Muscular Tissue By Dr. Hanan Said Seleem

MUSCLE TISSUE Muscle tissue is responsible for: Body movement as a whole. According to its function and structure, muscle tissue is classified into three types:

MUSCLE TISSUE 1- Skeletal muscle: It is voluntary and striated It is attached to bone and is responsible for the movement of the axial and peripheral skeleton. 2- Cardiac muscle: It is involuntary and striated. It forms the wall of the heart. 3- Smooth muscle: It is involuntary and non-striated (in which the cells do not exhibit cross striations). It is present in the body viscera and blood vessels.

State which of the following contains skeletal muscle A) tongue B) esophagus C) aorta

Connective Tissue Wrappings Skeletal Muscle Investment Endomysium Perimysium Epimysium Tendon Deep Fascia Muscle Fiber Skeletal Muscle art, vein, nerve Fascicle Connective Tissue Wrappings

Organization of skeletal muscle Whole muscle Bundles Fibers Fibrils Filaments.

L/M Shape: Nucleus: peripheral, flattened and multinucleated Long, cylindrical, parallel. Non-branching except in face and tongue. Surrounded by sarcolemma and basal lamina. Nucleus: peripheral, flattened and multinucleated Sarcoplasm: acidophilic, myofibrils.

Longitudinal sections (LS) Parallel fibers. Striated. Peripheral, multiple, flat nuclei.

Transverse section (TS) Rounded fibers Myofibrils (dots in Cohenheim groups). Inbetween sarcolemma and basal lamina are satellite stem cells for repair.

Types of skeletal muscle fiber Red (type I) White (type II) Intermediate According to morphology, histochemistry and biochemistry Sk. Ms. Contain 3 types but white fibers predominate.

Type I red fibers Type II white fibers Central nuclei Peripheral nuclei Irregular striations Regular striations Fewer myofibrils Numerous myofibrils Abundant sarcoplasm Less abundant Rich in myoglobin, mitochondria Poor in myoglobin & mitochondria Fibers contract slowly over prolonged period & don’t fatigue easily Fibers contract rapidly over short period & fatigue easily

Skeletal muscle Fibers (each is one cell) have striations Myofibrils are organelles of the cell: these are made up of filaments Sarcomere Basic unit of contraction Myofibrils are long rows of repeating sarcomeres Boundaries: Z discs (or lines) This big cylinder is a fiber: 1 cell -an organelle

EM of myofibrils

Sliding Filament Model __relaxed sarcomere__ _partly contracted_ fully contracted “A” band constant because it is caused by myosin, which doesn’t change length Sarcomere shortens because actin pulled towards its middle by myosin cross bridges

Sarcomere is the distance between: A) 2 successive A bands B) 2 successive I bands C) 2 successive M lines D) 2 successive Z lines

Sarcoplasmic reticulum It represents a special type of SER that is present in muscle. The sarcoplasmic reticulum forms a longitudinally arranged tubules around the A band, with cross connections in the region of the H band. At the A-I junctions the tubules form dilated rings around the myofibrils called terminal cisterna.

Transverse tubules (T-tubules) These are tubular invaginations of sarcolemma into the interior of the muscle fiber. They form anastomosing network that encircle the boundaries of each sarcomere in every myofibrils at the junctions between A and I bands. Thus, each sarcomere possesses two sets of T tubules one at each A-I junction.

function facilitate the conduction of waves of depolarization along the sarcolemma.

Cardiac muscle fibers L/M: Cylindrical branching anastomosing. Composed of several cardiac muscle cells. Size smaller and Striations less than skeletal. 1to 2 central oval pale nucleus. acidophilic cytoplasm Rich in myoglobin. Step-like intercalated disks.

Cardiac muscle fibers E/M:. No satellite cells. Mitochondria (40% of the cytoplasm) and glycogen more than skeletal. SR: less developed and less regular than skeletal (diad at Z line).

SMOOTH MUSCLE Involuntary. Non striated. Contraction: weak, slow, long duration. Site: 6 major locations: inside the eye walls of vessels respiratory tubes digestive tubes urinary organs reproductive organs

Structure Shape: Fusiform (spindle-shaped )cells. Nucleus: central single oval. Cytoplasm: acidophilic. Surrounded by: basal lamina and reticular network. Grouped into sheets: often running perpendicular to each other Peristalsis No striations (no sarcomeres) Contractions are slow, sustained and resistant to fatigue

Feature Skeletal Muscle Cardiac Muscle Smooth Muscle Sarcomeres and myofibrils Yes No Distinctive features Long; cylinder-shaped; striations Branched cells; striations Fusiform cells with no striations; Nuclei Multinucleated; peripheral flattened One (or two); rounded centrally located One; centrally located Sarcoplasmic reticulum Well-developed with terminal cisterns Poorly defined; some small terminals Some smooth endoplasmic reticulum T tubules Yes; small, triad formation Yes; large, diad formation Cell junctions Intercalated disks Nexus (gap junctions) Contraction Voluntary Involuntary; rhythmic and spontaneous Involuntary; slow forceful; Regeneration Yes, via satellite cells Mitosis Connective tissue Epimysium, perimysium, and endomysium Connective tissue sheaths and endomysium

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