Muscles Flashcards
Functions of the muscle
Contraction to cause movement of the skeleton, changing shape of internal organs and rhythmic contractions of the heart
What are the three types of muscle and what to they each control?
Skeletal - Skeleton,eyes,tongue
Smooth - BV,airways, internal
organ shape
Cardiac- Heart
Which muscle types are under voluntary control?
What about involuntary control?
Skeletal
Smooth,Cardiac
Skeletal Muscle Histology
Long cells with multiple nuclei located at the periphery of the cell to make space for contractile system.
Striations (alternating dark and light bands)
Cardiac Muscle Histology
Short cells with centrally located nuclei ( 1 or 2) with branching that allows cells to connect
Striations
Intercalated discs (stain as dark pink lines)
Smooth Muscle Histology
Small tapered cells appearing as sheets of cells.
Myo- means ______.
Sarco- means ________.
Muscle
Flesh
Sarcoplasmic reticulum is ________.
The smoother ER within muscle
Sarcolemma
Muscle cell plasma membrane
Which embryonic layer to muscles come from?
Describe the formation of muscle development from the embryonic stage.
Mesoderm
During gastrulation, the neural tube forms. Somites, blocks of mesoderm, on either side of the neural tube give rise to sclerotomes and dermomyotomes.
What are the embryonic precursors to muscle that arise from somites and what to they form?
- Sclerotomes - Vertebra and Ribs (Bone)
- Dermomyotomes (Dermatome and myotome)
Dermatome- Dermis of Skin
Myotome- Myoblasts; skeletal muscle
What happens to myoblasts in order for them to become ________ muscle?
Skeletal
Myoblasts migrate and fuse to form mature skeletal muscle cells.
What are other names for mature muscle cells?
Myotubes
Myofibers
Muscle Fiber
Extrafusal Fibers
What are satellite cells?
Progenitor stem cells near muscle cells responsible for growth and limited muscle repair.
Skeletal muscle is organized by sheaths of ______ tissue.
Describe the structure of skeletal muscle from the inner most structure.
Connective
Myofiber(muscle cell) is surrounded by endomysium
A bundle of endomysium-surrounded myofibers form a fasicle surrounded by perimysium.
A group of perimysium covered fasicles are surrounded by epimysium which is continuous with tendons.
What do tendons bind?
Muscle to bone
What kind of connective tissue is epimysium?
DRCT
In a skeletal muscle cross section, can you see striations?
What can help us identify if it is a muscle cell?
NO!
Multiple peripherally located nuclei per cell
Abundant Capillaries (space between cells for nutrition)
Describe the internal structure of an individual muscle FIBER.
What does the internal structure allow for?
Muscle cell
MyofibRILS (smaller fibers within the cell) span the length of the cell and are composed of repeating sarcomeres.
Sarcomeres are made of horizontal proteins called myofilaments which appear as dark and light bands.
Striations in muscle cell
What are myofilaments and how do they react to light when staining?
Myofilaments are the thick and thin overlapping horizontal organization of a sarcomere.
These sarcomeres repeat several times to form a myofibril which comprises a myofiber.
The thick (myosin) filaments dye darker.
The thin (actin) filaments dye lighter
What is the contractile unit of the cell?
What is it comprised of?
Sarcomere
Myosin (thick)
Actin (thin)
Describe the structure of a sarcomere
Z-Disc to Z-Disc
In the center of the sarcomere is an A band. The A band is comprised of the myosin and actin filaments in the center.
On either side of the A-band is an I band which hosts the actin filaments. The I band is NOT overlapping with myosin.
The Z-band separate the I-band actin filaments into each “half” of the sarcomere the actin filaments are being shared by. The Z-disc anchors actin filaments in place via proteins
The Sarcomere itself consists of Z-Disc to Z-Disc
A contracted sarcomere will look different than a relaxed sarcomere on an EM. Describe the difference.
The A-band will not change. However, the I-band will shrink in size and become incredibly thin compared to the relaxed sarcomere as the more acting and myosin filaments overlap.
How does contraction occur?
Myosin heads bind to actin filaments to form cross-bridges.
Myosin changes formation and pulls actin towards center of sarcomere causing thick and thin filaments to slide past one another.
Do sarcomeres contract one by one?
No! Sarcomeres contract together.
What starts a contraction?
- A nerve impulse triggers the release of Ach (acetycholine) from at the neuromuscular junction and stimulates receptors in SARCOlemma.
- The sarcoplasmic reticulum (smooth ER) surrounding each myoFIBRIL holds calcium critical for muscle contraction. It is located at the junction of the A and I band of sarcomeres of a myofibril. Terminal cisternae of the SER are here.
- In between 2 of the terminal cisternal, infoldings of the sarcolemma (plasma membrane of myoFIBER) form tubes.
- Stimulation of the T-Tubule membrane by nerve impulse triggers the muscle contraction by allowing the plasma membrane (sarcolemma) to interact with all sarcomeres at once to release Ca2+ Sarcoplasmic Reticulum.
Where is the sarcoplasmic reticulum found?
At the junction of the A and I band in muscle sarcomeres. (Terminal Cisternae are here)