HISTO MIDTERMS

• MUSCLE TISSUE

  Composed of cells that optimize the universal cell property of contractility. Mesodermal in origin
• sarcoplasm

  Cytoplasm of muscle cells
• sarcoplasmic reticulum

  Smooth Endoplasmic Reticulum of Muscle
• sarcolemma

  Cell membrane and external lamina
• Three types of muscle tissue

  Skeletal Muscle

  Cardiac Muscle

  Smooth Muscle
• SKELETAL MUSCLE

  Multi nucleated cells with cross striations.

  Quick, Forceful, Usually voluntary contractions
• CARDIAC MUSCLE

  Branched cells bound to one another at structures called intercalated discs

  Contraction is involuntary, vigorous, and rhythmic
• SMOOTH MUSCLE

  Fusiform cells which lack striations

  Slow, involuntary contractions
• SKELETAL MUSCLE / STRIATED MUSCLE


  Consists of muscle fibers, which are long, cylindrical multinucleated cells with diameters of 10-100 μm.

  Elongated nuclei are found peripherally just under the sarcolemma

  Reserve Progenitor cells called satellite cells remains adjacent to most fibers of differentiated skeletal muscle.
• 4 Layers of Connective Tissue

  Endomysium

  Perimysium

  Epimysium

  Deep Fascia
• Endomysium

  dense irregular tissue surrounding the external lamina of individual muscle fibers.
• Perimysium

  Thin connective tissue layer that immediately surrounds each bundle of muscle fibers termed as fascicle
• Epimysium

  external sheath of dense irregular connective tissue, surrounds the entire muscle
• Deep Fascia

  Dense Irregular Connective Tissue overlying epimysium

  Myotendinous junctions
• Dark bands are called A Bands

  Light bands are called I Bands
• Sarcoplasm is highly organized, containing primarily long cylindrical filament bundles called myofibrils.

  I bands are bisected by a dark transverse line, the Z disc.

  The repetitive functional subunit of the contractile apparatus, the sarcomere, extends from Z disc to Z disc
• ORGANIZATION OF MUSCLE FIBERS

  The repetitive functional subunit of the contractile apparatus, the sarcomere, extends from Z disc to Z disc

  The A and I banding pattern in sarcomeres is due mainly to the regular arrangement of thick and thin myofilaments, composed of myosin and F-actin, respectively

  Myosin heads bind both actin, forming transient cross bridges between the thick and thin filaments, and ATP, catalyzing energy release (actomyosin ATPase activity)

  I bands consist of the portions of the thin filaments which do not overlap the thick filaments in the A bands
• 1. A bands contain both the thick filaments and the overlapping portions of thin filaments
  2. Presence of a lighter zone in its center, the H zone, corresponding to a region with only the rodlike portions of the myosin molecule and no thin filaments
• Sarcoplasmic Reticulum

  membranous smooth ER in skeletal muscle fibers
• Transverse or T-tubules

  long fingerlike invaginations of the cell membrane encircling each myofibril near the aligned A and I band boundaries of sarcomeres
• Terminal cisternae

  expanded structures adjacent to each T-Tubule
• Functions

  Ca2+ sequestration during muscle contraction
• Contraction

  occurs as the overlapping thin and thick filaments of each sarcomere slide past one another.
• Mechanism of Contraction

  (1.) Nerve impulse triggers release of ACh from the synaptic knob into the synaptic cleft.

  ACh binds to ACh receptors in the motor end plate of the neuromuscular junction, initiating a muscle impulse in the sarcolemma of the muscle fiber.

  (2.) As the muscle impulse spreads quickly from the sarcolemma along T tubules, calcium ions are released from terminal cisternae into the sarcoplasm
• Mechanism of contraction

  (3.) Calcium ions bind to troponin.

  Troponin changes shape, moving tropomyosin on the actin to expose active sites on actin molecules of thin filaments.

  Myosin heads of thick filaments attach to exposed active sites to form cross bridges

  (4.) Myosin heads pivot, moving thin filaments toward the sarcomere center. ATP binds myosin heads and is broken down into ADP and P.

  Myosin heads detach from thin filaments and return to their prepivot position.

  The sarcomere shortens and the muscle contracts
• Mechanism of contraction

  5. When the impulse stops, calcium ions are actively transported into the sarcoplasmic reticulum

  Tropomyosin re-covers active sites, and filaments passively slide back to their relaxed state.
• SKELETAL MUSCLE FIBER

  Different types of fibers can be identified on the basis of

  (1) their maximal rate of contraction (fast or slow fibers) and

  (2) their major pathway for ATP synthesis (oxidative phosphorylation or glycolysis).
• 3 types of Muscle fibers

  Type I ( Slow Oxidative Fibers)

  Type IIa (Fast Oxidative Glycolytic Fibers)

  Type IIb (Fast Glycolytic Fibers)
• Type I ( Slow Oxidative Fibers).

  Small fibers, appear red in fresh specimens, contain many mitochondria and large amounts of myoglobin and cytochrome complexes

  Slow-twitch fatigue-resistant motor units;
• twitch

  is a single brief contraction of the muscle
• Type IIa (Fast Oxidative Glycolytic Fibers)

  Intermediate fibers seen in fresh tissue

  Medium size w/ many mitochondria and a high myoglobin content

  Fast-twitch fatigue-resistant motor units that generate high peak muscle tension
• Type IIb (Fast Glycolytic Fibers)

  Large fibers, w/c appear light pink in fresh specimens, contain less myoglobin & fewer mitochondria than type I & IIa fibers.

  Low levels of oxidative enzymes but exhibit high anaerobic enzyme activity and store a considerable amount of glycogen

  Fast-twitch fatigue-prone motor units & generate high peak muscle tension
• CARDIAC MUSCLE

  Has same types and arrangements of contractile filaments as skeletal muscle

  Cardiac muscle nucleus lies in the center of the cell

  Numerous large mitochondria and glycogen stores are adjacent to each myofibril

  The intercalated disks represent junctions between cardiac muscles
• 3 Components of intercalated disk contain specialized cell to cell junction between adjoining cardiac muscle cells

  Fascia adherens (adhering junction)

  Maculae adherentes (desmosomes)

  Gap junctions (communicating junctions)
• Fascia adherens (adhering junction)

  is the major constituent of the transverse component of the intercalated disk
• Maculae adherentes (desmosomes)

  bind the individual muscle cells to one another.
• Gap junctions (communicating junctions)

  provide ionic continuity between adjacent cardiac muscle cells allowing informational macromolecules to pass from cell to cell
• Cardiac muscle cell possesses only one or two centrally located pale- staining nuclei (unlike multinucleated skeletal muscle).

  Unique and distinguishing characteristic of cardiac muscle is the presence of dark staining transverse lines that cross the chains of cardiac cells at irregular intervals --- >intercalated disk
• Fatty acid major fuel of the heart (stored as triglycerides)
• 2 types of cardiac muscle fiber

  Atrial cardiac muscle fiber

  Ventricular cardiac muscle fiber