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MCAT Content / Muscle System / Structure Of Three Basic Muscle Types

Structure of Three Basic Muscle Types

Topic: Muscle System

There are three forms of muscle tissue that perform a wide range of diverse functions: striated (skeletal) muscle, cardiac, and smooth.

MCAT Structure of Three Basic Muscle Types

Muscle is a soft tissue that is highly specialized for the production of tension which results in the generation of force. Muscle cells, or myocytes, contain myofibrils comprised of actin and myosin myofilaments which slide past each other producing tension that changes the shape of the myocyte. Numerous myocytes make up muscle tissue and the controlled production of tension in these cells can generate significant force.

Muscle tissue can be classified functionally, voluntary or involuntary and morphologically striated or non-striated. Voluntary refers to whether the muscle is under conscious control, striation refers to the presence of visible banding within myocytes which occurs due to organization of myofibrils to produce a constant direction of tension.

Skeletal muscle mainly attaches to the skeletal system via tendons to maintain posture and control movement. For example, contraction of the biceps muscle, attached to the scapula and radius, will raise the forearm. Some skeletal muscle can attach directly to other muscles or to the skin, as seen in the face where numerous muscles control facial expression.

Skeletal muscle is under voluntary control, although this can be subconscious when maintaining posture or balance. Morphologically skeletal myocytes are elongated and tubular and appear striated with multiple peripheral nuclei.

Cardiac muscle tissue is found only in the heart, where cardiac contractions pump blood throughout the body and maintain blood pressure.

As with skeletal muscle, cardiac muscle is striated; however, it is not consciously controlled and so is classified as involuntary. Cardiac muscle can be further differentiated from skeletal muscle by the presence of intercalated discs that control the synchronized contraction of cardiac tissues. Cardiac myocytes are shorter than skeletal equivalents and contain only one or two centrally located nuclei.

Smooth muscle tissue is associated with numerous organs and tissue systems, such as the digestive system and respiratory system. It plays an important role in the regulation of flow in such systems, such as aiding the movement of food through the digestive system via peristalsis.

Smooth muscle is non-striated and involuntary. Smooth muscle myocytes are spindle shaped with a single centrally located nucleus.

Practice Questions

Khan Academy

MCAT Official Prep (AAMC)

Biology Question Pack, Vol. 1 Question 100

Key Points

• Muscle tissue can be divided functionally, is it under voluntary or involuntary control; and morphologically, striated or non-striated.

• By applying these classifications three muscle types can be described; skeletal, cardiac and smooth.

• Skeletal muscle is voluntary and striated, cardiac muscle is involuntary and straited and smooth muscle is involuntary and non-striated.

Key Terms

skeletal muscle: The voluntary muscle of vertebrates, which is striated and anchored by tendons to bone, is used to effect skeletal movement such as locomotion.

involuntary: A muscle movement not under conscious control e.g. the beating of the heart.

striated: The striped appearance of certain muscle types in which myofibrils are aligned to produce a constant directional tension.

voluntary: A muscle movement under conscious control e.g. deciding to move the forearm.

smooth muscle: Involuntary muscle that is found within the intestines, throat, uterus, and blood vessel walls.

cardiac muscle: The striated and involuntary muscle of the vertebrate heart.

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