Skeletal Muscle

Skeletal muscle is a type of striated muscle, attached to the skeleton. Skeletal muscles are used to facilitate movement, by applying force to bones and joints; via contraction. They generally contract voluntarily (via nerve stimulation), although they can contract involuntarily.

Muscles have an elongated, cylindrical shape, and are multinucleated. The nuclei of these muscles are located just under the plasma membrane, which vacates the central part of the muscle fiber for myofibrils. This unique arrangement of the nuclei allows for higher efficiency. These muscles usually have one end (the "origin") attached to a relatively stationary bone, (such as the scapula) and the other end (the "insertion") is attached across a joint, to another bone (such as the humerus).

How skeletal muscle works

The strength of skeletal muscle is directly proportional to its cross-sectional area. The strength of a body, however, is determined by biomechanical principles (the distance between muscle insertions and joints, muscle size, and so on). Muscles are normally arranged in opposition so that as one group of muscles contract, another group relaxes or expands.

Skelatal muscle cells are stimulated by acetylcholine, which is released at neuromuscular junctions by motor neurons. Once the cells are "excited", their sarcoplasmic reticulums will release ionic calcium (Ca2+), this interacts with the myofibrils and, thus, induces muscular contraction (via the sliding filament mechanism). Besides calcium, this process requires adenosine triphosphate (ATP). The ATP is produced by metabolizing creatine phosphate and glycogen, which are stored within the muscle cells; as well by metabolizing glucose and fatty acids, obtained from blood.

Each motor neuron "controls" a group of muscle cells, known as "motor units". When more strength is required, than what can be obtained from a single motor unit, more units will be stimulated; this is known as "motor unit recruitment". If more strength is required than what can be obtained from the current degree of unit contraction, the motor neurons will send additional stimuli; this causes a process of contractile summation, which increases the degree of contraction. If a muscle is maximally contracted, it is said to be in a state of tetanic contraction.

Red and White Fibers

Skeletal muscles contain two types of fibers, used to produce ATP; the amount of each varies from muscle to muscle, and from person to person.

· Red ("slow-twitch") fibers have more mitochondria, store oxygen in myoglobin, rely on aerobic metabolism, and are associated with endurance; these produce ATP more slowly. Marathoners tend to have more red fibers.

· White ("fast-twitch") fibers have fewer mitochondria, are capable of more powerful (but shorter) contractions, metabolize ATP more quickly, and are more likely to accumulate lactic acid. Weightlifters and Sprinters tend to have more white fibers.

Skeletal Muscle: Form and Function - 2nd Edition Author: Brian MacIntosh Description Skeletal Muscle: Form and Function, Second Edition, provides readers with a detailed understanding of the different facets of muscle physiology. Meticulously researched and updated, this text examines motoneuron and muscle structure and function...

Skeletal Muscle Structure, Function, and Plasticity Author: Richard L. Lieber Description In its Third Edition, this text addresses basic and applied physiological properties of skeletal muscle in the context of the physiological effects from clinical treatment. Anyone interested in human movement analysis and the understanding of generation and control from the musculoskeletal and neuromuscular systems in implementing movement will find this a valuable resource...

Skeletal Muscle Damage and Repair:Mechanisms & Interventions Author: Peter Tiidus Description Professionals and students interested in understanding the physiological mechanisms of skeletal muscle damage and repair will welcome this uniquely comprehensive text. Presenting both research-based information and applied clinical topics, Skeletal Muscle Damage and Repair assists readers in understanding the interrelationships of basic physiology, specific populations, and practical treatments for muscle injury and damage...

An Illustrated Atlas of the Skeletal Muscles, 3rd Edition Author: Bradley S. Bowden Description An Illustrated Atlas of the Skeletal Muscles , Third Edition is designed as a functional reference, supplement, and study guide for students and health professionals with a broad diversity of interests in the normal structure and function of skeletal-muscular systems...

The Muscular System Manual: The Skeletal Muscles of the Human Body, 3e Author: Joseph E. Muscolino DC Description The Muscular System Manual by Dr. Joseph E. Muscolino makes the study of musculoskeletal anatomy easier and more engaging with a highly visual approach! This innovative, vibrantly illustrated atlas details the muscles and bones of the human body with unrivaled clarity and helps you build the strong anatomic understanding needed for success in practice...

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