A&P 1 Study Module ~ 9.1-9.5

In skeletal muscle fibers, a "triad" consists of which of the following? A pair of transverse tubules plus a terminal cisternae A pair of terminal cisternae plus a transverse tubule Two I bands plus one Z line Two Z lines plus one M line

A pair of terminal cisternae plus a transverse tubule (The combination of a pair of terminal cisternae plus a transverse tubule is known as a triad. Each I band, which contains thin filaments but no thick filaments, extends from the A band of one sarcomere to the A band of the next. Z lines mark the boundary between adjacent sarcomeres.)

Which is false regarding myoblasts? All of the myoblasts in an individual will eventually fuse with developing muscle fibers. Each nucleus in a skeletal muscle fiber represents the contribution of a single myoblast. The fusion of myoblasts results in multinucleated cells. Unfused myoblasts may remain in the endomysium of adult skeletal muscle.

All of the myoblasts in an individual will eventually fuse with developing muscle fibers. (All of the myoblasts in an individual DO NOT!!! eventually fuse with developing muscle fibers. Some myoblasts do not fuse with developing muscle fibers. These unfused cells remain in the endomysium of adult skeletal muscle tissue as myosatellite cells. Each nucleus in a skeletal muscle fiber represents the contribution of a single myoblast. During development, groups of embryonic cells called myoblasts fuse, forming multinucleate cells. These large cells then develop into distinctive skeletal muscle fibers.)

feature of a sarcomere? ANSWER Lighter region that contains thick filaments, but no thin filaments Thin filaments are interspersed among the thick filaments Contains thin filaments, but no thick filaments Dense region that contains thick filaments Connects the central portion of each thick filament

Connects the central portion of each thick filament

Which of the following is the correct description of an A band, a structural feature of a sarcomere? Connects the central portion of each thick filament Contains thin filaments, but no thick filaments Thin filaments are interspersed among the thick filaments Lighter region that contains thick filaments, but no thin filaments Dense region that contains thick filaments

Dense region that contains thick filaments (The A band is the dense region of the sarcomere that contains thick filaments. In a resting sarcomere, the H band is a lighter region on either side of the M line, which contains thick filaments, but no thin filaments. Each I band, which contains thin filaments but no thick filaments. The M line connects the central portion of each thick filament. In the zone of overlap, thin filaments are interspersed among the thick filaments.)

Which portion of a thick filament contains two globular protein subunits, and interacts with the thin filaments during muscle contraction? Myosin tails Titins Free heads Nebulin

Free heads (The free head has two globular protein subunits. During contraction, the myosin heads interact with the thin filaments. Each long myosin tail is bound to other myosin molecules within the thick filament. Each thick filament has a core of titin. From either end of the thick filament, a strand of titin continues across the I band to the Z line on that side. Nebulin is a large protein that extends along the F-actin strand in the cleft between the rows of G-actin molecules. It holds the F-actin strand together. It is part of a thin filament.)

What is the region of a sarcomere that contains only thick filaments called? I band A band H band Zone of overlap

H band (The H band of a sarcomere contains thick filaments, but no thin filaments. Each I band contains thin filaments but no thick filaments. In the zone of overlap, thin filaments are arranged in a 6:1 ratio around each thick filament. The A band is the dense region of the sarcomere that contains thick filaments. It contains the zones of overlap and the H band.)

Which of the following is characterized as extending from the A band of one sarcomere to the A band of the next? ANSWER Z line H band I band M line

I band Each I band, which contains thin filaments but no thick filaments, extends from the A band of one sarcomere to the A band of the next. The M line connects the central portion of each thick filament. In a resting sarcomere, the H band is a lighter region on either side of the M line. The H band contains thick filaments, but no thin filaments. Z lines mark the boundary between adjacent sarcomeres.

All of the following are true of the plasma membranes of skeletal muscle fibers, except __________. K+ leak channels in the membrane are responsible for maintaining the cell's resting potential there is very little diffusion of Cl- ions across the plasma membrane Na+ and K+ ions require specific leak channels to cross the plasma membrane proteins that cannot cross the membrane are the main contributors of negative charges in the cell plasma membranes are selectively permeable

K+ leak channels in the membrane are responsible for maintaining the cell's resting potential (K+ leak channels in the membrane ARE NOT!!! responsible for maintaining the cell's resting potential. Sodium-potassium ion pumps constantly export 3 Na+ from the cell and import 2 K+ to maintain the cell's resting potential. Although there is an excess of negatively charged chloride ions (Cl-) in the ECF, little diffusion of these ions occurs across the plasma membrane. The main contributors of negative charges within a cell are proteins that cannot cross the plasma membrane. Plasma membranes are selectively permeable, and the cytosol and extracellular fluid (ECF) differ in composition. Na+ and K+ require ion-specific "leak" membrane channels to cross the plasma membrane.)

Which of the following is the correct description of T tubules, microscopic structures in a typical skeletal muscle? ANSWER Tubular network around each individual myofibril Cylindrical structures 1-2 µm in diameter and as long as the entire cell Repeating functional units Narrow tubes that form passageways through the muscle fiber Strands composed primarily of actin or myosin

Narrow tubes that form passageways through the muscle fiber

Which of the following is the correct description of the protein, nebulin? ANSWER A double-stranded protein that covers the active sites on G-actin Protein molecule consisting of three globular subunits Primary protein component of thick filaments Primary protein component of thin filaments Protein that holds the F-actin strand together

Protein that holds the F-actin strand together

All of the following are true of the resting potentials of neurons and skeletal muscle cells, except __________. ANSWER the resting potential of a skeletal muscle fiber is about -85 mV the inside surface of the plasma membrane has a slight positive charge, compared to the outside surface there is an excess of sodium (Na+) outside the cell there is an excess of potassium (K+) inside the cell

The inside surface of the plasma membrane DOES NOT!!! have a slight positive charge, compared to the outside surface. For a resting cell, the inside surface of its plasma membrane has a slight negative charge with respect to its outside surface. In undisturbed neurons and skeletal muscle fibers, typical resting potentials are about -70 mV and -85 mV, respectively. There is an excess of sodium (Na+) outside of a cell (in the ECF) and an excess of potassium (K+) inside a cell (in the cytosol).

Strands of which of the following cover the active sites on G-actin? Troponin Tropomyosin Myosin Titin

Tropomyosin (Strands of tropomyosin cover the active sites on G-actin and prevent actin-myosin interaction. A tropomyosin molecule is a double-stranded protein that is bound to one molecule of troponin midway along its length. A troponin molecule consists of three globular subunits. One subunit binds to tropomyosin, locking them together as a troponin-tropomyosin complex. A second subunit binds to one G-actin, holding the troponin-tropomyosin complex in position. And the third subunit has a receptor that binds two calcium ions. Each thick filament has a core of titin. From either end of the thick filament, a strand of titin continues across the I band to the Z line on that side. Thick filaments are 10-12 nm in diameter and 1.6 µm long. A thick filament contains about 300 myosin molecules, each made up of a pair of myosin subunits twisted around one another.)

How is repolarization accomplished during an action potential in a neuron or skeletal muscle fiber? ANSWER A small increase in sodium ion membrane permeability occurs. Voltage-gated potassium channels open and potassium ions move out of the cell. Voltage-gated potassium channels close. Voltage-gated sodium channels open and sodium ions move into the cell.

Voltage-gated potassium channels open and potassium ions move out of the cell. (Repolarization accomplished during an action potential in a neuron or skeletal muscle fiber when voltage-gated potassium channels open and potassium ions move out of the cell. Here are the steps: 1. A charge reversal begins with a small increase in sodium ion membrane permeability up to a set threshold (-55 mV in neurons). 2. Once the threshold is reached, voltage-gated Na+ channels open and positively charged sodium ions rush into the cell. The membrane potential becomes positive and the cell is said to be depolarized. 3. The depolarization peaks at a membrane potential of +30 mV, at which point the voltage-gated Na+ channels close and voltage-gated K+ channels open. As potassium ions move out of the cell, repolarization (returning to the polarized state) begins. 4. Rapid repolarization continues until the resting potential is reached, when the voltage-gated K+ channels begin closing.)

When a skeletal muscle fiber contracts, __________. ANSWER the H bands and I bands get larger the width of the A band remains constant the zones of overlap get smaller the Z lines move apart

When a skeletal muscle fiber contracts, thin filaments slide past the thick filaments. In this process, (1) the H bands and I bands get smaller, (2) the zones of overlap get larger, (3) the Z lines move closer together, and (4) the width of the A band remains constant.

The two muscle proteins that "slide across" each other as described by the sliding filament model are __________. ANSWER tropomyosin and troponin nebulin and titin actin and myosin actin and troponin

actin and myosin (The muscle proteins that slide past each other in the sliding filament model are actin (the main component of thin filaments) and myosin (the main component of thick filaments). Nebulin is a large protein that extends along the F-actin strand in the cleft between the rows of G-actin molecules. It holds the F-actin strand together. Each thick filament has a core of titin. From either end of the thick filament, a strand of titin continues across the I band to the Z line on that side. Strands of tropomyosin cover the active sites on G-actin and prevent actin-myosin interaction. A tropomyosin molecule is a double-stranded protein that is bound to one molecule of troponin midway along its length. A troponin molecule consists of three globular subunits. One subunit binds to tropomyosin, locking them together as a troponin-tropomyosin complex. A second subunit binds to one G-actin, holding the troponin-tropomyosin complex in position. The third subunit has a receptor that binds two calcium ions.)

A broad sheet of connective tissue that provides muscle attachment over a broad area that may involve more than one bone is called a(n) __________. fascicle aponeurosis tendon perimysium

aponeurosis (At the ends of a skeletal muscle, collagen fibers of the connective tis sue layersmerge to form either a bundle known as a tendon, or a broad sheet called an aponeurosis. An aponeurosis provides attachment over a broad area that may involve more than one bone. A tendon attaches the muscle to a specific point on a bone. A muscle fascicle is a bundle of muscle fibers. The perimysium is a fibrous layer that divides the skeletal muscle into a series of compartments.)

The fibrous outer covering of a muscle that contains the muscle and allows it to slide over adjacent structures is the __________. ANSWER epimysium perimysium aponeurosis endomysium

epimysium

Which type of molecule on a thin filament contains an active site for myosin to bind to? Troponin F-actin G-actin Nebulin Tropomyosin

g-actin (Each G-actin molecule contains an active site to which myosin can bind. Nebulin is a large protein that extends along the F-actin strand in the cleft between the rows of G-actin molecules. It holds the F-actin strand together. F-actin (filamentous actin) is a twisted strand composed of two rows of 300-400 individual molecules of G-actin (globular actin). A troponin molecule consists of three globular subunits. One subunit binds to tropomyosin, locking them together as a troponin-tropomyosin complex. A second subunit binds to one G-actin, holding the troponin-tropomyosin complex in position. And the third subunit has a receptor that binds two calcium ions. Strands of tropomyosin cover the active sites on G-actin and prevent actin-myosin interaction.)

The endomysium surrounds __________. ANSWER skeletal muscles muscle fibers aponeuroses muscle fascicles

muscle fibers (The endomysium is a thin layer of areolar connective tissue that surrounds each muscle fiber. The epimysium is a dense layer of collagen fibers that surrounds the entire muscle. A muscle fascicle is a bundle of muscle fibers. The fibrous perimysium layer separates the fascicles from each other. At the ends of a skeletal muscle, collagen fibers of the connective tissue layers merge to form either a bundle known as a tendon, or a broad sheet called an aponeurosis.)

All of the following are functions of skeletal muscle tissue, except __________. production of skeletal movements maintenance of body temperature maintenance of posture and body position production of blood cells guarding entrances and exits of the body

production of blood cells (Skeletal muscle tissue DOES NOT!!! produce blood cells; the bones of the skeleton produce blood cells. Tension in skeletal muscles stabilizes joints to help maintain body posture—for example, holding your head still when you read a book, or balancing your body weight above your feet when you walk. Muscle contractions require energy; whenever energy is used in the body, some of it is converted to heat. The heat released by working muscles keeps body temperature in the range required for normal functioning. Skeletal muscles (sphincters) encircle (guard) the openings of the digestive and urinary tracts. They provide voluntary control over swallowing, defecation, and urination. Skeletal muscle contractions pull on tendons and move the bones.)

Within a sarcomere, each thick filament has a core of __________. actin troponin titin tropomyosin

titin (Within a sarcomere, each thick filament has a core of titin. Myofibrils consist of bundles of protein filaments called myofilaments. The most abundant myofilaments are thin filaments composed primarily of actin, and thick filaments composed primarily of myosin. Each thick filament has a core of titin. Strands of Tropomyosin cover the active sites on G-actin and prevent actin-myosin interaction. A tropomyosin molecule is a double-stranded protein that is bound to one molecule of troponin midway along its length.)