Lec 14 - Muscle Tissue Flashcards
What is the unit of structure in muscle tissue?
muscle cell or muscle fiber
In muscle tissue, the term “muscle” is used to describe which specific structure?
the entire cell
What is a key characteristic of muscle fibers?
Contractility is an especially well-developed characteristic.
Muscle tissue makes up the majority of what in an organism?
The flesh or meat
Muscle fibers are covered by a?
Sarcolemma (combined plasmalemma and basal lamina) and fine reticular fibers
Explain the role of muscle in tubular organs.
It serves as a primary wall element.
Name the proteins found in myofilaments.
Actin and myosin.
Describe the Greek origin of the word “sarcos” in muscle tissue.
It means “flesh” or “meat.”
Group of Myofibrils
Myofilament
Sarcoplasm (Cytoplasm) contains?
Typical organelles and contractile elements
How is muscle functionally and structurally classified?
Functionally, muscle can be voluntary or involuntary.
Structurally, muscle can be smooth (non-striated) or striated
What are the structural differences between smooth, skeletal, and cardiac muscle?
Smooth muscle is non-striated.
Skeletal muscle is striated.
Cardiac muscle is striated.
What shape are smooth muscle cells and how are they arranged?
Elongated, spindle-shaped cells with tapered ends, arranged in a staggered pattern.
Where is the nucleus located in smooth muscle cells?
The nucleus is located in the central region of the widest part of the cell.
How are smooth muscle cells arranged in terms of layers?
They are arranged in extensive sheets, a few to many layers thick.
What type of contraction characterizes smooth muscle?
Smooth muscle has slow, sustained contractions that are resistant to fatigue.
What factors influence the contraction of smooth muscle?
Contraction is influenced by calcium ions, neuronal stimulation, and hormones.
Why might nuclei not be visible in all smooth muscle cells?
Due to the staggered arrangement of the cells, not all nuclei are seen in sectioned tissue.
How are smooth muscle cells shaped?
They are elongated, spindle-shaped with tapered ends.
Where is the nucleus located in smooth muscle cells?
In the widest part of the cell at the central region.
Why are nuclei not always visible in all sectioned smooth muscle cells?
Due to the staggered arrangement of the cells.
How are smooth muscle fibers arranged in tissue?
In extensive sheets, a few to many layers thick.
Describe the contraction characteristics of smooth muscle.
Slow to contract, with sustained contraction that resists fatigue.
What factors influence smooth muscle contraction?
Calcium ions, neuronal stimulation, and hormones.
How does the shape of skeletal muscle fibers compare to smooth muscle fibers?
Skeletal muscle fibers are elongated but slightly tapered or blunt at the ends.
How many nuclei are found in skeletal muscle fibers, and where are they located?
They are multinucleated, with nuclei located at the periphery of the cells.
How are skeletal muscle fibers arranged within a muscle?
In an unbranched, parallel array, separated by loose connective tissue with blood vessels and nerves.
What separates the skeletal muscle fibers from the surrounding connective tissue?
The basal lamina
What are the “fields of Cohnheim” seen in cross-section of skeletal muscle?
Clumps of myofibrils appearing as acidophilic dots.
Explain the positioning of actin and myosin filaments in a relaxed muscle.
In a relaxed muscle, actin filaments extend from the Z band toward the middle of the sarcomere, stopping before reaching the H band.
Myosin filaments are located in the middle part of the sarcomere, extending toward the ends but not reaching them.
Why do the H and I bands appear pale in a relaxed muscle?
The H and I bands appear pale because the H band lacks actin filaments, and the I band lacks myosin filaments, creating a lighter area.
What causes the dark appearance of the A band in a relaxed muscle?
The A band appears dark due to the overlap of both actin and myosin filaments in that region.
Describe the role of the M line in the sarcomere.
The M line bisects the H band and is composed of myomesin and C proteins. It helps to maintain the structural integrity of the sarcomere
What happens to the Z disks during muscle contraction according to Huxley’s sliding filament model?
During contraction, the actin filaments slide in between the myosin filaments, pulling the Z disks closer together, shortening the sarcomere.
Huxley’s Sliding Filament Model:
According to Huxley’s model, muscle contraction occurs when myosin filaments pull actin filaments toward the center of the sarcomere. This sliding motion shortens the sarcomere, pulling the Z disks closer together and causing the muscle to contract.
Role of Desmin and Vimentin in Myofibril Structure:
Desmin and vimentin are intermediate filaments that hold myofibrils in register with one another by securing the Z disks of neighboring myofibrils to each other.
Structural Proteins That Contribute to the Organization of Myofibrils:
• Dystrophin: Binds actin filaments and attaches myofibril bundles to the cytoplasmic side of sarcolemma.
• α-Actinin: Holds thin filaments in place and is part of the Z disk that binds thin filaments in parallel array.
• Titin: Connects myosin filaments to the Z disk (providing structural support).
• Nebulin: Connects actin filaments to the Z disk (helping maintain actin alignment)
Movement of Myosin Cross-Bridges and Energy Source for Muscle Contraction:
Myosin cross-bridges repeatedly attach, detach, and reattach to new sites along the actin filaments.
The energy for this movement is provided by the breakdown of ATP into ADP that is used for contraction process.
Changes in Actin Filaments and Z Disks During Full Muscle Contraction:
During full contraction, the free ends of the actin filaments meet or even overlap at the center of the sarcomere. This movement pulls the Z disks closer together, shortening the sarcomere and causing the muscle to contract.
The triad in muscle cells consist of? What is its function?
A triad consists of two terminal cisterns and one transverse tubule. The function of the triad is to transmit the action potential from the transverse tubules to the sarcoplasmic reticulum, leading to the release of calcium ions for muscle contraction.
What is the structure of the sarcoplasmic reticulum in muscle fibers?
The sarcoplasmic reticulum is an extensive network of cisterns and tubules (sarcotubules) found among and on the myofibrillar units. At specific locations, these tubules merge to form terminal cisterns, which are separated by transverse tubules.
What organelles are found in the sarcoplasm?
The organelles found in the sarcoplasm are:
• Mitochondria
• A system of transverse tubules (extensions of the sarcolemma)
• Smooth endoplasmic reticulum (sarcoplasmic reticulum)
• Golgi apparatus
• Ribosomes
How do transverse tubules contribute to muscle contraction?
The transverse tubules carry the action potential to the cisternae of the sarcoplasmic reticulum. This results in the opening of calcium channels in the membranes of the cisternae, which leads to the release of calcium ions to adjacent myofibrils. The calcium ions bind to troponin C, initiating contraction.
What are the transverse tubules, and how do they connect to the sarcolemma?
The transverse tubules are slender invaginations of the sarcolemma that extend deep into the muscle fiber. They form part of the tubular system that connects the action potential from the cell membrane to the interior of the muscle cell.
What are the structural differences between cardiac muscle and skeletal muscle?
Cardiac muscle fibers are branched, whereas skeletal muscle fibers are long and unbranched.
What is the perinuclear halo, and where is it found in cardiac muscle cells?
The perinuclear halo is a pale-staining cytoplasmic region surrounding the centrally located nucleus in cardiac muscle cells.
How does the connective tissue in cardiac muscle differ from that in skeletal muscle?
The connective tissue surrounding each muscle fiber is more prominent in cardiac muscle compared to skeletal muscle.
What is the function of intercalated disks in cardiac muscle, and what are their components?
Intercalated disks allow for end-to-end contact between cardiac muscle fibers. They consist of fasciae adherentes, desmosomes, and gap junctions, which help in cell adhesion and communication.
What do cardiac muscle cells have to meet their high metabolic demands?
Cardiac muscle cells have abundant mitochondria, an extensive vascular supply, and large quantities of myoglobin to meet their high metabolic demands.
What is hypertrophy in cardiac muscle cells, and how does it relate to the heart’s response to increased workload?
Hypertrophy refers to the increase in size of cardiac muscle cells. It is one of the ways the heart adapts to increased workload, such as during growth or in response to a higher demand for blood circulation.
What are Purkinje fibers, and what is their function?
Purkinje fibers are specialized cardiac muscle cells modified to conduct impulses. They conduct electrical signals from the A-V node through the interventricular septum to the ventricles.
What are Purkinje fibers, and what is their function?
Purkinje fibers are specialized cardiac muscle cells modified to conduct impulses. They conduct electrical signals from the A-V node through the interventricular septum to the ventricles.
How do Purkinje fibers differ from ordinary cardiac muscle cells in structure?
Purkinje fibers are larger than ordinary cardiac muscle cells and have abundant, pale-staining sarcoplasm with few myofibrils located at the periphery. In longitudinal section, they appear as swollen cells with scattered myofibrils.
How does smooth muscle regenerate after injury?
Smooth muscle retains its mitotic ability and can regenerate by mitosis of existing muscle cells or through differentiation of pericytes into smooth muscle cells. For example, the pregnant uterus undergoes both hypertrophy and hyperplasia.
How does skeletal muscle regenerate after injury?
Skeletal muscle cells cannot undergo mitosis. Instead, regeneration occurs through satellite cells, which can divide (hyperplasia) or fuse with existing muscle fibers, increasing muscle mass during hypertrophy.
How does cardiac muscle repair itself after injury?
Cardiac muscle does not regenerate. Damaged muscle tissue is replaced by scar tissue formed by invading fibroblasts.
