How does a neuron cell membrane become depolarized?
Na⁺ channels close and Na⁺ ions cannot enter the cell
K⁺ channels open and K⁺ diffuses into the cell
Na⁺ channels open and Na⁺ ions diffuse into the cell
Chloride ions enter the cell causing hyperpolarization
The Correct Answer is C
Neuronal excitability depends on changes in membrane potential, which is the electrical difference across the cell membrane. At rest, neurons maintain a negative resting membrane potential due to ion gradients established by the sodium-potassium pump and selective membrane permeability. Depolarization is the process by which the membrane potential becomes less negative and moves toward zero or positive values. This event is essential for initiating action potentials and allowing nerve impulse transmission along neurons.
A. Na⁺ channels close and Na⁺ ions cannot enter the cell: closure of sodium channels would prevent sodium influx and therefore maintain or reinforce the resting membrane potential. Without sodium entry, the inside of the neuron remains negatively charged relative to the outside. Depolarization specifically requires an influx of positive ions, not their exclusion. This describes inhibition of depolarization rather than its initiation.
B. K⁺ channels open and K⁺ diffuses into the cell: potassium movement typically involves efflux, not influx, during neuronal activity. When potassium channels open, K⁺ generally leaves the cell, contributing to repolarization or hyperpolarization rather than depolarization. The movement of positive ions out of the cell increases negativity inside the membrane.
C. Na⁺ channels open and Na⁺ ions diffuse into the cell: depolarization occurs when voltage-gated sodium channels open and allow Na⁺ ions to flow into the neuron. Sodium ions enter the cell down their electrochemical gradient, making the inside of the membrane less negative. This rapid influx of positive charge initiates the rising phase of the action potential. It is the fundamental event that triggers neuronal firing.
D. Chloride ions enter the cell causing hyperpolarization: chloride influx typically makes the inside of the neuron more negative, leading to hyperpolarization rather than depolarization. Increased negativity moves the membrane potential further from the threshold required for action potential generation. Chloride entry stabilizes or inhibits neuronal firing.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
The marked structure is the pubic symphysis, a midline fibrocartilaginous joint located at the anterior aspect of the pelvis where the left and right pubic bones meet. It is composed of hyaline cartilage-covered pubic surfaces joined by an interpubic disc of fibrocartilage. This joint is classified as an amphiarthrosis, allowing only limited movement while providing strong stability to the anterior pelvic ring. It plays an important role in weight distribution during standing and walking and undergoes slight widening during childbirth due to hormonal influence (relaxin).
A. Pubic symphysis: The pubic symphysis is a cartilaginous joint located at the anterior midline of the pelvis, formed by the articulation of the left and right pubic bones. It contains a fibrocartilaginous disc that allows minimal movement, contributing to pelvic stability and shock absorption. It is particularly important in weight transfer between the lower limbs and axial skeleton. Since the circled structure is centrally located at the anterior pelvis, it corresponds to the pubic symphysis.
B. Iliac crest: The iliac crest is the superior curved border of the ilium, forming the prominent “hip bone” ridge that can be palpated on the lateral waist. It serves as an attachment site for abdominal muscles and fascia. Unlike the pubic symphysis, it is a broad lateral bony ridge rather than a midline joint structure.
C. Ischial tuberosity: The ischial tuberosity is a roughened, weight-bearing prominence on the inferior aspect of the ischium. It serves as the attachment site for the hamstring muscles and bears body weight during sitting. Compared to the pubic symphysis, it is posterior and inferior rather than anterior and midline.
D. Sacroiliac joint: The sacroiliac joint is the articulation between the sacrum and the ilium located posteriorly in the pelvis. It is a strong synovial joint that transfers weight from the axial skeleton to the lower limbs. Unlike the pubic symphysis, it is posterior and lateral rather than central at the anterior midline.
Correct Answer is D
Explanation
Bone is a dynamic tissue that undergoes continuous remodeling throughout life to maintain strength, repair damage, and regulate calcium homeostasis. This remodeling process involves the coordinated activity of specialized bone cells, including osteoblasts, osteocytes, and osteoclasts. Osteoclasts are responsible for bone resorption, a process that removes old or damaged bone tissue. Their activity is essential for skeletal growth, fracture repair, and maintaining normal mineral balance within the body.
A. Bone-forming cells that secrete new bone matrix: This option describes osteoblasts, not osteoclasts. Osteoblasts are responsible for synthesizing and secreting osteoid, the organic component of bone matrix composed primarily of type I collagen. They promote bone formation and mineralization during growth and repair.
B. Mature bone cells that maintain the matrix: This option refers to osteocytes, which are mature bone cells derived from osteoblasts that become trapped within the mineralized matrix. Osteocytes maintain bone tissue, monitor mechanical stress, and help regulate remodeling by communicating with osteoblasts and osteoclasts. Their primary role is maintenance rather than bone resorption.
C. Cartilage cells found in the epiphyseal plate: This option describes chondrocytes, the cells responsible for producing and maintaining cartilage. Chondrocytes are found within structures such as articular cartilage and the epiphyseal growth plate, where they contribute to longitudinal bone growth. They are not involved in bone resorption and are not classified as bone cells.
D. Bone cells that break down bone matrix: osteoclasts are large, multinucleated cells specialized for bone resorption. They attach to the bone surface and release hydrogen ions and lysosomal enzymes that dissolve the mineralized matrix and degrade collagen fibers. This process releases calcium and phosphate into the bloodstream and allows old or damaged bone to be replaced with new bone tissue. Osteoclast activity is essential for normal bone remodeling, skeletal growth, and mineral homeostasis.
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