The Vestibular System: Definition, Anatomy & Function

The Vestibular System: Definition, Anatomy & Function
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  • 1:07 Anatomy
  • 2:31 Function
  • 5:22 Lesson Summary
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Lesson Transcript
Instructor: Sarah Phenix
You rely on your sense of balance to do everything from walking and running to skateboarding, snowboarding, and surfing. In this lesson, we'll explore the vestibular system and find out how it constructs your sense of balance.

Definition

Have you ever had an ear infection and noticed that you had difficulty with balance or dizziness? That's because your ears aren't just for hearing. They also serve as your centers for balance and spatial equilibrium, without which your brain wouldn't have the necessary information to understand your body's relationship with your external environment.

The vestibular system is a collection of structures in your inner ear that provides you with your sense of balance and an awareness of your spatial orientation, meaning a sense of whether you are right-side up or upside-down. Your brain then integrates that information with other sensory information from your body to coordinate smooth and well-timed body movements.

It's a pretty complex series of actions and not something we're born innately knowing to do. We all learned to walk as toddlers by honing and refining these interacting systems, and every time you learn something new that requires balance (like riding a bike, snowboarding, surfing, or paddle boarding) your brain further modifies and refines these integration processes.

Anatomy

Let's take a quick look at the structures of the ear to discern which are primarily auditory, or hearing, in nature and which are part of the vestibular system.

The auricle, Latin for 'outer ear', also known as the pinna, meaning 'wing' or 'fin', is the external, funnel-shaped outer ear that directs sound into the ear canal, otherwise known as the external acoustic meatus, 'meatus' being Latin for 'canal' or 'passageway'. This passageway carries sound down to the tympanic membrane, or ear drum, which reverberates to transmit sound into the bones of the inner ear.

Within the tympanic cavity, there are three auditory ossicles, or bones, that pound against one another, transmitting the sound waves that vibrate against the tympanic membrane onto something called the oval window of the inner ear. The oval window is the membranous connection point between the auditory ossicles and the fluid-filled structure of the inner ear, called the membraneous labyrinth. Half of the membraneous labyrinth, the cochlea, is dedicated to converting sound waves into neural signals, while the other half, the vestibular system, is dedicated to deriving your sense of balance. Both halves use the vestibulocochlear nerve, which conducts neural signals to the brain for interpretation and integration.

Function

In the vestibular half of the inner ear, there are three semicircular canals, so named for their semicircular shape, which run in three different orientations. These orientations effectively enable your vestibular system to triangulate the orientation of your head and, consequently, your sense of balance, based on the canals' three points of reference. The vestibular system does this via three sensory structures, called cristae ampularis, that join the ends of the semicircular canals

Cristae ampularis are sensory structures that border either end of the semicircular canals and transmit signals to the vestibulocochlear nerve regarding your head's rotation. How do they do this? Well, each cristae ampularis is lined with a collection of little hair cells, so named for the hair-like filaments, called stereocilia, that project from their tops. The stereocilia are embedded in a large gelatinous substance, called the cupula, that, when depressed by the fluid on either side, stimulates the stereocilia of the hair cells, which then conduct signals to the ventibulocohlear nerve. Let's put this description of the cristae ampularis into action.

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