How do intracellular calcium levels decrease in smooth muscle relaxation?
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By SERCA or calcium being pumped out of the cell.
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How do intracellular calcium levels decrease in smooth muscle relaxation?
By SERCA or calcium being pumped out of the cell.
What role does calmodulin play in smooth muscle relaxation?
Calmodulin is released from a complex with calcium.
What is the function of myosin phosphatase in smooth muscle relaxation?
It removes phosphate from the myosin head.
How does myosin detach from actin in smooth muscle?
Very slowly.
How is smooth muscle regulated by the nervous system?
Through autonomic nerve fibers that secrete neurotransmitters from varicosities.
What connects unitary (visceral) smooth muscle cells?
Gap junctions, allowing rapid depolarization to spread.
How is multiunit smooth muscle stimulated?
Each cell is stimulated independently by neurotransmitters released from autonomic nerve varicosities.
What is a key difference between smooth muscle and skeletal muscle in terms of neuromuscular junctions?
Smooth muscle has no neuromuscular junctions like in skeletal muscle.
What is the role of sarcoplasmic endoplasmic reticulum calcium ATPase (SERCA) in skeletal muscle?
It transports two molecules of Ca²⁺ into its lumen for each molecule of ATP hydrolyzed.
Where is SERCA most abundantly found in skeletal muscle?
In the sarcoplasmic reticulum (SR).
What is the mechanism of muscle relaxation involving Ca²⁺?
Ca²⁺ moves back into the sarcoplasmic reticulum by active transport, requiring ATP.
What happens to sarcomeres during muscle contraction?
Sarcomeres shorten due to actin myofilaments sliding over myosin.
What happens to the troponin-tropomyosin complex during muscle relaxation?
Ca²⁺ moves away from the complex, allowing tropomyosin to block actin binding sites for myosin.
What is the role of ATPase enzymes in muscle contraction?
They break down ATP, releasing energy used to bend the hinge region of the myosin molecule.
What is the periosteum of the groove transformed into?
The endosteum of the tunnel.
What is a muscle twitch?
A muscle contraction in response to a stimulus that causes action potential in one or more muscle fibers.
What type of receptor does Isoproterenol act on?
β-adrenergic receptor.
What is the function of titin in muscle tissue?
Titin filaments provide extensibility and elasticity to muscles.
What do fibroblasts produce?
Collagen and granulation tissue.
What type of growth do osteoblasts from the endosteum contribute to?
Appositional growth.
What are the three phases of a muscle twitch?
Lag (latent), contraction, and relaxation.
What effect does Isoproterenol have on intracellular Ca2+ levels?
It increases the amount of intracellular Ca2+.
What is a motor unit?
A single motor neuron and all muscle fibers innervated by it.
Do actin and myosin change length during contraction?
No, actin and myosin do not change length during contraction.
What is the major function of the heart?
It is the major source of movement of blood.
What are the two layers of the periosteum?
The outer fibrous layer and the inner layer of bone cells.
What do chondroblasts produce?
Cartilage within the collagen.
What is formed as a result of appositional growth by osteoblasts?
A new concentric lamella.
How does Isoproterenol affect the force of contraction?
It results in a higher force of contraction.
How do motor units differ in large muscles compared to small muscles?
Large muscles have motor units with many muscle fibers, while small muscles have motor units with few muscle fibers.
What is the function of Nebulin in the thin filament?
To serve as a ruler to gauge the length of the F-actin filament during assembly.
What is the process of bone formation by osteoblasts called?
Ossification.
What is the role of osteoblasts in bone formation?
Osteoblasts invade and form new bone.
What completes the formation of the osteon?
The production of additional concentric lamellae that fill in the tunnel.
What causes sarcomeres to lengthen during relaxation?
External forces, such as the contraction of antagonistic muscles.
What types of cells are found in the inner layer of the periosteum?
Osteoblasts, osteoclasts, and osteochondral progenitor cells.
How is the heart controlled?
Involuntarily by the endocrine and autonomic nervous systems.
How does the cycling of myosin cross bridges in smooth muscle compare to skeletal muscle?
Myosin cross bridges cycle more slowly in smooth muscle.
What is the molecular weight range of Nebulin?
600 - 900 kDa.
What is the Frank Starling Law?
Stretching of the heart increases the force of contraction.
How do osteoblasts communicate with each other?
Through gap junctions.
What does the all-or-none law state regarding muscle fibers?
Muscle fibers contract with equal force in response to each action potential.
What stabilizes the two pieces of bone during healing?
The bone/cartilage collar.
What hormone is secreted by the parathyroid gland?
Parathyroid hormone (PTH).
What stimulates the release of PTH?
A reduction in blood calcium levels.
What is one direct effect of PTH?
Activates osteoclasts, increasing their number and preventing inhibition of their formation.
What is the structure of skeletal muscle fibers?
They have several nuclei just inside the sarcolemma.
What are Sharpey's fibers?
Periosteal fibers that penetrate into the bone to strengthen tendon attachment.
What factors determine the size and shape of a bone?
Genetics, nutrition, and hormones.
What is a synapse in the context of the neuromuscular junction?
It is the axon terminal resting in an invagination of the sarcolemma.
What is a key difference in myosin attachment to actin between smooth and skeletal muscle?
Myosin remains attached to actin longer in smooth muscle.
What are the main components of skeletal muscle?
Muscle cells (fibers), connective tissue, blood vessels, and nerves.
What type of muscle fibers are involved in sprinting and walking?
Type IIb Fast-Twitch Glycolytic Fibers.
What happens with a sub-threshold stimulus?
There is no action potential and no contraction.
What are the components of myosin structure?
Two heavy chains and four light chains.
What happens during callus ossification?
Callus is replaced by woven, spongy bone.
What causes the increased force of contraction according to the Frank Starling Law?
Increased sensitivity of contraction to Ca2+ and closer interaction between actin and myosin.
What are osteocytes?
Mature bone cells that are stellate and surrounded by matrix.
What are myofibrils?
They are packed within the cytoplasm (sarcoplasm) of muscle fibers.
What can a lack of calcium, protein, and other nutrients during growth lead to?
Smaller bones.
What does the endosteum line?
All internal spaces, including those in spongy bone.
What is the energy requirement for sustaining contraction in smooth muscle?
Smooth muscle requires less energy to sustain contraction.
What happens to bone when osteoclast activity increases due to PTH?
Bone is resorbed and calcium is released into the blood.
What occurs with a threshold stimulus?
An action potential occurs, leading to contraction.
What is the primary function of Type IIb fibers?
Short-term rapid and intense movement.
What is the structure of skeletal muscle fibers?
They are long, cylindrical, and multinucleated.
What is the process of bone remodeling?
Replacement of spongy bone and damaged material by compact bone.
How do the globular regions of myosin interact?
Each heavy chain interacts with two light chains.
What is the function of osteocytes in relation to the matrix?
They can make small amounts of matrix to maintain it.
What are the two types of myofilaments in skeletal muscle?
Thin (actin) and thick (myosin) myofilaments.
What happens to the ventricles when the heart receives a lot of blood?
The ventricles are stretched, resulting in an increased force of contraction.
Why is Vitamin D important for bone health?
It is necessary for the absorption of calcium from the intestines.
What forms the filamentous actin (F-actin) in thin filaments?
Globular actin (G-actin) molecules.
How does PTH affect calcium in the kidneys?
It stimulates the reabsorption of calcium from urine in the kidney tubules.
What is the structure of flat bones?
They have no diaphysis or epiphyses and consist of a sandwich of spongy bone between compact bone.
What gives skeletal muscle its striated appearance?
The light and dark banding.
What hormone does PTH promote the activation of?
Calcitriol.
What is the Treppe effect?
A graded response in muscle contractions due to multiple stimuli of the same strength.
How does the maximum force of contraction in smooth muscle compare to skeletal muscle?
The maximum force of contraction is usually greater in smooth muscle.
What happens when the stimulus is stronger than the threshold?
An action potential occurs, and contraction is equal to that with the threshold stimulus.
How does the diameter of skeletal muscle fibers vary?
They tend to be smaller in small muscles and larger in large muscles.
What are the characteristics of smooth muscle fibers?
Not striated, smaller than skeletal muscle fibers, spindle-shaped with a single central nucleus.
What is the major storage site for calcium in the body?
Bone.
What is the role of calcitriol?
It increases calcium absorption in the small intestine.
What role do cross-bridges and hinges play in muscle contraction?
They are important for contraction.
What is the role of tropomyosin in thin filaments?
It binds as dimers and winds along the groove of the F-actin double helix.
What are lacunae?
Spaces occupied by osteocyte cell bodies.
What is the primary structure of the diaphysis of a long bone?
Primarily compact bone.
What are sarcomeres?
Highly ordered repeating units of myofilaments, extending from Z disk to Z disk.
What is the function of calcitonin?
It lowers blood calcium by inhibiting osteoclast activity.
When does the Treppe effect occur?
In muscle that has rested for a prolonged period of time.
What is the epimysium?
Connective tissue that surrounds a whole muscle, encompassing many fascicles.
What is Duchenne Muscular Dystrophy (DMD) commonly identified in?
Children 3 years of age.
What is the primary function of osteoclasts?
Resorption of bone.
What role do calcium ions (Ca2+) play in the excitation-contraction coupling of smooth muscle?
Calcium ions are crucial for initiating contraction by binding with calmodulin.
How do short and irregular bones differ from long bones?
They have compact bone surrounding a spongy bone center and do not have diaphyses or elongated structures.
What is the length range of skeletal muscle fibers?
1 mm to 4 cm.
How is the strength of contraction graded?
It ranges from weak to strong depending on stimulus strength.
What does the prefix 'ARTHR-' refer to?
Joint.
What is the ATPase function of myosin?
It provides energy for muscle contraction.
What are the three subunits of the troponin complex?
Troponin T, Troponin I, and Troponin C.
What are canaliculi?
Canals occupied by osteocyte cell processes.
What is the epiphysis of a long bone primarily composed of?
Primarily spongy bone.
What is the function of the Z disk?
It serves as an attachment for actin myofilaments.
What hormones control blood calcium levels?
Parathyroid hormone (PTH), Calcitriol, and Calcitonin.
What is the role of caveolae in smooth muscle?
They are indentations in the sarcolemma that may act like T tubules.
What does 'CHONDR-' refer to?
Cartilage.
What is the rugose border in osteoclasts?
The area where the cell membrane borders bone and resorption occurs.
What does the perimysium do?
It is denser connective tissue surrounding a group of muscle fibers, known as a fasciculus.
What happens to the strength of contractions during the Treppe effect?
Each subsequent contraction is stronger than the previous until they all equal after a few stimuli.
From what do skeletal muscle fibers develop?
They develop from myoblasts.
What happens when calcium ions bind with calmodulin in smooth muscle?
The calcium-calmodulin complex activates myosin light chain kinase (MLCK).
What is Multiple Motor Unit Summation?
The process by which the strength of contraction is increased by recruiting more motor units.
What do both perforating and central canals contain?
Blood vessels.
What is the importance of myosin heads?
They can bind to active sites on actin molecules to form cross-bridges.
What does Troponin T bind to?
Tropomyosin.
How do nutrients transfer between osteocytes?
Nutrients diffuse through a tiny amount of liquid surrounding the cells and filling lacunae and canaliculi.
What replaces Z disks in smooth muscle?
Dense bodies, which have noncontractile intermediate filaments.
What gives skeletal muscle its striated appearance?
The arrangement of I bands, A bands, and H zones.
How does calcium enter and leave the bone?
Calcium enters when osteoblasts create new bone and leaves when osteoclasts break down bone.
What is the function of the epiphyseal plate?
It serves as the growth plate made of hyaline cartilage.
Why do contractions become stronger in the Treppe effect?
More Ca2+ remains in the sarcoplasm and is not all taken up into the sarcoplasmic reticulum.
How do osteoclasts contribute to bone resorption?
By pumping H+ ions across the membrane to form acid that eats away bone and releasing enzymes that digest bone.
What is the endomysium?
Loose connective tissue with reticular fibers that surrounds individual muscle fibers.
What gives skeletal muscle its striated appearance?
Light and dark banding.
What is the function of blood vessels in the canals?
To provide direct flow of nutrients through cell processes of osteoblasts.
What does Troponin I bind to?
Actin.
What occurs in the Zone of Proliferation?
New cartilage is produced as chondrocytes divide and form stacks of cells.
How are myosin heads attached to the rod portion?
By a hinge region that can bend.
What are precursors of hydroxyapatite stored in?
Vesicles, then released by exocytosis.
What is the result of myosin light chain kinase (MLCK) activation?
Myosin head is phosphorylated, allowing it to bind to actin and cause contraction.
What is required to initiate contractions in smooth muscle?
Calcium ions (Ca2+), which bind to calmodulin to regulate myosin kinase.
What does the strength of muscle contraction depend on?
Recruitment of motor units.
What are I bands?
Regions from Z disks to the ends of thick filaments.
What is muscular fascia?
A connective tissue sheet that holds muscles together and separates them into functional groups.
From what cells are osteoclasts derived?
Monocytes, which are formed from stem cells in red bone marrow.
How does increased temperature affect muscle contractions?
It makes muscle enzymes more efficient.
What happens at the epiphyseal line?
Bone stops growing in length.
What is the function of Troponin C?
It binds Ca²⁺ ions.
What happens in the Zone of Hypertrophy?
Chondrocytes mature and enlarge.
What enzyme causes relaxation in smooth muscle?
Myosin Phosphatase.
What surrounds the central canal in compact bone?
Concentric lamellae of bone.
What are the types of stimuli that affect muscle contraction?
Submaximal, maximal, and supramaximal stimuli.
What is the function of Type I skeletal muscle fibers?
Endurance; maintain posture; used in activities like marathon running.
What is the role of motor neurons in muscle contraction?
They stimulate muscle fibers to contract, with cell bodies located in the brain or spinal cord.
What is the H zone?
The region in the A band where actin and myosin do not overlap.
What does 'COST' refer to in medical terminology?
Rib.
What type of cells can mesenchymal stem cells become?
Chondroblasts or osteoblasts.
What type of marrow is found in the medullary cavity of children?
Red marrow.
How is the actin site involved in muscle contraction?
It can bind myosin during muscle contraction.
What type of bones in the skull have sinuses lined by mucous membranes?
Some flat and irregular bones.
What characterizes the Zone of Calcification?
The matrix is calcified, and chondrocytes die.
What initiates crossbridge formation in muscle contraction?
ATP binds to the myosin head, causing the dissociation of the actin-myosin complex.
What are the two types of smooth muscle?
Visceral (or unitary) smooth muscle and multi-unit smooth muscle.
What do lacunae and canaliculi contain?
Osteocytes and fluid.
What is tetanization in muscle contraction?
A state where successive contractions occur so rapidly that they fuse together, resulting in a smooth and continuous contraction.
What is Rib Costalgia?
Pain in the ribs.
What is the M line?
The middle of the H zone, holding delicate filaments.
What characterizes woven bone?
Collagen fibers that are randomly oriented.
How do axons connect to muscle fibers?
Axons branch so that each muscle fiber is innervated.
What are Type I skeletal muscle fibers also known as?
Slow-twitch oxidative fibers.
What is the neuromuscular junction (NMJ)?
The synapse between a motor neuron and a muscle fiber.
What replaces red marrow in the medullary cavity of adults?
Yellow marrow, except for proximal epiphyses of arm and thigh bones.
What happens to cartilage in the ossified bone?
The cartilage on the diaphyseal side of the plate is replaced by bone.
What is the structure of the thin filament in terms of actin?
Two strands of fibrous (F) actin form a double helix.
What is intramembranous ossification?
Ossification that takes place in connective tissue membrane.
What happens after ATP is hydrolyzed during muscle contraction?
Myosin heads return to their resting conformation.
How do visceral smooth muscle cells function?
They are arranged in sheets and function as a unit.
What are circumferential lamellae?
Layers on the periphery of a bone.
What happens as the frequency of stimulation increases?
Each new contraction occurs before the preceding one is over, leading to a progressive rise in total strength of contraction.
What surrounds muscle fibers and provides blood supply?
Capillary beds.
What type of muscle fibers are Type IIa?
Fast-twitch oxidative fibers.
What does 'OSTEO' refer to?
Bone.
What happens when an action potential arrives at the presynaptic terminal?
It causes voltage-gated Ca2+ channels to open.
How do nutrients and wastes travel to and from osteocytes?
Via interstitial fluid of lacunae and canaliculi, and from osteocyte to osteocyte by gap junctions.
When is woven bone typically formed?
During fetal development and during fracture repair.
Where is the tropomyosin/troponin complex located?
In the groove between the F-actin strands.
What is endochondral ossification?
Ossification that takes place in cartilage.
How does growth at articular cartilage affect bone size?
It increases the size of bones without epiphyses, such as short bones.
What occurs when a crossbridge forms?
The myosin head binds to a new position on actin.
What is frequency summation?
The principle where individual twitch contractions add together as stimulation frequency increases.
What role do Ca2+ ions play in the neuromuscular junction?
They enter the presynaptic terminal and trigger the release of ACh.
What are interstitial lamellae?
Remnants of osteons located between osteons.
What do both intramembranous and endochondral ossification produce?
Woven bone that is then remodeled.
What is Osteosarcoma?
A type of bone tumor.
What is the process of remodeling in bone?
Removing old bone and adding new bone, where woven bone is remodeled into lamellar bone.
What do chondrocytes near the surface of the articular cartilage resemble?
They are similar to those in the zone of resting cartilage.
How do hormones regulate smooth muscle contraction?
By interacting with hormone-gated receptors in the membrane.
What is released during the power stroke of muscle contraction?
Inorganic phosphate (P) is released.
What occurs at a critical frequency level during muscle contraction?
Successive contractions fuse together, making the muscle contraction appear smooth and continuous.
What is released into the synaptic cleft?
Acetylcholine (ACh).
What is the role of perforating canals?
To deliver blood to central canals.
What happens to bone after remodeling in ossification?
It cannot be distinguished as intramembranous or endochondral.
What happens when ACh binds to ligand-gated Na+ channels?
Na+ enters the postsynaptic cell, causing depolarization.
What happens when a hormone binds to its receptor in smooth muscle?
It activates a G protein mechanism or causes depolarization of the plasma membrane.
What does 'SCOLIO' indicate?
Curved or crooked.
How does bone growth in width occur?
Osteoblasts beneath the periosteum lay down bone to form ridges separated by grooves.
What results from the conformational change of myosin heads?
The power stroke occurs, causing the filaments to slide past each other.
What is lamellar bone?
A type of bone that is organized in layers, unlike woven bone.
Where does intramembranous ossification take place?
In connective tissue membrane formed from embryonic mesenchyme.
