Cellular Basis of Animal Physiology

• Role of $Ca^{2+}$ in Neuromuscular Transmission: When a motor nerve action potential depolarizes the presynaptic motor nerve terminal, voltage-gated $P/Q$-type calcium channels open, allowing rapid influx of extracellular $\text{Ca}^{2+}$.
• Vesicular Fusion Mechanism: Intracellular $\text{Ca}^{2+}$ binds to synaptotagmin-1, triggering conformational changes in the core SNARE complex (syntaxin-1, SNAP-25, and synaptobrevin/VAMP). This forces the presynaptic synaptic vesicles to fuse with the presynaptic terminal membrane, releasing acetylcholine (ACh) into the synaptic cleft via exocytosis (Option 4).

Correct option: (4) Fuse the presynaptic vesicle with the presynaptic membrane, thus releasing the transmitter

• Olfactory Processing Pathways: In the olfactory system, axons of olfactory bulb mitral and tufted cells project directly via the lateral olfactory tract to the primary olfactory cortex (pyriform cortex) and amygdala without an obligatory thalamic relay.
• Conscious Perception: Higher-order conscious discrimination and identification of distinct odors depends on projections to the Orbitofrontal Cortex (via direct pathways and via the mediodorsal nucleus of the thalamus) [Option 3].

Correct option: (3) Conscious discrimination of odors is dependent on the pathway to the orbitofrontal cortex.

• Vestibular Receptors for Angular Acceleration: The Crista Ampullaris—located within the dilated ampullae of the three orthogonal semicircular canals—contains hair cells embedded in a gelatinous cupula that specifically detects angular acceleration and rotational deceleration of the head.
• Linear Acceleration: The maculae of the utricle and saccule detect linear acceleration, tilt, and gravity.

Correct option: (3) Crista ampullaris