11
Electromyogram
11.1 INTRODUCTION AND OVERVIEW
Electromyogram stems from three terms: electro, which means pertaining to electric activity; myo, which has a Greek root meaning muscle; and gram, which stands
for recording. Electromyography, or EMG, refers to recording of muscle’s electric
activities.
As mentioned in the previous chapters, every cell creates some electric activity as
part of its normal functioning. This rule is also applicable to the muscle cells. Having
this rule in mind, EMG can be defined as a signal that records the electric activities
generated by the depolarization of muscle cells during muscle contraction, and the
nerve impulses that initiate the depolarization of the muscle.
The first action potentials generated by human muscle contraction were recorded
by Hans Piper in 1907, and ever since EMG has emerged as vital signal in medicine. Specifically, in today’s medicine, a number of neuromuscular disorders are
diagnosed using EMG. In this section, the nature of this signal, as well as the
computational methods to process this signal for different medical applications,
is discussed. We start this section with a brief review of muscle, its structure, and
electric activities. The anatomy and physiology of the muscle provides a better
insight to the origin of the EMG signal itself.
11.2 MUSCLE
Muscles provide motion in response to nerve impulses. From the system theory
standpoint, the roles of muscles can be better understood when focusing on a typical
neuromuscular activity such as a “reflex.” The reflex loop is described as follows.
An assortment of external stimuli, for example, the touch of a hot object, is received
by the receptors in the body. The nervous system processes this information, either
consciously or involuntarily, and issues a response to respond and react to the situation perceived. This response is transmitted to the muscles through the network
of nerves. As the muscles execute the command, a mechanical motion is created to
react to the stimuli. For instance, in the previous example of touching a hot object,
as a result of the muscle activations, the head retracted. As can be seen from the
earlier example, muscles are at the end of a reflex loop and often respond by forming
a muscle contraction.
There are two main categories of muscle that can be distinguished based on their
anatomy and on the particular functions they perform. The largest group of muscles is
the group of skeletal muscles, which control posture, generate heat, and provide motion
control. The skeletal muscles are mostly influenced by the brain in a conscious act.
The second group of muscles is the group of smooth muscles. Smooth muscles
provide rhythmic motion outside the control of the brain (involuntary). The heart is
217
Electromyogram
11.1 INTRODUCTION AND OVERVIEW
Electromyogram stems from three terms: electro, which means pertaining to electric activity; myo, which has a Greek root meaning muscle; and gram, which stands
for recording. Electromyography, or EMG, refers to recording of muscle’s electric
activities.
As mentioned in the previous chapters, every cell creates some electric activity as
part of its normal functioning. This rule is also applicable to the muscle cells. Having
this rule in mind, EMG can be defined as a signal that records the electric activities
generated by the depolarization of muscle cells during muscle contraction, and the
nerve impulses that initiate the depolarization of the muscle.
The first action potentials generated by human muscle contraction were recorded
by Hans Piper in 1907, and ever since EMG has emerged as vital signal in medicine. Specifically, in today’s medicine, a number of neuromuscular disorders are
diagnosed using EMG. In this section, the nature of this signal, as well as the
computational methods to process this signal for different medical applications,
is discussed. We start this section with a brief review of muscle, its structure, and
electric activities. The anatomy and physiology of the muscle provides a better
insight to the origin of the EMG signal itself.
11.2 MUSCLE
Muscles provide motion in response to nerve impulses. From the system theory
standpoint, the roles of muscles can be better understood when focusing on a typical
neuromuscular activity such as a “reflex.” The reflex loop is described as follows.
An assortment of external stimuli, for example, the touch of a hot object, is received
by the receptors in the body. The nervous system processes this information, either
consciously or involuntarily, and issues a response to respond and react to the situation perceived. This response is transmitted to the muscles through the network
of nerves. As the muscles execute the command, a mechanical motion is created to
react to the stimuli. For instance, in the previous example of touching a hot object,
as a result of the muscle activations, the head retracted. As can be seen from the
earlier example, muscles are at the end of a reflex loop and often respond by forming
a muscle contraction.
There are two main categories of muscle that can be distinguished based on their
anatomy and on the particular functions they perform. The largest group of muscles is
the group of skeletal muscles, which control posture, generate heat, and provide motion
control. The skeletal muscles are mostly influenced by the brain in a conscious act.
The second group of muscles is the group of smooth muscles. Smooth muscles
provide rhythmic motion outside the control of the brain (involuntary). The heart is
217