Intro to Skeletal Muscle

Skeletal Muscle Overview

Skeletal muscle is called skeletal because it is usually attached at one or both ends to bones. In the lab, students are often required to know about 40 different muscles, which represents a small minority of the hundreds of muscles in the body. While it can be overwhelming to memorize, understanding muscle attachments is crucial. Attachments are noted as either an insertion or an origin; the insertion refers to the muscle's attachment to the bone that moves most when the muscle contracts, while the origin is the attachment at the bone that is less likely to move.

For example, the biceps brachii is located on the anterior part of the arm and has attachments on the scapula, including the coracoid process and above the glenoid cavity. The muscle also attaches to the radial tuberosity on the radius. When the biceps brachii contracts, it is more likely to move the radius (the insertion) than the scapula (the origins). A muscle applies tension when it contracts, pulling on its attachment points, as muscles only pull; they do not push.

It’s also important to understand the roles of muscles: they often work in pairs. When flexing the forearm, an anterior muscle contracts while a posterior muscle, known as the antagonist, opposes the movement. The agonist is the muscle that performs the desired action, while the antagonist opposes it, and this classification is relative to the movement in question. Additionally, synergists assist the primary agonist, and fixators stabilize the origin to ensure only the insertion moves during muscle contraction.

There are three basic types of muscle contractions. A concentric contraction occurs when a muscle shortens as it exerts more tension than required to move a load, such as lifting an object. Conversely, during an eccentric contraction, the muscle lengthens while exerting tension because it is not sufficient to move the load. Lastly, in isometric contractions, the muscle generates a force equal to the load without altering its shape, resulting in no movement. Understanding these contractions is vital for recognizing how muscles function in various physical activities.