emg-221206124218-eb820e93.pdf

DR NILESH KATE
MBBS,MD
PROFESSOR
DEPT. OF PHYSIOLOGY
ELECTRO-MYO-
GRAPHY

Objectives.
 Def – Electromyography, electromyograph,
electromyogram
 How it is done
 Applications
 Abnormal patterns.
Tuesday, December 6, 2022

ELECTROMYOGRAPHY
 A technique of
recording of total
electrical activity of
the motor nerve and
the muscle under
study. (Motor UNIT)

Important terms
 Electromyography –
technique
 Electromyograph – A
machine used to
record a graph.
 Electromyogram – A
record obtained
(graph)

Instrument used.
 Cathod ray
oscilloscope –
 Why not
galvanometer –
needle made up of
metal – metal having
mass – inertia – so
cannot measure fine
fluctuations in mv

Electrodes
 Surface electrodes –
metal disc
 Needle electrodes –
hypodermic needle
 Advantages
 Disadvantages
 Amplifier
 Monitor

Recording of EMG
 During rest – little
activity
 Then subject asked to
contract muscle
slightly –record – then
asked to contract
more

Sr no Pattern of EMG Recorded Findings
1 Resting activity Muscle relaxed No activity (Basal
Activity)
2 Insertion Activity Due to movement of
needle within insertion
tract..
Brief action
potential.
3 Motor Unit Potential Slight reading due to
contraction of few motor
units
A few motor unit
AP, biphasic or
triphasic, short
duration
4 Recruitment Progressive stronger
muscle contraction
Increase no of
contraction -
interference

Effect
 Muscle contraction.
 frequency of nerve
impulse to motor unit
 no of contracting
motor units.

Motor units
 The motor neuron &
muscle fiber supplied
by it.

Motor units
 Back muscle
 Each nerve fiber
supplies many muscle
fibers (100-200)
 Gross movements
 Extraocular muscles
 Each nerve fiber
supplies few muscle
fibers (3-6)
 Fine movements..

Types of muscle contractions
 Muscle fasciculations
 Visible to naked eye
 Only seen in
neurogenic disease
 Muscle fibrillations
 Not visible to naked eye
 Seen in neurogenic &
myogenic disease..
 So………to find out
fibrillations we perform
EMG……

NORMAL EMG
 During Rest
 Almost no activity…

NORMAL EMG
 With increase force of
contractions.
 Recruitments of more
motor units
 Why different shapes
 Using different motor
units..

NORMAL EMG
 Amplitude
 Represents no of
muscle fibers within
the unit.

Normal EMG
 With fully contracted
(Active) muscle –
overlap &
interference..

Motor unit potential
 The sum of action
potential produced in
the muscle fiber
stimulated by single
motor neuron
 Characterized by
duration, phases,
amplitude..

Factors affecting motor unit
potential
 Technical factors
 Type of electrode
 Characteristics of recording muscle
 Electrical characteristics of cable
 Preamplifier & amplifier
 Method of recording.

Factors affecting motor unit
potential
 Physiological factors.
 Age of the patients
 Muscle examined
 Temperature

Analysis of EMG
 Qualitative
 Visual inspection of
record.
 Quantitative
 Amplitude
 Duration
 Frequency
 Power spectrum
analysis

Clinical
application of
EMG

Difference in types of diseases
 Neurogenic disease.
 Problem in nerve fibre
 no of motor units.(but
surviving ones are bigger)
 Denervated muscle may
become supplied by
surviving neurons
 Fasciculations (visible)
 Fibrillations (invisible)
 Myopathies.
 Problem in muscle fiber
 size of motor units
 Fibrillations

EMG IN
DIFFERENT
DISEASES.

Neurogenic
disease
Myopathies (MG)
During rest – spontaneous
activity (due to loss
of inhibition)
No activity
With increase force
of contraction -
no of motor
units, but surviving
ones are bigger
BIGGER
AMPLITUDE
Size of motor
units
amplitude &
durations
Maximum
contraction
interference
pattern
amplitude,
duration &
interference

Applications of EMG
 Kinesiology – to assess degree and sequence
of contraction of muscles in a movements
 Grading the force of muscular contraction
 Clinical diagnosis & follow up of
neurogenic & myopathic diseases.

emg-221206124218-eb820e93.pdf

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