Transcript Biol 155 Human Physiology - University of British Columbia

Physiology of the
Nervous System
Ion channels
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Remember Ohm’s
Law: I=E/R
When a channel
opens, it has a
fixed resistance.
Thus, each channel
has a fixed current.
Using the patchclamp technique,
we can measure
the current
through individual
channels
Ionic basis of Em
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NaK-ATPase
pumps 3Na+
out for 2 K+
pumped in.
Some of the
K+ leaks back
out, making
the interior of
the cell
negative
Gated channels: ligand-gated
Gated channels: voltage-gated
Gated channels: mechanically-gated
Physiology of Nerves

There are two major regulatory systems in the
body, the nervous system and the endocrine
system.

The endocrine system regulates relatively slow,
long-lived responses

The nervous system regulates fast, short-term
responses
Divisions of the nervous system
Neuron structure

Neurons all have same basic structure, a cell body
with a number of dendrites and one long axon.
Types of neurons
Non-excitable cells of the nervous
system
Structure of gray matter
Signal transmission in neurons
Membrane potential
Resting potential
Induction of an action potential I
Induction of an action potential II
Transmitter effects on Em
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Most chemical stimuli result in an influx of cations
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This causes a depolarization of the membrane potential
At least one transmitter opens an anion influx
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This results in a hyperpolarization.
EPSPs and IPSPs
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If the transmitter opens a cation influx, the
resulting depolarization is called an Excitatory
Post Synaptic Potential (EPSP).
These individual potentials are sub-threshold.
If the transmitter opens an anion influx, the
resulting hyperpolarization is called an Inhibitory
Post Synaptic Potential (IPSP
All these potentials are additive.
Signal integration
Signal integration cont.
Voltage-gated
+
Na
channels
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These channels have
two voltage sensitive
gates.
At resting Em, one gate
is closed and the other
is open.
When the membrane
becomes depolarized
enough, the second
gate will open.
After a short time, the
second gate will then
shut.
Voltage-gated
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Voltage-gated K+
channels have only
one gate.
This gate is also
activated by
depolarization.
However, this gate is
much slower to
respond to the
depolarization.
+
K
channels
Cycling of V-G channels
Action potential propagation
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When the V-G Na+
channels open, they
cause a depolarization
of the neighboring
membrane.
This causes the Na+
and K+ channels in
that piece of
membrane to be
activated
AP propagation cont.
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The V_G chanels in
the neighboring
membrane then open,
causing that membrane
to depolarize.
That depolarizes the
next piece of
membrane, etc.
It takes a while for the
Na+ channels to
return to their voltagesensitive state. Until
then, they won’t
respond to a second
depolarization.
Changes in Em

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When the V-G Na+
channels open, there is a
rush of Na+ into the cell,
making the inside positive.
The Na+ channels close at
the same time the V-G K+
channels open.
When this happens, there is
a rush of K+ out of the cell,
making the inside more
negative.
Synaptic transmission
Presynaptic inhibition
Presynaptic facilitation
Post-synaptic integration
Neural circuits I
Neural circuits II
Saltatory AP propagation in
myelinated nerves
Myelination I
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In the central nervous
system, myelin is formed
by the oligodendrocytes.

One oligodendrocyte can
contribute to the myelin
sheath of several axons.
Myelination II
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In the peripheral nervous
system, myelin is formed
by Schwann cells.

Each Schwann cell
associates with only one
axon, when forming a
myelinated internode.
Schwann cells cont.
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In unmyelinated nerves,
each Schwann cell can
associate with several
axons.
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These axons become
embedded in the
Schwann cell, which
provides structural
support and nutrients.
White and gray matter in the nervous
system
Structure of the spinal cord I

The CNS is made
up not only of the
brain, but also the
spinal cord.

The spinal cord is
a thick, hollow
tube of nerves
that runs down
the back, through
the spine.
Structure of the spinal cord II
Structure of the spinal cord III
Structure of the spinal cord IV