Bioelectricity
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Electromyography (EMG)
Electromyography (EMG) is
an electro-diagnostic
medicine technique for evaluating
and recording the electrical activity
produced by skeletal muscles
EMG Amplifiers
A Bioamplifier is an electrophysiological device, a variation of
the instrumentation amplifier, used to gather and increase the EKG
signal integrity of physiologic electrical activity for output to
various sources.. https://en.wikipedia.org/wiki/Bioamplifier
EMG
EEG
EMG recording electrodes
• Surface EMG
• intramuscular EMG---needle electrodes
Peter Konrad. The ABC of EMG. A Practical Introduction to Kinesiological
Electromyography
Peter Konrad. The ABC of EMG. A Practical Introduction to Kinesiological
Electromyography
Limitations of the surface electorodes
• Mostly records from superficial muscles
• variable subcutaneous tissue……..inter-individual differences of the
subcutaneous tissue.
• Crosstalk---may record the discharges of adjacent muscles.
Limitations of the needle electorodes
• less informative in patients unwilling or unable to cooperate, children
and infants, and in individuals with paralysis.
Sampling rate
• Number of data points (cycles) collected per unit of time - usually
seconds
Peter Konrad. The ABC of EMG. A Practical Introduction to Kinesiological
Electromyography
EMG signals
• 0 to 10 mV
• 0 to 500 Hz frequency range,
• with the dominant energy being in the 50-150 Hz range.
Signal to Noise Ratio
• That is, the ratio of the energy in the EMG signal to the energy in the
noise signal.
• Noise is defined as electrical signals that are not part of the wanted
EMG signal
Carlo J. De Luca. 2002. Surface Electromyography Detection And Recording
CHARACTERISTICS OF THE ELECTRICAL NOISE
• Inherent noise in the electronics components in the detection and
recording equipment--- 0 Hz to several thousand Hz.
• Electronic equipments around
➢50 Hz or 60 Hz noise from the power sources
➢Or from other equipment, radio, phone, television
• Motion artefacts…movement of the electrode connected to the
amplifier; Loose cable connections.
Carlo J. De Luca. 2002. Surface Electromyography Detection And Recording
The factors that mainly affect the EMG signal
Causative Factors:
• Extrinsic: This is due to electrode structure and placement. Factors like area
of the detection surface, shape of electrode, distance between electrode
detection surface, location of electrode with respect to the motor points in
the muscle, location of the muscle electrode on the muscle surface with
respect to the lateral edge of the muscle, orientation of the detection
surfaces with respect to the muscle fibers mainly have an effect on EMG
signal.
• Intrinsic: Physiological, anatomical, biochemical factors take place due to
number of active motor units, fiber type composition, blood flow, fiber
diameter, depth and location of active fibers and amount of tissue between
surface of the muscle and the electrode
Reaz et al. 2006
Interindividual differences in EMG recording
• Subjects will have muscles with
• different physiological cross-sections
• different lengths - geometry
• different ratios of slow- to fast-twitch fibers
• different recruitment patterns
• different firing frequencies
www.nyu.edu/classes/mcdonough/signal3.ppt
Peter Konrad. The ABC of EMG. A Practical Introduction to
Kinesiological Electromyography
Peter Konrad. The ABC of EMG. A Practical Introduction to
Kinesiological Electromyography
Electrode placement
• The electrode should be placed between a motor point and the
tendon insertion or between two motor points, and along the
longitudinal midline of the muscle. The longitudinal axis of the
electrode (which passes through both detection surfaces) should be
aligned parallel to the length of the muscle fibers.
• Motor points: The motor point is that point on the muscle where the
introduction of minimal electrical current causes a perceptible twitch
of the surface muscle fibers.
Carlo J. De Luca. 2002. Surface Electromyography Detection And Recording
• Electrodes near to the tendon…muscle fibers are fewer in number near to
tendon…causes reduced EMG amplitudes.
• Do not put the electrodes on motor points---EMG signal will have higher
frequency components.
• Do not put the electrodes at the outside of the muscle…causes crosstallk
from adjacent muscles.
• Put the electrodes parallel to the muscle fibers ….longitudinal axis of the
electrodeshould be aligned parallel to the length of the muscle fibers
• Most easiest way…place the electrode in the middle of the muscle
between the origin and insertion point.
Carlo J. De Luca. 2002. Surface Electromyography Detection And Recording
Carlo J. De Luca. 2002. Surface Electromyography Detection And Recording
REFERENCE ELECTRODE PLACEMENT
• The reference electrode is necessary for providing a common
reference to the differential input of the preamplifier in the electrode.
• For this purpose, the reference electrode should be placed as far
away as possible and on electrically neutral tissue (say over a bony
prominence).
Why the EMG is recorded
• How well a muscles contract----maximal voluntary contraction
• nerve conduction study--- damage of the peripheral nervous system.
MOTOR UNIT ACTION
POTENTIAL (MUAP)
• The human body as a whole is electrically neutral; it has the same
number of positive and negative charges. But in the resting state, the
nerve cell membrane is polarized due to differences in the
concentrations and ionic composition across the plasma membrane.
A potential difference exists between the intra-cellular and
extracellular fluids of the cell. In response to a stimulus from the
neuron, a muscle fiber depolarizes as the signal propagates along its
surface and the fiber twitches
• This depolarization, accompanied by a movement of ions, generates
an electric field near each muscle fiber. An EMG signal is the train of
Motor Unit Action Potential (MUAP) showing the muscle response to
neural stimulation. The EMG signal appears random in nature.
A basic concept in electromyography is the so called motor unit (MU),
which represents the anatomical and functional element of the
neuromuscular system. The MU is formed by the alpha spinal
motorneuron and its innervated set of muscular cells. The electrical
changes generated by activity of the MU can be acquired and amplified
by electrodes located in muscle mass and these changes can be
recorded and edited using electromyographic (EMG) devices. The
representation of the changes generated by a MU is the so called motor
unit action potential (MUAP).
The recording and analysis of the electrical activity of MFs and MUs (myoelectrical
activity) is the subject of electromyography. Conventional EMG studies are
performed with needle electrodes that capture the activity of MFs within a
hemisphere of 2.5 mm radius from the tip of the needle electrode.
To study the MUAPs of a certain muscle, a needle electrode is inserted into the
muscle mass, which the subject is asked to maintain under slight contraction. In this
way, a low number of MUs are activated and the successive discharges of the
corresponding MUAPs can be collected. If the degree of contraction is excessive, too
many MUs are discharging and the recorded waveforms of their MUAPs are
distorted by their superposition.
During routine needle EMG, most MUAPs analyzed are thus
from the smaller motor units that innervate type I muscle
fibers
http://clinicalgate.com/basic-electromyography-analysis-of-
motor-unit-action-potentials/
A: Normal state. B: Following partial denervation. C:
Reinnervation
http://clinicalgate.com/basic-electromyography-analysis-of-
motor-unit-action-potentials/
Nerve Conduction Studies
Nerve Conduction Studies
• The aim is to measure the nerve conduction
• Placement of the electrode to the muscle
• Electrical stimulation to the nerve
• Recording of action potential of the muscle…
cal.vet.upenn.edu
cal.vet.upenn.edu
Example
• Median Nerve
• Distal stimulation (wrist) ---elicited 3 milisecond distal latency
• Proximal stimulation (elbow)---elicited 7 milisecond proximal latency
• Distance between stimulation sites is 240 mm
• What is the motor conduction velocity of median nerve?
• 240/4=60 milimeter/milisecond
Mustafa Ertaş.Elektromiyografi.Nörolojide Laboratuvar
incelemeleri
Mustafa Ertaş.Elektromiyografi.Nörolojide Laboratuvar
incelemeleri
Elektroensefalografi
1873-1941 Hans Berger
Intracranial EEG.....Epilepsi cerrahisi sırasında
Odd numbers on the left, even on the right
z indicates midline electrodes
F = frontal
C = central
T = temporal
P = parietal
O = occipital
A1 and A2 are on the ears.
Resim 2: EEG 10-20 sistemine göre elektrotlar arası mesafeler:
Resim Kaynak: http://www.trans-cranial.com/local/manuals/10_20_pos_man_v1_0_pdf.pdf
EEG Montages
• Bipolar Montage
• Each channel represents the voltage difference between a
pair of adjacent electrodes, with a unique pairing for each
channel.
• Referential Montage
With referential montages, all electrodes are referenced to a
single common reference point that commonly consists of
linked ears
Bipolar Montaj
Resim Kaynak:Foldvary-Schaefer, Nancy & Grigg-Damberger, Madeleine. (2012). Identifying Interictal and Ictal Epileptic Activity in
Polysomnograms. Sleep Medicine Clinics. 7. 39–58. 10.1016/j.jsmc.2012.01.002.
http://eegatlas-online.com/index.php/en/montages/bipolar/double-
banana
Bipolar Montajlar
Resim Kaynak:Foldvary-Schaefer, Nancy & Grigg-Damberger, Madeleine. (2012). Identifying Interictal and Ictal Epileptic Activity in
Polysomnograms. Sleep Medicine Clinics. 7. 39–58. 10.1016/j.jsmc.2012.01.002.
Referential Montage
• ipsi ear montage
• contra ear montage
• average montage
• A1 + A2 montage
With referential montages, all electrodes are referenced
to a single common reference point
Referans Montaj: Tüm elektrotların bağlı olduğu ortak bir referans
elektrot vardır
Resim kaynak:https://clinicalgate.com/electroencephalographic-
electrodes-channels-and-montages-and-how-they-are-chosen/
Resim Kaynak EEG Signal Analysis
and Classification
Resim Kaynak EEG Signal Analysis
and Classification
Kaynak: http://eegatlas
online.com/index.php/en/montages/referential/ipsi-
ear
Kaynak: http://eegatlas
online.com/index.php/en/montages/referential/ipsi-
ear
Ortalama Referans Montaj:
Resim Kaynak http://apetrilla.blogspot.com.tr/2009/06/eeg- Resim Kaynak EEG Signal Analysis
system.html
and Classification
Clinical EEG
Diagnosis of Epilepsy
Sağlıklı bir insanda EEG kaydı
EEG Frequency Bands
Delta – 0,5-3,5 Hz
Theta—4-7 Hz
Alpha---8-13 Hz
Beta---15-30 Hz
Gamma 28-48 Hz
Artefacts in EEG Recordings
Artefact: EEG’de açığa çıkan istenmeyen gürültüler
1) 50 Hz
2) Eye Blink
3) Muscle artefacts
Elektroretinografi
Retinanın işlevsel kısımları dışarıdan iceriye doğru
tabakalar halinde şu şekilde sıralanmıştır: (1)
Pigment tabakası, (2) pigmente doğru uzanan basil
ve koni hucreleri tabakası, (3) basil ve konilerin
hucre govdelerini barındıran dış nukleer tabaka,
(4) dış pleksiform tabaka, (5) iç nukleer tabaka, (6)
ic pleksiform tabaka, (7) gangliyon tabakası, (8)
optik sinir lifleri tabakası ve (9) ic sınırlayıcı
membran.
Guyton & Hall, Tıbbı Fizyoloji, 2007
basiller ve Koniler
Electroretinography
• Electroretinography measures the electrical responses of various cell
types in the retina, including
• the photoreceptors (rods and cones),
• inner retinal cells (bipolar and amacrine cells)
https://en.wikipedia.org/wiki/Electroretinography
• Electrodes (DTL silver/nylon fiber string) are usually placed on the
surface of the cornea for Full Field/Global/Multifocal ERG's
• and brass/copper electrodes are placed on the skin near the eye for
EOG type testing
https://en.wikipedia.org/wiki/Electroretinography
Electrodes for clinical electroretinography. A. Variety of
electrodes and electrode types used for clinical
electrophysiology of vision. Contact lens, foil, fiber, or skin
electrodes may be used
http://www.oculist.net/downaton502/prof/ebook/duanes/pages/v3/ch005/004f.html
Electroretinography
http://www.oculist.net/downaton502/prof/ebook/duanes/pages/v3/ch005/004f.html
• During a recording, the patient's eyes are exposed to standardized
stimuli and the resulting signal is displayed showing the time course
of the signal's amplitude (voltage).
• Signals are very small, and typically are measured in microvolts or
nanovolts.
• The ERG is composed of electrical potentials contributed by different
cell types within the retina.
https://en.wikipedia.org/wiki/Electroretinography
• If a dim flash ERG is performed on a dark-adapted eye, the response
is primarily from the rod system.
• Flash ERGs performed on a light adapted eye will reflect the activity
of the cone system.
https://en.wikipedia.org/wiki/Electroretinography
• Bright flashes will elicit ERGs containing an a-wave (initial negative
deflection) followed by a b-wave (positive deflection).
• The leading edge of the a-wave is produced by the photoreceptors,
while the remainder of the wave is produced by a mixture of cells
including photoreceptors, bipolar, amacrine, and Muller cells or
Muller glia.
https://en.wikipedia.org/wiki/Electroretinography
• Both a and b waves originate in the outer retinal layers.
• The a wave is produced primarily by the photoreceptors; the b wave
is produced by the Müller cells, largely at the level of the bipolar cells.
• The ganglion cells do not contribute to the ERG because their
electrical signals are in the form of spikes that cannot be recorded
externally.
http://www.oculist.net/downaton502/prof/ebook/duanes/pages/v3/ch005/004f.html
Electroretinography
Electrocardiography
Electrocardiography (ECG or EKG) is the process of recording the
electrical activity of the heart over a period of time using electrodes
placed on the skin
Einthoven triangle
• Two arms and left leg are the
edge of the Einthoven triangle
•Lead I is the voltage between the (positive) left arm (LA) electrode and right arm (RA) electrode:
•Lead II is the voltage between the (positive) left leg (LL) electrode and the right arm (RA) electrode:
•Lead III is the voltage between the (positive) left leg (LL) electrode and the left arm (LA) electrode:
The limb leads form the points of what is known as Einthoven's triangle.
https://en.wikipedia.org/wiki/Electrocardiography
Bipolar Derivations
•Lead I is the voltage between the (positive) left
arm (LA) electrode and right arm (RA) electrode:
•Lead II is the voltage between the (positive) left
leg (LL) electrode and the right arm (RA)
electrode:
•Lead III is the voltage between the (positive) left
leg (LL) electrode and the left arm (LA) electrode
Şekil: http://www.oytunerbas.com.tr/tip-fizyoloji-ders-notu/22/
The unipolar limb leads are named aVR, aVL and
aVF. The electrodes are placed on the same
positions as in the bipolar technique. Each lead is
formed by one active and one reference electrode.
The position of the active electrode is determined by
the last letter of the lead name:
• R – right = the right wrist
• L – left = the left wrist
• F – foot = the left foot
Thus lead aVR has the active electrode located on the right wrist and the reference
electrode is formed by the connection of electrodes placed on the left wrist and left
foot through 5 kΩ resistances (Fig. 2.4).
The unipolar limb leads are named aVR, aVL and
aVF. The electrodes are placed on the same
positions as in the bipolar technique. Each lead is
formed by one active and one reference electrode.
The position of the active electrode is determined by
the last letter of the lead name:
• R – right = the right wrist
• L – left = the left wrist
• F – foot = the left foot
The reference electrode called the central Wilson
terminal (identical for all chest leads) is formed by the
connection of all three limb leads through 5 kΩ
resistances (Fig. 2.7).
Normal ECG
• P wave-atriyum depolarization
• QRS= ventrikül depolarization
• T wave; ventrikül repolarization
R
P T
Q
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