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

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 7.12a–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 Figure 7.15 Delayed effect (1 msec) Open potassium channels Membrane sodium permeability Membrane sodium permeability Sodium flow into cell Sodium flow into cell Potassium flow 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 8.8a–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

Figure 9.3c Cerebral Spinal Fluid

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 Crossed- Extensor Reflexes Figure 9.20