodium One directional dendrites terminal o Can not reverse because of refractory period channels behind are inactivated o Channels behind ARE depolarized but channels are inactivated Propagated Action potential starts when graded potentials depolarize to threshold Exam 1 Review