The pupil, controlled by the iris, regulates the amount of light entering the eye, expanding in darkness and contracting in brightness to protect from excessive light. Receptors, responding to various stimuli, include gustatory for taste and olfactory for smell, translating external signals into internal impulses. Sensory receptors detect touch, temperature, and light, while chemical receptors sense chemical changes. The ear, crucial for hearing, also maintains body balance through the vestibular system. The semicircular canals and otolithic organs within the inner ear sense motion and gravity, signaling brain about head and body's position, ensuring balance.