Cardiac muscle

Cardiac muscle

The cardiac muscle is a type of involuntary striated muscle found in the walls of the heart. "A-band" redirects here For other uses of the term see A band. Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the The heart is a muscular organ in all Vertebrates responsible for pumping Blood through the Blood vessels by repeated rhythmic As it contracts, it propels blood into the heart and through the blood vessels of the circulatory system. A muscles contraction (also known as a muscle twitch or simply twitch) occurs when a Muscle fibre generates tension through the action of Actin Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products This is an article about the rock music band "Circulatory System"

1 Metabolism
2 Appearance
3 References
4 See also

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. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Cellular respiration is the set of the metabolic reactions and processes that take place in Organisms cells to convert biochemical energy from Myoglobin is a single-chain globular Protein of 153 Amino acids containing a Heme ( Iron -containing Porphyrin) Prosthetic Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The heart is so tuned to aerobic metabolism that it is unable to pump sufficiently in ischaemic conditions. In Medicine, ischemia ( Greek ισχαιμία, isch- is restriction hema or haema is Blood) is a restriction At basal metabolic rates, about 1% of energy is derived from anaerobic metabolism. 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 Fermentation is the process of deriving energy from the oxidation of organic compounds such as carbohydrates using an endogenous electron acceptor which is 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. Chronic Hypoxia is a pathological condition in which the body as a whole ( generalized hypoxia) or region of the body ( tissue hypoxia) is deprived of adequate Lactic acid ( IUPAC Systematic name: 2-hydroxypropanoic acid) also known as milk acid, is a Chemical compound that plays a role 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 ^[1]

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. This is very energy efficient, because one NAD⁺ is reduced to NADH and H⁺ (equal to 2. 5 or 3 ATP) when lactate is oxidized to pyruvate, which can then be burned aerobically in the TCA cycle, liberating much more energy (ca 14 ATP per cycle).

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. GLUT4 is the Insulin -regulated Glucose transporter found in Adipose tissues and Striated muscle (skeletal and cardiac that is responsible for 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.

Unlike skeletal muscle, which contracts in response to nerve stimulation, specialized pacemaker cells at the entrance of the right atrium termed the sinoatrial node display the phenomenon of automaticity and are myogenic, meaning that they are self-excitable without a requisite electrical impulse coming from the central nervous system. Skeletal muscle is a type of Striated muscle, which usually attaches to tendons A nerve is an enclosed cable-like bundle of peripheral Axons (the long slender projections of Neurons. The Sinoatrial node (abbreviated SA node or SAN, also called the sinus node) is the impulse generating (pacemaker tissue located in the Right atrium Myogenic contraction refers to a Myocyte Contraction that originates from a property of the Myocyte itself The rest of the myocardium conducts these action potentials by way of electrical synapses called gap junctions. A gap junction or nexus is a specialized Intercellular connection between certain animal cell -types It is because of this automaticity that an individual's heart does not stop when a neuromuscular blocker (such as succinylcholine or rocuronium) is administered, such as during general anesthesia. Suxamethonium chloride (also known as succinylcholine, scoline, or colloquially as sux) is a medication widely used in Emergency medicine and Rocuronium is an Aminosteroid non-depolarizing (that is it does not cause initial stimulation of muscles before weakening them neuromuscular blocker or In modern medical practice general anaesthesia ( AmE: anesthesia) is a state of total unconsciousness resulting from General anaesthetic drugs

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. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called This inherent contractile activity is heavily regulated by the autonomic nervous system. &trade The autonomic nervous system ( ANS) (or visceral nervous system) is the part of the Peripheral nervous system that acts as a Control If synchronization of cardiac muscle contraction is disrupted for some reason (for example, in a heart attack), uncoordinated contraction known as fibrillation can result. Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply Fibrillation is the rapid irregular and unsynchronized contraction of the muscle fibers of the Heart.

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 is a ribbon like structure that stabilizes non-epithelial tissue A desmosome, also known as macula adherens or macula adherentes ( Latin: adhering spot) is a cell structure specialized for cell-to-cell A gap junction or nexus is a specialized Intercellular connection between certain animal cell -types

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 chemical impulses which 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

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:

(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. &trade The autonomic nervous system ( ANS) (or visceral nervous system) is the part of the Peripheral nervous system that acts as a Control The Sympathetic Nervous System ( SNS) is a branch of the Autonomic nervous system along with the Enteric nervous system and Parasympathetic nervous The parasympathetic Nervous system ( PSNS) is a division of the Autonomic nervous system (ANS along with the Sympathetic nervous system 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. Fibrillation is the rapid irregular and unsynchronized contraction of the muscle fibers of the Heart. Note that the heart can still beat properly even if its connections to the central nervous system are completely severed.

Role of calcium

In contrast to skeletal muscle, cardiac muscle cannot contract in the absence of extracellular calcium ions as well as extracellular sodium ions. Skeletal muscle is a type of Striated muscle, which usually attaches to tendons Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 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). Smooth muscle is a type of non- Striated muscle, found within the Tunica media layer of large and small Arteries and Veins, the bladder Skeletal muscle is a type of Striated muscle, which usually attaches to tendons The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle

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. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Calcium-induced calcium release (CICR is a mechanism of Calcium release from muscle Sarcoplasmic reticulum that was proposed in the 1970s

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. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of Myosins are a large family of Motor proteins found in Eukaryotic tissues. 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.

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. A T-tubule (or transverse tubule) is a deep Invagination of the Plasma membrane found in skeletal and Cardiac muscle cells 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. The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle

Intercalated Discs

Under light microscopy, intercalated discs appear as thin, typically dark-staining lines dividing adjacent cardiac muscle cells. Microscopy is the technical field of using microscopes to view samples or objects 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. A gap junction or nexus is a specialized Intercellular connection between certain animal cell -types Fascia Adherens is a ribbon like structure that stabilizes non-epithelial tissue Adherens junctions (or zonula adherens) are protein complexes that occur at cell-cell junctions in epithelial tissues usually more basal than Tight junctions. A desmosome, also known as macula adherens or macula adherentes ( Latin: adhering spot) is a cell structure specialized for cell-to-cell In transverse section, the intercalated disk's appearance is labyrinthine and may include isolated interdigitations.

References

^ Ganong, Review of Medical Physiology, 22nd Edition. p81
^ 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.
^ Histology at BU 22501loa

Dictionary

-noun

(anatomy) The striated and involuntary muscle of the vertebrate heart.

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