What is a function of transverse tubules?
To store calcium ions needed for activating tropomyosin
To transmit action potentials (impulses) into the cell interior
To synthesize ATP for muscle contraction
To break down acetylcholine at the neuromuscular junction
The Correct Answer is B
Skeletal muscle fibers are highly specialized cells designed for rapid and coordinated contraction. To achieve this, they require an efficient system for transmitting electrical signals from the cell surface deep into the muscle fiber. Transverse (T) tubules are invaginations of the sarcolemma that penetrate into the cell interior. They work closely with the sarcoplasmic reticulum to ensure uniform and rapid activation of muscle contraction throughout the fiber.
A. To store calcium ions needed for activating tropomyosin: calcium storage in muscle cells is primarily handled by the sarcoplasmic reticulum, not the T-tubules. The sarcoplasmic reticulum releases calcium ions in response to an action potential, allowing calcium to bind troponin and shift tropomyosin away from actin binding sites. T-tubules do not store calcium; they serve as conduits for electrical signals.
B. To transmit action potentials (impulses) into the cell interior: transverse tubules are invaginations of the sarcolemma that rapidly conduct action potentials from the cell surface into the deeper regions of the muscle fiber. This ensures that the entire muscle fiber contracts simultaneously rather than in a wave-like fashion. The electrical signal traveling through T-tubules triggers calcium release from the sarcoplasmic reticulum. This coupling is essential for coordinated and efficient muscle contraction.
C. To synthesize ATP for muscle contraction: ATP production occurs primarily in mitochondria through oxidative phosphorylation and in the cytoplasm via glycolysis. T-tubules have no role in energy metabolism or ATP synthesis. Their function is electrical signal transmission, not biochemical energy production. Therefore, this option describes a mitochondrial function rather than a T-tubule function.
D. To break down acetylcholine at the neuromuscular junction: acetylcholine breakdown is performed by the enzyme acetylcholinesterase located in the synaptic cleft of the neuromuscular junction. T-tubules are located inside the muscle fiber and are not involved in synaptic transmission or neurotransmitter degradation.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
The marked structure is the cervical region, which corresponds anatomically to the neck portion of the vertebral column and surrounding soft tissues. It extends from the base of the skull to the level of the first thoracic vertebra (C1–C7). This region supports the head, allows a wide range of head and neck movements, and provides a passage for critical structures including the trachea, esophagus, carotid arteries, jugular veins, and cervical spinal cord. It also contains important muscle groups such as the sternocleidomastoid and scalene muscles that contribute to posture, respiration, and head mobility.
A. Acromial region: The acromial region refers to the lateral aspect of the shoulder over the acromion process of the scapula. It forms part of the shoulder girdle and serves as an attachment point for the deltoid muscle. Unlike the cervical region, it is located on the upper lateral shoulder rather than the neck and is primarily involved in upper limb movement.
B. Cervical region: The cervical region is the neck portion of the body consisting of the cervical vertebrae and surrounding soft tissues. It supports the head, allows flexion, extension, rotation, and lateral bending, and houses vital neurovascular and airway structures. It forms the transition between the skull and thorax, making it essential for both structural support and communication pathways. Its location corresponds directly with the highlighted neck area.
C. Vertebral region: The vertebral region refers broadly to the entire spinal column, including cervical, thoracic, lumbar, sacral, and coccygeal segments. It provides axial support and protection for the spinal cord. Unlike the cervical region, it is not limited to the neck but spans the entire back from skull to pelvis.
D. Gluteal region: The gluteal region refers to the buttock area, composed mainly of the gluteus maximus, medius, and minimus muscles. It plays a key role in hip movement and locomotion. Compared to the cervical region, it is located in the lower posterior trunk and is unrelated to neck structures.
E. Lumbar region: The lumbar region refers to the lower back area containing the lumbar vertebrae (L1–L5). It supports body weight and allows trunk flexion and extension. Unlike the cervical region, it is situated between the thoracic spine and sacrum, forming the lower posterior trunk rather than the neck.
F. Sacral region: The sacral region is located at the base of the spine and consists of the fused sacral vertebrae forming the sacrum. It contributes to pelvic stability and transfers weight from the spine to the lower limbs. Compared to the cervical region, it is positioned inferiorly within the pelvis rather than in the neck.
Correct Answer is A
Explanation
The marked structure is the sacrum, a large triangular bone formed by the fusion of five sacral vertebrae located at the base of the vertebral column. It forms the posterior wall of the pelvis and articulates with the ilium at the sacroiliac joints, contributing to pelvic stability and weight transmission from the axial skeleton to the lower limbs. The sacrum also contains sacral foramina that allow passage of spinal nerves.
A. Sacrum: The sacrum is a fused bone consisting of five vertebrae (S1–S5) located between the lumbar spine and coccyx. It forms the posterior portion of the pelvic girdle and articulates with the ilium to distribute body weight during standing and movement. It contains sacral foramina for nerve passage and supports pelvic organs.
B. Coccyx: The coccyx is the small terminal segment of the vertebral column, commonly called the tailbone. It is formed by fusion of 3–5 small vertebrae and lies inferior to the sacrum. It serves as an attachment site for ligaments and pelvic floor muscles. Compared to the sacrum, it is much smaller and more distal, making it unlikely to be the marked structure.
C. Ilium: The ilium is the largest and superior portion of the hip bone, forming the broad flared structure of the pelvis. It articulates with the sacrum at the sacroiliac joint and contributes to the acetabulum. Its main role is weight-bearing and muscle attachment for the abdominal and gluteal muscles. Unlike the midline sacrum, the ilium is lateral and paired on both sides.
D. Lumbar vertebrae: The lumbar vertebrae are five large vertebrae located in the lower back above the sacrum. They provide major support for body weight and allow flexion and extension of the trunk. While they articulate directly with the sacrum, they are separate segmented bones rather than a fused triangular structure.
Whether you are a student looking to ace your exams or a practicing nurse seeking to enhance your expertise , our nursing education contents will empower you with the confidence and competence to make a difference in the lives of patients and become a respected leader in the healthcare field.
Visit Naxlex, invest in your future and unlock endless possibilities with our unparalleled nursing education contents today
Report Wrong Answer on the Current Question
Do you disagree with the answer? If yes, what is your expected answer? Explain.
Kindly be descriptive with the issue you are facing.