Cardiac muscle in the context of "Smooth muscle"

Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to contract. Muscle tissue contains special contractile proteins called actin and myosin which interact to cause movement. Among many other muscle proteins present are two regulatory proteins, troponin and tropomyosin. Muscle is formed during embryonic development, in a process known as myogenesis.

Skeletal muscle tissue is striated, consisting of elongated, multinucleate muscle cells called muscle fibers, and is responsible for movements of the body. Other tissues in skeletal muscle include tendons and perimysium. Smooth and cardiac muscle contract involuntarily, without conscious intervention. These muscle types may be activated both through the interaction of the central nervous system as well as by innervation from peripheral plexus or endocrine (hormonal) activation. Skeletal muscle only contracts voluntarily, under the influence of the central nervous system. Reflexes are a form of non-conscious activation of skeletal muscles, but nonetheless arise through activation of the central nervous system, albeit not engaging cortical structures until after the contraction has occurred.

A muscle cell, also known as a myocyte, is a mature contractile cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal, smooth, and cardiac (cardiomyocytes). A skeletal muscle cell is long and threadlike with many nuclei and is called a muscle fiber. Muscle cells develop from embryonic precursor cells called myoblasts.

Skeletal muscle cells form by fusion of myoblasts to produce multinucleated cells (syncytia) in a process known as myogenesis. Skeletal muscle cells and cardiac muscle cells both contain myofibrils and sarcomeres and form a striated muscle tissue.

Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the voluntary muscular system and typically are attached by tendons to bones of a skeleton. The skeletal muscle cells are much longer than in the other types of muscle tissue, and are also known as muscle fibers. The tissue of a skeletal muscle is striated – having a striped appearance due to the arrangement of the sarcomeres.

A skeletal muscle contains multiple fascicles – bundles of muscle fibers. Each individual fiber and each muscle is surrounded by a type of connective tissue layer of fascia. Muscle fibers are formed from the fusion of developmental myoblasts in a process known as myogenesis resulting in long multinucleated cells. In these cells, the nuclei, termed myonuclei, are located along the inside of the cell membrane. Muscle fibers also have multiple mitochondria to meet energy needs.

Organogenesis is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the internal organs of the organism.

The cells of each of the three germ layers undergo differentiation, a process where less-specialized cells become more-specialized through the expression of a specific set of genes. Cell differentiation is driven by cell signaling cascades. Differentiation is influenced by extracellular signals such as growth factors that are exchanged to adjacent cells which is called juxtracrine signaling or to neighboring cells over short distances which is called paracrine signaling. Intracellular signals – a cell signaling itself (autocrine signaling) – also play a role in organ formation. These signaling pathways allow for cell rearrangement and ensure that organs form at specific sites within the organism. The organogenesis process can be studied using embryos and organoids.

Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non-striated, so-called because it has no sarcomeres and therefore no striations (bands or stripes). It can be divided into two subgroups, single-unit and multi-unit smooth muscle. Within single-unit muscle, the whole bundle or sheet of smooth muscle cells contracts as a syncytium.

Smooth muscle is found in the walls of hollow organs, including the stomach, intestines, bladder and uterus. In the walls of blood vessels, and lymph vessels, (excluding blood and lymph capillaries) it is known as vascular smooth muscle. There is smooth muscle in the tracts of the respiratory, urinary, and reproductive systems. In the eyes, the ciliary muscles, iris dilator muscle, and iris sphincter muscle are types of smooth muscles. The iris dilator and sphincter muscles are contained in the iris and contract in order to dilate or constrict the pupils. The ciliary muscles change the shape of the lens to focus on objects in accommodation. In the skin, smooth muscle cells such as those of the arrector pili cause hair to stand erect in response to cold temperature and fear.

Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity through repeated cardiac cycles. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin. These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle (heartbeat). Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including:

• Cardiac rhythm disturbances, such as atrial fibrillation and ventricular tachycardia;
• Inadequate coronary artery blood flow, such as myocardial ischemia and myocardial infarction;

• and electrolyte disturbances, such as hypokalemia.

Traditionally, "ECG" usually means a 12-lead ECG taken while lying down as discussed below.However, other devices can record the electrical activity of the heart such as a Holter monitor but also some models of smartwatch are capable of recording an ECG.ECG signals can be recorded in other contexts with other devices.