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刘 琼 副教授
复旦大学基础医学院解剖与组织胚胎学系
Department of Human Anatomy, Histology and Embryology
Human Histology & Embryology
Chapter 10Muscle Tissue
3 Types of Muscle Tissue
• Skeletal muscle• attaches to bone, skin or fascia• striated with light & dark bands visible with scope • voluntary control of contraction & relaxation
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3 Types of Muscle Tissue
• Cardiac muscle• striated in appearance• involuntary control• autorhythmic because of built in pacemaker
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3 Types of Muscle Tissue
• Smooth muscle• attached to hair follicles in skin• in walls of hollow organs -- blood vessels & GI• nonstriated in appearance• involuntary
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Functions of Muscle Tissue• Producing body movements• Stabilizing body positions• Regulating organ volumes
• bands of smooth muscle called sphincters
• Movement of substances within the body• blood, lymph, urine, air, food and fluids, sperm
• Producing heat• involuntary contractions of skeletal muscle (shivering)
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Muscle Histology
• Elongated cylindrical cells = muscle fibers• Plasma membrane = sarcolemma• Transverse (T) tubules tunnel from surface to center of each fiber• Multiple nuclei lie near surface of cell• Cytoplasm = sarcoplasm
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Transverse Tubules
• T (transverse) tubules are invaginations of the sarcolemma into the center of the cell
• filled with extracellular fluid• carry muscle action potentials down into cell
• Mitochondria lie in rows throughout the cell• near the muscle proteins that use ATP during contraction
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Myofibrils & Myofilaments
• Muscle fibers are filled with threads called myofibrils separated by SR (sarcoplasmic reticulum)
• Myofilaments (thick & thin filaments) are the contractile proteins of muscle
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Sarcoplasmic Reticulum (SR)
• System of tubular sacs similar to smooth ER in nonmuscle cells
• Stores Ca+2 in a relaxed muscle• Release of Ca+2 triggers muscle contraction
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Sarcomere• Filaments overlap in repeating patterns• Unit structure is called sarcomere• Separated by Z discs• Darker area = A band associated with thick filaments• H zone has no thin filaments• I band has thin filaments no thick filaments
Functional Structure• Thick filament (myosin) has moveable heads (like “heads” of
golf clubs)• Thin filaments (actin) are anchored to Z discs
• Contain myosin binding sites for myosin head• Also contain tropomyosin & troponin
• Tropomyosin blocks myosin binding site when muscle is at rest
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Sliding filaments and sarcomere shortening in contraction.Diagrams and TEM micrographs show sarcomere shortening during skeletal muscle contraction. (a) In the relaxed state the sarcomere, I band, and H zone are at their expanded length. The springlike action of titin molecules, which span the I band, helps pull thin and thick filaments past one another in relaxed muscle. (b) During muscle contraction, the Z discs at the sarcomere boundaries are drawn closer together as they move toward the ends of thick filaments in the A band. Titin molecules are compressed during contraction.
Ø Sarcolemma invaginate into sarcoplasm to form a transverse distributed tubular systemØFunction: transfer stimulation into cytoplasm (A-I band boundary)
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Ø Sarcoplasmic reticulum enlarge to form flattened sacØ Function: store and release Ca 2+ (Ca2+ pump on membrane)
One T-tubule + two terminal cisternae
Neuromuscular junction
MEP: motor end-plateNB: nerve bundleS: skeletal muscle
Neuromuscular junction
Structures of NMJ Region
• Synaptic end bulbs are swellings of axon terminals
• End bulbs contain synaptic vesicles filled with acetylcholine (ACh)
• Motor end plate membrane contains 30 million ACh receptors.
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HE Special stain
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Tissue Features:• Striated (same contractile machinery)• Self-excitatory and electrically coupled• Rate of contractions modulated by autonomic nervous system
• innervation is neuroendocrine in nature (i.e. no “motor end plates”) Cell Features:• 1 or 2 centrally placed nuclei• Branched fibers with intercalated discs• Numerous mitochondria (up to 40% of cell volume)• Sarcoplasmic reticulum & T-tubules appear as diads at Z lines
Smooth Muscle • Fusiform, non-striated cells• Single, centrally-placed nucleus• Contraction is non-voluntary• Contraction is modulated in a neuroendocrine manner• Found in blood vessels, GI and urogenital organ walls, dermis of skin
(a) Skeletal muscle
Description: Long, cylindrical,multinucleate cells; obviousstriations.
Function: Voluntary movement;locomotion; manipulation of theenvironment; facial expression;voluntary control.
Location: In skeletal musclesattached to bones oroccasionally to skin.
Photomicrograph: Skeletal muscle (approx. 460x).Notice the obvious banding pattern and thefact that these large cells are multinucleate.
Nuclei
Striations
Part ofmuscle fiber (cell)
(b) Cardiac muscle
Description: Branching, striated, generally uninucleate cells that interdigitate atspecialized junctions (intercalated discs).
Function: As it contracts, it propels blood into the circulation; involuntary control.Location: The walls of the heart.
Photomicrograph: Cardiac muscle (500X);notice the striations, branching of cells, andthe intercalated discs.
Intercalateddiscs
Striations
Nucleus
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(c) Smooth muscle
Description: Spindle-shapedcells with central nuclei; nostriations; cells arranged closely to form sheets.
Function: Propels substancesor objects (foodstuffs, urine,a baby) along internal passage-ways; involuntary control.
Location: Mostly in the wallsof hollow organs.
Photomicrograph: Sheet of smooth muscle (200x).
Smoothmusclecell
Nuclei
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