Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 1.5a–c Body Fluids and Compartments Figure 1.5c–e 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 Resting Potential: Neuron – Chemical driving forces • K+ out • Na+ in Figure 7.8a Resting Potential: Neuron – Membrane more permeable to K+ – More K+ leaves cell than Na+ enters – Inside of cell becomes negative Figure 7.8b Resting Potential: Neuron – Electrical forces develop • Na+ into cell • K+ into cell – Due to electrical forces • K+ outflow slows • Na+ inflow speeds Figure 7.8c Resting Potential: Neuron – Steady state develops • Inflow of Na+ is balanced by outflow of K+ – Resting membrane potential = -70mV Figure 7.8d Resting Potential: Neuron – Sodium pump maintains the resting potential Figure 7.8e Resting Membrane Potential The resting membrane potential is closer to the potassium equilibrium potential +60 mV ENa -70 mV Resting Vm -94 mV EK 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 – EK = -94mV – Vm is 24mV less negative than EK • 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 – ENa = +60mV – Vm is 130mV less negative than ENa • 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+ 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 Figure 7.8e 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 7.12a–b 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 Threshold stimulus Depolarization of membrane Open sodium channels Positive feedback Net positive charge in cell (depolarization) Membrane sodium permeability Sodium flow into cell Delayed effect (1 msec) Sodium channel inactivation gates close Membrane sodium permeability Delayed effect (1 msec) Negative feedback Open potassium channels Membrane potassium permeability Potassium flow out of cell Sodium flow into cell Net positive charge in cell (repolarization) Figure 7.15 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 Extracellular fluid Axon hillock Unmyelinated axon Plasma membrane (a) Resting Site of original action potential + Extracellular fluid + + – + + + + + + + + + + + + + + + + + – – – – – – – – – – – – – – – – – – – Intracellular fluid – – – – – – – – – – – – – – – – – – – – + + + + + + + + + + + + + + + + + + + Extracellular fluid + + + + – + – – – – – – – + + + + Site A – + + + + – – – + – – – – + + + + + + + – – – – Site B – – – – + + + + + + + + + + + + – – – – – – – – – – – – – – – – + + + + + + + + Region of depolarization (b) Initiation Direction of action potential propagation + + + – + + + + + – – – – – – – Site A – – – – – – – – + + + + + + + + (c) Propagation – – – – + + + + Site B + + + + – – – – + + + + – – – – Site C – – – – + + + + + + + + – – – – – – – – + + + + RefractoryRegion of state depolarization + + + + + + + + – – – – – – – Site A – – – – – – – – + + + + + + + + – (d) Propagation continues + + + + – – – – Site B – – – – + + + + – – – – + + + + Site C + + + + – – – – + + + + – – – – Site D – – – – + + + + Region of Refractory Region of depolarization repolarization state (resting state) 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 Extracellular fl uid Axon hillock Myelinated axon Myelin sheath + Node of Ranvier + + + + + + + + + + + + + + – – – + + + + – + + + – – – – – – – – – – – – – – – – – – Intracellular – + + + – – – – – – – – – – – – – – – – – – – – – + + + + + + + + + + + + + + + + + + + Extracellular + + + – – – fl uid – – – + + + fl uid Direction of action potential propagation + + + + + + + + + + + + + + + + + + + – – – + + + – – – – – – – – – – – ++ + – – – – – – – – – – – – – – – – – – – – – – ++ + – – – – – – – – – – – + + + + + + – – – + + + + + + + + + + + + + + + + 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 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 8.8a–b 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 Cerebral Spinal Fluid Figure 9.3c CSF Production – Total volume of CSF = 125–150 mL – Choroid plexus produces 400–500 mL/day – Recycled three times a day Blood Supply to the CNS – CNS comprises 2% of body weight (3–4 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 CrossedExtensor Reflexes Figure 9.20