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Home , Cardiac muscle, Muscle contraction, Muscle fascicle, Muscle tissue, Sarcoplasm, Sarcoplasmic reticulum

HISTOLOGY OF MUSCLE

Dr. Sangeeta Kotrannavar Assistant Professor Dept. of , USM-KLE IMP, Belagavi Objectives

Distinguish the microscopic features of • Skeletal • Cardiac • Smooth muscles

Muscle

• Latin musculus =little mouse (mus) • Muscle cells are known as MYOCYTES. • Myocytes are elongated so referred as muscle fibers Fleshy • Definition • Muscle is a contractile tissue which brings about movements

Muscle makes up 30-35% (in women) & 40-45% (in men) of body mass Type of muscles

BASED ON BASED ON BASED ON LOCATION STRIATIONS CONTROL Skeletal / Somatic STRIATED / STRIPED VOLUNTARY

Smooth / Visceral UN-STRIATED / IN-VOLUNTARY UNSTRIPED Cardiac STRIATED / STRIPED IN-VOLUNTARY Skeletal muscle organization

Muscles are complex structures: arranged in fascicles Muscle bundles / fascicles • surrounds entire muscle – Dense CT that merges with – Epi = outer, Mys = muscle • surrounds muscle fascicles – Peri = around – Within a are many muscle fibers • surrounds muscle fiber – Endo = within

SKELETAL MUSCLE

• Each bundles contains many muscle fiber Structure of a skeletal muscle fiber • Elongated, unbranched cylindrical fibers • Length- 1 mm – 5 cm, Width – 10 mm - 100μm • Fibers have striations of dark & light bands • Many flat nuclei beneath • Plasma membrane = sarcolemma • Smooth endoplsmic reticulum = (SR) • = • Mitochondria = sarcosomes

• Each muscle fiber made of long cylindrical Structure of a

• Contractile, unbranched parallel threads situated along long axis of entire length of muscle fiber

• Cross striations on myofibril (under LM) are due to uniform arrangement of within it. Arrangement of myofilaments

• Consist of 2 types of myofilaments

• Thick filament - & occupy A band

• Thin filament - protein & also tropomysin &

Sarcomere

• I band = Isotropic - light band composed of mainly actin / thin filament and is bisected by z line • A band = Anisotropic - Dark band corresponds to the length of the myosin / thick filament • H zone – lighter zone in the center of A band • M line – connection between thick filaments in middle of H zone

• is structural and functional contractile unit of muscle • Is defined as distance between two z lines Transverse(T)Tubules & Sarcoplasmic reticulum (SR) Transverse(T)Tubules & Sarcoplasmic reticulum (SR)

• SR surrounds each myofibrils at junction of A & I band • T tubules derived from sarcolemma • Expanded of SR & T tubules form triads & located at A–I junctions • Stimulus for carried by T tubules to every myofiber, myofibril, and SR • After stimulation, SR releases into • Calcium activates the binding of actin and myosin, causing muscle contraction and shortening • After the end of stimulus, calcium is actively transported and stored in sarcoplasmic reticulum

Muscle Contraction

• During contraction no shortening of thick & thin filaments, but increase in degree of overlapping. • A band remains constant in width whereas I & H bands become narrow & Z lines comes closer Skeletal muscle Skeletal muscle

Longitudinal section

Transverse section Skeletal muscle histology

Imp. features

• Long & parallel cylindrical fibers • No branching • Cross striations are present (A & I bands) • Multinucleated flat peripheral nuclei High power, Longitudinal section

Innervation of skeletal muscle

• Motor fibers (60%) • Myelinated Alpha efferent - supply extrafusal muscle fibers –produces contraction • Myelinated Gamma efferent - supply intratrafusal muscle fibers –maintains • Unmyelinated sym. Fibers – vasomotor to vessels • Sensory fibers (40%) • Muscle spindles. • – One & muscle fiber supplied by it . • Motor end plate– Junction between muscle fiber & terminal that supplies it .

Cardiac Muscle

• Has characteristics of both skeletal and

• Functions to provide the contractile activity of the

• Is very fatigue resistant

• Activation of is involuntary (like smooth muscle) Cardiac muscle

• Distinct cross-striations as a result of regular arrangements of actin and myosin filaments (less prominent than skeletal muscle) • Sarcoplasmic reticulum is less well developed • T tubules are located at the Z lines and are much larger than those in skeletal muscles. • Mitochondria are larger & more abundant in the cardiac cells, which is needed for continuous function.

Cardiac Muscle • Short cylindrical with branching fibers • Cross striations present • Cells joined by junctional complexes called intercalated disks • Contain one central nucleus (rarely two)

Intercalated disks

• Cardiac cells are joined end to end by specialized, interdigitating junctional complexes called intercalated discs (which consist of adherens, , and gap junctions). • Intercalated disks permits rapid spread of contractile stimuli from one to another. So act as a functional APPLIED ASPECT

•Myocardial infarct--- Sudden reduction in supply to myocardium leads to death. Smooth Muscle

• Actin and myosin fi laments are present, but they do not show regular arrangement or striations, instead they form lattice network, and they insert into dense bodies in sarcoplasm.

• Dense bodies act as Z disk, contain alpha-

• Numerous vesicular invaginations of called as caveolae which act similar to T tubules • Zonula adherens binds muscle cells, whereas gap junctions provide functional coupling

Smooth Muscle

• Sarcoplasmic reticulum is not well developed for calcium storage • Following stimulation, calcium enters sarcoplasm from caveolae and sarcoplasmic reticulum, stimulates actin & myosin that brings the contraction • Gap junctions couple muscles and allow ionic communication between all fibers

Smooth Muscle Smooth Muscle

• No striations • spindle-shaped cells with tapering ends. • An elongated or ovoid single centrally placed nucleus • The cytoplasm (sarcoplasm) of each muscle fiber stains dark. Smooth Muscle; location

• In intestines, , ureters & other hollow organs ; smooth muscles are arranged in concentric layers around the organs. Peristaltic contractions propel contents in the organs

• In the blood vessels, smooth muscle fibers are arranged in a circular pattern, where they control by altering luminal diameters.

Other contractile cells

• Myoepithelial cells– Relation to gland helps in squeezing Muscular MCQ Regarding muscle

A Skeletal muscles show branching pattern B Smooth muscle shows striation C Intercalated discs seen in smooth muscle D Cardiac muscles is under voluntary control E Skeletal muscle has single nucleus SEQ ; compare and write the features of muscles Thank you