The equilibrium sense is involved in maintaining balance. It is hard to think of equilibrium as a sense, because it does not see, hear, taste, smell or feel. Equilibrium is helped maintained by the vestibular system inside the inner ear.

For interesting slideshows about equilibrium, visit SlideShares on the Vestibular System and on Balance!

Ear Anatomy

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Outer Ear Anatomy
1.) Pinna (auricle) - the shell shaped structure commonly known as the "ear" that surrounds the auditory canal opening
2.) Auditory Canal - Also called the external acoustic meatus, commonly called the "ear canal", is a short narrow canal lined with skin. It also contains ceruminous glands, earwax (cerumen) , and the eardrum (tympanic membrane)
3.) Ceruminous Glands - are the glands within the auditory canal that secrete a yellow, waxy substance also known as "earwax"
4.) Tympanic Membrane - known as the "eardrum", it vibrates when sound waves hit it. This membrane separates the outer ear from the middle ear

Middle Ear Anatomy
1.) Tympanic Cavity - a small, air filled cavity within the temporal bone
2.) Oval Window - a small opening on the lateral part of the tympanic cavity
3.)Round Window - another small opening of the tympanic cavity, inferior to the oval window, and is membrane covered
4.) Pharyngotympanic Tube - a tube that runs down the throat to link the middle ear to the throat. It is usually flat and closed, but temporarily opens while swallowing or yawning to help equalize pressure between the middle ear, outer ear and atmospheric pressure
5.) Ossicles - three small bones that transmit the vibrations from the eardrum to fluids in the inner ear
Hammer (malleus) - when the eardrum moves, the hammer moves with it, and transfers the vibrations to the anvil which passes it on to the stirrup. The stirrup then presses on the oval window, which causes motion of the fluids in the inner ear, exciting the hearing receptors

Inner Ear Anatomy
Made up of the bony or osseous, labyrinth, which is deep within the temporal bone, just behind the eye socket. The three subdivisions of the bony labyrinth are the cochlea, the vestibule and the semicircular canals. The vestibule is between the cochlea and the vestibule. Theses three subdivisions are actually just cavities, and not actual "structures". The bony labyrinth is filled with plasma-like fluid called perilymph. In the perilymph is the suspended membranous labyrinth, which is a set of membrane sacs filled with a thicker fluid called endolymph.


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For information regarding the physiology of equilibrium, visit the Encyclopedia Britannica.
Equilibrium can be divided into two subdivisions - Dynamic and Static Equilibrium.

Static Equilibrium

The membrane sacs in the vestibule are receptors called maculae. They send signals about the position of the head to tell the brain about that position of gravity on the body. There are "hairs" embedded in the otolithic membrane called otoliths that sense the change in direction of the fluid. The hair cells send impulses to the cerebellum informing it of the position of the head. These sacs respond to up and down movements.

Dynamic Equilibrium

The dynamic equilibrium receptos, found in the semicircular canals respond to rotating and angular movements. Within each membranous semicircular canal is a receptor called a crista ampullaris that consists of hair cells that that are covered in the gel cap called a cupula. When your head rotates the cupula lags behind, and drags against the endolymph, and the cupula bends with the body's motion. This then stimulates the hair cells, which send impulses up the vestibular nerve to the cerebellum. When you are moving at a constant rate, the receptors gradually stop sending the impulses.

For a complete overview of the vestibular system, visit the YBU pdf!

Please visit Mannys Wiki!

For sources, please visit Diigo.