A simplified, global view of a neuromuscular junction:
1. Axon
2. Neuromuscular junction
3. Muscle fiber
4. Myofibril

A top-down view of skeletal muscle

A muscle fiber (or muscle fibre), also known as a myocyte, is a single cell of a muscle. Muscle fibers contain many myofibrils, the contractile unit of muscles. Muscle fibers are very long; a single fiber can reach a length of 30cm. Image File history File links Synapse_diag3. ... Image File history File links Synapse_diag3. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... A neuromuscular junction is the junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscles surface. ... A diagram of the structure of a Myofybril Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. ... http://training. ... http://training. ... 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... A top-down view of skeletal muscle Muscle (from Latin musculus little mouse [1]) is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. ... A diagram of the structure of a Myofybril Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. ... A centimetre (American spelling centimeter, symbol cm) is a unit of length that is equal to one hundredth of a metre, the current SI base unit of length. ...

Muscle fibers can be grouped according to what kind of tissue they are found in: skeletal muscle, smooth muscle, and cardiac muscle. The muscle cells of heart muscle tissue are called cardiomyocytes. Biological tissue is a collection of interconnected cells that perform a similar function within an organism. ... A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, usually attached to the skeleton. ... Cultured Smooth muscle of the aorta. ... Cardiac muscle is a type of involuntary striated muscle found within the heart. ...

Skeletal muscle fibers

Skeletal muscle fibers can be further divided into two basic types, type I (slow-twitch fibers) and type II (fast-twitch fibers). Type II is further divided, as follows: A top-down view of skeletal muscle Skeletal muscle is a type of striated muscle, usually attached to the skeleton. ...

Glycolysis is a metabolic pathway by which a molecule of glucose (Glc) is oxidized to two molecules of pyruvic acid (Pyr). ... An X-ray diffraction image for the protein myoglobin. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ...

Type I

Type I muscle fibers (slow-oxidative fibers) use primarily cellular respiration and, as a result, they have relatively high endurance. Cellular respiration was discovered by mad scientist Mr. ...

To support their high-oxidative metabolism, these muscle fibers typically have lots of mitochondria and myoglobin, and thus appear red (what is typically termed "dark" meat in poultry.) 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. ... An X-ray diffraction image for the protein myoglobin. ... This article does not cite any references or sources. ...

Type I muscle fibers are typically found in muscles of animals that require endurance, such as chicken leg muscles or the wing muscles of migrating birds (e.g., geese). This article or section does not adequately cite its references or sources. ... Geese redirects here. ...

Type II

Type II muscle fibers use primarily anaerobic metabolism and have relatively low endurance. These muscle fibers are typically used during tasks requiring short bursts of strength, such as sprints or weightlifting. Type II muscle fibers cannot sustain contractions for significant lengths of time, and are typically found in the white meat (e.g., the breast) of chicken. For other uses, see Fermentation. ... Sprints are races where the runner tries to go as fast as humanly possible. ... This article is about the sport of weightlifting. ...

There are two sub-classes of type II muscle fibers, type IIa (Fast-Oxidative) and IIb (Fast-Glycolytic).

• Type IIa (fast-oxidative) fibers also appear red, due to their high content of myoglobin and mitochondria.

• Type IIb (fast-glycolytic) are the fastest firing and most powerful, twitching in upwards of 120 times per second, are the fiber type of choice to a power lifter. They also tire the fastest. These fibers appear white histologically, due to their low oxidative demand, manifested by the lack of myoglobin and mitochondria (relative to the Type I and Type IIa fibers)

An X-ray diffraction image for the protein myoglobin. ... 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. ... An X-ray diffraction image for the protein myoglobin. ... 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. ...

Other terminology

Most sources use the I/IIa/IIb division described above. However, this distinction is much more clear in other animals (such as chickens) than they are in humans, where the muscle tissue usually contains combinations of different kinds of fibers in varying proportions. This article or section does not adequately cite its references or sources. ...

Some terms used to describe this blending include:

• "Type III" or "Intermediate fast-twitch fibers" are a cross between Type I and Type IIb. They can utilize both aerobic and anaerobic pathways for energy metabolism.

• "Type IIc" fibers are created from a fusion of satellite cells to the corrupted Type IIb, so long as the cortisone hormone is inhibited, and offer the attributes of both Type IIa and Type IIb.

Cortisone (IPA:ˈkôrtəˌsōn) is a steroid hormone. ...

Extrafusal and intrafusal

All fibers described above are extrafusal muscle fibers. In addition, however, there are intrafusal muscle fibers, which constitute muscle spindles. These belong to the somatosensory system and sense the extent of stretch of a muscle. They are innervated by different sensory nerve fibers as well as motor nerve fibers. Extrafusal muscle fibers are a class of muscle fiber innervated by alpha motor neurons. ... Intrafusal muscle fibers are muscle fibers that comprise the muscle spindle. ... A muscle spindle is a specialized muscle structure innervated by both sensory and motor neuron axons. ... Somatic sensation consists of the various sensory receptors that trigger the experiences labelled as touch or pressure, temperature (warm or cold), pain (including itch and tickle), and the sensations of muscle movement and joint position including posture, movement, and facial expression (collectively also called proprioception). ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ... An axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neurons cell body or soma. ...

See also

• Myopathy, muscle pathology/diseases
• myoblast

In medicine, a myopathy is a neuromuscular disease in which the muscle fibers do not function for any one of many reasons, resulting in muscular weakness. ... Myoblasts are a type of stem cells that exist in muscles. ...

External links

• http://www.coachr.org/fiber.htm - Article at coachr.org xplaining muscle fibers, especially in relation to training.
• Physiology at MCG 2/2ch6/2ch6obj
• Duke Orthopedics muscle_fiber_types