Human Ear, Hearing, Taste, Smell and Touch

The Human Ear: Structure and Function

The ear is the organ that allows us to capture sound, which consists of vibrations and waves. Audition has two essential characteristics: intensity and tone. Intensity depends on the amplitude of the sound waves, and tone depends on the number of waves received per second.

Parts of the Ear

• External Ear: Includes the pinna (or auricle) and the external auditory canal. The pinna captures sound vibrations, which are then transmitted to the middle ear. The auditory canal contains ceruminous glands that produce wax for protection, hygiene, and cleanliness.
• Middle Ear: Starts with the tympanic membrane (eardrum), which vibrates upon receiving sound waves. These vibrations are transmitted to the ossicles (three small bones: malleus (hammer), incus (anvil), and stapes (stirrup)). The stapes connects to the inner ear via the oval window.
• Eustachian Tube: Connects the middle ear to the nasopharyngeal cavity. Its purpose is to equalize the pressure between the inside and outside of the ear, preventing damage to the tympanic membrane. It is about 3.5cm long.
• Inner Ear: Contains the cochlea, which houses the organ of Corti. This organ consists of a fluid called endolymph and cells with microvilli that detect the movement of the fluid.

Operation

The stapes strikes the oval window, transmitting vibrations to the cochlea. The endolymph moves, causing the cells' microvilli to vibrate. These cells transform the motion into auditory nerve impulses, which are then picked up by the auditory nerve.

Other Components

• Vestibular Apparatus: This organ captures the position and acceleration of our body in space and is involved in maintaining balance.
• Tympanic Membrane: The boundary between the external and middle ear, it transmits vibrations to the ossicles.

Ear Diseases

• Earwax Plug: Wax accumulation in the auditory canal can irritate the tympanic membrane.
• Otitis Media: Inflammation of the middle ear lining, typically treated with antibiotics.
• Otosclerosis: A disease causing rigidity of the oval window, leading to hearing loss due to impaired vibration transmission.
• Deafness: The inability to perceive spoken communication.
• Vertigo: A sensation of spinning, often accompanied by pallor, sweating, and tachycardia. It can be caused by earwax plugs, nerve lesions, epilepsy, migraines, etc.

Taste, Smell, and Touch

• Flavors: Taste is perceived through taste buds located on the tongue. We distinguish four basic tastes: sweet, salty, bitter, and sour.
• Olfaction: Olfactory receptors are located in the mucous membrane of the nostrils, called the pituitary gland. Olfactory neurons containing these receptors converge into the two olfactory nerves, which enter the skull and connect to the brain.

• The Skin and Touch: Touch allows us to perceive the shape and texture of objects. The skin also contains receptors for:

  • Temperature: Specific receptors for heat and cold.
  • Pain: Captured by nerve endings.
  • Pressure: Captured by skin corpuscles; the sensation is more noticeable when there is greater pressure in a specific area of the skin.

Illustrations

• Tympanum
• Vestibular apparatus
• Auditory nerve
• Ossicles (Malleus, Incus, Stapes)
• Eustachian tube
• Cochlea