Mcat Biology (Chapter 11)

skeletal muscle, smooth muscle and cardiac muscle

involved in support and movement, propulsion of blood in the venous system and thermoregulation; appears striated, is under voluntary (somatic) control, is polynucleated and can divide into red (slow-twitch) fibers that carry out oxidative phosphorylation and white (fast-twitch) fibers that rely on anaerobic metabolism

in the respiratory, reproductive, cardiovascular and digestive systems; appears nonstriated, is under involuntary (autonomic) control, and is uninucleated; it can display myogenic activity, or contraction without neural input

comprises the contractile tissue of the heart; it appeares striated, is under involuntary (autonomic) control, and is uninucleated (sometimes binucleated); it can also display myogenic activity; cells are connected with intercalated discs that contain gap junctions

the basic contractile unit of striated muscle; made of thick (myosin) and thin (actin) filaments

found on the thin filament and regulate actin-myosin interactions

it can be divided into different lines, zones and bands:

- the boundaries of each sarcomere are defined by Z-lines

- the M-line is located in the center of the sarcomere

- the I-band contains only thin filaments

- the H-zone consists of only thick filaments

- the A-band contains the thick filaments in their entirety; it is the only part of the sarcomere that maintains a constant size during contraction

sarcomeres attach end-to-end to become this; surround by the sarcoplasmic reticulum, a calcium-containing modified endoplasmic reticulum

contains many myofibrils; its cell membrane is known as the sarcolemma

connected to the sarcolemma and oriented perpendicularly to the myofibrils, allowing the incoming signal to reach all parts of the muscle

begins at the neuromuscular junction, where the motor neuron releases acetylcholine that binds to receptors on the sarcolemma, causing depolarization

this depolarization spreads down the sarcolemma to the T-tubules, triggering the release of calcium ions

calcium binds to troponin, causing a shift in tropomyosin and exposure of the myosin-binding sites on the actin thin filament

shortening of the sarcomere occurs as myosin heads bind to the exposed sites on actin, forming cross bridges and pulling the actin filament along the thick filament, resulting in contraction; this is known as the sliding filament model

occurs when acetylcholine is degraded by acetylcholinesterase, terminating the signal and allowing calcium to be brought back into the SR; ATP binds to the myosin head, allowing it to release from actin

and all-or-nothing response that muscle exhibit

addition of multiple simple twitches before the muscle has an opportunity to fully relax

simple twitches that occur so frequently as to not let the muscle relax at all can lead to this; a more prolonged and stronger contraction

difference between the amount of oxygen needed and the amount present; muscle cells have additional energy reserves to reduce this and forestall fatigue

can transfer a phosphate group to ADP, forming ATP

a heme-containing protein that is a muscular oxygen reserve

internal skeletons like those in humans

external skeletons like those in arthropods

axial and appendicular skeletons

consists of structures in the midline such as the skull vertebral column, ribcage and hyoid bone

consists of the bones of the limbs, the pectoral girdle and the pelvis

derived from embryonic mesoderm and includes both compact and spongy (cancellous) types

provides strength and is dense

has a lattice-like structure consisting of bony spicules known as trabeculae; the cavities are filled with bone marrow

contain shafts called diaphyses that flare to form metaphyses and that terminate in epiphyses

contains an epiphyseal (growth) plate that causes linear growth of the bone

a layer of connective tissue which surrounds the bone

attach bones to muscles

attach bones to each other

has both organic components, like collagen, glycoproteins and other peptides, and inorganic components, like hydroxyapatite

bone is organized into concentric rings called lamellae around a central Haversian or Volkmann's canal; this structural unit is called an osteon or Haversian system

located between lamellar rings; this is where osteocytes reside

connect osteocytes to allow for nutrient and waste transfer

carry out bone remodeling by building bone

carry out bone remodeling by resorbing bone

increases resorption of bone, increasing calcium and phosphate concentrations in the blood

also increases resorption of bone, leading to increased turnover and, subsequently, the production of stronger bone

increases bone formation, decreasing calcium concentrations in the blood

secrete cartilage, a firm elastic material; its matrix is called chondrin

usually found in areas that require more flexibility or cushioning; avascular and is not innervated

in fetal life this is how bone forms from cartilage

some bones, especially those of the skull, form directly from undifferentiated tissue (mesenchyme) through this process

immovable or movable

fused together to form sutures or similar fibrous joints

usually strengthened by ligaments and contain a synovial capsule

secreted by the synovium; aids in motion by lubricating the joint

coats each bone in the joint to aid in movement and provide cushioning

muscles that serve opposite functions; when one muscle contracts, the other lengthens