Summary
Highlights
The nervous system processes outside information for reactions, communication, and safety. Much of this information comes through sensory organs: the Eyes, Ears, Nose, Tongue, and Skin, which are our five senses.
The sclera protects the eye, the cornea allows light in. The pupil, an opening in the iris, adjusts light entering and focusing on the lens. The retina, with rods and cones, translates light into nervous signals carried by the optic nerve to the brain for visual interpretation.
The outer ear funnels sound waves to the eardrum, creating vibrations. These vibrations transfer to auditory ossicles (malleus, incus, stapes), which knock against the inner ear's fluid-filled canals. Specialized hair cells in the cochlea detect pressure waves, sending signals via the cochlear nerve to the brain to be interpreted as sound.
Smell begins with nerve receptors on hair-like cilia in the nasal cavity. Chemicals bind to these receptors, triggering signals to the olfactory bulbs and then along cranial nerves to the olfactory area of the cerebral cortex for interpretation.
When eating, chemicals from food enter the papillae on the tongue and reach taste buds. These stimulate specialized gustatory cells, activating nervous receptors. Signals are carried to the medulla oblongata, which relays them to the thalamus and cerebral cortex of the brain.
Skin has three layers: epidermis, dermis, and hypodermis. Specialized receptor cells detect tactile sensations and relay signals via peripheral nerves to the brain. Different receptor types (Merkel cells, Meissner corpuscles, Pacinian corpuscles) detect touch, pressure, and vibration, making certain body parts more sensitive.