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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-DU

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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=pbg5E9GCNVE

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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_3XsBOg

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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=related

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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=related

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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=HXx9qlJetSU

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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=NjgBnx1jVIU

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http://www.youtube.com/watch?v=NjgBnx1jVIU

http://www.youtube.com/watch?v=NjgBnx1jVIUhttp://www.youtube.com/watch?v=NjgBnx1jVIU

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End