Special Senses: Balance

By: Amanda SherryZack Black

Meghan DesaiDarin Johnson

Mazbura Rahman

What is Balance?

• Balance is the ability to keep the body’s center of mass over its base of support

• It is necessary because of voluntary movements made possible by skeletal muscle that alter the body’s position and change the body’s equilibrium

• Vestibular system is necessary for the body to maintain balance

Associated Structures

Ear/Vestibular System

Associated Structures

• Muscular system allows shifts in equilibrium

Two types of Equilibrium

• Static Equilibrium– Determines equilibrium when the head is

at rest or following vertical movements – If the head is tilted or if it’s upright this

type of equilibrium helps to determine position• Ex. A diver would know which way is up if

suspended in the water because of this system

Two Types of Equilibrium

• Dynamic Equilibrium– Determines equilibrium when the head

is moving, specifically in angular or rotary movements• If the head is moving from side to side, or

rotating as if to stretch the neck this type of equilibrium would be utilized– Ex. An dancer twirling on the dance floor

Internal Ear

• Internal ear is comprised of many chambers or osseous labyrinths

• 3 subdivisions of the labyrinths are the cochlea, vestibule, and semicircular canals

• Vestibule is situated between the semicircular canals

and the cochlea

Internal Ear

• Bony labyrinth filled with plasma like fluid called perilymph

• Membranous labyrinth is suspended in the perilymph

• Membranous labyrinth contains a thicker fluid called endolymph

Receptors

• Receptors in the inner ear are called the Vestibular apparatus – Vestibular apparatus has two functional

arms– One arm is responsible for static

equilibrium– One arm is responsible for dynamic

equilibrium

ReceptorsStatic• -Maculae – reports changes on the

position of the head in space with respect to the pull of gravity when the body is not moving– Each Macula is a patch of hairs connected to

the otolithic hair membrane– Otolithic membrane- jellylike mass with

otoliths that shift in regards to changes in gravity

– This bends hairs and activate cells within the hairs that send impulses along the vestibular nerve to the brain/cerebellum

Pathway

• Vestibulocochlear Nerve- runs from equilibrium receptors/ hearing receptors to the brain stem and cerebellum

• This is an afferent nerve pathway

Disorders

• Labyrinthitis- infection causing inflammation of the inner ear that causing dizziness and loss of balance, frequently associated with upper respiratory infections like the flu. When there is sensory imput from the eyes, and inflammation in the inner ear, the messages from the vestibular system and optic system don’t match up. This is why vertigo occurs.

Disorders

• Perilymph fistula - leaking of the fluid in the periylmph into the middle ear. This usually results from head injuries, chronic ear infections, or changes in atmospheric pressure. This causes dizziness, nausea, and imbalance when standing.

Works CitedBrody, Jane E. (2008). Preserving a Fundamental Sense: Balance. Retrieved Feb. 6, 2013 from http://www.nytimes.com/2008/01/08/health/08brod.html?_r=0. Hanes DA, McCollum G. (2006). Balance. Journal of Vestibular Research, 16, 75–91. Retrieved Feb. 6, 2013 from http://www.scimagojr.com/journalsearch.php?q=23481&tip=sid. Marieb, Elaine N. (2009). Essentials of Human Anatomy & Physiology. San Francisco: Pearson. National Dizzy & Balance Center. (2012). The Human Balance System. Retrieved on Feb. 6, 2013 from http://www.stopdizziness.com/resources_balance.asp. Watson, Mary Ann & Black, F. Owen. (2011). The Human Balance System - Good Balance is often taken for Granted. Retrieved Feb. 6, 2013 from   http://vestibular.org/understanding-vestibular-disorder/human-balance-system