Analyze the distribution of ions across a non-conducting resting axonal membrane:
Statement I: The resting axonal membrane is comparatively more permeable to potassium ions (K+) and nearly impermeable to sodium ions (Na+). Statement II: The axoplasm inside the resting axon contains a high concentration of K+ and negatively charged proteins. Statement III: The axoplasm inside the resting axon contains a high concentration of sodium ions (Na+). Statement IV: The fluid outside the axon contains a high concentration of Na+ and a low concentration of K+.
Statements I, II and IV are correct. Statement III is incorrect because the axoplasm contains a low concentration of Na+ and a high concentration of K+.
Question 32 of 100
📘 CLASS XI
Regarding the active transport mechanism that maintains the resting membrane potential:
Statement I: The active transport of ions across the resting membrane is driven by the sodium-potassium pump. Statement II: The sodium-potassium pump actively transports 3 Na+ ions inwards for every 2 K+ ions pumped outwards. Statement III: The sodium-potassium pump actively transports 3 Na+ ions outwards for every 2 K+ ions pumped inwards. Statement IV: This electrogenic pumping makes the outer surface of the axonal membrane positively charged relative to the negatively charged inner surface.
Statements I, III and IV are correct. Statement II is incorrect because the sodium-potassium pump transports 3 Na+ out of the cell and 2 K+ into the cell.
Question 33 of 100
📘 CLASS XI
Consider the ionic events that take place when a stimulus is applied to a specific site A on a polarized axonal membrane:
Statement I: The membrane at site A becomes freely permeable to sodium ions (Na+). Statement II: This permeability change leads to a rapid influx of Na+ at site A. Statement III: The polarity at site A is reversed; the outer surface becomes positively charged and the inner side becomes negatively charged. Statement IV: The polarity at site A is reversed; the outer surface becomes negatively charged and the inner side becomes positively charged.
Statements I, II and IV are correct. Statement III is incorrect because during depolarization the polarity is reversed, making the outer surface negative and the inner surface positive due to rapid influx of Na+ ions.
Question 34 of 100
📘 CLASS XI
Regarding the conduction of an action potential along an axon from point A to point B:
Statement I: At site B (ahead of site A), the outer membrane surface is positively charged and the inner membrane surface is negatively charged. Statement II: On the inner surface of the axonal membrane, current flows from site A to site B. Statement III: On the outer surface of the axonal membrane, current flows from site B to site A to complete the circuit. Statement IV: The current flow on the outer surface reverses the polarity at site B, generating an action potential at site B.
All four statements are correct. They describe the mechanism of action potential propagation where local currents flow inside from site A to B and outside from B to A, producing depolarization at the adjacent region.
Question 35 of 100
📘 CLASS XI
Analyze how a depolarized neural membrane recovers its resting potential:
Statement I: The stimulus-induced increase in permeability to Na+ is extremely long-lasting. Statement II: The rise in Na+ permeability is extremely short-lived. Statement III: The increase in Na+ permeability is quickly followed by a rise in permeability to potassium ions (K+). Statement IV: Within a fraction of a second, K+ diffuses outside the membrane to restore the resting potential at the site of excitation.
Statements II, III and IV are correct. Statement I is incorrect because the increase in Na+ permeability is extremely short-lived. It is rapidly followed by increased K+ permeability, restoring the resting membrane potential.
Question 36 of 100
📘 CLASS XI
Compare the features of electrical synapses and chemical synapses:
Statement I: At electrical synapses, the membranes of pre- and post-synaptic neurons are in very close proximity. Statement II: At chemical synapses, the pre- and post-synaptic membranes are separated by a fluid-filled space called the synaptic cleft. Statement III: Transmission of an impulse across a chemical synapse is always faster than across an electrical synapse. Statement IV: Electrical synapses are very rare in the human neural system.
Statements I, II and IV are correct. Statement III is incorrect because transmission across an electrical synapse is faster than across a chemical synapse due to direct electrical continuity.
Question 37 of 100
📘 CLASS XI
Study the sequence of events at a chemical synapse when an action potential arrives:
Statement I: The arrival of an action potential at the axon terminal stimulates the movement of synaptic vesicles towards the pre-synaptic membrane. Statement II: Synaptic vesicles fuse with the pre-synaptic plasma membrane. Statement III: Neurotransmitters are released into the synaptic cleft by the fusing vesicles. Statement IV: The released neurotransmitters bind to specific receptors located on the pre-synaptic membrane.
Statements I, II and III are correct. Statement IV is incorrect because neurotransmitters bind to receptors on the post-synaptic membrane, initiating the next electrical event.
Question 38 of 100
📘 CLASS XI
Analyze the physiological outcome of neurotransmitter binding on the post-synaptic membrane:
Statement I: The binding of neurotransmitters to specific receptors opens ligand-gated ion channels. Statement II: The opening of ion channels allows the entry of ions into the post-synaptic neuron. Statement III: The entry of these ions generates a new potential in the post-synaptic neuron. Statement IV: This newly developed potential is always inhibitory to prevent over-excitation of the brain.
Statements I, II and III are correct. Statement IV is incorrect because the post-synaptic potential may be either excitatory or inhibitory, depending on the neurotransmitter and receptor involved.
Question 39 of 100
📘 CLASS XI
Examine the structure and layers of the cranial meninges protecting the brain:
Statement I: The cranial meninges consist of three distinct protective layers inside the skull. Statement II: The outer layer is a tough membrane called dura mater. Statement III: The middle layer is a very thin membrane called the arachnoid. Statement IV: The inner layer in direct contact with the brain tissue is the pia mater.
All four statements are correct. The cranial meninges consist of three protective layers arranged from outside to inside as dura mater, arachnoid mater, and pia mater, with the pia mater lying directly on the brain surface.
Question 40 of 100
📘 CLASS XI
Consider the gross anatomical structure of the human cerebrum:
Statement I: A deep cleft divides the cerebrum longitudinally into two halves, the left and right cerebral hemispheres. Statement II: The left and right cerebral hemispheres are connected by a tract of nerve fibres called the corpus callosum. Statement III: The corpus callosum consists of grey matter containing highly concentrated neuron cell bodies. Statement IV: The layer of cells covering the cerebral hemispheres is called the cerebral cortex.
Statements I, II and IV are correct. Statement III is incorrect because the corpus callosum is composed of myelinated nerve fibres (white matter), not grey matter containing neuron cell bodies.
