Physiology of Equilibrium and Balance

Flashcards covering the key concepts of equilibrium and balance, including receptor organs, pathways to the brain, and related anatomy.

What are the two components of the special sense of equilibrium?

A dynamic component (movement through space) and a static component (head position).

What type of sensory information is combined with signals from joint and muscle proprioceptors for equilibrium?

Sensory information from the inner ear.

What role does visual information play in equilibrium?

An important role.

What mediates our sense of equilibrium?

Hair cells lining the fluid-filled vestibular apparatus of the inner ear.

What forces move the stereocilia in vestibular hair cells?

Gravity and acceleration.

What is the single long cilium called on vestibular hair cells?

Kinocilium.

What is another name for the vestibular apparatus?

Membranous labyrinth.

What two saclike otolith organs make up the vestibular apparatus?

The saccule and the utricle.

What do the otolith organs tell us about?

Linear acceleration and head position.

What do the three semicircular canals sense?

Rotational acceleration in various directions.

How are the three semicircular canals oriented?

At right angles to one another.

What does the horizontal semicircular canal monitor?

Rotations associated with turning (e.g., shaking head no).

What does the posterior semicircular canal monitor?

Left-to-right rotation (e.g., tilting head toward shoulders).

What does the superior semicircular canal monitor?

Forward and back rotation (e.g., nodding head yes).

What is the enlarged chamber at one end of each semicircular canal?

Ampulla.

What sensory structure is contained within the ampulla?

Crista.

What does the crista consist of?

Hair cells and a gelatinous mass called the cupula.

What are the two otolith organs?

Utricle and saccule.

What are the sensory structures of the otolith organs called?

Maculae.

What do maculae consist of?

Hair cells, otolith membrane, and otoliths.

What happens when gravity or acceleration cause the otoliths to slide?

The otolith membrane slides, bending hair cell cilia.

When is the maculae horizontal?

When the head is in its normal upright position.

What do the maculae of the utricle sense?

Forward acceleration or deceleration and head tilt.

When are the maculae of the saccule oriented vertically?

When the head is erect.

What are the maculae of the saccule sensitive to?

Vertical forces (e.g., dropping in an elevator).

Which part of the inner ear contains cristae?

Semicircular canals.

What is the role of endolymph in the semicircular canals?

It pushes on the cupula to activate hair cells.

What is the function of otoliths in the macula?

They move in response to gravitational forces.

What is the main function of the vestibular nerve?

Transmits sensory axons from the vestibular ganglion.

Vestibular hair cells release neurotransmitter onto primary sensory neurons of which nerve?

Vestibular nerve (cranial nerve VIII, vestibulocochlear nerve).

Where do sensory neurons from the vestibular nerve synapse?

Vestibular nuclei of the medulla or the cerebellum.

What is the primary site for equilibrium processing?

Cerebellum.

What is the function of descending pathways from the vestibular nuclei to motor neurons?

To help keep the eyes locked on an object as the head turns.

Besides the vestibular nuclei, where else do sensory axons from the vestibular ganglion pass through?

Vestibular nerve.

Where do vestibular neurons send axons to influence postural muscles?

Cerebellum.

Which motor nuclei receive axons from vestibular neurons to control extrinsic eye muscles?

Oculomotor, trochlear, and abducens nuclei.

Which nucleus of the thalamus receives axons from vestibular neurons?

Posterior ventral nucleus.

Where do thalamic neurons project to regarding equilibrium?

Vestibular area of the cortex.

What sensory inputs are integrated by the vestibular nuclei?

Visual, cutaneous, proprioceptive, and vestibular input.

What are the three main outputs resulting from coordinated processing in the vestibular system?

Maintenance of balance, control of eye movement, and perception of motion.