Muscle tissues. Dr. Hersh Abdul Ham-Karim BVM&S, PG Dip, MSc and PhD

Transcription

1 Muscle tissues Dr. Hersh Abdul Ham-Karim BVM&S, PG Dip, MSc and PhD

2 Muscle tissue is a soft tissue that composes muscles in animal bodies, and gives rise to muscles' ability to contract. Muscle tissue is composed of cells; Are known as fibers Have the special ability to shorten or contract depends on two types of myofilaments (contractile proteins) One type contains actin Another type contains myosin The tissue is highly cellular and is well supplied with blood vessels. Muscle tissue

3 Unique terms are used for certain structures in muscle cells: Individual muscle cells are called muscle fibers. The cytoplasm of muscle fibers is called sarcoplasm. The muscle fiber plasma membrane is called the sarcolemma. The smooth endoplasmic reticulum is called the sarcoplasmic reticulum

4 Characteristics of Muscles All muscles have 4 common characteristics Excitability ability to respond to a stimulus (ie: nerve impulse). Contractibility muscle fibers that are stimulated by nerves contract (become shorter) and causes movement. Extensibility ability to be stretched. Elasticity allows the muscle to return to its original shape after it has been stretched.

5 Functions of muscle tissue Movement Skeletal muscle: Attached to skeleton, moves body by moving the bones. Smooth muscle squeezes fluids and other substances through hollow organs. Maintenance of posture enables the body to remain sitting or standing. Joint stabilization- the ability to maintain or control joint movement or position. Heat generation: Muscle contractions produce heat, helps maintain normal body temperature.

6 Classification of Muscle Functional classification is based on the type of neural control. Voluntary. Involuntary. Structural classification is based on the presence or absence of cross striations. Striated Non-striated (smooth) Combined functional and structural classification: Skeletal muscle Cardiac muscle Smooth (visceral) muscle

7 Skeletal Muscle

8 1. Skeletal muscle Each muscle is an organ Consists mostly of muscle tissue Connective tissue Blood vessels Nerves Skeletal muscles are: striated, voluntary, and multinucleated long, thin and cylindrical; they are attached to bones and move our skeleton striations -- cross stripes (bands) run perpendicular to the cells, composed of myofibrils. nucleus Muscle fiber (cell) Striations

9 Connective tissue and fascicles Connective tissue sheaths bind a skeletal muscle and its fibers together Endomysium: a fine sheath of connective tissue wrapping each muscle cell Perimysium: surrounds each fascicle (group of muscle fibers) Epimysium: dense regular connective tissue surrounding entire muscle Aponeuroses-connective tissue that attaches muscle to muscle

10 Skeletal Muscle as seen in longitudinal section in the light microscope...

11 Skeletal Muscle as seen in transverse section in the light microscope...

12 Structural organization of skeletal muscle fiber

13 Structural organization of skeletal muscle fiber Muscle fascicle: Collection of muscle fibers surrounded by perimysium. Muscle fiber: Specialized term for a muscle cell, Individual muscle fibers vary considerably in diameter from 10 to 100μm and may extend throughout the whole length of a muscle and, in some sites, may be many centimeters in length. Fibers are adept to hypertrophy (increase in size of cell) and hyperplasia (increase in number of cell). - Satellite cells are proposed source of regenerative cells

14 Myofibrils: 1 2 microns wide, composed of bundles of overlapping myofilaments. Myofilaments: Visible only with the electron microscope; composed primarily of actin, which forms 5-nm wide thin filaments, and myosin, this forms 15-nm wide thick filaments.

15 Ultra structure of the myofilaments

16 Skeletal muscle A band I band Z line

17 A band appears dark and contains actin and myosin. I band appears light and contains actin only. Z band, composed of alpha-actinin, is located in the center of the I band. H band is located in the center of the A band and represents the area where actin is not present. M band is located in the center of the H band and represents areas of crossconnections between myosin filaments. Sarcomere: Contractile unit of striated muscle fibers, seen in both skeletal and cardiac muscle fibers. Extends from Z-line to Z-line. Ultra structure of the myofilaments Sarcomeres are repeated in series along the length of each myofibril.

18 Mechanism of skeletal muscle contraction

19 Mechanism of skeletal muscle contraction During the contraction of skeletal muscle tissue, the actin filaments slide inwards between the myosin filaments. Mitochondria provide the energy for this to take place. This action causes a shortening of the sarcomeres (Z-lines move closer together), which in turn causes the whole muscle fiber to contract. This can bring about a shortening of the entire muscle such as the biceps, depending on the number of muscles fibers that were stimulated. The contraction of skeletal muscle tissue is very quick and forceful.

20 Cardiac Muscle

21 2. Cardiac Muscles Cardiac muscle occurs only in the myocardium of the heart and, to a variable extent, in the roots of large vessels where they join the heart. Functions a. Cardiac muscle tissue plays the most important role in the contraction of the atria and ventricles of the heart. b. It causes the rhythmical beating of the heart, circulating the blood and its contents throughout the body as a consequence.

22 Cardiac muscle cells

23 Cardiac Muscle as seen in longitudinal section in the light microscope...

24 Cardiac Muscle Muscle Muscle

25 Cardiac Muscle as seen in transverse section in the light microscope...

26 Cardiac Muscle Skeletal Muscle

27 Cardiac muscle cells (Cardiocytes): Intermediate in size between skeletal and smooth muscle. Long cylindrical, involuntary, and usually one nucleus per fiber located in the center Striated but more irregular due to branching of cells. branching cells connect at intercalated disks which allow contractions to occur faster are regulated by pacemaker cells which control contraction of the heart muscles

28 Myofilaments organization into myofibrils is identical to skeletal muscle. Cross-striations and bands identical to skeletal muscle are present, but not as prominent. High vascularity and with large numbers of mitochondria reflect the high metabolic requirements of cardiac muscle fibers. Increase in size (hypertrophy) Formerly thought to be non-proliferative Post-infarction tissue remodeling by fibroblasts (fibrosis/scarring) New evidence suggests mitotic cardiomyocytes and regeneration by blood or vascular-derived stem cells

29 Intercalated discs

30 Intercalated discs

31 Intercalated discs

32 Intercalated discs Cardiac muscle consists of individual heart muscle cells (cardiomyocytes) connected by intercalated discs to work as a single functional organ. Contain three types of junctions: Fascia adherence: where actin filaments attach thin filaments in the muscle sarcomeres to the cell membrane. Desmosomes: Bind ends of fibers together, In order to prevent separation during contraction. Gap junctions: Provide ionic coupling between fibers. [ions, regulatory proteins, and metabolites (products of metabolism) cross this cannel]

33 Smooth Muscle

34 3. Smooth Muscles Smooth muscle occurs mostly as sheets, which form the walls of most hollow organs with the exception of the heart. Smooth muscle is also prominent in the walls of blood vessels, many respiratory passageways, and some genital ducts. The name smooth muscle comes from the fact that this muscle tissue lacks the visible striations that are a noticeable characteristic of the other two muscle tissues.

35 Functions of Smooth Muscle Tissue 1. Smooth muscle controls slow, involuntary movements such as the contraction of the smooth muscle tissue in the walls of the stomach and intestines. 2. The muscle of the arteries contracts and relaxes to regulate the blood pressure and the flow of blood.

36 Smooth Muscle cells Smallest fiber type, length varies from 20 microns in blood vessels to 500 microns in the uterus. Unbranched spindle-shaped fibers are elongated with pointed ends. Possess a single, centrally placed, oval nucleus. Non-striated; no myofibrils are present so called Smooth Muscle. Increase in size (hypertrophy) and in number (regeneration/proliferation)

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38 Myofilaments in smooth muscle Ratio of thick to thin filaments (1:13) is much lower than in skeletal muscle (1:2). Myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner. Dense bodies: proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals the dense bodies also attach to the Actin filaments thus acting as a type of Z-line

39 1. Multiunit Smooth Muscle Types of smooth muscle Richly innervated and gap junctions are rare Specialized for precise, graded contraction (e.g., iris of the eye).

40 2. Single unit Smooth Muscle Occurs in sheets in the wall of hollow organs (e.g., digestive tract). Minimally innervated; contraction spreads in peristaltic waves facilitated by large numbers of gap junctions. Specialized for slow, prolonged contraction.

41 skeletal Cardiac Smooth Location Near bones Heart wall Walls of hollow organs and blood vessels Nuclei Many, peripheral, flat 1 per cell, central, plump Cell diameter Largest intermediate Smallest Striations Yes Yes No Sarcoplasmic reticulum Yes Yes No 1 per cell, central, oval Motor control Voluntary Involuntary Involuntary Contraction Quick and strong Quick, strong, rhythmic Slow, in waves Blood supply Moderate Extensive Less abundant Other features Prominent fascicles Intercalated disks, branching cells Cells overlap; can synthesize collagen and elastin