BIO 342 HUMAN PHYSIOLOGY

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S 1
Family WeekendDr. Davis in Office or
Lab10-1130 am
Concerning Test 1 Types of questions Recall
information Apply to situations Chapter
questions Refugee physiology Check Moodle site
for 1QQ grades
28 September TopicsGraded potentialsAction
PotentialsProperties of V-gated ion channelsAP
conduction
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1QQ 10 for 830 class

• At resting membrane potential
• The concentration gradient favors the entry of
  Na
• The electrostatic driving force favors the entry
  of Na
• The concentration gradient favors the exit of K
• The electrostatic driving force favors the exit
  of K
• The membrane is more permeable to Na than to K.
• Suppose you have a cell with the normal
  concentrations of Na and K on either side of
  the membrane, and you were able to make the
  membrane absolutely and completely impermeable to
  Na. A) What would the membrane potential be?
  (include the units.)B) What equation would you
  use to calculate the membrane potential?

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1QQ 10 for 930 class

• At the equilibrium potential for Na
• The concentration gradient favors the entry of
  Na
• The electrostatic driving force favors the entry
  of Na
• The concentration gradient favors the exit of K
• The electrostatic driving force favors the exit
  of K
• The membrane is more permeable to Na than to K.
• Suppose you have a cell with the normal
  concentrations of Na and K on either side of
  the membrane, and you were able to make the
  membrane absolutely and completely impermeable to
  K. A) What would the membrane potential be.
  (include the units.)B) What equation would you
  use to calculate the membrane potential?

4
S 1
5
Excitable membranes special structures make
Neurons good Electrical Communicators
S 2
Ligand-gated ion channels in membranes of
dendrites and soma. Graded potentialconducted
decrementally
receiving
Axon hillock integrates and produces an
all-or-nothing Action Potential conducted
non-decrementally and unidirectionally.
Synapse onother neurons, skeletal muscle, smooth
muscle, cardiac muscle, glands
sending
Voltage-gated ion channels in membrane of axon
hillock and axon..Action potentials all or
nothing!
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S 3
Types and locations of Ion Channels
Sensory neuron
Leak Channels Gated Channels .. Ligand-gated..
Mechanically-gated .. Voltage-gated
w/ LGCs and MGCs
Intracellular Recording Electrode or Stimulating
Electrode
Interneurons Motoneurons
w/ LGCs
w/ VGCs
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S 4
What happens when the membrane is depolarized by
more than about 15 mV?
Action potentials are all or nothing.
Analogy of shutter release pressure on a camera,
either trips shutter or not.
How is the intensity of a stimulus encoded by
action potential if all action potentials have
the same size (amplitude)?
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S 5
Relevance of the GHK equation
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S 6
To reset from inactivated state to closed state,
membrane must repolarize.
Open at -55 mV
Membrane must repolarize to reset Na Channels
to be capable of opening again.
Compare and contrast voltage-gated Na and K
channels based on time to open and duration of
open time.
10
Voltage-gated Na channel
S 7
Tetrodotoxin from ovary of Puffer fish, used in
Japanese sushi (fugu)
scienceblogs.com/.../upload/2006/03/channel.jpg
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What types of ion-channels are labeled in this
neuron in red?
S 8
TTX with red fluorescent marker
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S 9
Relative permeabilities Duration of AP Refractory
periods absolute RP relative RP
RisingPhase
FallingPhase
Why does the peak of the action potential not
reach ENa?
Properties of V-gated Na and K channels account
for the shape of the action potential and the
refractory periods.
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S 10
14
Natural ways to Initate an Action Potential
S 11
Graded depolarization in cell body reach
threshold at axon hillock
Unstable membrane potential cycles pacemaker
potentials in pacemaker cells of heart, smooth
muscles of gut, and medullary neurons for
respiratory rhythm.
Graded depolarization in in receptive membranes
of sensory neurons reach threshold for AP. i.e.
nociceptors and stretch receptors.
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S 12
Who Cares?
Novacaine, lydocaine, xylocaine, All block
voltage-gated Na channels Prevent action
potentials, so stimulus does not result in an
action potential in sensory neurons which would
convey that information to the brain where person
would be conscious of the stimulus!
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S 13
Questions About Action Potential Conduction How
does an action potential move along the axon?
Why doesnt the amplitude get smaller with
distance? Why is the conduction of an action
potential unidirectional? What is the absolute
refractory period and what is going on with
voltage gated sodium channels that accounts for
the absolute refractory period? What is the
relative refractory period and what is going on
with voltage gated sodium channels that accounts
for the relative refractory period?
Axon Hillock
Axon
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S 14
In unmyelinated axons, action potential must be
generated at each point along the membrane, a
relatively slow process that involves influx of
Na which sets up positive feedback cycle.
In myelinated axons, action potential must be
generated only at the nodes of Ranvier, which
allows AP to be conducted much faster and with
fewer ions moving, and thus less energetically
expensive.