Lecture 26: Vestibular System

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Questions and Answers

What is the effect of deflecting the stereocilia toward the kinocilium?

  • It depolarizes the cell membrane. (correct)
  • It inhibits the release of neurotransmitters.
  • It hyperpolarizes the cell membrane.
  • It opens K+ channels allowing K+ to flow out.

What happens to the cell membrane after the stimulus subsides?

  • Voltage-gated K+ channels remain closed.
  • The cell membrane hyperpolarizes and returns to resting potential. (correct)
  • The cell membrane remains depolarized for an extended period.
  • Calcium channels stay open longer, increasing neurotransmitter release.

How does deflection of the stereocilia away from the kinocilium affect the neurotransmitter release rate?

  • It increases the neurotransmitter release rate.
  • It results in only increased firing rate of afferent fibers.
  • It has no effect on the neurotransmitter release rate.
  • It decreases the neurotransmitter release rate. (correct)

How many semicircular canals are present in the vestibular system?

<p>Six total, three on each side. (B)</p> Signup and view all the answers

What characterizes the orientation of the semicircular canals?

<p>They are oriented orthogonally to each other. (B)</p> Signup and view all the answers

What are the primary components of the vestibular system?

<p>Semicircular canals and otolith organs (D)</p> Signup and view all the answers

What role does the vestibular system play during motion?

<p>Maintains postural stability (D)</p> Signup and view all the answers

How do vestibular hair cells respond to motion?

<p>Depolarization occurs when stereocilia move towards kinocilium (C)</p> Signup and view all the answers

What is the result of stereocilia movement away from the kinocilium?

<p>Hyperpolarization of hair cells (B)</p> Signup and view all the answers

What fluid is found within the membranous canal of the semicircular canals?

<p>Endolymph (A)</p> Signup and view all the answers

What happens to the afferent neurons at rest in the vestibular system?

<p>They have spontaneous activity due to open Ca2+ channels (A)</p> Signup and view all the answers

Which structure connects the hair cell region in the ampulla to the opposite side?

<p>Cupula (A)</p> Signup and view all the answers

What sensation might indicate an issue with the vestibular system?

<p>Nausea and dizziness (C)</p> Signup and view all the answers

How do coplanar semicircular canals function during angular movements?

<p>One excites while the other inhibits (C)</p> Signup and view all the answers

Which function does the vestibular system NOT support?

<p>Enhancing auditory perception (D)</p> Signup and view all the answers

What common characteristic do the auditory and vestibular systems share?

<p>Use of the same cranial nerve for innervation (B)</p> Signup and view all the answers

What primary structure detects motion within the vestibular system?

<p>Semicircular canals (C)</p> Signup and view all the answers

In what way does angular head motion affect the endolymph in the semicircular canals?

<p>It induces inertially-driven endolymph motion (A)</p> Signup and view all the answers

What results from the movement of stereocilia towards the kinocilium?

<p>Increased transmitter release from the hair cells (B)</p> Signup and view all the answers

What happens if there is a problem with the common fluid system of the auditory and vestibular systems?

<p>Both hearing and balance can be affected (C)</p> Signup and view all the answers

What characteristic of hair cells in the auditory and vestibular systems is similar?

<p>They operate on nearly identical principles for motion detection (D)</p> Signup and view all the answers

What is the primary function of the utricle and saccule in the inner ear?

<p>Provide information about linear acceleration (A)</p> Signup and view all the answers

How do the hair cells in the utricle and saccule differ in orientation?

<p>Utricle hair cells are towards and saccule hair cells are away from the striola (A)</p> Signup and view all the answers

What initiates the motion of the otoliths in the utricle and saccule?

<p>Inertially-driven motion due to acceleration (C)</p> Signup and view all the answers

What is the role of otoliths in the otolith organs?

<p>Create a shear force on hair cell stereocilia during motion (B)</p> Signup and view all the answers

What distinguishes the orientation of hair cells in semicircular canals from those in otolith organs?

<p>Otolith organs have hair cells oriented in opposing directions (B)</p> Signup and view all the answers

What is the significance of the striola in the otolith organs?

<p>It creates a boundary for hair-cell polarity reversal (B)</p> Signup and view all the answers

How does the size of otolith crystals differ in humans compared to those found in other species, such as cats?

<p>Human otoliths are smaller, ranging from 3 - 30 µm (A)</p> Signup and view all the answers

Which best describes the similarity between otolith organs and semicircular canals?

<p>Both use hair cells to detect motion (A)</p> Signup and view all the answers

Flashcards

Vestibular Hair Cells

Specialized sensory cells in the inner ear that detect head movement and position.

Depolarization (Hair Cells)

Stimulation from stereocilia movement towards kinocilium, increasing firing rate.

Hyperpolarization (Hair Cells)

Stimulation from stereocilia movement away from kinocilium, decreasing firing rate.

Stereocilia

Hair-like structures on vestibular hair cells that sense movement.

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Kinocilium

A single large hair cell that acts as a reference point for stereocilia movement.

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Vestibular System Function

Responsible for sensing head movement, maintaining posture, and stabilizing images.

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Otolith Organs

Part of the vestibular system, containing saccule and utricle, sensitive to gravity and linear acceleration.

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Semicircular Canals

Part of the vestibular system that senses rotational head movement.

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Vestibular Hair Cell Depolarization

Depolarization results from potassium (K+) flowing into the cell, triggered by stereocilia deflection toward the kinocilium, opening K+ channels.

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Vestibular Hair Cell Hyperpolarization

Hyperpolarization occurs when stereocilia deflect away from the kinocilium, causing K+ channels to open, leading to K+ flowing out of the cell.

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Vestibular Hair Cell Firing Rate

The firing rate of afferent fibers (nerve cells) increases with depolarization and decreases with hyperpolarization. These respond to the flow of K+ ions.

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Stereocilia Deflection

Movement of stereocilia (tiny hair-like structures) on hair cells triggers opening or closing of K+ ion channels in the cells, leading to depolarization or hyperpolarization, respectively, causing changes in the nerve firing rate.

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Endolymph

Fluid within the membranous canal of the semicircular canals, high in potassium (K+) and low in sodium (Na+).

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Perilymph

Fluid between the membranous canal and bony canal of the semicircular canals, low in potassium (K+) and high in sodium (Na+).

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Ampulla

A bulbous expansion at the base of each semicircular canal containing hair cells and a gelatinous structure called the cupula.

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Cupula

A gelatinous structure in the ampulla that bends in response to endolymph movement, triggering hair cell activation.

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Semicircular Canals: Functionally Paired

Semicircular canals work in pairs to detect rotational head movement. Movement in one canal excites hair cells, while the corresponding canal in the opposite ear inhibits hair cells.

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Vestibular System: Common Fluid System

The auditory and vestibular systems share a common fluid system (membranous labyrinth) that carries sound waves and detects head movement. Disruptions in this fluid can affect both hearing and balance.

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Vestibular System: Hair Cell Motion Detectors

Both hearing and balance use hair cells to detect motion. These hair cells function similarly, responding to different types of motion.

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Utricle and Saccule

Two fluid-filled chambers within the inner ear that detect linear acceleration and gravitational forces.

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Otoliths

Tiny calcium carbonate crystals embedded in a gelatinous mass within the utricle and saccule, acting as weight sensors.

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How do otoliths detect acceleration?

When you accelerate, the otoliths lag behind due to inertia, bending the hair cells' cilia and triggering a signal.

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Striola

A central stripe in the macula that divides it into two regions with opposite hair cell orientations.

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Utricle hair cell orientation

Hair cells in the utricle are oriented towards the striola, responding to acceleration in that direction.

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Saccule hair cell orientation

Hair cells in the saccule are oriented away from the striola, responding to acceleration in that direction.

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Otolith organs vs. semicircular canals

Both detect motion but use different mechanisms: semicircular canals sense rotational movement, otoliths sense linear acceleration and gravity.

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Study Notes

Lecture 26: Vestibular System

  • The vestibular system, comprised of otolith organs (saccule and utricle) and semicircular canals, detects motion, maintains posture, and stabilizes images during head movement.
  • Vestibular receptors are located within the labyrinth of the inner ear.
  • These receptors provide the brain with information about head motion and orientation relative to gravity.
  • The system's functions are generally unnoticed unless experiencing unusual conditions, such as motion sickness.
  • This system works in tandem with other sensory information to coordinate body position.

Topics

  • Vestibular Hair Cells
  • Semicircular Canals
  • Otolith Organs

Overview

  • The vestibular system detects motion, posture, and image stability during head movement, relying on otolith organs (saccule and utricle) and semicircular canals.
  • Located in the labyrinth of the inner ear, these receptors convey motion and orientation data to the brain.

Vestibular Hair Cells

  • Similar to auditory hair cells, motion is detected through hair cell (kinocilium and stereocilia) deflections.
  • Hair cell depolarization or hyperpolarization is direction dependent.
  • Depolarization is caused by stereocilia movement toward the kinocilium.
  • Hyperpolarization occurs with stereocilia movement away from the kinocilium.
  • This polarization change impacts firing rates of primary vestibular afferents to the brainstem.
  • At rest, spontaneous activity arises from calcium channels causing steady neurotransmitter release.
  • Movement in one direction stimulates the cranial 8th nerve, whereas the opposite direction inhibits firing.

Semicircular Canals

  • Inner ear canals with endolymph, crucial for angular head acceleration detection during head rotation.
  • Each canal is oriented orthogonally to the other, effectively monitoring rotations in different planes.
  • A membranous canal carrying endolymph sits inside bony canals; perilymph occupies the outer space.
  • Endolymph inertia triggers cupula deflection, impacting hair cell stereocilia movement and altering firing rates in response to the angular head velocity.
  • Semicircular canals are paired—right and left horizontal; right anterior/left posterior; and left anterior/right posterior—functioning as push-pull pairs. Excitation of one leads to inhibition in the other.

Otolith Organs: Utricle and Saccule

  • Otolith organs detect linear acceleration, including gravity and head position changes.
  • The utricle is horizontally oriented, while the saccule is vertically positioned.
  • Hair cells (the macula) embedded in gelatinous masses house calcium carbonate crystals (otoliths).
  • Otolith inertia, due to gravity or linear motion, causes shear forces on stereocilia.
  • Motion toward the kinocilium excites hair cells; motion away inhibits.
  • The striola in the macula divides the organ, causing differing hair-cell polarizations for linear motion detection in various directions.
  • Otolith organs and semicircular canals differ in how they detect motion.

Similarities Between Auditory and Vestibular Systems

  • Shared fluid system (membranous labyrinth).
  • Both use hair cells to detect motion.
  • Both systems are innervated by branches of the same cranial nerve (8th).

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NPB 110B Fall 2024 Lecture 26 Vestibular System I PDF

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