Lec 14 - Muscle Tissue

Question 1

What is the unit of structure in muscle tissue?

Answer 1

muscle cell or muscle fiber

Question 2

In muscle tissue, the term “muscle” is used to describe which specific structure?

Answer 2

the entire cell

Question 3

What is a key characteristic of muscle fibers?

Answer 3

Contractility is an especially well-developed characteristic.

Question 4

Muscle tissue makes up the majority of what in an organism?

Answer 4

The flesh or meat

Question 5

Muscle fibers are covered by a?

Answer 5

Sarcolemma (combined plasmalemma and basal lamina) and fine reticular fibers

Question 6

Explain the role of muscle in tubular organs.

Answer 6

It serves as a primary wall element.

Question 7

Name the proteins found in myofilaments.

Answer 7

Actin and myosin.

Question 8

Describe the Greek origin of the word “sarcos” in muscle tissue.

Answer 8

It means “flesh” or “meat.”

Question 9

Group of Myofibrils

Answer 9

Myofilament

Question 10

Sarcoplasm (Cytoplasm) contains?

Answer 10

Typical organelles and contractile elements

Question 11

How is muscle functionally and structurally classified?

Answer 11

Functionally, muscle can be voluntary or involuntary.

Structurally, muscle can be smooth (non-striated) or striated

Question 12

What are the structural differences between smooth, skeletal, and cardiac muscle?

Answer 12

Smooth muscle is non-striated.
Skeletal muscle is striated.
Cardiac muscle is striated.

Question 13

What shape are smooth muscle cells and how are they arranged?

Answer 13

Elongated, spindle-shaped cells with tapered ends, arranged in a staggered pattern.

Question 14

Where is the nucleus located in smooth muscle cells?

Answer 14

The nucleus is located in the central region of the widest part of the cell.

Question 15

How are smooth muscle cells arranged in terms of layers?

Answer 15

They are arranged in extensive sheets, a few to many layers thick.

Question 16

What type of contraction characterizes smooth muscle?

Answer 16

Smooth muscle has slow, sustained contractions that are resistant to fatigue.

Question 17

What factors influence the contraction of smooth muscle?

Answer 17

Contraction is influenced by calcium ions, neuronal stimulation, and hormones.

Question 18

Why might nuclei not be visible in all smooth muscle cells?

Answer 18

Due to the staggered arrangement of the cells, not all nuclei are seen in sectioned tissue.

Question 20

How are smooth muscle cells shaped?

Answer 20

They are elongated, spindle-shaped with tapered ends.

Question 21

Where is the nucleus located in smooth muscle cells?

Answer 21

In the widest part of the cell at the central region.

Question 22

Why are nuclei not always visible in all sectioned smooth muscle cells?

Answer 22

Due to the staggered arrangement of the cells.

Question 23

How are smooth muscle fibers arranged in tissue?

Answer 23

In extensive sheets, a few to many layers thick.

Question 24

Describe the contraction characteristics of smooth muscle.

Answer 24

Slow to contract, with sustained contraction that resists fatigue.

Question 25

What factors influence smooth muscle contraction?

Answer 25

Calcium ions, neuronal stimulation, and hormones.

Question 26

How does the shape of skeletal muscle fibers compare to smooth muscle fibers?

Answer 26

Skeletal muscle fibers are elongated but slightly tapered or blunt at the ends.

Question 27

How many nuclei are found in skeletal muscle fibers, and where are they located?

Answer 27

They are multinucleated, with nuclei located at the periphery of the cells.

Question 29

How are skeletal muscle fibers arranged within a muscle?

Answer 29

In an unbranched, parallel array, separated by loose connective tissue with blood vessels and nerves.

Question 30

What separates the skeletal muscle fibers from the surrounding connective tissue?

Answer 30

The basal lamina

Question 31

What are the “fields of Cohnheim” seen in cross-section of skeletal muscle?

Answer 31

Clumps of myofibrils appearing as acidophilic dots.

Question 32

Explain the positioning of actin and myosin filaments in a relaxed muscle.

Answer 32

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.

Question 33

Why do the H and I bands appear pale in a relaxed muscle?

Answer 33

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.

Question 34

What causes the dark appearance of the A band in a relaxed muscle?

Answer 34

The A band appears dark due to the overlap of both actin and myosin filaments in that region.

Question 35

Describe the role of the M line in the sarcomere.

Answer 35

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

Question 36

What happens to the Z disks during muscle contraction according to Huxley’s sliding filament model?

Answer 36

During contraction, the actin filaments slide in between the myosin filaments, pulling the Z disks closer together, shortening the sarcomere.

Question 37

Huxley’s Sliding Filament Model:

Answer 37

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.

Question 38

Role of Desmin and Vimentin in Myofibril Structure:

Answer 38

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.

Question 39

Structural Proteins That Contribute to the Organization of Myofibrils:

Answer 39

• 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)

Question 40

Movement of Myosin Cross-Bridges and Energy Source for Muscle Contraction:

Answer 40

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.

Question 41

Changes in Actin Filaments and Z Disks During Full Muscle Contraction:

Answer 41

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.

Question 42

The triad in muscle cells consist of? What is its function?

Answer 42

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.

Question 43

What is the structure of the sarcoplasmic reticulum in muscle fibers?

Answer 43

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.

Question 44

What organelles are found in the sarcoplasm?

Answer 44

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

Question 44

How do transverse tubules contribute to muscle contraction?

Answer 44

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.

Question 45

What are the transverse tubules, and how do they connect to the sarcolemma?

Answer 45

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.

Question 46

What are the structural differences between cardiac muscle and skeletal muscle?

Answer 46

Cardiac muscle fibers are branched, whereas skeletal muscle fibers are long and unbranched.

Question 47

What is the perinuclear halo, and where is it found in cardiac muscle cells?

Answer 47

The perinuclear halo is a pale-staining cytoplasmic region surrounding the centrally located nucleus in cardiac muscle cells.

Question 48

How does the connective tissue in cardiac muscle differ from that in skeletal muscle?

Answer 48

The connective tissue surrounding each muscle fiber is more prominent in cardiac muscle compared to skeletal muscle.

Question 49

What is the function of intercalated disks in cardiac muscle, and what are their components?

Answer 49

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.

Question 50

What do cardiac muscle cells have to meet their high metabolic demands?

Answer 50

Cardiac muscle cells have abundant mitochondria, an extensive vascular supply, and large quantities of myoglobin to meet their high metabolic demands.

Question 51

What is hypertrophy in cardiac muscle cells, and how does it relate to the heart’s response to increased workload?

Answer 51

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.

Question 52

What are Purkinje fibers, and what is their function?

Answer 52

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.

Question 53

What are Purkinje fibers, and what is their function?

Answer 53

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.

Question 54

How do Purkinje fibers differ from ordinary cardiac muscle cells in structure?

Answer 54

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.

Question 55

How does smooth muscle regenerate after injury?

Answer 55

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.

Question 56

How does skeletal muscle regenerate after injury?

Answer 56

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.

Question 57

How does cardiac muscle repair itself after injury?

Answer 57

Cardiac muscle does not regenerate. Damaged muscle tissue is replaced by scar tissue formed by invading fibroblasts.