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Bioelectric Signal Recording
MOURA, Guilherme, NUNES, Sandro, PORTEIRA, Ana
[email protected] 67323
[email protected] 67945
[email protected] 67305
INTRODUÇÃO À ENGENHARIA BIOMÉDICA – 1ST YEAR – 1ST SEMESTER – MEBIOM - IST
How can we evaluate our mind and look closer in our running thoughts? What makes us act like robots or maybe like a new
person when we drink alcohol? Is it a simple electric signal as those in our computers? Or do we have special agents helping
the ions moving in and out of the membrane, polarizing the extracellular solution?
Basic Concepts
What is this poster about?
Bioelectrical signals are transient pulsations propagated throughout the
membrane of living cells such as muscular cells and neurons. Recording
of bioelectrical signals is, thus, essential to understand how these
signals are propagated and, ultimately, how communication is
established through our entire body. This work shows how Biomedical
Engineering, in association with Electrophysiology, may act in this area
to create and develop new materials, instruments and techniques to
help measuring bioelectric signals. Therefore, along with the basic
anatomic and physiological concepts, we briefly present the
bioelectrical transmission.
What is an Action Potential?
How Synaptic Transmission is Processed?
An Action Potential is a rapid alteration of the
transmembrane voltage generated by the activity
of voltage-gated ion channels embedded in the
cell membranes. It can be divided into five
phases: the resting potential (1), threshold, the
rising phase (2), the falling phase (3) and the
recovery phase (4).
It occurs at specialized junctions called synapses.
The most common type of synapse is the chemical
synapse:
Basic structure and components of
a synapse.
A few sodium channels open,
bringing the potential past the
Only a few potassium channels
are opened during resting phase. threshold level.
The resulting depolarization, due to
opening of voltage-gated sodium
channels, initiates a sequence of
events leading to the release of the
transmitter.
The Ca2+ ions trigger the release of
neurotransmitter by causing the
synaptic vesicles to fuse with the
presynaptic membrane.
How Do We Record the Signals?
Intracellular
Extracellular
The cell is impaled (a
neuron, for e.g.) with a
sharp glass electrode and
the voltage (current-clamp)
or the current (voltageclamp) is recorded across
the membrane.
Intra-Corporal VS
(Cell Surface)
records
Population of
cells
After the overshoot phase, many
sodium channels begin to close
and potassium channels begin to
open.
Activation of potassium channels
reaches its maximum.
EEG
Vesicles empty their content of
neurotransmitter
into
the
synaptic cleft.
This fusion process is regulated by
the interaction between protein
complexes expressed on the vesicle
and presynaptic membranes.
How Can We Clamp a Cell?
Extra-corporal
(Skin Surface)
ECG
The neurotransmitter binds to
receptors on the postsynaptic
membrane; depolarization signal
is thus propagated to the
postsynaptic cell.
Voltage Clamp
Current Clamp
 Holds the
membrane
potential at a set
level;
 Measures ion currents across a
neuronal membrane.
 Keeps the electrical current
constant;
 Records the membrane potential by
injecting current into a cell through a
microelectrode.
Patch Clamp Technique
TESTING Whole-cell
The different methods
Hodgkin & Huxley , Nobel Prize Winners in 1963
Patch Clamp
Modes:
Inside Out/
Outside Out
Whole Cell
Clamped Cell
50
Recording techniques and, especially, patch clamp is highly dependant on nanotechnology. As such,
future improvements in this area may help to develop precision and cost of this method:
Superior Designs of Integrated
nanoelectronic patch clamp
amplifiers
• lower background noise and increased signal bandwidth which
allows a more reliable and precise recording;
Development of New
Nanomaterials
• The implementation of more resistive nanomaterials in the
construction of the coating or the pipette may facilitate the gigaseal
formation and, thus, help isolate the patch being studied.
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Makes small holes on the patch with
pore-forming agents such as antibiotics
and other drugs, instead of applying
suction
Future Prospectives
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100
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Perforated Patch
RESULTS
150
% of control mEPSC
Advantages: record
individual channels;
good pharmacology and
the inside/outside
solutions can be changed
.
Disadvantage: channel
properties can be
changed.
Advantages: good
pharmacology and high
definition in the current
recording .
Disadvantage: dialysis of
cytoplasmatic contents
´´´´´´´´´´´´´´´´´´´´´´´´´´
Set-Up for
the experiement
Amplitude and frequency changes
over 40 min recording time
Action potential recording from a
pyramidal cell in a current clamp
mode
Conclusion/Discussion
The contribution of Biomedical Engineering Techniques on Bioelectrical Signal
Recording have brought new ideas and solutions for the understanding of the
mechanics involved on communication within our body.
The knowledge of how we can control ions conduction and maybe interact with
our neurons signals is directly related to the level of technological development,
thus it is important to simulate and test the dynamics of neuron cells as a path to
understand our own physiology and to improve people's health.
Acknowledgements: Prof. Ana M. Sebastião and Raquel Dias, Departamento de Neurociências, FMUL