Flashcards in Muscle Tissue Deck (32):
What are some properties of the muscle tissue?
Contractility (not unique) -actin, myosin and energy (ATP)
Conductivity with each other and also with nerve cells
What are the major types of muscle tissue?
Skeletal- fast, attached to bones, can be visceral (found in the head and neck regions -tongue, pharynx, part of esophagus)
Smooth muscle-Mostly visceral but found in the skin (erector pilae) and eyes (muscles of the pupils)
Cardiac muscle- evolutionary from smooth muscle but behaves like skeletal muscle.found solely in heart
What are the characteristics of the skeletal muscle?
Fast but gets tired quick
Originated from myoblasts which form a multinucleated syncytium (postmitotic myotube)
What is the composition of the skeletal muscle fibers?
Sarcolemma which is the plasma membrane has processes called the T-tubules which are extension of the membrane
Sarcoplasmic reticulum which is the depot of calcium ions
What is the content of the sarcoplasm?
Cross striated elements: myofibrils
Filamentous mitochondria sandwich between myofibrils
Myoglobin- oxygen binding protein and gives skeletal muscle its red color
What is the organization of the skeletal muscle?
Named muscle (biceps,etc) divides into muscle fascicles.
Each muscle fascicle is made of skeletal muscle fibers (skeletal muscle cell)
Each skeletal muscle fiber is made of myofibrils
Each myofibril contains myofilaments
Each myofilament is made of thin and thick filaments
What is the structure of a myofibril?
Hexagonal array with 1 thick filament surrounded by 6 thin filaments
What are the thin filaments that made the myofibril?
F-actin forms a double helix
Tropomyosin form a long filament that sit in the groove, support and strength the actin and block the binding sites for myosin
Troponin complex- not present in smooth muscle
What is the composition of the troponin complex?
Troponin T-Binds to tropomyosin
Troponin I-Binds to actin -inhibits the actin tropomyosin binding
Troponin C- Binds calcium ions- change the confirmation of the myosin complex to allow binding to actin.
What are the thick filaments that made the myofibril?
Myosin type II made of:
2 heavy chains
2 pairs of light chains
What are the characteristics of the heavy chains of the myosin Type II?
Coiled into alpha helix
Form 2 globular heads- ATP binding site and Actin binding site
What are the characteristics of the light chains of the myosin type II?
Attach to the heads
Have essential and regulatory properties.
In skeletal muscle regulatory properties are remnants of evolutionary path
What is the organization of the myofibril?
Light band formed by thin filaments are the I-band (isotropic)- Z disc
Dark band formed by the thick filaments are the A-band (anisotropic)
Sarcomere=distance between Z disc
H-zone= less dark area in A band made off myosin only
M-line=center of the A band
What are the changes that occur during contraction?
Sarcomere becomes shorter
I band shrinks
H-zone becomes smaller
A band stays the same
What are the accessory proteins of the myofibril?
Titin-Attaches myosin to Z disk
Myomesin- Holds thick filaments at M-line
Alpha-actinin- Attaches thin filaments to Z-disk
Nebulin-Helps anchor thin filaments, regulate thin filament during development
Desmin-Forms cross links between myofibrils, attaches Z disk to sarcolemma
Dystrophin- Links actin cytoskeleton to extracellular matrix
What is the structure of T-tubules?
The sarcoplasmic reticulum is a depot of calcium concentration and form terminal cisternae around the T tubules.
The T-tubules and the terminal cisternae on each side form a membrane triad
What is the mechanism of the skeletal muscle contraction?
Action potential travels down the T-tubule causing and excitation of the sarcoplasmic reticulum which release calcium ions into the sarcoplasm.
Calcium ions binds to troponin C and causes a configuration change of troponin
Tropomyosin is shifted revealing myosin binding site of actin
Myosin binds ta actin =myosin "walking"
Myosin uses ATP to slide actin
No ATP= rigor mortis
What is the mechanism of muscle relaxation?
calcium activated ATPase membrane pumps pull back calcium ions into SR
Dissociation of calcium ions and troponin C
Myosin binding site of coin concealed by tropomyosin
How do skeletal muscle fibers regenerated?
Regeneration is possible through satellite cells that are precursor cells that differentiate into skeletal muscle after injury.
After extensive damage the muscle is replaced by fibrous scar
What are the CT of the skeletal muscle?
Epimysium- Dense collagenous CT, surrounds the whole muscle
Perimysium-Dense collagenous CT, surrounds the muscle fascicles
Endomysium- Reticular fibers, surrounds individual muscle fibers
What are the characteristics of smooth muscle ?
No cross striations
Made of myocytes (20-200 microns)
Possess long cigar shaped central nuclei
Poorly organized myofilaments
Thin filaments attached to anchoring points-dense bodies (alpha actinin)
Dense bodies anchored to network of filaments formed by desmin
What is the structure of smooth muscle cells ?
Sarcoplasm with SR, mitochondria and myofilaments
Sarcolemma possess caveolae which are invaginations to pass AP, and gap junctions
CT are basal lamina and reticular fibers
What are the thin filaments of the smooth muscle ?
Tropomyosin-not masking the myosin binding sites
Caldesmon- Calcium dependent protein, masks the myosin binding sites.
What are the thick filaments of the smooth muscle cells ?
Myosin type II
Possess 2 heavy chains and 4 light chains
Folded when dephosphorylayted
Binds to actin when phosphorylated
What are the modes of excitation of smooth muscle?
Neural stimulation through the postganglionic fibers of autonomic nervous system, Neurotransmitters(norepinephrine, acetylcholine) are released in the vicinity since all muscle cell do not receive terminal nerves, impulse transmission done through gap junctions
Chemical stimulation through angiotensin II and vasopressin
Mechanical stimulation by passive stretching
What is the mechanism of smooth muscle contraction?
Calcium ions binds to calmodulin
Calcium ions-calmodulin complex binds to caldesmon opening the myosin binding site
Complex also activates myosin light chain kinase
Myosin light chain kinase phosphorylates myosin
Myosin unfolds and actin binding site opens
Myosin head binds to actin
Sliding of filaments
Shortening of the cell- nucleus becomes corkscrew
What is the mechanism of relaxation of the smooth muscle cell?
Calcium ions back into SR
Calcium ions in the sarcoplasm drop
Light chain kinase deactivated
Muscle able to prolonged effect by latch state mechanism
Latch state uses for long term contractions and toxine of blood vessels
What are the locations of the smooth muscle?
Large hollow organs
Walls of blood and larger lymphatic vessels
Large ducts of glands
Iris and ciliary body
Arrector pilorum muscles
Does muscle cell regenerated?
Active regeneracvtive response possible through mitosis
Moderate blood supply
What are the characteristics of cardiac muscle ?
Extensive blood supply
Central rounded nuclei
Branching chains of cells
Intercalated disks with transverse portion (desmosomes, fascia adherens) and lateral portion (gap junctions)
T tubules formed diads along Z disks
What is the mechanism of cardiac muscle contraction?
SER have terminal cisternae not well developed
Mechanism similar to skeletal muscle
Not initiated by nervous system but nervous system able to regulate it
Initiated by cardiac conducting system