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EEG (Electroencephalogram)
EEG (Electroencephalogram)
 The brain generates rhythmical potential which
originate in the individual neurons of the brain.
 These potential get summated as millions of cell
discharge synchronously & appear as a surface
waveform,
known
as
the
“Electroencephalogram”.
 a nerve impulse which is seen as a change in
membrane
potential,
resulting
from
depolarization of the cell, shortly afterwards,
repolarization occurs.
EEG
Generation of large EEG signals by
synchronous activity
Typical EEG signal waveform
Bands
F Range
Delta (δ)
0.5-4 Hz
Theta (θ)
4-8 Hz
Alpha (𝛼)
8-13 Hz
Beta (β)
13-22Hz
Gamma (γ)
>30Hz
 EEG signal can be picked up with electrodes from the scalp.
 Amplitude of wave from scalp is around 50μV PP to
hundreds of μ V PP from brain.
 Its normal Frequency range from 0.5 to 50Hz.
 Frequency information is significant thus its range classified
into 5 bands
Delta Wave
Theta Wave
Alpha Wave
Beta Wave
Gamm a wave
EEG signal waveform Results:
• Signal range : 2µV (brain death ) – several hundred µV.
• The frequency bands in EEG:
1- Delta (<4 Hz): sleep of infants & deep sleep stages of
normal adults.
2- Theta (4-8 Hz):normal children as well as during drowsiness
and sleep in adults.
3- Alpha (8-14 Hz): mostly around 50 µV, normal adults
during relaxed and mentally inactive awaken state.
4- Beta (14-30 Hz): mostly below 30 µV , by stress and tension.
5- Gamma (>30 Hz): Usually, it is not of clinical and
physiological interests and therefore often filtered out in EEG
recordings
Different types of brain waves in normal
EEG
Rhythm
Frequency Amplitude
(Hz)
(uV)
Recording
& Location
Beta(β)
14 - 30
20
mental activity,
emotional distress,
tension
Frontal region
Alpha(α)
8 – 13
50 – 100
Adults, rest, eyes closed.
Occipital region
Theta(θ)
5–7
50
Children, drowsy adult,
Occipital
Delta(δ)
2–4
50
infants in sleep
Use of EEG In Medical Science:
• Epilepsy
»Generalized seizures. (a sudden attack
of illness, especially a stroke or an
epileptic fit.)
• Localize brain tumors.
• Sleep disorders
»Narcolepsy
»Sleep apnea syndrome
»Insomnia and parasomnia
• Helpful in knowing the cortical activity, toxicity,
hypoxia and encephalopathy
Use of EEG In Medical Science:
• Detects cortical dysfunction.
• Helpful in paralytic patients.
• Determination of brain death.
– Flat EEG(absence of electrical activity) with
voltage around 2uV.
ELECTROMYOGRAM (EMG)
ELECTROMYOGRAM (EMG)
• Electromyogram (EMG) is a technique for
evaluating and recording the activation
signal of muscles.
• Electromyograph detects the electrical
potential generated by muscle cells when
these cells contract and relax.
Fluid Distribution
• Concentration of ions different inside vs. outside
of cell membrane
• This results in an electrical potential difference known as
a MEMBRANE POTENTIAL
• Typical magnitude of membrane potential is -60 and -90
mV (interior of cell is negatively charged) (resting)
• This potential can change within fractions of seconds to
+20 to +50 mV
• This rapid change is called an ACTION POTENTIAL
Skeletal Muscle Organization
• Series Elastic
Components
– Tendons & Bones
– Fascia, Endomysium,
Perimysium and the
Epimysium
• Excitable Vs NonExcitable
– Muscle tissue IS
The Muscle Fiber at the
electrophysiological level
•
•
•
Resting Potential – the voltage across an
unstimulated cell
Muscle Cell = -90mV
Established by
Depolarization- entering +ve ion inside cell
Repolarization -: +ve ion moves outside of cell
Action Potential
of a Neuron
EMG Waves
Raw EMG
Full-wave
Rectified EMG
EMG Waves
• Typical EMG signal has 0.1 to 0.5 mV peak
• They may contain frequency component up to
10 KHz.
Use of EMG:
• Detection of Sensory Loss
• In patient of paralysis.