Post on 03-Apr-2018
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Learning = new information + new
skills + new experience
Learning =making new connections
between information, skills andexperience
Learning = un-learn + re-learn
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Topics
1. Introduction
2.Energy and thermodynamics
3.Feeding and digestion
4. Ionic gradient, electrical potential
5.Electrical signals and neurons
6.Cytoskeletons, motor proteins and muscle
7.Heat production and body temperature
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Electrical signals and
neurons
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Neurons or nerve cells
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Neurons or
nerve cells
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For all living cells, there exist an electrical potentialacross the plasma membrane, with inside negative
relative to outside.
The formation of such a potential difference is due to
the facilitated diffusion of K
+
from inside to theoutside.
P -
Cl -
Na+
-
K+
Cl -
Na+
K+ channel
facilitated diffusion
K+
K+
K+
K+
+
At resting
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When stimulated, the Na+ channels in the
excitable membrane openand Na+ rushes in.
Inside become momentarily positive relative to
outside.
P -
Cl -
Na+
-
K+
Cl -
Na+
K+ channel
facilitated diffusion
K+
+
During
depolarization
Na+ channel
facilitated
diffusion
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IfPkincreases and the relative
permeabilityK : Na : Cl become 5 : 0.04 : 0.45
What will happen to Vm?
Vm =RTF
ln 5(20) + 0.04 (440) + 0.45(50)5(400) + 0.04(50) + 0.45(560)
= -71 mV
(closer to EK)
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Hyperpolarization
ENa
EK
+55
-60
-75
-71
K+Na+
Na+K+
+ + ++- - --
Ionic movement (K+) is
driven by the chemical
potential difference
(but slightly opposed
by the electric potential
difference)
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IfPNa increases and the relative
permeabilityK : Na : Cl become 1 : 100 : 0.45
What will happen to Vm?
Vmi-o =RTF
ln 20 + 100 (440) + 0.45(50)400 + 100(50) + 0.45(560)
= 52.6 mV
(closer to ENa)
Vmi-o
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Depolarization
ENa
EK
+55
-60
-75
+52.6
K+Na+
K+
Na++ + ++- - --
Ionic movement (Na+) isdriven by both the chemical
potential and electric
potential differences.
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Neurons or
nerve cells
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Receptor
cells
Nerve endings
Elaborated structures
Function 1) differential sensitivity
2) transducer and power amplification
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sound
light electrical
Mechanical electrical
chemical electrical
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How do we get proper sensation of
the environment?
Interpretation by the BRAIN
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The posterior (back) of the frontal lobe consists of the
premotor and motor areas. ... The parietal lobes contain the
primary sensorycortex which deals with sensation.
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How do we get proper sensation of
the environment?
Interpretation by the BRAIN
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Do our receptors measure the absolute
intensity of the stimuli ?!
(like a thermometer ?!
Like a pressure gauge ?!)
No !!!
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Beware that there are 2 coding
systems in the neural network
1) The intensity of the stimulus is coded in
the magnitude of the electrical potential.E.g. receptor membrane, chemical
synapses.
2) The intensity of the stimulus is coded in the
frequency of the electrical signal produced.
e.g. axon
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Neurons or
nerve cells
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Receptor potential cannot be
called action potential
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Beware that there are 2 coding
systems in the neural network
1) The intensity of the stimulus is coded in
the magnitude of the electrical potential.E.g. receptor membrane, chemical
synapses.
2) The intensity of the stimulus is coded in the
frequency of the electrical signal produced.
e.g. axon
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Beware that there are 2 coding
systems in the neural network
1) The intensity of the stimulus is coded in
the magnitude of the electrical potential.
E.g. receptor membrane, chemical
synapses.
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The Na+ channels in the receptormembrane open proportionally tothe intensity of the stimulus.
The signal generated is graded.
There is no all or none.
There is no threshold.There is no refractory period.
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Neurons or
nerve cells
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At the receptor membrane
1. There is no
all or none
phenomenon.
2. The receptor potential is non-self - generating.
3. It can spread (transmitted) only electrotonically(passively) to the spike - generating - zone of theneuron.
4. During such a spread, there is loss of magnitudeof the voltage.
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Neurons or
nerve cells
Signal spread electrotonically
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S g a sp ead e ect oto ca y
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How can intensity of stimuli betransmitted along the axon?
What is the range of intensity ofstimuli that our receptor cells are
sensitive to?
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Beware that there are 2 coding
systems in the neural network
1) The intensity of the stimulus is coded in
the magnitude of the electrical potential.
E.g. receptor membrane, chemical
synapses.
2) The intensity of the stimulus is coded in the
frequency of the electrical signal produced.
e.g. axon
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N ( ll )
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Neurons (nerve cells)
(A nerve is
a bundle ofaxons)
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Ion channels in axons
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Ion channels in axons
Channel Characteristics Function
Leak K+channel Produces relatively Largely responsible for(open in resting high Pk of resting cell Vrestaxon)
Voltage-gated Rapidly activated by Produces rising phase of
Na+ channel depolarization; action potential (Na+
becomes inactivated even influx)if Vm remains depolarize
Voltage-gated Activated by depolarization Carries current (K+ effux)
K+ channel but more slowly than Na+ that rapidly repolarizes
channel; inactivated slowly the membrane toand not completely if Vm terminate the action
remains depolarized potential
The Action Potential
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Na+ enters cell through Na+ channel.
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Conduction of action potentials
(a)
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Model of the voltage gated Na+ Channel
(a)
M d l f h l d N Ch l
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(b)
Model of the voltage gated Na+ Channel
M d l f th lt t d N + Ch l
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(c)
Model of the voltage gated Na+ Channel
M d l f th lt t d N + Ch l
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(d)
Model of the voltage gated Na+ Channel
M d l f th lt t d N + Ch l
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(e)
Model of the voltage gated Na+ Channel
Ions movement during the formation of action
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Ions movement during the formation of action
potential
C d ti f ti t ti l
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Conduction of action potentials
(a)
C d ti f ti t ti l
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Conduction of action potentials
(b)
C d ti f ti t ti l
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Conduction of action potentials
(c)
Refractory periods
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Refractory periods
Model of the voltage gated Na+ Channel
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(d)
Model of the voltage gated Na+ Channel
Model of the voltage gated Na+ Channel
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(e)
Model of the voltage gated Na+ Channel
Wh th i l h th th N + h l
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When the signal reaches the axon, the Na+ channels
there open all at once after the membrane voltage
reaches a threshold value. The amplitude of the action potential generated is
always the same, hence described as all or none
response.
Within one millisecond, the Na+ channels close and
enters the refractive period for 1 - 2 milliseconds.
K+ channels open up more than normal to bring the
voltage back to resting. The refractive property of the axon membrane
ensures an one way traffic of neural signals.
Summary videoWatch out for the word
diffusion which should
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http://www.youtube.com/watch?v=SCasruJT-DU
diffusion which should
be replaced with the
word rush (electric or
ionic current)
http://www.youtube.com/watch?v=SCasruJT-DUhttp://www.youtube.com/watch?v=SCasruJT-DUhttp://www.youtube.com/watch?v=SCasruJT-DUhttp://www.youtube.com/watch?v=SCasruJT-DU7/28/2019 5 Neuron Jan 2013
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Because of the existence of the threshold
phenomenon in the axon membrane,
action potential is self - generating.
There are 2 types of axon :
1) unmyelinated
2) myelinated
Is there any difference between axon and the
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y
electric cable?
What are their differences and similarities?
rm
re
good axon = rm
re
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How to make the transmission of
the signal along the axon moreefficient?
a. Re (resistance of axoplasm)
b. Rm(resistance of membrane)
Action potential along an
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unmyelinated axon
An unmyelinated axon has very small length constant
(~3 mm) due to small Rm.
http://www.youtube.com/watch?v=pbg5E9GCNVE
http://www.youtube.com/watch?v=pbg5E9GCNVEhttp://www.youtube.com/watch?v=pbg5E9GCNVE7/28/2019 5 Neuron Jan 2013
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Giant Squid Axon
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650 m 25 m / sec
Frog sciatic nerve10 m 25 m / sec
myelination
SALTATORY CONDUCTION (appear as though
the action potential jumps from node to node
which is not true)
Length constant 7.9 cm
Why not covering the whole length of the
axon?
Saltatory Conduction in myelinated axon
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Saltatory Conduction in myelinated axon
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Video on Schwann cells and transmission of neural signal along
the axon:
http://www.youtube.com/watch?v=DJe3_3XsBOg
Transmission along an unmyelinated axon
http://www.youtube.com/watch?v=pbg5E9GCNVE
Note: the word diffusion should be replaced with
http://www.youtube.com/watch?v=DJe3_3XsBOg
http://www.youtube.com/watch?v=DJe3_3XsBOghttp://www.youtube.com/watch?v=pbg5E9GCNVEhttp://www.youtube.com/watch?v=pbg5E9GCNVEhttp://www.youtube.com/watch?v=DJe3_3XsBOg7/28/2019 5 Neuron Jan 2013
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Note: the word diffusion should be replaced with
electrical current for Na+ movement within the axon
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Action
potential
Cannot be called
action potential
Electrotonic spread as
a current; Decrease in
amplitude
Multiple sclerosis
http://www.youtube.com/watch?v=qgySDmRRzxY&feature=relatedhttp://www.youtube.com/watch?v=qgySDmRRzxY&feature=relatedhttp://www.youtube.com/watch?v=qgySDmRRzxY&feature=related7/28/2019 5 Neuron Jan 2013
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http://www.youtube.com/watch?v=qgySDmRRzxY&feature=related
Neurons (nerve cells)
http://www.youtube.com/watch?v=qgySDmRRzxY&feature=relatedhttp://www.youtube.com/watch?v=qgySDmRRzxY&feature=related7/28/2019 5 Neuron Jan 2013
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( )
(A nerve is
a bundle of
axons)
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http://www.youtube.com/watch?v=HXx9qlJetSU
http://www.youtube.com/watch?v=HXx9qlJetSUhttp://www.youtube.com/watch?v=HXx9qlJetSU7/28/2019 5 Neuron Jan 2013
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Action
potential
Cannot be called
action potential
Electrotonic spread as
a current; Decrease in
amplitude
Postsynaptic potential is graded !! (not all ornone)
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none).
Neural Zones
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Figure 4.2
Neural Zones
Alzheimer disease
htt // t b / t h? Nj B 1jVIU
http://www.youtube.com/watch?v=NjgBnx1jVIUhttp://www.youtube.com/watch?v=NjgBnx1jVIU7/28/2019 5 Neuron Jan 2013
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http://www.youtube.com/watch?v=NjgBnx1jVIU
http://www.youtube.com/watch?v=NjgBnx1jVIUhttp://www.youtube.com/watch?v=NjgBnx1jVIU7/28/2019 5 Neuron Jan 2013
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End