Flashcards in Muscle Tissue Deck (116):
Cardiac muscle blood supply
-receives extensive blood supply through a network of capillaries
-double-stranded helical filament (composed of G-actin)
-portion of a myofibril between two adjacent Z-disks
-basic contractile unit of skeletal muscle
-measures 2-3 microns
-sarcomere of individual myofibrils are in register in one muscle fiber, so the entire muscle cell exhibits cross-striations.
Smooth muscle contraction
-driven by the high Ca++ concentration in the sarcoplasm
-relaxed muscle cells the highest concentration of Ca++ is in the sarcoplasmic reticulum
Smooth muscle fibers in the dermis of the skin
-attached to the hair follicles and form so called arrectores pilorum muscles
Troponin T binds to?
-binds to tropomyosin, anchoring the Troponin complex
-formed by deep invaginations of the sarcolemma
-allow the impulse to travel down into the cell and excite the terminal cisternae of the sarcoplasmic reticulum
Lateral portion of intercalated disks
-runs parallel to the myofilaments
-contains communication, of gap junctions that provide ionic continuity b/t adjacent cardiac muscle cells and allow the signal to contract to pass from cell to cell and generate a wave of contraction
-pale area formed primarily by thin filaments
-proteins such as Titian and nebulin are also found in the I-band
-is bisected by the Z-line (Z-disk)
-formed by connective tissue sheath
Reticular fibers of smooth
-important role in the force transduction in the smooth muscle tissue
-an oxygen-binding protein
-gives muscle it's red color. May store glycogen. DM pt's can lower sugar by working out
2 principle components of myofibril
-thick and thin filaments
Excitation of smooth muscle
-neural stimulation occurs through the postganglionic fibers of the autonomic nervous system
-neurotransmitter is released in the close proximity of a muscle cell and has to diffuse to the muscle sells through the CT that surrounds the muscle cells
-impulse transmission from cell to cell occurs through gap junctions
Nuclei of smooth muscle
-centrally placed and long (cigar-shaped) with tapered ends
*similar looking to fibroblasts
What does conductivity allow muscle cells to do?
-allows muscle cells to transmit electrical impulse to other cells and to receive impulses from nerve cells.
Two pairs of Myosin II light chains?
-attach to the heads.
-they are essential and regulatory (structural support)
Organization of skeletal muscles
-consist of fascicles or bundles of skeletal muscle fibers surrounded by a connective tissue sheath
Ex. Biceps->fascicles->skeletal muscle fiber (cell)->myofibril->myofilaments (thin/thick)
Nuclei of skeletal muscle cells?
-are peripheral in location and are found immediately beneath the sarcolemma.
-are peripheral because they are pushed near sarcolemma by myofibrils. This is unique to skeletal muscle
Trendelenburg (waddling) gait
-use forelimbs to push off hindlimbs to erect pelvis and upper body.
-variation of muscle fibers
-CT taking up place of fibers (endomysial)
-nuclei in abundance means inflammation
Signs of Duchenne muscular dystrophy
Troponin C binds to?
-binds to Ca++, which is an essential step in the initiation of the muscular contraction.
What 3 things does sarcoplasm of skeletal muscle cells contain?
-numerous myofibrils (found inside of fibers)
-numerous filamentous mitochondria
Thick filament are formed by?
-formed by hundreds of myosin molecules.
-Myosin II molecules is the muscle myosin
Skeletal muscle contraction
1. resting muscle cell, myosin-binding site on the actin filament is concealed by tropomyosin filament
2. Presence of high concentration of Ca++ ions, Ca++ binds to Troponin C
3. Changes the spatial configuration of the Troponin molecule and causes the tropomyosin filament to shift->opens myosin-binding site on the actin filament
4. Myosin starts "walking" along the actin fibers
5. Myosin uses ATP to slide the actin along, myosin is an ATPase
How is a skeletal muscle fiber (skeletal muscle cell) formed?
-"cells" of the skeletal muscle is actually a multinucleated syncytium.
Syncytium is cytoplasm that is shared
-takes a long time and a lot of effort to repair
Thick filament (smooth)
-formed by Myosin II
Troponin I binds to?
-binds to actin inhibiting the interaction with myosin
Mechanical stimulation of smooth
-passive stretching of the organ, can lead to the initiation of a muscular contraction
Long-term contraction of smooth muscle
-secondary mechanism that requires minimum energy
-after injury they become activated, proliferate and give rise to new myoblasts, which fuse to from a new fiber
-extensive damage results in the formation of a CT scar
6 types of accessory proteins found in the skeletal muscle
Arrangement of microfibrils
-composed of thin and thick filaments
-thin (actin) filaments are arranged in a hexagonal array with 6 thin filaments surrounding 1 thick (myosin) filament
Depolarized membrane of sarcolemma
-develops a positive membrane potential when it becomes more permeable for Na+ ions
-depolarization of membrane of muscle cell starts a cascade of reactions that cause muscular contraction
-most external thick layer of connective tissue that surrounds a group of fascicles that constitutes a named muscle
*dense CT collagen type 1
Filamentous mitochondria location and function?
-lie between myofibrils and close to the sarcolemma.
-represent the source of ATP for the myofibrils
Adherens junctions (fasciae adherentes) of transverse portion of intercalated disks
-connect the microfilaments of the two neighboring cardiac muscle cells.
-similar to the zonula adherentes found in the epithelial cells
-make up skeletal muscle fiber.
-extend the whole length of the muscle fiber.
-individual myofibril is striated
-membrane-associated protein complex that links actin cytoskeleton to the extracellular matrix stabilizing the thin filaments
-holds the thick filaments in register at the M-line
Note: M-line runs through the middle of the H-zone
-line formed by accessory proteins, such as myomesin that hold the thick filaments in register
-attached to the Z-disk and runs parallel to thin filaments.
-anchor the thin filaments and to regulate the length of thin filaments during muscular fiber development
T-tubules of cardiac muscles
-large and found at the Z-disks and not at the junction of A and I bands like skeletal muscle fibers
-contraction is Ca++ dependent and similar to contraction of skeletal muscle
Skeletal muscle origin?
-originate from myoblasts (myocytes line up) that fuse with each other to form long multinucleated postmitotic myotubes
What causes muscle contractility?
Skeletal muscle that is attached to bone function
primarily for locomotion, respiration, and other functions
Latch state of smooth muscle
-caused by the decrease of ATP activity while the myosin head is attached to actin
-causes prolonged contraction used to sustain the tone of blood vessels
-condition resembles the rigor Morris of the skeletal muscle
Two heavy chains of Myosin II characteristics?
-form coiled alpha-helices and two globular heads that exhibit ATPase and motor activity.
-globular heads contain binding sites for actin and ATP
-is a dimer
Sarcoplasm of smooth muscle
-contains myofilaments and organelles (numerous mitochondria)
-myofilaments of smooth muscle cells are more randomly distributed throughout the cytoplasm than in skeletal muscle and are poorly organized
How does muscle respond to:
-increasing in diameter
What causes skeletal muscle striation?
-due to arrangement of filaments in the cytoplasm
Cardiac muscle fibers arrangement
-fibers are formed by individual cells that are about 100 micrometers long
-different from the skeletal muscle fibers, which are formed by a syncytium
What does Myosin II consist of?
-2 heavy chains
-2 light chains
Microstructues of a muscular fiber
-composed of hundreds of myofibrils that span the entire length of the muscle cell
Excitation of smooth muscle steps
1. Ca++ is releases into sarcoplasm
2. Ca++ binds calmodulin (specific to smooth muscle)
3. Ca++/calmodulin complex binds to caldesmon releasing it from actin and opening the myosin-binding site on F-actin
4. Ca++/calmodulin complex activates myosin light-chain kinase (has to unfold)
Chemical stimulation of smooth muscle contraction
-elicited by various hormones, angiotensin II (kidney), vasopressin, etc
Smooth muscle (simplest type of muscular tissue) characteristics?
-does not exhibit cross striation in the cytoplasm, contractile filaments are not well organized inside the cell
-specialized for slow/rhythmic prolonged contractions of visceral organs, can provide rapid and precise contraction (eye)
Specialized plasmalemma (plasma membrane) term?
-forms filaments that lie in the grooves between the two actin monomers.
-in the resting muscle tropomyosin masks the myosin-binding sites on the actin filament (sits over the actin binding site)
Smooth muscle regeneration and blood supply
-moderate blood supply through capillaries in the CT immediately surrounding the muscle cells (uses less energy than skeletal and cardiac)
-capable of active regenerative response. Can go through mitosis and replace the damaged or lost cells
Transverse portion of intercalated disks
-runs across the fiber at a right angle, contains anchoring junctions that provide mechanical stability for the tissues and prevent cells from being pulled apart during contraction
-two parts: adherens junctions and desmosomes
-pale area in the middle of the A-band that contains thick filaments
-has no thin filaments
Microstructure of a myofibril
-myofibril exhibits striations formed by alternating dark (A-bands) and light (I-bands) regions
A=anisotropic (same value when measured in different directions)
I=isotropic (different value when measured in different directions)
-cardiac conduction cells
-modified for the conduction of electric impulses in a way similar to nerve cells
-from nodes and bundles including the sinoatrial and atrioventricular nodes and the bundle of His
-largest protein that anchors the thick filaments to the Z-disk
-extends to the M-line
-function is to keep the thick filaments in their position in the central part of the sarcomere
-formed by sarcolemma and the sarcoplasmic reticulum.
-on triad consists of one T-tubule and two cisternae of sarcoplasmic reticulum running parallel to it
-composed of accessory proteins and its major function is to provide anchoring points for thin filaments and to support the architecture of the myofibril
Smooth muscle in walls of larger hollow organs:
-walls of veins, arteries and lymphatic vessels
-extramural part of large ducts of glands
-GI tract, from distal esophagus to the anal canal
-M/F reproductive tract (ductus deferents, uterus, vagina)
-urinary system (bladder, ureter)
Cardiac muscle regeneration
-no ability of regeneration
-localized injury result in the replacement of muscle cells with fibrous CT that forms a scar
-function is lost in area of scar
-injury and repair is seen in the myocardial infarction
What do accessory proteins do?
-provide attachment of filaments to the Z-disk and attachment of Z-disks to each other and to the sarcolemma.
Dense bodies of smooth muscle
-anchoring points of thin filaments, formed by a-actinin.
-are anchored into the network of intermediate filaments by desmin
*dense bodies are somewhat analogous to the Z-disks of skeletal muscle fibers
*thick filaments are scattered throughout the sarcoplasm
Skeletal muscle innervation?
-an intermediate filament that forms a lattice that surrounds Z-disks and attaches them to one another and also attaches Z-disks to the plasma membrane
Where are accessory proteins found?
-primarily in the Z-disk and in the M-line
What happens in phosphorylation in smooth muscle contraction?
-myosin light-chain kinase phosphorylares the regulatory (light) chain of the myosin molecule
-when light regulatory chain is phosphorylated, myosin molecule unfolds and actin-binding site on the myosin head becomes open and myosin binds to actin
A. Filaments slide at an angle
B. Cell shortens, nucleus folds and becomes corkscrew-shaped
C. Slow action (1 second) ant it often takes over a second to achieve the contraction
Action potential of muscle cell
-brief positive going changes in the membrane potential that are propagated along the length of the membrane at a speed up to 120 m/sec
F-actin and tropomyosin (smooth)
F-actin: principal component of thin filaments in the smooth muscle
Tropomyosin: wraps around actin in a fashion similar to skeletal muscle
-no troponin is present in the thin filaments of smooth muscle
Communicating junctions of smooth muscle
-found interconnecting individual muscle cells
-small molecules or ions can pass through junctions from cell to cell and regulate contraction of the entire bundle of muscle cells
-can initiate contraction of neighboring muscle cells by allowing ions to pass through gap junctions and depolarize plasma membranes of other cells
Proteins that make up thin filaments
-Troponin complex (Troponin T, I, and C)
Visceral skeletal muscle location and function
-tongue, pharynx, and the proximal 1/3 of esophagus.
-aid with swallowing and speech
Characteristics of skeletal muscle fibers?
-numerous cross striations
-are quick, but usually get tired fast: use up energy quick
-most internal layer of reticular fibers that surround individual muscle fibers
Location of smooth muscles (broad)
-walls of larger hollow organs
-iris and ciliary body
-present in dermis of skin
Smooth muscle of iris and ciliary body
-responsible for the constriction and dilation of the pupil
Cardiac conducting system
-heartbeat is initiated, coordinated, and regulated by modified cardiac muscle cells that form the cardia conducting system
-Contains both thick and thin filaments.
-central part is called the H-zone (only thick filaments)
-overlap b/t thick and thin filaments cause darker part of A-band
-highly speacialized form of smooth endoplasmic reticulum and is used as a depot of Ca++
-when excited, the sarcoplasmic reticulum releases Ca++ into cytoplasm initiating the muscular contraction
Smooth muscle fiber location? Striated? Innervation?
-found in the walls of the internal organs (GI tract and middle walls of blood vessels)
-do not show striations in the cytoplasm
Specialized smooth endoplasmic reticulum term?
Cardiac muscle cell organelles
-centrally placed rounded nuclei
-myofibrils pass around the nucleus outlining a nuclear region where most organelles, including numerous mitochondria are concentrated, as well as inclusions, such as glycogen granules
-large flattened mitochondria are densely packed b/t the myofibrils
Troponin complex, what does it attach to?
What are the three globular subunits?
--attached to tropomysin
-Troponin T, Troponin I, Troponin C
FYI: tested for for possible MI
-smooth muscle cells are elongated spindle shaped (fusiform cells) and are 20-200 micrometers in length (20 in walls of small blood vessels and 500 in the pregnant uterus)
Skeletal muscle location
-attached to the skeleton and are also present in some visceral organs.
Caveolae-like invaginations of sarcolemma
-act as sarcolemmal vesicles and deliver the depolarization to the chambers of sarcoplasmic reticulum, located beneath the caveolae
-may act similar to T-tubules of skeletal muscle
Desmosomes (maculae adherentes) of the transverse portion of intercalated disks
-connect intermediate filaments (formed by desmin) of two adjacent cells
Skeletal muscle contraction
-What happens with the I and A band? H-zone?
-due to the sliding of filaments which results in the shortening of the sarcomere, while the length of individual filaments does not change
-length of A-band does not change during contraction
-I-band and H-zone shrink during contraction due to the increase of overlap between thick and thin filaments
-travels along the membrane
-descends down into the cell along the T-tubules, which causes excitation of the SR and release of Ca++ into sarcoplasm
Skeletal muscle relaxation
1. Following depolarization, Ca++activated ATPase membrane pumps transport Ca++ back into the sarcoplasmic reticulum. Ca++ disassociates from the Troponin C
2. Troponin complex returns to its original configuration and pulls the tropomyosin filament over the myosin binding site blocking the actin-myosin interaction. This stops the contraction unless there are new waves of depolarization coming with the nerve impulses
3. Rapid action that only takes 30 msec
Cardiac muscle fiber location? Innervation?
-found in the heart
FYI: Evolved from smooth muscle but structurally like skeletal muscle
-smooth muscle-specific actin-binding protein that masks the myosin-binding site on the actin fibers
-opens Ca++ binding site when Ca++ is near
Terminal cisternae (formed by long chambers of sarcoplasmic reticulum)
-run parallel to the T-tubules on both sides
-contain high concentration of Ca++ ions
-running near the boundary of A-band and I-band
-anchors thin filaments into the Z-disk
Smooth muscle relaxation
-Ca++ is pumped back into sarcoplasmic reticulum
-Ca++ levels in the sarcoplasm drop
-Calmodulin disassociates from the light-chain kinase, which deactivates the latter
-myosin is dephosphorylated and becomes inactive (folds to cover actin binding site)
-Caldesmon binds to the myosin-binding site on the actin filament
-slow action, has a prolonged effect on the tissue and requires very little energy spent compared to the skeletal muscle (10% of ATP that skeletal muscle uses)
Sarcoplasmic reticulum of cardiac muscle
-not as well-developed as in the skeletal muscle
-no large terminal cisternae; instead there are small chambers that run parallel to the T-tubules only on one side of the tubule forming diads
Myosin II of smooth muscle
-composed of two heavy polypeptide chains and four light chains
-only binds to actin when phosphorylated
-Myosin molecule is folded (inactive!) when dephosphorylated
Muscle cells of cardiac
Shape and arrangement?
-rectangular in outline
-formed by long chains of muscle cells that attach to each other like cars in a train
-connections b/t individual cells are marked with intercalated disks
-when two cells attach there is branching of muscle fibers
Cardiac muscle characteristics
-exhibit cross-striations (same arrangement of contractile filaments as skeletal)
-involuntary (rhythmic contractions to pump blood through the cardiovascular system)
Connective tissue role in muscles?
-protection and force transduction
-provides passage for nerves and blood vessels that supply the muscle
Most smooth muscle is slow, what smooth muscle is fast?
-ciliary muscle of the eye is fast
-erector pili of the skin is also smooth muscle
Electric capacitor of Sarcolemma
-voltage inside cell is negative
-outside cell is 0
-is a negative membrane potential in a resting cell, achieved by actively pumping Na+ ions out of the cell
-thicker layer of collagenous connective tissue that surrounds groups of muscle fibers, known as fascicles
Sarcolemma of skeletal muscle fibers forms long process called ______? What is _____ important for?
T-tubules. (Only found in skeletal muscle)
T-tubules that extend into the cytoplasm are important for carrying the wave of depolarization deep into the sarcoplasm.
FYI: action potential in a neuron is along the surface. In muscle cells the action potential runs inside the cell through T-tubules
Cytoplasm of muscle cells term?
Intercalated disks of cardiac
-represent junctions b/t individual muscle cells
-step-like Junction that consists of transverse and lateral portions
Skeletal muscle fiber
-multinucleated cell or syncytium
Thin filaments of smooth muscle
-similar to skeletal but w/out Troponin complex