AIM
SWBAT describe synaptic transmission and impulse processing.
Criteria for Success
[ ] I can list and describe the components of a synapse.
[ ] I can describe process of synaptic transmission.
[ ] I can differentiate between action potential and resting potential.
[ ] I can compare and contrast neuronal pools, convergence and
divergence.
The Synapse
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Nerve impulses pass
from neuron to neuron at
synapses, moving from
a pre-synaptic neuron
to a post-synaptic
neuron.
Synaptic
cleft
Impulse
Dendrites
Axon of
presynaptic
neuron
Axon hillock of
Postsynaptic neuron
Axon of
presynaptic
neuron
Impulse
Cell body of Impulse
postsynaptic
neuron
3
Synaptic Transmission
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Direction of
nerve impulse
• Neurotransmitters are
released when impulse
reaches synaptic knob
Axon
Ca+2
Synaptic knob
Synaptic
vesicles
Presynaptic neuron
Ca+2
Cell body or dendrite
of postsynaptic neuron
Mitochondrion
Ca+2
Synaptic
vesicle
Vesicle releasing
neurotransmitter
Axon
membrane
Neurotransmitter
Synaptic cleft
Polarized
membrane
Depolarized
membrane
(a)
4
Animation: Chemical Synapse
Please note that due to differing
Please
note
that duesome
to differing
operating
systems,
animations
operating
systems,
some
animations is
will not appear until the presentation
will
not in
appear
until theMode
presentation
viewed
Presentation
(Slide is
viewed
in Presentation
Mode
(Slide
Show view).
You may see
blank
slides
Show
view).
You
may
see
blank
in the “Normal” or “Slide Sorter”slides
views.
in
the
“Normal”
or
“Slide
Sorter”
views.
All animations will appear after viewing
All
animations will
appear
after viewing
in Presentation
Mode
and playing
each
in
Presentation
Mode
and
playing
each
animation. Most animations will require
animation.
Most animations
will
require
the latest version
of the Flash
Player,
the
latest
version of
which
is available
at the Flash Player,
which
is available at
http://get.adobe.com/flashplayer.
http://get.adobe.com/flashplayer.
5
Cell Membrane Potential
• A cell membrane is usually electrically charged, or
polarized, so that the inside of the membrane is negatively
charged with respect to the outside of the membrane (which is
then positively charged).
• This is as a result of unequal distribution of ions on the
inside and the outside of the membrane.
6
Distribution of Ions
• Potassium (K+) ions are the major intracellular positive ions (cations).
• Sodium (Na+) ions are the major extracellular positive ions (cations).
• This distribution is largely created by the Sodium/Potassium Pump
(Na+/K+ pump).
• This pump actively transports 3 sodium ions out of the cell and 2
potassium ions into the cell.
7
Action Potentials
• At rest, the membrane is
polarized (RMP = -70)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Na+
• Threshold stimulus
reached (-55)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
Na+
–0
–70
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
(a)
• Sodium channels open
and membrane
depolarizes (toward 0)
K+
Na+
Na+
K+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
–0
K+
Threshold
stimulus K+
K+
Na+
Na+ channels open
K+ channels closed
K+
Na+
Na+
–70
• Potassium leaves
cytoplasm and
membrane repolarizes
(+30)
• Brief period of
hyperpolarization (-90)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Region of depolarization
(b)
K+
K+
Na+
K+
Na+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
Region of repolarization
(c)
Na+
Na+
Na+
Na+
Na+
–0
K+ channels open
Na+ channels closed
–70
Na+
8
Action Potentials
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
+40
Membrane potential (millivolts)
Action potential
+20
0
–20
Resting potential
reestablished
–40
Resting
potential
–60
–80
Hyperpolarization
0
1
2
3
4
5
Milliseconds
6
7
8
9
Action Potentials
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Region of
action potential
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
–
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
–
–
–
+
+
+
(a)
+
–
+
+
–
–
+
+
Direction of nerve impulse
–
–
–
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
(b)
–
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
–
+
+
–
–
+
(c)
+
+
+
+
+
+
+
+
10
Animation: Action Potential
Propagation in Myelinated Neurons
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
11
Animation: Action Potential
Propagation in Unmyelinated Neurons
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
12
All-or-None Response
• If a neuron axon responds at all, it responds completely –
with an action potential (nerve impulse)
• A nerve impulse is conducted whenever a stimulus of
threshold intensity or above is applied to an axon
• All impulses carried on an axon are the same strength
13
Animation: The Nerve Impulse
Please note that due to differing
Please
note
that duesome
to differing
operating
systems,
animations
operating
systems,
some
animations is
will not appear until the presentation
will
not in
appear
until theMode
presentation
viewed
Presentation
(Slide is
viewed
in Presentation
Mode
(Slide
Show view).
You may see
blank
slides
Show
view).
You
may
see
blank
in the “Normal” or “Slide Sorter”slides
views.
in
the
“Normal”
or
“Slide
Sorter”
views.
All animations will appear after viewing
All
animations will
appear
after viewing
in Presentation
Mode
and playing
each
in
Presentation
Mode
and
playing
each
animation. Most animations will require
animation.
Most animations
will
require
the latest version
of the Flash
Player,
the
latest
version of
which
is available
at the Flash Player,
which
is available at
http://get.adobe.com/flashplayer.
http://get.adobe.com/flashplayer.
14
Impulse Processing
• Way the nervous system processes nerve impulses and acts
upon them
• Neuronal Pools
• Interneurons
• Work together to perform a common function
• May excite or inhibit
• Convergence
• Various sensory receptors
• Can allow for summation of impulses
• Divergence
• Branching axon
• Stimulation of many neurons ultimately
15
Neuronal Pools
• Groups of interneurons that make synaptic connections
with each other
• Interneurons work together to perform a common function
• Each pool receives input from other neurons
• Each pool generates output to other neurons
16
Convergence
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Neuron receives input from several
neurons
• Incoming impulses represent
information from different types of
sensory receptors
1
2
• Allows nervous system to collect,
process, and respond to information
• Makes it possible for a neuron to
sum impulses from different sources
3
(a)
17
Divergence
• One neuron sends impulses
to several neurons
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Can amplify an impulse
4
• Impulse from a single neuron
in CNS may be amplified to
activate enough motor units
needed for muscle contraction
6
5
18
(b)