Questions & explanations
1. How do intercalated discs contribute to the rapid transmission of impulses in cardiac muscle?
- They contain tight junctions that prevent ion leakage.
- They have gap junctions that allow direct electrical coupling between cells.
- They are rich in myoglobin which speeds up oxygen delivery.
- They act as chemical synapses that release neurotransmitters.
Answer: They have gap junctions that allow direct electrical coupling between cells.
Gap junctions in intercalated discs form channels that permit ions to flow directly from one cardiomyocyte to the next, enabling rapid spread of depolarization and coordinated contraction. Option A is incorrect because tight junctions seal cells but do not transmit impulses. Option C is incorrect because myoglobin stores oxygen, not impulses. Option D is incorrect because intercalated discs are not synapses; they are specialized cell junctions.
2. Which of the following best describes why cardiac muscle is classified as involuntary?
- It is not innervated by any nerves.
- Its contractions are not under conscious control.
- It contracts only in response to hormonal signals.
- It lacks striations and is thus not under voluntary control.
Answer: Its contractions are not under conscious control.
Cardiac muscle is involuntary because its contractions are initiated and regulated by the autonomic nervous system and intrinsic pacemaker cells, not by conscious will. Option A is incorrect because cardiac muscle is innervated by autonomic nerves. Option C is incorrect because while hormones can modulate, they are not the sole trigger. Option D is incorrect because cardiac muscle is striated, and striation is not related to voluntary control.
3. What is the primary function of intercalated discs in cardiac muscle?
- To store calcium ions for contraction.
- To fuse cardiac muscle cells so they contract as a unit.
- To provide insulation between adjacent cardiomyocytes.
- To anchor the muscle fibers to the skeleton.
Answer: To fuse cardiac muscle cells so they contract as a unit.
Intercalated discs contain gap junctions and desmosomes that mechanically and electrically connect cardiac muscle cells, allowing them to contract synchronously. Option A is incorrect because calcium storage occurs in the sarcoplasmic reticulum. Option C is incorrect because intercalated discs facilitate, not prevent, impulse transmission. Option D is incorrect because cardiac muscle does not attach to the skeleton.
4. Simple cuboidal epithelium is found in which of the following locations?
- Lining of blood vessels
- Ducts of glands and tubular parts of nephrons
- Inner surface of bronchioles
- Lining of stomach and intestine
Answer: Ducts of glands and tubular parts of nephrons
Simple cuboidal epithelium consists of a single layer of cube-like cells and is present in ducts of glands and the tubular parts of nephrons in the kidney, where it functions in secretion and absorption. The other options correspond to simple squamous epithelium (blood vessels), ciliated epithelium (bronchioles), and simple columnar epithelium (stomach and intestine).
5. The coordinated contraction of cardiac muscle cells is essential for which primary function?
- Regulating blood pressure through vasoconstriction.
- Pumping blood effectively as a pump.
- Filtering metabolic wastes from the blood.
- Producing red blood cells in the heart chambers.
Answer: Pumping blood effectively as a pump.
The heart functions as a pump by contracting in a coordinated manner to eject blood into the circulation. Option A is incorrect because vasoconstriction is a function of blood vessels, not the heart. Option C is incorrect because filtration occurs in the kidneys. Option D is incorrect because red blood cells are produced in bone marrow, not the heart.
6. Which of the following is a characteristic feature of simple squamous epithelium?
- It forms the lining of blood vessels and body cavities.
- It is found in the ducts of glands.
- It has tall cells with nuclei at the base.
- It bears cilia on its free surface.
Answer: It forms the lining of blood vessels and body cavities.
Simple squamous epithelium is a single layer of flat cells that lines blood vessels (endothelium) and body cavities (mesothelium), such as the peritoneum. The other options describe other epithelial types: ducts of glands (simple cuboidal), tall cells with basal nuclei (simple columnar), and ciliated surface (ciliated epithelium).
7. What happens when the electrical disturbance reaches the neuron's ending?
- It causes the neuron to divide
- It releases neurotransmitters that affect adjacent cells
- It stops the neuron from functioning
- It generates a new action potential in the same neuron
Answer: It releases neurotransmitters that affect adjacent cells
Arrival of the action potential at the synaptic knob triggers the release of neurotransmitters into the synaptic cleft, which then bind to receptors on the next cell (neuron, muscle, or gland) to generate a response. The neuron does not divide, does not stop functioning, and the action potential does not re-enter the same neuron.
8. Glandular epithelium is formed when columnar or cuboidal cells become specialized for:
- Absorption
- Secretion
- Protection
- Filtration
Answer: Secretion
Glandular epithelium consists of columnar or cuboidal cells that are specialized for secretion. These cells may be unicellular (e.g., goblet cells) or multicellular (e.g., salivary glands). Absorption is a function of simple columnar or cuboidal epithelium; protection is general; filtration is typical of simple squamous.
9. Which part of a neuron receives impulses and conducts them towards the cell body?
- Axon
- Dendrite
- Synaptic knob
- Cell body
Answer: Dendrite
Dendrites are the branched projections of a neuron that receive signals from other neurons and conduct them toward the cell body. The axon conducts impulses away from the cell body, the synaptic knob is involved in neurotransmitter release, and the cell body integrates signals but does not primarily receive impulses.
10. In which tissue are fibroblasts and collagen fibers oriented differently, and is it found in the skin?
- Dense regular connective tissue
- Dense irregular connective tissue
- Loose connective tissue
- Adipose tissue
Answer: Dense irregular connective tissue
Dense irregular connective tissue has fibroblasts and collagen fibers arranged in multiple directions, providing strength in various directions. It is found in the dermis of the skin. Dense regular tissue has parallel fibers, loose connective tissue has fewer fibers, and adipose tissue stores fat.
11. The brush border of microvilli on cuboidal cells of the proximal convoluted tubule primarily functions to:
- Secrete mucus
- Move particles in a specific direction
- Increase surface area for absorption
- Provide structural support
Answer: Increase surface area for absorption
Microvilli form a brush border that greatly increases the surface area of the cuboidal cells in the proximal convoluted tubule, enhancing absorption. Secretion of mucus is a function of goblet cells; moving particles is done by cilia; structural support is not the primary role of microvilli.
12. When a neuron is suitably stimulated, an electrical disturbance that travels along its plasma membrane is called:
- Neurotransmitter release
- Action potential
- Synaptic transmission
- Resting potential
Answer: Action potential
An action potential is the rapid electrical impulse that travels along the neuron's membrane in response to a stimulus. Neurotransmitter release occurs at the synapse, synaptic transmission is the overall process, and resting potential is the stable voltage when the neuron is not stimulated.