Prep for Quiz 1,2,3

1
Prep for Quiz 1,2,3

• Sept 7, 2007

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Organ Systems
Table 1.1
3
A Simplified Body Plan
Figure 1.4
4
Body Fluids and Compartments
Figure 1.5ac
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Body Fluids and Compartments
Figure 1.5ce
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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)

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Homeostasis

• Ability to maintain a relatively constant
  internal environment
• Conditions of the internal environment which are
  regulated include
• Temperature
• Volume
• Composition

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Resting Potential Neuron

• Chemical driving forces
• K out
• Na in

Figure 7.8a
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Resting Potential Neuron

• Membrane more permeable to K
• More K leaves cell than Na enters
• Inside of cell becomes negative

Figure 7.8b
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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
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Resting Potential Neuron

• Steady state develops
• Inflow of Na is balanced by outflow of K
• Resting membrane potential -70mV

Figure 7.8d
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Resting Potential Neuron

• Sodium pump maintains the resting potential

Figure 7.8e
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Resting Membrane Potential

• The resting membrane potential is closer to the
  potassium equilibrium potential

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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

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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

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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

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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
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Graded Potentials

• Spread by electrotonic conduction
• Are decremental
• Magnitude decays as it spreads

Figure 7.11
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Graded Potentials Can Sum

• Temporal summation
• Same stimulus
• Repeated close together in time
• Spatial summation
• Different stimuli
• Overlap in time

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Temporal Summation
Figure 7.12ab
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Spatial Summation
Figure 7.12c
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Summation Cancelling Effects
Figure 7.12d
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Graded Versus Action Potentials
Table 7.2
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Phases of an Action Potential

• Depolarization
• Repolarization
• After-hyperpolarization

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Phases of an Action Potential
Figure 7.13a
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Sodium and Potassium Gating
Figure 7.15
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Sodium and Potassium Gating Summary
Table 7.3
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Causes of Refractory Periods
Figure 7.17a
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Causes of Refractory Periods
Figure 7.17b
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Causes of Refractory Periods
Figure 7.17c
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Consequences of Refractory Periods

• All-or-none principle
• Frequency coding
• Unidirectional propagation of action potentials

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Conduction Unmyelinated
Figure 7.19
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Factors Affecting Propagation

• Refractory period
• Unidirectional
• Axon diameter
• Larger
• Less resistance, faster
• Smaller
• More resistance, slower
• Myelination
• Saltatory conduction
• Faster propagation

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Conduction Myelinated Fibers
Figure 7.20
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Conduction Velocity Comparisons
Table 7.4
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Fast Response EPSP
Figure 8.4a
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Slow Response EPSP
Figure 8.4b
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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

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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

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Inhibitory Synapse K Channels
Figure 8.5
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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

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Temporal Summation
Figure 8.8ab
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Spatial Summation
Figure 8.8a, c
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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

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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

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Cerebral Spinal Fluid
Figure 9.3c
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CSF Production

• Total volume of CSF 125150 mL
• Choroid plexus produces 400500 mL/day
• Recycled three times a day

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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

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Blood-Brain Barrier

• Capillaries
• Sites of exchange between blood and interstitial
  fluid
• Blood-brain barrier
• Special anatomy of CNS capillaries which limit
  exchange

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Blood-Brain Barrier
Figure 9.4b
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Reflex Arc
Figure 9.18
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Stretch Reflex
Figure 9.19
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Withdrawal and Crossed-Extensor Reflexes
Figure 9.20