Understanding the Human Senses and Their Disorders

Sense of Smell: Enables the body to detect chemical molecules in the air. Molecules are detected by chemoreceptors in the nasal cavities. Sensations they receive are called smells.

Types of Nasal Mucous Membranes:

• Respiratory Mucous Membrane: Has blood vessels that warm inhaled air and hairs that trap dust particles.
• Olfactory Mucous Membrane: Contains the olfactory receptors. Chemoreceptors converge in the olfactory bulb. Receptors transmit impulses along the olfactory nerve to the brain when stimulated by chemicals.

Sense of Taste: Enables the body to detect flavors. Four basic tastes: sweet, salty, sour, and bitter. Chemoreceptors respond to chemicals dissolved in saliva, located mainly on the tongue, but also on the palate, pharynx, and larynx. They are clustered in taste buds located in epithelial cells called taste papillae.

Sense of Hearing: Ears are located in a cavity of the temporal bone. They have receptors sensitive to sound waves. The ear is divided into three areas: external, middle, and internal, each with several parts.

Parts Involved in Hearing:

1. Pinna
2. External auditory canal
3. Eardrum
4. Chain of bones
5. Cochlea
6. Auditory nerve

Parts Involved in Balance: Semicircular canals.

Health of Sense Organs: Diseases that affect the sense organs are as diverse as their causes: infections, vascular or hereditary disorders related to the nervous system, poor hygiene, and bad habits.

Eye Disorders:

• Short-Sightedness (Myopia): Distant objects appear out of focus because the eyeball is too long, so images are focused in front of the retina. Convex lenses or surgery can correct the problem.
• Long-Sightedness (Hypermetropia): Close objects appear out of focus because the eyeball is too short. Images are focused behind the retina. Convex lenses and/or surgery can correct it.
• Astigmatism: Objects appear distorted or blurred, caused by an irregularly shaped cornea. Lenses or surgery can correct the problem.
• Cataracts: The crystalline lens loses its transparency until it becomes opaque, causing progressive loss of vision and possibly blindness.
• Conjunctivitis: An inflammation of the conjunctiva, usually caused by an infection or allergy.