Transcript Neurophysiology - Learn District 196

Neurophysiology
pages 373-389
I. Resting Potential
• All neural activity begins with a change in the
resting membrane potential of a neuron
• The resting membrane potential is -70mV (the
minus indicating the interior is negatively
charged)
• Passive leak channels and the sodiumpotassium pump maintain the resting
membrane potential (RMP).
The diffusion of potassium K+ and sodium Na+ ions along
their electrochemical gradients is responsible for creating the
resting membrane potential.
Gated channels present
on the plasma membrane
open or close in response
to a specific stimuli.
In turn, changing the
trans-membrane potential.
Chemical gated channels: open when they bind to specific chemicals
(neurotransmitters).
Voltage gated channels: open or close in response to changes in the “transmembrane” potential.
Mechanical gated channels: open in response to physical distortion of membrane
surface.
II. Graded Potentials
• Temporary, localized change in the RMP.
• Opening of gated channels creates a change in the
permeability of Na+ or K+ ions.
• Depolarization: a shift towards a less negative value
in the trans-membrane potential.
• Hyperpolarization: a shift in a more negative transmembrane potential.
• The stronger the stimulus the greater the change in
the trans-membrane potential.
• Graded potentials will decrease with distance.
Question 1: A neuron whose polarization has changed from -70 mV to -68 mV
a. shows depolarization
b. has received excitation from other neurons
c. a. and b. are both correct
d. neither
Question 2:
a. -60 mV
b. -72 mV
c. -78 mV
d. -68 mV
An electrode records the following voltages from inside the dendrites of a
neuron. Which of the following polarizations reflects the strongest inhibitor?
III. Action Potential
• Propagated (spread out) changes in the transmembrane potential.
• Dependent upon voltage-gated channels.
• Threshold: depolarization of trans-membrane
potential where voltage-gated channels open (-55
mV)
• Occur at the axon hillock of a neuron cell body.
• “All-or-none-principle”: stimulus either triggers or
fails to trigger an action potential.
Question 1: What event(s) happen at the stimulus threshold (-55 mV)?
a. voltage-gated sodium (Na+) channels open
b. voltage-gated potassium (K+) channels open
c. both
d. neither
Question 2:
At -60 mV to +30 mV, which ions cross the membrane and in which
direction will they cross?
a. Na+ out of neuron
c. K+ out of neuron
b. Na+ into neuron
d. K+ into neuron
Question 3:
What event(s) happen
at +30 mV?
a. sodium (Na+) channel
inactivation
b. voltage-gated potassium (K+)
channels open
c. both
d. neither
Question 4:
Which statement is
true of the refractory
period?
a. Sodium (Na+) channels remain
inactivated
b. potassium (K+) channels begin
closing
c. membrane cannot respond to
further stimulation
d. all of the above
Propagation of an Action Potential
(continuous vs. Saltatory)
• Continuous:
– unmyelinated axons
– relatively slow
(1 meter/second)
• Saltatory:
– myelinated axons
– fast
(100 meters/second)
IV. Postsynaptic Potentials
• Graded potentials that develop on the
postsynaptic membrane in response to a
neurotransmitter.
• Two types of postsynaptic potentials:
– excitatory (EPSP)
• depolarization of postsynaptic membrane
– inhibitory (IPSP)
• hyperpolarization of postsynaptic membrane
Summation of Postsynaptic Potentials
(summation: cumulative effect)
• Temporal summation:
– single synapse is active
repeatedly
– “machine gun”
• Spatial summation:
– multiple synapses that
are active
simultaneously.
– “firing squad”
Question 1:
a. -77 mV
b. 77 mV
Question 2:
a. yes
A postsynaptic neuron receives temporal EPSPs from four sources. They are
as follows: E1= +2 mV; E2= +1 mV; E3= +3 mV; E4= +1 mV. Assuming the
resting membrane potential is -70mV, what will the polarization be in
response to the four EPSP?
c. -63 mV
d. 63 mV
Will the above postsynaptic potentials result in an action potential?
b. no
Question 3:
Assuming the resting
membrane potential is -70 mV,
what will the final polarization
of a neuron be if the following
synapses are active
simultaneously? E1= +1 mV;
E2= +3 mV; E3= +4 mV;
I1= -1 mV; I2= -2 mV
a. -74 mV
b. 65 mV
c. -65 mV
d. 60 mV
Question 4:
What type of summation is
described in the above
question?
a. temporal
b. spatial
V. Information Processing
• Integration of stimuli at the level of the
individual neuron is the simplest form of
information processing.
• Factors influencing the response of the
postsynaptic neuron
– neurotransmitters
– extracellular chemicals
– regulatory neurons
– frequency of action potentials
Pufferfish for dinner? Better have an
experienced sushi chef
Fugu is Japanese for pufferfish and the dish
prepared from it. Research the neurophysiology
behind fugu and answer the questions below.
Hand in for an extra credit card.
1. What is the name of the toxin
2. What happens to an individual who consumes the toxin.
3. Neurology: Describe in detail the neurophysiology behind the
toxin. Description should include, but not limited to the
following terms; sodium gated channels, depolarization,
threshold, action potential, propagation, neuromuscular
junction, muscle contraction.
4. Is the victim conscious or unconscious when poisoned?