Sense Organs and Ear Structure

Sense Organs

• Sense organs are organs that respond to external stimuli and send impulses to the sensory nervous system.
• The five main sense organs are the nose (smell), ear (hearing), tongue (taste), eyes (vision), and skin (touch).

Ears

• Otology is the study of the ear.
• Otolaryngology focuses on the ears, nose, and throat (ENT).
• The ears have two main functions: hearing and maintaining balance.
• The human ear can hear sounds in the range of 20-20,000 Hz.

Ear Structure

• The ear is divided into three regions: the outer ear, middle ear, and inner ear.
• The outer ear includes the pinna, ear canal, and eardrum.
• The pinna is the funnel-shaped structure made of cartilage; it is a vestigial organ.
• The ear canal contains fine hairs and ceruminous glands (wax glands) and carries soundwaves to the middle ear.
• The eardrum (tympanum) separates the outer ear from the middle ear.
• The middle ear is an air-filled cavity containing three small bones called ear ossicles: malleus, incus, and stapes.
• The malleus is hammer-shaped, the incus is anvil-shaped, and the stapes is stirrup-shaped.
• The stapes is the smallest bone in the human body.
• The stapedius is the smallest muscle in the body.
• The eustachian tube connects the middle ear to the nasopharynx, helping to equalize pressure on both sides of the eardrum.
• The inner ear is a fluid-filled cavity called the labyrinth, consisting of the bony labyrinth and the membranous labyrinth.
• The membranous labyrinth is located within the bony labyrinth and is surrounded by a fluid called perilymph.
• The membranous labyrinth is filled with a fluid called endolymph.

Inner Ear Structures

• Semicircular canals are involved in balance.
• Vestibule is involved in balance.
• Cochlea is responsible for hearing and contains the Organ of Corti.
• The Organ of Corti has hair-like cells on its basilar membrane.
• When fluid in the cochlea moves and vibrates due to sound waves, the hair cells also vibrate, sending electrical signals to the brain via the auditory nerve.

Skin

• The skin is the largest organ in the human body.
• Dermatology is the study of the skin.
• Melanin is the pigment that gives color to the skin.
• Melanin protects the skin from harmful UV rays from the sun.
• Albinism is a genetic disorder that causes low melanin production.
• The skin has general receptors that detect touch, pain, pressure, and temperature.
• The skin also plays a role in excretion.
• The skin has two types of glands: sweat glands and sebaceous glands.

Skin Layers

• The epidermis is the outer layer of the skin, lacking nerves and blood vessels. It provides protection.
• The dermis is the middle layer of the skin, containing blood vessels, nerves, hair follicles, sweat glands, and sebaceous glands. The blood vessels in the dermis provide nutrients to the epidermis.
• The subcutaneous layer is the innermost layer of the skin, made of fat and connective tissue. It helps regulate temperature.

Nose

• The nose is the olfactory organ.
• Rhinology is the study of the nose.
• The nasal mucosa and epithelium are called the olfactory epithelium.
• The nasal cavity is lined with olfactory cells (chemoreceptors), which conduct nerve impulses to the brain via the olfactory nerve.
• Anosmia is the inability to smell.