Muscle Tissue Xing Wenying 邢文英

Introduction Components: Muscle cells(muscle fibers) Elongated, thread-like, containing myofilaments and being contractile cell membrane → sarcolemma; cytoplasm → sarcoplasm; SER → sarcoplasmic reticulum CT: contain blood vessels, lymphatics and nerves.

classification : According to the structure and function striated unstriated striated functionstructure

Skeletal muscle

Long cylindrical, 1-40mm long, um in diameter Multinucleate, ovoid nuclei, just under the sarcolemma Cross-striations: alternating dark and light bands Histological features of skeletal muscle fibers

Dark bands--A bands ： H band, M line Light bands--I bands ： Z line Histological features of skeletal muscle fibers

sarcomere: The sarcomere is the basic contractile unit of striated muscle. It is the segment of a myofibril between two adjacent Z line. 1 sacromere = 1/2 I band+1 A band+1/2 I band

Myofibrils: Sarcoplasm is filled with long cylindrical filamentous bundles called myofibrils.

Myofibril Sarcoplasmic reticulum Mitochondrium Transverse tubule Ultrastructure of skeletal muscle fibers

Myofibrils are composed of bundles of myofilaments. Thick filaments and thin filaments. myofibrils and myofilaments

1.5μm long and 10nm in diameter Occupy A band Made up of myosin molecules: --rods: overlap --heads: cross bridges, have ATPase activity. Thick filaments

1um long, 5nm in diameter situated in both ending sides of each sarcomere; Run between and parallel to thick filaments; One end attached to the Z line, the other is free at H band composed of actin, tropomyosin, troponin Thin filaments

A. Actin : binding site for myosin. Thin filaments

B. Tropomyosin Thin filaments

C. Troponin: is a complex of three sub-units. Tn T(troponin T) Tn C(troponin C) Tn I(troponin I) Thin filaments

I band -- only thin filaments A band -- both thick and thin filaments H band -- only thick filaments Z line -- anchor for thin filaments M line – fixation of thick filaments Arrangement

Transverse tubule (T tubule)  Definition: A transverse distributed tubular system formed by Sarcolemma invaginating into sarcoplasm, encircling each myofibrils.  Location: A-I junctional part  Function: Rapidly conduct impulses for contraction to every myofibrils

Transverse tubule (T tubule) Sarcolemma with opening to T-tubule T tubule

Sarcoplasmic reticulum (SR)  Definition: A longitudinal distributed tubular system formed by SER, encircling each myofibril between 2 adjacent T tubules.  Terminal cisternae: Ends of L tubule dilate and fuse to form flattened sac.

Sarcoplasmic reticulum (SR)  Triad: 1 T tubule + 2 terminal cisternae  Function: store and release calcium ions regulating concentration of Ca 2+ within sarcoplasm

providing the energy necessary for the reactions involved in contraction. Other organelles and inclusion Mitochondria Glycogen lipid droplet

Mechanism of contraction -- sliding filament hypothesis  The thin filaments slide past the thick filaments and insert further into the A band.  I band and sarcomere become shorter, H band shortens or disappears, whereas A band remains the same length.  Ca 2+ and ATP play an important role.

Cardiac muscle Mainly distributed in the wall of heart; Has more connective tissue and capillaries; Some specialized as Purkinje fibers.

Microstructure of cardiac muscle Short cylindrical, um long,10-20um in diameter, with branches, associated with each other; 1 or 2, ovoid, centrally-located pale-staining nuclei; Exhibit cross striations, but less distinct;

Intercalated disk: unique characteristic

Ultrastructure of cardiac muscle Myofibril have different diameter, the boundary of myofibril is not very clear. T tubules are larger, located at Z-line level.

Ultrastructure of cardiac muscle Sarcoplasmic reticulum is not well-developed, forms less and smaller terminal cisternae, so Diads are common consisting of 1 T tubule and 1 terminal cisternae on one side.

Intercalated discs Specialized cell junctions at Z lines. Ultrastructure of cardiac muscle

rich in mitochondria, glycogen,pigment.

Smooth muscle Seen in blood vessels and hollow viscera, arranged in layers.

Structure of Smooth Muscle fiber

Summary The structure of skeletal muscle. The structure of cardiac muscle. The structure of smooth muscle. Mechanism of contraction -- sliding filament hypothesis

Summary The structure of cardiac muscle.

Summary The structure of smooth muscle.

Homework  Review the characteristics of skeletal muscle and cardiac muscle.  Prepare for nerve tissue.