Muscle Tissue Flashcards
What is muscle tissue specialized for?
Specialized for contractions that produce movement
What type of movement occurs in muscle tissue?
Movement of body itself and its parts
Pumping of blood through heart/vessels
Force air into/out of the body
Moves food through gut
What are characteristics of muscle tissue? (cells, ECM, CT, innervation/vascularized, embryo origin)
cells > ECM
cells in direct contact with each other in most types of muscle tissue
Amount of ECM depends on muscle type - muscle cells have own external lamina
Some type of muscle tissue are compartmentalized by CT
Always innervated and well vascularized
From mesoderm
What are the 2 categories of muscle and the types of muscle tissue?
- Striated muscle - cells have striations; skeletal muscle and cardiac muscle
- Non-striated muscle - cells lack striations; smooth muscle
What is the orientation of striations in striated muscle?
Striations are perpendicular to the long axis of a muscle cell
What is a generic term for muscle cells?
Myocytes
What are skeletal and cardiac cells called?
Muscle Fibers
What is a muscle cell membrane?
Sarcolemma
What is the muscle cell cytoplasm?
Sarcoplasm
What is the smooth endoplasmic reticulum of the muscle cell?
Sacroplasmic reticulum
What are contractile cytoskeletal filaments of muscle cells?
Myofilaments - Actin (thin) filaments and myosin (thick) filaments
What is the function of skeletal muscle tissue?
Moves the skeleton as well as some soft tissue structures (eyeball, tongue, esophagus, and scrotum)
Has roles in stability, balance, breathing, speaking
Skeletal muscle tissue is under ______ control in response to _____ signals
Voluntary
In response to CNS signals (motor nerves)
Where is skeletal muscle located?
Most skeletal muscle tissue attaches to bone indirectly via tendons (dense regular CT)
Some skeletal muscle tissue is embedded within other structures
What are the 2 types of resident cells in skeletal muscle? What are their functions?
Skeletal muscle fibers - contraction (contractile cells)
Satellite cells - stem cells; help repair and regenerated injured skeletal muscle fibers
What 3 CT sheaths surround and subdivide a skeletal muscle at organ and tissue levels?
Endomysium
Perimysium
Epimysium
What is the composition of endomysium?
Reticular CT around 1 muscle fibers and its EL
Capillary rich
Good environment for calcium, potassium, and sodium exchange
What is the composition of perimysium?
Loose CT around each fascicle (fascicle = bundle of muscle fibers)
What is the composition of epimysium?
Dense irregular collagenous CT surrounding entire muscle
Binds all fascicles together
What are the benefits of sheaths around skeletal muscle?
Blood/Nerve supply and lymph drainage are very close to muscle fibers
Facilitates more powerful contractions
Helps connects a muscle to its tendons
What are key features of skeletal muscle fibers in LM?
Fibers are very long, cylindrical and parallel within a fascicle
Multinucleated - heterochromatic nuclei at periphery
Endomysium and capillaries between muscle fibers
Perimysium around fascicles
What is the sarcoplasm mainly made up of?
Most of sacroplasm/cell volume is myofibrils
What is each myofibril composed of?
Repeating sarcomeres that line up end to end down entire length of myofibril
What is the smallest functional contractile unit in skeletal muscle?
Sarcomeres
Where are the nuclei in the sarcoplasm?
Nuclei lie just inside sarcolemma, in the peripheral sarcoplasm
What are the two myofilaments?
Myosin (thick) filaments
Actin (thin) filaments
What is myosin made of and what does it do?
Mostly myosin II
Binding sites for ATP and actin
What are actin filaments made of and what is the function of each part?
Mostly actin - binding sites for myosin and TnI
Tropomyosin
Troponin - 3 subunits
1. TnT - binds tropomyosin
2. TnC - binds calcium
3. TnI - binds actin; when TnI binds actin, it inhibits actin from interacting with myosin
What myofilaments are in the sarcomere?
Actin (thin) and myosin (thick) myofilaments
What is the Z disk in the sarcomere? What does it do?
Z line
Ends of a sarcomere
Proteins (alpha-actinin) that anchor thin filaments
Bisects I band
What is the I band made of and where is it located?
Thin filaments only
Straddles adjacent sarcomeres
What is the A band made of?
Thin and thick filaments
What is the H band made of and where is it?
Thick filaments only
Bisects A band
What is the M line made of and where is it?
Proteins that bind thick filaments
Middle of sarcomere
Bisects H band
What does the sarcolemma have a lot of and what is that?
Sarcolemma has many T tubules which are tubular invaginations that extend deep into the cell
T tubule lumens are continuous with extracellular space and are important for initiating contraction
What is the function and structure of the sarcoplasmic reticulum?
Sarcoplasmic reticulum is extensive and elaborate
Regulates contraction
Sequesters calcium in its terminal cisterns (when cell is relaxed) and released calcium into cytosol to initiate contraction
What is a triad in reference to the sarcoplasmic reticulum?
Group of 2 sarcoplasmic reticulum terminal cisterns flanking a T tubule
What is the short version of skeletal muscle contraction? 8 steps
- Motor neurons trigger depolarization of sarcolemma
- T tubules carry depolarization deep into sarcoplasm
- Depolarization reaches triad -> large amounts of calcium released from SR terminal cisterns into cytosol
- Calcium in cytosol binds troponin in actin filaments
- Actin filaments slide along thick filaments toward M line and thick filaments do not move
- Z discs pulled along - shortens length of sarcomere
- Actin filament sliding and sarcomere shortening happens simultaneously in all sacromere in 1 myofibril and all myofibrils in fiber contract so muscle fiber shorten
- Calcium returns to SR - actin filaments slide back into resting position
Does the sarcoplasm have a lot of mitochondria?
yes! Many mitochondria
What does the myoglobin in the sarcoplasm do?
Oxygen binding
How does skeletal muscle fibers get fuel for glycolysis?
Skeletal muscle fibers contain varying amounts of glycogen
What is type I skeletal muscle fibers? What is the myoglobin content, mitochondria, contractions, and primary method of ATP generation of type I?
Red, slow twitch
High myoglobin
Many mitochondria
Slow and repetitive contractions, not easily fatigued
Slow aerobic respiration
What is type IIa skeletal muscle fibers? What is the myoglobin content, mitochondria, contractions, and primary method of ATP generation of type IIa?
Intermediate
Intermediate myoglobin content
Intermediate number of mitochondria
Fast and not easily fatigued contractions
Aerobic respiration but can switch to anaerobic glycolysis
What is type IIb skeletal muscle fibers? What is the myoglobin content, mitochondria, contractions, and primary method of ATP generation of type IIb?
White, fast twitch
Low myoglobin
Few mitochondria
Fast and easily fatigued
Anaerobic glycolysis
What is the sarcolemma dual anchored by?
Sarcolemma is surrounded by external lamina and endomysium - satellite cells lie between sarcolemma and EL
Costamere (dystrophin-associated protein complex) - link cytoskeleton, sarcolemma, EL, and endomysium
Dystrophin - large intracellular linker protein that binds sarcolemma and actin filaments in peripheral myofibrils
What is the purpose of the sarcolemma being dual anchored?
Anchoring cells to the CT layer that extends throughout the muscle strengthens the force of contraction
Balancing/distributing forces on both sides of sarcolemma protects it from being torn by strong tensile forces during muscle contraction
What is skeletal myogenesis?
Initial formation of muscle tissue in embryos
Mesenchymal cells in somites or paraxial mesoderm differentiates to myoblasts
Myoblasts fuse end to end and form syncytia called myotubules
Some myoblasts remain unfused and do not differentiate into satellite cells
Myotubules make myofilaments which organize into sarcomeres
What is the function of cardiac muscle tissue? How does it accomplish this?
Contracts the heart wall and moves blood from chamber to chamber and into arteries
Rigorous and rhythmic contractions in response to electrical signals generated by heart itself
Contraction rate modulated by ANS nerves and hormones, but they do not initiate contraction
What is the control and location of cardiac muscle tissue?
Involuntary control
Located in heart wall and forms the myocardium of atria and ventricles
What are the 4 main types of cardiac muscle tissue?
Contractile cardiomyocytes - contraction
Myoendocrine cells - secrete peptide hormones
Nodal cells (in SA or AV nodes) - generate electrical impulses and coordinate the contraction of cells in atria and ventricle
Purkinje fibers - very rapid conduction of electrical impulses
What are the key features of cardiac muscle fibers?
Shorter than skeletal muscle fibers
Y-shaped cells
1-2 large euchromatic nuclei in center of cell
Striation present but weak
Cells directly contact each other end to end at intercalated discs
What are the characteristics of the sarcolemma and intercalated discs in cardiac muscle?
Sarcolemma surrounded by an EL and capillary rich endomysium - no satellite cells
Cardiac muscle has a dystrophin complex
Cardiac muscle fibers are in direct contact with each other
Intercalated discs are specialized regions of sarcolemma where 2 cells meet - lots of cell junctions
What are the sarcoplasm contents of cardiac muscle fibers?
Most of sarcoplasm is myofibrils
Sarcomeres have thin and thick filaments
Dyads instead of triads in SR
Abundant myoglobin
More glycogen granules and more lipid droplets
Rows of very large mitochondria
What is the heart’s conduction system? What is the system modulated by?
System generates and transmits electrical impulses to contractile cardiomyocytes
System is modulated by ANS nerves and hormones - can influence changes in contraction rates, but nerves don’t contact cells or initiate contractions
What is the mechanism of contraction for cardiac muscle?
- Depolarization transferred from conducting cells (purkinje fibers) to contractile cardiomyocytes
- Depolarization travels down T tubules into sarcoplasm - triggers calcium release from SR and binds to TnC
- Thin filaments slide across thick filaments, pulling Z discs towards M line
- Contraction simultaneous in all sarcomeres in cardiac muscle fiber
- After contraction, calcium return to SR, binds to calsequestrin in SR terminal cisterns
What is the function of smooth muscle tissue? How does it accomplish these tasks?
Functions:
- peristalsis in GI, repro, and urinary tracts - moves lumen contents
- blood vessel constriction and dilation - regulates blood flow (volume, rate)
- airway constriction and dilation
Slow and sustained contraction in response to variety of signals/stimuli
What is the control and locations of smooth muscle tissue? What are the resident cells of smooth muscle tissue?
Involuntary control
Located in walls of blood vessels and tract (resp, GI, GU)
Resident cells - smooth muscle cells - contractile cells that can undergo mitosis and also synthesize and secrete EL and endomysium components
What is contraction of smooth muscle cells triggered by?
Contraction may be triggered by ANS nerves, hormones, chemical stimuli
Mechanical stretching cells or electrical signals traveling between adjacent smooth muscle cells.
Contraction can depend on location - unitary (visceral) smooth muscle in wall of GI and GU has poor innervation and multiunit smooth muscle in iris of eye is richly innervated
What are the characteristics of smooth muscle tissue?
Hard to see boundaries between adjacent smooth muscle cells
1 nucleus located in the cell center and is euchromatic
Look like inchworms - no striations or intercalated discs or branches
What are characteristics of smooth muscle - sarcolemma and sarcoplasm?
Smooth muscle cells in extensive contact
Abundant gap junctions - rapid ion transmission from cell to cell and allows smooth muscle cells to coordinate and contract as a unit
Focal adhesions anchors smooth muscle cells to neighboring cells
Has dystrophin complex
Numerous calcium channels - bring extracellular calcium into cell and release it into cytosol to initiate smooth muscle cell contraction
Numerous caveolae (lipid rafts) form caveolin-dependent endocytotic vesicles and pinocytotic vesicles
What are the contents of smooth muscle cell sarcoplasm?
No t tubules and SR not as well developed
Numerous mitochondria, some glycogen granules
Numerous intermediate filaments
No sarcomeres, no myofibrils, and no striations
Dense plaques - where thin filaments attach to sarcolemma
Dense bodies - attachment pints between thin filaments and intermediate filaments
What are the steps of smooth muscle cell contraction?
- Stimulus triggers depolarization of smooth muscle cell sarcolemma
- Voltage gated calcium channels bring in extracellular calcium - triggers release of calcium stored in SR
- Calcium binds to smooth muscle cell specific version of myosin
- Thin filaments slide across myosin, drawing dense plaques closer to cell center
