Cardiac muscle

'Cardiac muscle' is a type of involuntary striated muscle found within the heart. Its function is to "pump" blood through the circulatory system through muscular contraction. Image File history File links Download high-resolution version (1280x1024, 201 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cardiac muscle ... Image of sarcomere A sarcomere is the basic unit of a cross striated muscles myofibril. ... For other uses of Muscles, see Muscles (disambiguation). ... The heart and lungs, from an older edition of Grays Anatomy. ... Purpose in its most general sense is the anticipated aim which guides action. ... This article is about a mechanical device. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... For transport in plants, see Vascular tissue. ... A top-down view of skeletal muscle A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. ...

Metabolism

Cardiac muscle is adapted to be highly resistant to fatigue: It has a large number of mitochondria, enabling continuous aerobic respiration, numerous myoglobins (oxygen-storing pigment), and a good blood supply, which provides nutrients and oxygen. The heart is so tuned to aerobic metabolism that it is unable to pump sufficiently in ischaemic conditions. At basal metabolic rates, about 1% of energy is derived from anaerobic metabolism. This can increase to 10% under moderately hypoxic conditions, but, under more severe hypoxic conditions, not enough energy can be liberated by lactate production to sustain ventricular contractions. ^[1] Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... This article or section should be merged with aerobic metabolism. ... An X-ray diffraction image for the protein myoglobin. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colourless (gas) colourless (liquid) Standard atomic weight 15. ... In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. ... Basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). ... Glycolysis is the initial metabolic pathway of carbohydrate catabolism. ... Hypoxia may refer to: Hypoxia (medical), the lack of oxygen in tissues Hypoxia or Oxygen depletion, a reduced concentration of dissolved oxygen in a water body leading to stress or even death in aquatic organisms This is a disambiguation page: a list of articles associated with the same title. ... For the production of milk by mammals, see Lactation. ... In the heart, a ventricle is a heart chamber which collects blood from an atrium (another heart chamber that is smaller than a ventricle) and pumps it out of the heart. ...

Under basal aerobic conditions, 60% of energy comes from fat (free fatty acids and triacylglycerols/triglycerides), 35% from carbohydrates, and 5% from amino acids and ketone bodies. However, these proportions vary widely according to nutritional state. For example, during starvation, lactate can be recycled by the heart. There is a cost to lactate recycling, since one NAD+ is reduced to get pyruvate from lactate, but the pyruvate can then be burnt aerobically in the TCA cycle, liberating much more energy.

In the condition of diabetes, more fat and less carbohydrate is used, due to the reduced induction of GLUT4 glucose transporters to the cell surfaces. However, contraction itself plays a part in bringing GLUT4 transporters to the surface. ^[2] This is true of skeletal muscle, but relevant in particular to cardiac muscle, since it is always contracting. To meet Wikipedias quality standards, this article or section may require cleanup. ...

Contractions

Initiation

Unlike skeletal muscle, which contracts in response to nerve stimulation, and like single unit smooth muscle, cardiac muscle is myogenic, meaning that it is self-excitable stimulating contraction without a requisite electrical impulse coming from the central nervous system. A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, usually attached to the skeleton. ... Nerves (yellow) Nerves redirects here. ... Structure of a skeletal muscle Muscle is one of the four tissue types. ...

A single cardiac muscle cell, if left without input, will contract rhythmically at a steady rate; if two cardiac muscle cells are in contact, whichever one contracts first will stimulate the other to contract, and so on. This inherent contractile activity is heavily regulated by the autonomic nervous system. If synchronization of cardiac muscle contraction is disrupted for some reason (for example, in a heart attack), uncoordinated contraction known as fibrillation can result. Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... This article or section is in need of attention from an expert on the subject. ... Heart attack redirects here. ... Fibrillation is the rapid, irregular, and unsynchronized contraction of the muscle fibers of the heart. ...

This transmission of impulses makes cardiac muscle tissue similar to nerve tissue, although cardiac muscle cells are notably connected to each other by intercalated discs. Intercalated discs conduct electrochemical potentials directly between the cytoplasms of adjacent cells via gap junctions. In contrast to the chemical synapses used by neurons, electrical synapses, in the case of cardiac muscle, are created by ions flowing from cell to cell, known as an action potential. An intercalated disc is an undulating double membrane separating adjacent cells in cardiac muscle fibers. ... gap junction A gap junction is a junction between certain animal cell-types that allows different molecules and ions to pass freely between cells. ... Illustration of the major elements in a prototypical synapse. ... This article is about cells in the nervous system. ... Illustration of the major elements in a prototypical synapse. ...

Intercalated disc

An intercalated disc is an undulating double membrane separating adjacent cells in cardiac muscle fibers. Intercalated discs support synchronized contraction of cardiac tissue. They can easily be visualized by a longitudinal section of the tissue.

Three types of membrane junctions exist within an intercalated disc—fascia adherens, macula adherens, and gap junctions.

Fascia adherens are anchoring sites for actin, and connects to the closest sarcomere. Macula adherens stop separation during contraction by binding intermediate filaments joining the cells together, also called a desmosome. Gap junctions allow action potentials to spread between cardiac cells by permitting the passage of ions between cells, producing depolarization of the heart muscle. When observing cardiac tissue through a microscope, intercalated discs are an identifying feature of cardiac muscle

Rate

Specialized pacemaker cells in the sinoatrial node normally determine the overall rate of contractions, with an average resting pulse of 72 beats per minute. The contractions of the heart are controlled by electrical impulses, these fire at a rate which controls the beat of the heart. ... The sinoAtrial node (abbreviated SA node or SAN, also called the sinus node) is the impulse generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of sinus rhythm. ...

The central nervous system does not directly create the impulses to contract the heart, but only sends signals to speed up or slow down the heart rate through the autonomic nervous system using two opposing kinds of modulation: This article or section is in need of attention from an expert on the subject. ...

• (1) sympathetic nervous system (fight or flight response)
• (2) parasympathetic nervous system (rest and repose)

Since cardiac muscle is myogenic, the pacemaker serves only to modulate and coordinate contractions. The cardiac muscle cells would still fire in the absence of a functioning SA node pacemaker, albeit in a chaotic and ineffective manner. This condition is known as fibrillation. Note that the heart can still beat properly even if its connections to the central nervous system are completely severed. The Sympathetic Nervous System (SNS) is a branch of the autonomic nervous system. ... Autonomic nervous system innervation, showing the sympathetic and parasympathetic (craniosacral) systems, in red and blue, respectively The parasympathetic nervous system is one of three divisions of the autonomic nervous system. ... Fibrillation is the rapid, irregular, and unsynchronized contraction of the muscle fibers of the heart. ...

Role of calcium

In contrast to skeletal muscle, cardiac muscle cannot contract in the absence of extracellular calcium ions as well as extracellular potassium ions. In this sense, it is intermediate between smooth muscle, which has a poorly developed sarcoplasmic reticulum and derives its calcium across the sarcolemma; and skeletal muscle which is activated by calcium stored in the sarcoplasmic reticulum (SR). A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, usually attached to the skeleton. ... For other uses, see Calcium (disambiguation). ... Smooth muscle Layers of Esophageal Wall: 1. ... A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, usually attached to the skeleton. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ...

The reason for the calcium dependence is due to the mechanism of calcium-induced calcium release (CICR) from the SR that must occur under normal excitation-contraction (EC) coupling to cause contraction. For other uses, see Calcium (disambiguation). ... Ryanodine receptors (RyRs) form a class of calcium channels in various forms of muscle and other excitable animal tissue. ...

Appearance

Striation

Cardiac muscle exhibits cross striations formed by alternation segments of thick and thin protein filaments which are anchored by segments called T-lines.

The primary structural proteins of cardiac muscle are actin and myosin. The actin filaments are thin causing the lighter appearance of the I bands in muscle, while myosin is thicker and darker lending a darker appearance to the alternating A bands in cardiac muscle as observed by a light enhanced microscope. G-Actin (PDB code: 1j6z). ... Myosin is a motor protein filament found in muscle tissue. ...

T-Tubules

Another histological difference between cardiac muscle and skeletal muscle is that the T-tubules in cardiac muscle are larger, broader and run along the Z-Discs. There are fewer T-tubules in comparison with Skeletal muscle. Additionally, cardiac muscle forms dyads instead of the triads formed between the T-tubules and the sarcoplasmic reticulum in skeletal muscle. Also called transverse tubules, t tubules are deep invaginations of the plasma membrane found in skeletal and cardiac muscle cells. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ...

Intercalated Discs

Under light microscopy, intercalated discs appear as thin, typically dark-staining lines dividing adjacent cardiac muscle cells. The intercalated discs run perpendicular to the direction of muscle fibers. Under electron microscopy, an intercalated disc's path appears more complex. At low magnification, this may appear as a convoluted electron dense structure overlying the location of the obscured Z-line. At high magnification, the intercalated disc's path appears even more convoluted, with both longitudinal and transverse areas appearing in longitudinal section.^[3] Gap junctions (or nexus junctions) fascia adherens (resembling the zonula adherens), and desmosomes are visible. In transverse section, the intercalated disk's appearance is labyrinthine and may include isolated interdigitations. Microscopy is any technique for producing visible images of structures or details too small to otherwise be seen by the human eye. ... gap junction A gap junction is a junction between certain animal cell-types that allows different molecules and ions to pass freely between cells. ... This article is considered orphaned, since there are very few or no other articles that link to this one. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Cell adhesion in desmosomes A desmosome is a cell structure specialized for cell-to-cell adhesion. ...

References

1. ^ Ganong, Review of Medical Physiology, 22nd Edition. p81
2. ^ S Lund, GD Holman, O Schmitz, and O Pedersen. Contraction Stimulates Translocation of Glucose Transporter GLUT4 in Skeletal Muscle Through a Mechanism Distinct from that of Insulin. PNAS 92: 5817-5821.
3. ^ Histology at BU 22501loa

• Indiana State University, Muscle action
• [1]

• Physiology at MCG 2/2ch7/2ch7line

For the similarly named institution in Chestnut Hill, see Boston College. ... In 1828 the Medical Academy of Georgia was chartered by the state of Georgia with plans to offer a single course of lectures leading to a bachelors degree. ...

See also

• Heart
• Circulatory system
• Cardiac action potential
• Calcium sparks

((suck my balls!)) Myoblasts are a type of stem cells that exist in muscles. ... Satellite cells are found in the mature muscle around the muscle fibres, and differentiate from myoblasts. ... The Sarcoplasm of a muscle fiber is comparable to the cytoplasm of other cells, but it houses unusually large amounts of glycosomes (granules of stored glycogen) and significant amounts of myoglobin, an oxygen binding protein. ... Muscle system The sarcolemma is the cell membrane of a muscle cell. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... A T-tubule (or Transverse tubule), is a deep invagination of the plasma membrane found in skeletal and cardiac muscle cells. ... Myocardium is the muscular tissue of the heart. ... An intercalated disc is an undulating double membrane separating adjacent cells in cardiac muscle fibers. ... Nebulette is an isoform of the protein nebulin. ... Smooth muscle Layers of Esophageal Wall: 1. ... oommen sir is a fool. ... Vascular smooth muscle refers to the particular type of smooth muscle found within, and composing the majority of the wall of blood vessels. ...