Properties and Major Features of Muscular Tissue

Vocabulary flashcards detailing the core properties of muscular tissue and comparing the histological, anatomical, and physiological characteristics of skeletal, cardiac, and smooth muscle.

Electrical excitability

A property of muscular tissue that enables it to produce electrical signals called action potentials.

Contractility

The property of muscular tissue that allows it to contract forcefully.

Extensibility

The ability of muscular tissue to stretch without sustaining damage.

Elasticity

The ability of muscular tissue to return to its original length and shape after contraction or extension.

Skeletal muscle

long cylindrical fibers with many peripherally located nuclei, most commonly attached by tendons to bones, and controlled voluntarily by the somatic nervous system.

Cardiac muscle

branched cylindrical fibers with one centrally located nucleus, joined by intercalated discs and regulated involuntarily by the autonomic nervous system.

Smooth muscle

fibers thickest in the middle and tapered at each end with one centrally positioned nucleus, found in the walls of hollow viscera, airways, blood vessels, iris, ciliary body, and arrector pili muscles.

Intercalated discs

Specialized transverse junctions that connect neighboring cardiac muscle fibers and contain gap junctions and desmosomes.

Connective tissue components of skeletal muscle

The three investing connective tissue layers: endomysium, perimysium, and epimysium.

Connective tissue components of cardiac muscle

Endomysium and perimysium (epimysium is absent).

Connective tissue component of smooth muscle

Endomysium only.

Transverse tubules alignment in skeletal muscle

T tubules are present and aligned specifically at each A–I band junction.

Transverse tubules alignment in cardiac muscle

T tubules are present and aligned specifically at each Z disc.

Autorhythmicity

The capacity to initiate intrinsic, rhythmic contractions; present in cardiac muscle and visceral smooth muscle, but absent in skeletal muscle and multi-unit smooth muscle.

Source of $\text{Ca}^{2+}$ for skeletal muscle contraction

The sarcoplasmic reticulum exclusively.

Source of $\text{Ca}^{2+}$ for cardiac and smooth muscle contraction

Both the sarcoplasmic reticulum and interstitial fluid.

Regulator proteins in skeletal and cardiac muscle

Troponin and tropomyosin.

Regulator proteins in smooth muscle

Calmodulin and myosin light chain kinase.

Satellite cells

Myogenic stem cells that provide skeletal muscle with its limited capacity for regeneration.

Pericytes

Cells that provide smooth muscle tissue with a considerable capacity for regeneration compared with other muscle tissues (though limited compared with epithelium).

Contraction regulation in smooth muscle

Regulated by acetylcholine and norepinephrine released by autonomic motor neurons, several hormones, local chemical changes, and stretching.

Fiber diameter across muscle types

Very large ($10\text{--}100\,\mu\text{m}$) in skeletal muscle; large ($10\text{--}20\,\mu\text{m}$) in cardiac muscle; small ($3\text{--}8\,\mu\text{m}$) in smooth muscle.

Fiber length across muscle types

Very large ($100\,\mu\text{m}\text{--}30\,\text{cm} = 12\,\text{in.}$) in skeletal muscle; large ($50\text{--}100\,\mu\text{m}$) in cardiac muscle; intermediate ($30\text{--}200\,\mu\text{m}$) in smooth muscle.