Transcript Organ Systems

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