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Neural Communication: 1Communication within and
between cells
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Transmission o inormation
Inormation must be transmitted
within each neuron
and between neurons
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The Membrane
The membrane surrounds the neuron!
It is com"osed o lipid and protein!
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The #esting Potential
There is an electrical charge across the membrane! This is the membrane potential! The resting potential $when the cell is not iring% is a
&'mV dierence between the inside and the outside!
inside
outside
Resting potential of neuron = -70mV
+
-
+
-
+
-
+
-
+
-
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(rtist)s rendition o a t*"ical cell membrane
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Ions and the #esting Potential
Ions are electrically-charged molecules e!g! sodium $Na+%, "otassium $+%,chloride $Cl-%!
The resting "otential e.ists because ions are concentrated on dierent sides othe membrane!
Na+ and Cl- outside the cell! K+ and organic anions inside the cell!
inside
outsideNa+Cl-Na+
K+
Cl-
K+Organic anions (-)
Na+Na+
Organic anions (-)
Organic anions (-)
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Ions and the #esting Potential
Ions are electrically-charged molecules e!g! sodium $Na+%, "otassium $+%,chloride $Cl-%!
The resting "otential e.ists because ions are concentrated on dierent sides othe membrane!
Na+ and Cl- outside the cell! K+ and organic anions inside the cell!
inside
outsideNa+Cl-Na+
K+
Cl-
K+Organic anions (-)
Na+Na+
Organic anions (-)
Organic anions (-)
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Maintaining the #esting
Potential Na+ ions are actively transported $this uses
energ*% to maintain the resting "otential!
The sodium-potassium pump $a membrane"rotein% e.changes three Na+ ions or two + ions!
inside
outside
Na+
Na+
K+ K+
Na+
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Neuronal iring: the action
"otential The action potential is a ra"id
depolarization o the membrane!
It starts at the axon hillock and "asses
/uic0l* along the axon!
The membrane is /uic0l* repolarized to
allow subse/uent iring!
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Beore e"olari2ation
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(ction "otentials: #a"id
de"olari2ation 3hen "artial de"olari2ation reaches the activation
threshold, voltage-gated sodium ion channels o"en! 4odium ions rush in! The membrane "otential changes rom -&'mV to +5'mV!
Na+
Na+
Na+
-
+
+
-
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e"olari2ation
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(ction "otentials: #e"olari2ation
4odium ion channels close and become refractory! e"olari2ation triggers o"ening o voltage-gated potassium ion channels. K+ ions rush out o the cell, re"olari2ing and then h*"er"olari2ing the
membrane!
K+ K+
K+Na+
Na+
Na+
+
-
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#e"olari2ation
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The (ction Potential
The action "otential is all-or-none!!
It is alwa*s the same si2e!
6ither it is not triggered at all - e!g! too
little de"olari2ation, or the membrane is
7reractor*89
Or it is triggered com"letel*!
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Course of the Action Potential• The action potential begins with a partial depolarization (e.g. from firing of another
neuron ) [A].
• When the excitation threshold is reached there is a sudden large depolarization [B].
• This is followed rapidly by repolarization [C] and a brief hyperpolarization [D].
• There is a refractory period immediately after the action potential where nodepolarization can occur [E]
Membranepotential(mV)
[A]
[B] [C]
[D] excitation threshold
Time (msec)
-70
+40
0
0 1 2 3
6;
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(ction Potential
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Conduction o the action
"otential! "assive conduction will ensure that ad=acent
membrane de"olari2es, so the action "otential7travels8 down the a.on!
But transmission b* continuous action "otentialsis relativel* slo# and energy-consuming $Na+@+ "um"%!
( aster, more eicient mechanism has evolved:saltatory conduction. $yelination "rovides saltator* conduction!
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M*elination
Most mammalian a.ons are myelinated!
The m*elin sheath is "rovided b* oligodendrocytes and
%ch#ann cells!
M*elin is insulating, "reventing "assage o ions over the
membrane!
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4altator* Conduction
M*elinated regions o a.on are electrically insulated! 6lectrical charge moves along the axon rather than across the
membrane! (ction "otentials occur onl* at unmyelinated regions: nodes of
&anvier !
Node of RanvierMyelin sheath
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4*na"tic transmission Inormation is transmitted rom the presynaptic
neuron to the postsynaptic cell. Chemical neurotransmitters cross the synapse,
rom the terminal to the dendrite or soma.
The s*na"se is ver* narrow, so transmission isfast.
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terminal
dendritic spine
synaptic cleftpresynaptic membrane
postsynaptic membrane
extracellular fluid
4tructure o the s*na"se (n action "otential causes neurotransmitter
release rom the presynaptic membrane. Neurotransmitters diffuse across the synaptic
cleft!
The* bind to receptors within the postsynapticmembrane, altering the membrane "otential!
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Neurotransmitter release
CaA+ causes vesicle membrane to fuse with"res*na"tic membrane!
Vesicle contents em"t* into clet: exocytosis! Neurotransmitter diuses across s*na"tic
clet!
Ca2+
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'onotropic receptors (ligand gated)
4*na"tic activit* at ionotro"ic rece"torsis fast and brief $milliseconds%!
*cetylcholine $(ch% wor0s in this wa*
at nicotinic rece"tors! Neurotransmitter binding changes the
rece"tor)s sha"e to o"en an ion
channel directl*!ACh ACh
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Ionotro"ic #ece"tors
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Metabotro"ic #ece"tors $-Protein%
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6.citator* "osts*na"tic
"otentials $6P4Ps% O"ening o ion channels which leads to
depolarization ma0es an action "otential more likely ,hence 7e.citator* P4Ps8: "%"s. Inside o "ost-s*na"tic cell becomes less negative!
Na+ channels (NB remember the action potential) Ca+ ! $(lso activates structural intracellular changes -
learning!%
inside
outsideNa+
Ca2+
+
-
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Inhibitor* "osts*na"tic
"otentials $IP4Ps% O"ening o ion channels which leads to
hyperpolarization ma0es an action "otential lesslikely , hence 7inhibitor* P4Ps8: '"%"s. Inside o "ost-s*na"tic cell becomes more negative! K+ (NB remember termination of the action potential)
Cl- $i alread* de"olari2ed%
K+
Cl- +
-inside
outside
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Posts*na"tic Ion motion
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#e/uirements at the s*na"se
Dor the s*na"se to wor0 "ro"erl*, si. basic events need to ha""en: Production o the Neurotransmitters
4*na"tic vesicles $4V% 4torage o Neurotransmitters
4V #elease o Neurotransmitters Binding o Neurotransmitters
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Integration o inormation
P4Ps are small! (n individual 6P4P will not "roduceenough de"olari2ation to trigger an action "otential! IP4Ps will counteract the eect o 6P4Ps at the
same neuron! %ummation means the eect o man* coincident
IP4Ps and 6P4Ps at one neuron! I there is suicient de"olari2ation at the axon
hillock, an action "otential will be triggered!
axon hillock
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Three Nobel Pri2e 3inners on
4*na"tic Transmission*rvid Carlsson discovered do"amine is a neurotransmitter!
Carlsson also ound lac0 o do"amine in the brain o
Par0inson "atients!
"aul reengard studied in detail how neurotransmitters
carr* out their wor0 in the neurons! o"amine activated a
certain "rotein $(#PP-EA%, which could change the unction
o man* other "roteins!
ric Kandel "roved that learning and memor* "rocessesinvolve a change o orm and unction o the s*na"se,
increasing its eicienc*! This research was on a certain
0ind o snail, the 4ea 4lug $("l*sia%! 3ith its relativel* low
number o A',''' neurons, this snail is suitable or
neuron research!
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Neuronal iring: the action
"otential The action potential is a ra"id
depolarization o the membrane!
It starts at the axon hillock and "asses/uic0l* along the axon!
The membrane is /uic0l* repolarized to
allow subse/uent iring!
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Overview
Course introduction
Neural Processing: Basic Issues
Neural Communication: Basics
Vision, Motor Control: Models
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Motor Control: Basics
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Hierarchical Organization of
Motor System
• Primary Motor Cortex and Premotor Areas
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Primary motor cortex (M1)
Foot
Hip
Trunk
Arm
Hand
Face
Tongue
Larynx
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Motor Control Basics
• Reflex Circuits
– Usually Brain-stem, spinal cord based
– Interneurons control reflex behavior
– Central Pattern Generators
• Cortical Control
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postsynaptic
neuron
science-education.nih.gov
Dle.or
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Dle.or-
Crossed
6.tensor
#ele.
$4heridan
1F''%
Painul 4timulus
#ele.
Circuits
3ith
Inter-neurons
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