Prep for Quiz 1,2,3 Sept 7, 2007 Organ Systems Table 1.1 A Simplified Body Plan Figure 1.4 Body Fluids and Compartments Figure 1.5ac Body Fluids and Compartments Figure 1.5ce Body Fluid Compartments Internal environment = fluid surrounding cells = extracellular fluid (ECF) 70 kg man - Total body water = 42 liters 28 liters intracellular fluid (ICF) 14 liters extracellular fluid (ECF) -Three liters plasma -11 liters interstitial fluid (ISF) Homeostasis Ability to maintain a relatively constant internal environment Conditions of the internal environment which are regulated include Temperature Volume Composition Figure 7.8a Resting Potential: Neuron Chemical driving forces K + out Na + in Figure 7.8b Resting Potential: Neuron Membrane more permeable to K + More K + leaves cell than Na + enters Inside of cell becomes negative Figure 7.8c Resting Potential: Neuron Electrical forces develop Na + into cell K + into cell Due to electrical forces K + outflow slows Na + inflow speeds Figure 7.8d Resting Potential: Neuron Steady state develops Inflow of Na + is balanced by outflow of K + Resting membrane potential = -70mV Figure 7.8e Resting Potential: Neuron Sodium pump maintains the resting potential +60 mV E Na -94 mVEKEK -70 mVResting Vm Resting Membrane Potential The resting membrane potential is closer to the potassium equilibrium potential Forces Acting on Ions If membrane potential is not at equilibrium for an ion, then the Electrochemical force is not 0 Net force acts to move ion across membrane in the direction that favors its being at equilibrium Strength of the net force increases the further away the membrane potential is from the equilibrium potential Resting Potential: Forces on K+ Resting potential = -70mV E K = -94mV Vm is 24mV less negative than E K Electrical force is into cell (lower) Chemical force is out of cell (higher) Net force is weak: K + out of cell, but membrane is highly permeable to K + Resting Potential: Forces on Na+ Resting potential = -70mV E Na = +60mV Vm is 130mV less negative than E Na Electrical force is into cell Chemical force is also into cell Net force is strong: Na + into cell, but membrane has low permeability to Na + Figure 7.8e A Neuron at Rest Small Na + leak at rest (high force, low permeability) Small K + leak at rest (low force, high permeability) Sodium pump returns Na + and K + to maintain gradients Graded Potentials Spread by electrotonic conduction Are decremental Magnitude decays as it spreads Figure 7.11 Graded Potentials Can Sum Temporal summation Same stimulus Repeated close together in time Spatial summation Different stimuli Overlap in time Temporal Summation Figure 7.12ab Spatial Summation Figure 7.12c Summation: Cancelling Effects Figure 7.12d Graded Versus Action Potentials Table 7.2 Phases of an Action Potential Depolarization Repolarization After-hyperpolarization Phases of an Action Potential Figure 7.13a Sodium and Potassium Gating Figure 7.15 Delayed effect (1 msec) Open potassium channels Membrane sodium permeability Membrane sodium permeability Sodium ow into cell Sodium ow into cell Potassium ow out of cell Net positive charge in cell (depolarization) Net positive charge in cell (repolarization) Positive feedback Negative feedback Threshold stimulus Depolarization of membrane Open sodium channels Delayed effect (1 msec) Sodium channel inactivation gates close Membrane potassium permeability Sodium and Potassium Gating Summary Table 7.3 Causes of Refractory Periods Figure 7.17a Causes of Refractory Periods Figure 7.17b Causes of Refractory Periods Figure 7.17c Consequences of Refractory Periods All-or-none principle Frequency coding Unidirectional propagation of action potentials Conduction: Unmyelinated Figure 7.19 Factors Affecting Propagation Refractory period Unidirectional Axon diameter Larger Less resistance, faster Smaller More resistance, slower Myelination Saltatory conduction Faster propagation Conduction: Myelinated Fibers Figure 7.20 Conduction Velocity Comparisons Table 7.4 Fast Response EPSP Figure 8.4a Slow Response EPSP Figure 8.4b Inhibitory Synapses Neurotransmitter binds to receptor Channels for either K or Cl open If K channels open K moves out IPSP If Cl channels open, either Cl moves in IPSP Cl stabilizes membrane potential IPSPs Are Graded Potentials Higher frequency of action potentials More neurotransmitter released More neurotransmitter binds to receptors to open (or close) channels Greater increase (or decrease) ion permeability Greater (or lesser) ion flux Greater hyperpolarization Inhibitory Synapse: K + Channels Figure 8.5 Neural Integration The summing of input from various synapses at the axon hillock of the postsynaptic neuron to determine whether the neuron will generate action potentials Temporal Summation Figure 8.8ab Spatial Summation Figure 8.8a, c Frequency Coding The degree of depolarization of axon hillock is signaled by the frequency of action potentials Summation affects depolarization Summation therefore influences frequency of action potentials Cerebrospinal Fluid (CSF) Extracellular fluid of the CNS Secreted by ependymal cells of the choroid plexus Circulates to subarachnoid space and ventricles Reabsorbed by arachnoid villi Functions Cushions brain Maintains stable interstitial fluid environment Figure 9.3c Cerebral Spinal Fluid CSF Production Total volume of CSF = 125150 mL Choroid plexus produces 400500 mL/day Recycled three times a day Blood Supply to the CNS CNS comprises 2% of body weight (34 pounds) Receives 15% of blood supply High metabolic rate Brain uses 20% of oxygen consumed by body at rest Brain uses 50% of glucose consumed by body at rest Depends on blood flow for energy Blood-Brain Barrier Capillaries Sites of exchange between blood and interstitial fluid Blood-brain barrier Special anatomy of CNS capillaries which limit exchange Blood-Brain Barrier Figure 9.4b Reflex Arc Figure 9.18 Stretch Reflex Figure 9.19 Withdrawal and Crossed- Extensor Reflexes Figure 9.20