Share This Link

The myofibrillar network refers to the arrangement of actin and myosin filaments responsible for muscle contraction. While essential for force generation, it does not store calcium. Its role is mechanical, not regulatory in terms of calcium ion concentration.

T tubules (transverse tubules) are invaginations of the sarcolemma that help propagate action potentials into the interior of the muscle fiber. They facilitate communication between the sarcolemma and the sarcoplasmic reticulum but do not store calcium themselves.

Mitochondria are responsible for ATP production through oxidative phosphorylation. Although they can buffer calcium to some extent, they are not the primary calcium storage organelle in skeletal muscle cells.

A fossa is a shallow depression in a bone, often serving as an articular surface or a site for muscle attachment. It does not serve as a passageway like a foramen.

A meatus is a canal-like passageway through a bone, such as the external auditory meatus in the temporal bone. While it is a passage, it is more elongated and tunnel-like than a round or oval opening.

A sinus is a cavity within a bone, typically filled with air and lined with mucous membrane, such as the paranasal sinuses. It is not an opening for passage but rather a hollow space.

Thyroxine, produced by the thyroid gland, primarily regulates metabolism. While it influences bone growth and development indirectly, it does not directly stimulate osteoclast activity or calcium release.

Osteocalcin is a non-collagenous protein secreted by osteoblasts and is involved in bone mineralization and calcium ion homeostasis. However, it does not stimulate osteoclast activity or increase blood calcium levels.

Calcitonin is secreted by the parafollicular cells of the thyroid gland in response to high blood calcium levels. It inhibits osteoclast activity, thereby reducing bone resorption and lowering blood calcium levels. It acts in opposition to PTH.

While muscle names can reflect location (e.g., brachialis for the arm), the names "biceps," "triceps," and "quadriceps" specifically refer to the number of origins, not their anatomical position.

Muscle shape does influence naming in some cases (e.g., deltoid for triangular), but it is not the basis for naming biceps, triceps, or quadriceps.

Fascicle arrangement refers to the pattern of muscle fibers (e.g., parallel, pennate), which affects function and strength but is not the naming basis for these specific muscles.

Ossification of the ends of long bones (epiphyses) does not necessarily take twice as long as the shaft (diaphysis). The timing varies depending on the bone and developmental stage. The shaft begins ossifying earlier via the primary ossification center, typically during fetal development, while the ends ossify later via secondary centers, often after birth. However, the duration is not uniformly double.

Intramembranous ossification is responsible for forming flat bones such as the skull and clavicle. The ends of long bones undergo endochondral ossification, not intramembranous. Therefore, this choice incorrectly associates the process with the wrong ossification type.

Ossification of the diaphysis (shaft) begins earlier than the epiphyses. The primary ossification center in the shaft typically appears during fetal development, while secondary centers in the ends appear postnatally. Thus, this statement is factually incorrect.

Perforating canals (also known as Volkmann's canals) connect the central canals of different osteons and allow blood vessels and nerves to travel across bone. While they contribute to nutrient transport, they do not directly facilitate exchange between osteocytes.

Lamellae are concentric rings of bone matrix within osteons. They provide structural support but do not directly mediate nutrient or waste exchange between osteocytes.

Central canals (Haversian canals) contain blood vessels and nerves and run longitudinally through osteons. They help deliver nutrients to the bone but do not directly connect individual osteocytes.

Dense fibrous connective tissue forms tendons and ligaments, not the precursor to long bones. It lacks the structural and biochemical properties necessary for endochondral ossification.

Mesenchymal tissue is the embryonic connective tissue from which various structures, including cartilage and bone, originate. However, it is not the immediate precursor to long bones; it first differentiates into chondrocytes that form hyaline cartilage.

Elastic cartilage is found in structures like the ear and epiglottis. It is not involved in the formation of long bones and lacks the rigidity and mineralization capacity required for ossification.

Preventing muscle fatigue is not the primary function of wave summation. Fatigue is influenced by metabolic factors and sustained activity, not by the summation of muscle twitches.

While wave summation does increase muscle tension, this is a secondary effect. The main purpose is to produce a more sustained and coordinated contraction.

Wave summation enhances, not lessens, muscle contraction. It builds upon previous contractions to produce a more forceful and sustained response. Therefore, this choice is incorrect.

Nutrient foramina are openings in the bone that allow blood vessels to enter from the periosteum into the deeper bone layers. While they are essential for vascular access, they do not directly facilitate nutrient exchange with osteocytes. Their role is more about entry points for vessels rather than direct cellular communication.

Central canals, also known as Haversian canals, are longitudinal channels within osteons that contain blood vessels and nerves. They provide a conduit for nutrients and waste products but do not directly connect to individual osteocytes. Instead, they serve as a central hub from which smaller structures like canaliculi branch out.

Perforating canals, or Volkmann’s canals, run perpendicular to the central canals and connect them to the periosteum and medullary cavity. While they help integrate the vascular system of bone, they do not directly interface with osteocytes for nutrient or waste exchange.

Circumduction is a circular movement that combines flexion, extension, abduction, and adduction. It is typically seen in ball-and-socket joints like the shoulder or hip, not in the neck. It does not describe the backward bending of the head.

Rotation refers to the movement of a bone around its longitudinal axis, such as turning the head side to side. It does not involve bending the head backward.

Flexion is the movement that decreases the angle between two body parts, such as bending the head forward toward the chest. It is the opposite of the movement described in the question.