Block 2 Pace1 - 2011 Sem.1 Pace Quiz 3

Titin is a large protein that spans from the Z disk to the M line in the sarcomere. It acts as a molecular spring, providing elasticity and maintaining the alignment of the thick filaments. Therefore, it anchors the thick filaments to the Z disks in the sarcomeres. Nebulin, C protein, α-actinin, and myomesin are also accessory proteins in the sarcomeres, but they do not directly anchor the thick filaments to the Z disks.

Cardiac muscle cells are characterized by the presence of sarcomeres and myofibrils. Sarcomeres are the basic contractile units of muscle cells, composed of overlapping actin and myosin filaments. Myofibrils are the bundles of sarcomeres within a muscle cell, responsible for muscle contraction. This characteristic distinguishes cardiac muscle cells from other types of muscle cells, such as smooth muscle cells, which do not have well-defined sarcomeres and myofibrils.

Alkaline phosphatase is used clinically as a measure of the amount of bone formation that is occurring. This enzyme is primarily found in the liver, bones, and kidneys, and its levels in the blood can indicate the rate at which new bone is being formed. When bone formation is increased, such as during growth or healing of fractures, alkaline phosphatase levels tend to rise. Conversely, low levels of alkaline phosphatase may indicate decreased bone formation or certain medical conditions affecting the bones. Therefore, monitoring alkaline phosphatase levels can provide valuable information about bone health and the effectiveness of treatments aimed at promoting bone formation.

Based on the clinical presentation of weakness, difficulty breathing, bilateral ptosis, and cyanosis in a patient with a known diagnosis of myasthenia gravis who has been noncompliant with medication, it is likely that the patient is experiencing a myasthenic crisis. A myasthenic crisis is a worsening of symptoms in patients with myasthenia gravis, often triggered by medication noncompliance or infection. It is characterized by severe muscle weakness, including respiratory muscles, leading to respiratory distress.

The correct answer is Osteon. Osteon is a structural unit of compact bone, consisting of concentric layers of bone matrix called lamellae surrounding a central canal called the Haversian canal. The Haversian canal contains blood vessels and nerves. The drawing likely shows the arrangement of lamellae and the Haversian canal, which is characteristic of an osteon.

Smooth muscle is a type of muscle tissue that is found in various organs and structures in the body. It is characterized by its lack of striations or visible bands, unlike skeletal and cardiac muscle. Myofilaments are the contractile proteins found in muscle cells, and they are responsible for the contraction and relaxation of the muscle. Therefore, myofilaments can be found in smooth muscle, making them the correct answer. Triads, sarcomeres, intercalated discs, and troponin are structures that are typically found in skeletal or cardiac muscle, not smooth muscle.

The maldevelopment of the apical ectodermal ridge is the likely cause of the condition in the child. The apical ectodermal ridge is a specialized structure that plays a crucial role in limb development. It is responsible for signaling and organizing the growth of the limb bud, which eventually forms the upper limbs. If the apical ectodermal ridge is not properly developed, it can lead to abnormalities in limb formation, such as rudimentary upper limbs. The ingestion of the anti-nausea drug by the mother during the first trimester may have disrupted the development of the apical ectodermal ridge, resulting in this condition in the child.

The most likely cause of congenital torticollis in this case is the contraction of the left sternocleidomastoid muscle. Congenital torticollis is a condition characterized by the abnormal positioning of the head, typically with tilting to one side and rotation to the opposite side. The left sternocleidomastoid muscle is responsible for the rotation and tilting of the head to the opposite side. Therefore, the contraction of this muscle would result in the observed head position in the infant.

Parathyroid hormone is the correct answer because it functions to increase the levels of calcium in the blood by stimulating the release of calcium from the bones. This process is known as bone resorption, where bone is broken down and calcium is released into the bloodstream. Therefore, parathyroid hormone decreases bone production by promoting the breakdown of bone tissue.

Ryanodine receptors are physically coupled to Dihydropyridine receptors. This means that when the Dihydropyridine receptors are activated by a change in membrane potential, they physically interact with Ryanodine receptors, leading to the release of calcium from the sarcoplasmic reticulum. This calcium release is essential for muscle contraction to occur. Therefore, even if calcium does not influx through Dihydropyridine receptors, contraction can still occur due to the physical coupling between Dihydropyridine and Ryanodine receptors.

During total hip arthroplasty surgery using a posterior approach, ligating the profunda femoris artery at its origin disrupts the blood supply to the major muscles of the posterior compartment of the thigh. However, the sustained flow of blood to these muscles is maintained by the inferior gluteal artery, which provides a collateral blood supply to the posterior compartment. Additionally, the first perforating artery, a branch of the profunda femoris artery, also helps in maintaining blood flow to the muscles. Therefore, the correct answer is Inferior gluteal & first perforating.

Tetanic contractions produce more tension than a single twitch because increasing the frequency of skeletal muscle action potentials causes calcium to be released from the sarcoplasmic reticulum faster than it can be reabsorbed. This leads to a higher concentration of calcium in the muscle fibers, which allows for more cross-bridge formations between actin and myosin filaments. As a result, more force is generated, leading to a stronger contraction.

The correct answer is Femoral n. -> L2-L4 ventral rami -> L2-L4 dorsal roots -> L2-L4 dorsal root ganglia -> L2-L4 spinal cord. The pathway of sensory fibers that stimulate the deep tendon reflex is through the femoral nerve, which arises from the L2-L4 ventral rami. These fibers then enter the L2-L4 dorsal roots, where they synapse with neurons in the dorsal root ganglia. From there, the sensory information is transmitted to the L2-L4 spinal cord, resulting in the reflexive extension of the knees.

In endochondral ossification, the chondrocytes in the cartilage model undergo hypertrophy and eventually die. Zone 4 is the zone where the chondrocytes are hypertrophic and starting to die. This zone is also known as the zone of hypertrophy. Therefore, the correct answer is Zone 4.

When a single action potential travels down a motor neuron to the neuromuscular junction, it will directly cause a depolarizing graded potential in the skeletal muscle fiber. This graded potential will result in an increase in calcium influx from extracellular stores, which is necessary for muscle contraction. Therefore, all options A, B, and C are correct.