Study of Electrical Activity of Nervous System

1. VELTECH
DEPARTMENT OF ECE
Electromyography- EMG
Prepared By,
V.Mahalakshmi,
Assistant Professor,
Department of ECE,
Veltech

2. ELECTROMYOGRAPHY
(EMG)

3. What is EMG?
• The study of electrical activity of muscles is
called electromyography.
• The instrument used to measure the
electrical activity of muscles is called
electromyogram.
• The recorded pattern of the electrical activity
of muscles is called electromyograph.
• Recording the action potential of peripheral
nerve is known as Electro neurography.

4. Electrodes used for EMG
Types of electrodes are used for recording EMG.
• Surface electrodes are used when signals are
recorded on the surface and it cannot detect
deep potential from within the cell.
• Needle electrodes are inserted deep into the
tissue, which records the muscle potential.
• Microelectrode is used to record action
potential from single nerve.

6. EMG Recording System

7. EMG Recording System
• Electrodes record EMG potentials from the
tissue.
• Disc shaped surface electrodes made of
Ag/AgCl are used to pick the signals.
• The skin surface is cleaned and electrode gel is
applied on the skin surface.
• Elastic bands are used to attach the electrodes
to the skin.
• When electrodes are affixed tight on the skin,
it reduces the skin contact impedance to
below 10kΩ.

8. EMG Recording System
The amplitude of EMG signal depends on various
factors like
• Type of electrode used
• Placement of electrode on the muscle and
• The degree of muscular exertions.
• When surface electrodes are used, it picks signals
from nearby spikes. Therefore, it produces
average voltage value from the muscles ad motor
units.
• The needle electrodes pick signal from single
nerve fiber and it produces one voltage value.

9. EMG Recording System
• The voltage value of EMG signals varies between
0.1 to 0.5 mV.
• The frequency of the EMG signal is the range of
20 Hz to 10 KHz, which lies in the audio range.
• The normal frequency of EMG is 60 Hz.
• The differential amplifier has high gain and
frequency range between 10 Hz to 10 KHz. The
amplified output is given to the power amplifier
that helps to amplify the signal to a higher level.
• The amplified signal is given to the loudspeaker,
tape recorder and CRO.

10. Applications of Electromyography
• To study neuromuscular functions.
• To know the neuromuscular condition.
• To study reflex responses.
• To know about the extent of nerve lesions.
• Helps to diagnose the muscular diseases.

11. Measurement of Conduction Velocity
in Motor Nerves

12. Measurement of Conduction Velocity
in Motor Nerves
• In the motor nerves, to indicate the location and
type of nerve lesions, conduction velocity is
measured.
• An electric shock of duration 0.2 – 0.5 ms is
stimulated on the nerves.
• Conduction velocity along the peripheral nerve is
measured to calculate the latency.
• Latency is defined as difference in time between
stimulating impulse and action potential of the
muscle.

13. Measurement of Conduction Velocity
in Motor Nerves
• The conduction velocity is calculated using the
below formula.
• Normally the value of conduction velocity is
50 m/s.