Anatomy Of A Muscle Cell

Anatomy of Muscle Cells

There are three types of muscle tissue in the human body. These muscle tissues are skeletal muscles, smooth muscles and cardiac muscles. Each of these muscle tissues has it very own anatomical makeup, which vary from muscle to muscle. The muscle cells in a muscle are referred to as muscle fibers, these fibers are skeletal muscle fibers, smooth muscle fibers and cardiac muscle fibers.

The anatomy of a skeletal muscle fiber is formed during embryonic development. Skeletal muscle fibers arise from a hundred or more small mesodermal cells called myoblasts. The mature skeletal muscle fiber has a hundred or more nuclei. Once fusion occurs the skeletal muscle fiber will lose the ability to undergo cell division. This means that the number of muscle fibers is set before birth and most of these fibers will last a lifetime.

The muscle growth that occurs after birth is a result of the enlargement of these existing muscle fibers. The mature muscle fibers have a few myoblasts, which remain as satellite cells. These myoblasts retain the capacity to join with one another or with damaged muscle fibers in order to regenerate these muscle fibers.

John Centore2

Dr. Jain

Anatomy & Physiology

The many nuclei of skeletal muscle fiber are located underneath the sarcolemma, which is the fiber’s plasma membrane. Thousands of invaginations of the sarcolemma, which are called T Tubules, Tunnel from the surface to the center of the muscle fiber. These T Tubules are open to the outside of the fiber and are filled with extra-cellular fluid. Muscle action potentials propagate along the sarcolemma and through the T tubules and quickly spread through the muscle fiber. This process ensures that all parts of the muscle fiber become excited by an action potential virtually simultaneously.

The sarcoplasm is located inside the sarcolemma. Sarcoplasm is the cytoplasm of a muscle fiber, it contains a good amount of glycogen, which is used for ATP synthesis. The sarcoplasm also contains myoglobin, a red colored, oxygen binding-protein, that is found only in muscle fibers. The myoglobin binds oxygen molecules, which are needed for ATP production within the mitochondria. The Mitochondria lie in rows throughout the muscle fiber, strategically close to the proteins that use ATP during contraction.

The sarcoplasm is filled with little threadlike structures. These str...

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...sponse to nerve impulses, hormones and other local factors. These muscle fibers can also stretch considerably and still maintain their contractile function.

John Centore5

Anatomy & Physiology

Dr. Jain

The last of the three groups of muscle fiber is cardiac muscle fiber. The cardiac muscle fibers have the same arrangement of actin and myosin and the same bands, zones, and Z-disks as skeletal muscle fibers. However, the ends of cardiac muscle fibers connect to adjacent fibers by irregular transverse thickenings of the sarcolemma called intercalated disks. These disks contain desmosomes, which hold the fibers together, and gap junctions, which allow muscle action potential to spread from one cardiac muscle to another.

In cardiac muscle fibers, calcium ions enter the sarcoplasm both from the sarcoplasmic reticulum and from extracellular fluid. The mitochondria in cardiac muscle fiber are larger and more numerous than in skeletal muscle fiber. Cardiac muscle fibers can also use lactic acid produced by skeletal muscle fibers to make ATP, a benefit during exercise.

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