An electrogram (EGM) is a recording of electrical activity of organs such as the

brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...

and

heart The heart is a muscular organ found in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon diox ...

, measured by monitoring changes in

electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...

Brain

Electroencephalography (EEG)

An electroencephalogram (EEG) is an electrical recording of the activity of the brain taken from the

scalp The scalp is the anatomical area bordered by the human face at the front, and by the neck at the sides and back. Structure The scalp is usually described as having five layers, which can conveniently be remembered as a mnemonic: * S: The s ...

. An EEG can be used to diagnose

seizures An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with los ...

, sleep disorders, and for monitoring of level of anesthesia during surgery.

Electrocorticography (ECoG or iEEG)

An electrocorticogram is an electrical recording of the brain measured intracranially, that is, from within the brain.

Eye

Electrooculography (EOG)

An electrooculogram (EOG) is an electrical recording of the potential between the

cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...

and the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

, and does not change with visual stimuli. An EOG can measure movements of the eyes and can help in diagnosis of nystagmus.

Electroretinography (ERG)

An electroretinogram (ERG) is an electrical recording of the electrical activity of the retina.

Heart

Electrocardiogram (ECG)

An electrocardiogram (ECG or EKG) is an electrical recording of the activity of the heart. The typical meaning of an "ECG" is the 12-lead ECG that uses 10 wires or electrodes to record the signal across the chest. Interpretation of an ECG is the basis of a number of cardiac diseases including

myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which ...

(heart attack) and arrhythmias such as atrial fibrillation.

Cardiac electrogram

When electrical recordings are made from the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

, it is considered to be an ECG as described above. However, electrical recordings made from within the heart such as with an artificial cardiac pacemaker or during an electrophysiology study, the signals recorded are considered an "electrogram" instead of an ECG. These signals are not interpreted in the same manner as an ECG.

Muscle

An electromyogram (EMG) is an electrical recording of the activity of a

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

or muscle group. An EMG study can be combined with a nerve conduction study to diagnose neuromuscular diseases such as

peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...

and

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...