MDS PREP
What is the primary effect of excitatory postsynaptic potentials (EPSPs) on the excitability of a neuron?
1) Depolarization
2) Hyperpolarization
3) No change in excitability
4) Initiation of an action potential
Answer: 1) DepolarizationExplanation: EPSPs occur when the neurotransmitter binds to postsynaptic receptors that open sodium channels, allowing sodium ions to flow into the neuron and causing the membrane to depolarize. This increases the excitability of the neuron, bringing the membrane potential closer to the threshold for action potential firing.
What is the primary mechanism of action of the Na+/I+ symporter in thyroid cells?
1) Primary active transport
2) Facilitated diffusion
3) Secondary active transport
4) Osmosis
The Na+/I+ symporter (NIS) in thyroid cells uses the energy from the electrochemical gradient of sodium to actively transport iodide into the cells, which is an example of secondary active transport.
What is the mechanism of action of umami taste substances?
1) Activation of sodium-dependent glucose transporters
2) Stimulation of bitter G-protein coupled receptors
3) Activation of amiloride-sensitive sodium channels
4) Activation of glutamate taste sensors (glutamate receptors)
Umami taste is triggered by the activation of glutamate receptors present in taste cells, which leads to the perception of savoriness.
The average time required for spermatogenesis in humans is:
1) 30 days
2) 42 days
3) 74 days
4) 120 days
Spermatogenesis, the process of producing mature sperm cells from spermatogonia, takes approximately 74 days in humans. This includes the development of spermatids and their subsequent transformation into spermatozoa.
What is the role of calbindin in calcium absorption in the intestine?
1) It sequesters calcium in the intestinal lumen
2) It transports calcium across the brush border membrane
3) It binds calcium and prevents it from affecting epithelial signaling
4) It stimulates the release of calcium from the intestinal cells into the bloodstream
Calbindin binds calcium and prevents it from affecting epithelial signaling, facilitating calcium absorption in the intestine.
What is the role of the vagus nerve in the parasympathetic system?
1) Control of heart rate and gastric motility
2) Control of pupil dilation and salivation
3) Control of skeletal muscle contraction
4) Control of pituitary hormone secretion
The vagus nerve, as part of the parasympathetic system, innervates various organs in the thoracic and abdominal cavities, influencing heart rate and gastric motility among other functions.
What is the primary effect of epinephrine on the gastrointestinal tract during the fight-or-flight response?
1) Increases motility and secretions
2) Decreases motility and secretions
3) Relaxes the gastrointestinal muscles
4) Dilates blood vessels in the GI tract
Answer: 2) Decreases motility and secretionsExplanation: Epinephrine decreases gastrointestinal motility and secretions as part of the fight-or-flight response. This is because the body's priority shifts from digestion to the preparation for immediate action, diverting blood away from the GI tract and reducing its activity to focus on more critical bodily functions.
What are the two major functions of GH?
1) Stimulation of growth hormone-dependent lipolysis and glycogenolysis
2) Stimulation of gluconeogenesis and growth of the skeletal system
3) Stimulation of cortisol synthesis and thyroid hormone release
4) Regulation of insulin secretion and cardiovascular function
Answer: 2) The two major functions of GH are the growth of the skeletal system and metabolic effects, including gluconeogenesis.