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The human nervous system is an ultra-fast bio-electrical network operating on strict electro-chemical gradients. Neurons function as specialized cellular conductors, transmitting signals via transient shifts in membrane permeability to sodium () and potassium () ions. At rest, the axonal neurolemma maintains a negative resting membrane potential of approximately , actively sustained by the ATPase pump which extrudes for every brought inward. When a threshold stimulus of is reached, rapid depolarization spikes the potential to through voltage-gated channels. Synaptic transmission converts this electrical wave into a chemical signal via neurotransmitter release across the synaptic cleft. In NEET, mastery over this chapter hinges on understanding ion directionality during depolarization, brain region localization (hypothalamus, cerebellum), and sensory signal transduction in the organ of Corti and retino-foveal pathways.
Confusing the net direction of and ion movement during Depolarization vs Repolarization phases.
Assuming electrical synapses are slower or more predominant in human neurophysiology than chemical synapses.
Misinterpreting the cellular distribution in the Fovea Centralis versus the Blind Spot of the Retina.
Questions Asked: 3
Topics: Generation and Conduction of Nerve Impulse, Mechanism of Vision
Questions Asked: 2
Topics: Human Brain & Reflex Arc, Resting and Action Potential
Questions Asked: 3
Topics: Synaptic Transmission, Structure of Ear and Eye
During the propagation of a nerve impulse across an axon, the action potential (depolarization) results directly from the rapid movement of:
At the resting state, the outer surface of the axonal membrane possesses a net positive charge while the inner axoplasm is negative (), with high extracellular concentration.
When a stimulus of threshold intensity () is applied, voltage-gated channels open rapidly.
This causes a massive influx of ions from the extracellular fluid into the axoplasm, reversing local polarity to and generating the action potential.
Which of the following events correctly describes the chemical transmission mechanism at a neuromuscular or neuro-neuronal junction?
The arrival of an action potential at the presynaptic axon terminal depolarizes the presynaptic membrane.
Voltage-gated channels open in response to depolarization, leading to an influx of ions into the terminal from the extracellular fluid.
Elevated intracellular causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters (e.g., acetylcholine) into the synaptic cleft by exocytosis.
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Click HereThe inner negativity is established because the resting neurolemma is significantly more permeable to ions than to ions via passive leak channels. diffuses out down its concentration gradient faster than enters. Additionally, negatively charged non-diffusible proteins remain trapped inside the axoplasm, and the active ATPase pump actively extrudes outward for every brought inside.
Hyperpolarization occurs when the membrane potential drops below the resting potential to approximately or . It is caused by slow closure of voltage-gated channels allowing excess efflux. This hyperpolarized state creates an absolute refractory period, ensuring that the nerve impulse propagates strictly in one direction down the axon without reversing.
Prioritize high-yield direct recall regions. For the Brain, focus on the Hypothalamus (thermoregulation, satiety), Cerebellum (motor coordination), and Limbic System (emotions). For Sensory Organs, memorize the Organ of Corti (resting on the basilar membrane in the scala media) and the visual cycle (photoreceptive pigment rhodopsin dissociating into opsin and retinal upon light absorption).
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