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Questions and Answers
What is the role of the mechanical structures in the auditory system?
What is the role of the mechanical structures in the auditory system?
Which of the following best describes frequency in the context of sound?
Which of the following best describes frequency in the context of sound?
At what frequency range can humans typically perceive sound?
At what frequency range can humans typically perceive sound?
How is sound processed in the auditory system after it is perceived?
How is sound processed in the auditory system after it is perceived?
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What is the relationship between sound wave frequency and pitch?
What is the relationship between sound wave frequency and pitch?
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What is the primary function of the tensor tympani and stapedius muscles?
What is the primary function of the tensor tympani and stapedius muscles?
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Which cranial nerves innervate the tensor tympani and stapedius muscles, respectively?
Which cranial nerves innervate the tensor tympani and stapedius muscles, respectively?
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What role does the inner ear play in auditory and vestibular functions?
What role does the inner ear play in auditory and vestibular functions?
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Why is equalizing pressure important for the tympanic membrane?
Why is equalizing pressure important for the tympanic membrane?
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What can happen to the orientation of inner ear structures between the right and left ear?
What can happen to the orientation of inner ear structures between the right and left ear?
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What is the primary function of the Endolymph in the inner ear?
What is the primary function of the Endolymph in the inner ear?
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Which structure within the Cochlear Duct is primarily responsible for transduction of sound into nerve impulses?
Which structure within the Cochlear Duct is primarily responsible for transduction of sound into nerve impulses?
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Where is Perilymph located within the inner ear?
Where is Perilymph located within the inner ear?
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Which ion concentration is high in Endolymph compared to Perilymph?
Which ion concentration is high in Endolymph compared to Perilymph?
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What structure extends over the hair cells in the Organ of Corti?
What structure extends over the hair cells in the Organ of Corti?
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What is the primary function of the outer ear?
What is the primary function of the outer ear?
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Which of the following structures is NOT part of the inner ear?
Which of the following structures is NOT part of the inner ear?
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How do the ossicles function in the auditory system?
How do the ossicles function in the auditory system?
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What is the function of the tympanic membrane?
What is the function of the tympanic membrane?
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What role does the Eustachian Tube play in the auditory system?
What role does the Eustachian Tube play in the auditory system?
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Which ossicle is known as the 'stirrup'?
Which ossicle is known as the 'stirrup'?
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What must occur for sound vibrations to travel from the middle ear to the inner ear?
What must occur for sound vibrations to travel from the middle ear to the inner ear?
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Which of the following is NOT true about the cochlea?
Which of the following is NOT true about the cochlea?
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What is the primary purpose of the Vestibulo-ocular Reflex?
What is the primary purpose of the Vestibulo-ocular Reflex?
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Which reflex pathway is responsible for postural adjustments of the head during rotational movements?
Which reflex pathway is responsible for postural adjustments of the head during rotational movements?
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The Vestibulo-spinal Reflex contributes mainly to which of the following?
The Vestibulo-spinal Reflex contributes mainly to which of the following?
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Which cranial nerves are involved in the connections of the Vestibular Ocular Reflex?
Which cranial nerves are involved in the connections of the Vestibular Ocular Reflex?
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What would likely happen without the Vestibulo-ocular Reflex?
What would likely happen without the Vestibulo-ocular Reflex?
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What is the primary role of the Otolith Organs in the vestibular system?
What is the primary role of the Otolith Organs in the vestibular system?
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What structure connects the vestibular sensory hair cells to the central nervous system?
What structure connects the vestibular sensory hair cells to the central nervous system?
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Where is the Vestibular Nuclear Complex primarily located?
Where is the Vestibular Nuclear Complex primarily located?
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Which of the following is NOT a function of the vestibular nuclei?
Which of the following is NOT a function of the vestibular nuclei?
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Which layer covers the outer layer of the Otolith Membrane?
Which layer covers the outer layer of the Otolith Membrane?
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What is a function of the vestibular ganglion?
What is a function of the vestibular ganglion?
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In which pathway is the first synapse for nerve impulses of the vestibular system located?
In which pathway is the first synapse for nerve impulses of the vestibular system located?
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What type of acceleration do hair cells in the Utricle and Saccule primarily detect?
What type of acceleration do hair cells in the Utricle and Saccule primarily detect?
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Study Notes
OCT 1172Y: Introduction to Auditory and Vestibular Systems
- Course: Introduction to Auditory and Vestibular Systems
- Instructor: Mayleen Torres, OT Reg.(Ont.), MSCOT, 2024
- Date: October 4th, 2024
Auditory System
-
Overview:
- What is the Auditory System?
- Sound Wave
- Mechanical Ear Structures (where receptors are located and sensory stimulus is received)
- Neurological Pathway (where nerve signals synapse in CNS and are interpreted)
-
How Sound is Processed:
- Perceived (Ear collects sound)
- Processed (Mechanical vibration of inner structures)
- Relayed to higher centers (Transduction of nerve impulses)
- Reassembled for interpretation (Cortex of brain)
What is Sound?
- Vibration of air molecules: from a source (i.e., voice, object).
- Sound Wave: alternating or fluctuating pressures (High and low) of air molecules.
-
2 Types of Sound:
- Frequency (Hertz, Hz): Pitch (How many sound waves (#) in a period of time (cycle)). Higher frequency = higher pitch. Example: Human range (20-20,000 Hz), Animal range (45,000-123,000 Hz)
- Amplitude (Decibels, dB): Volume. Higher amplitude = higher volume.
Mechanical Structures of the Auditory System
-
3 Main Structures:
- Outer Ear: Pinna/Auricle, External Auditory Meatus (Auditory Canal), Tympanic Membrane
- Middle Ear: Ossicles (Malleus, Incus, Stapes), Oval Window, Pharyngotympanic (Eustachian) Tube
- Inner Ear: Cochlea, Organ of Corti
Auditory System: Outer Ear
- Function: collects and funnels sound waves onto eardrum
- Pinna/Auricle: additional function of sound localization
- External Auditory Meatus: canal to funnel sound waves/vibrations onto Tympanic Membrane
- Tympanic Membrane: eardrum, sound vibration first stop, vibration of Tympanic Membrane to Middle Ear (ossicles)
Auditory System: Middle Ear
- Function: Amplifies mechanical vibrations from eardrum to inner ear.
- Tympanic Cavity: Enclosed, air-filled space.
- Ossicles (3 small bones): Malleus, Incus, Stapes; Function: mechanical vibration from Tympanic Membrane to Oval Window.
- Oval Window: Smaller membrane than Tympanic Membrane; amplifies the vibration to push fluid in Inner Ear. Stronger vibration needed to go from air-filled to inner fluid-filled space.
Pharyngotympanic (Eustachian) Tube
- Connects middle ear to nasopharynx; regulates pressure within middle ear
- 2 Muscles: Tensor Tympani (CN V), Stapedius Muscle (CN VII) dampen ossicles' movement when contracting.
- Why is this important? Protective measure for the auditory nerve (by reducing vibration of ossicles), equalizes pressure on either side of Tympanic Membrane (e.g., popping ears on airplane, yawning), filters low-frequency background noises (like in a loud party).
Important Structures
- Vestibular and auditory structures: embedded in a bony labyrinth within the petrous part of the temporal bone of the skull.
- Inner Ear structures: on the right and left sides are oriented opposite to each other (mirror orientation).
Inner Ear Structures
- Function: Houses structures for Auditory and Vestibular organs where nerve impulses occur. Neurological signals are initially detected here before travelling to cerebral cortex destination.
- Enclosed, fluid-filled space: Location: Petrous portion of Temporal Lobe.
Inner Ear: Perilymph & Endolymph
- Perilymph: Fluid in space between Bony Labyrinth and Membranous Labyrinth. Low K+; high Na+; Composition: similar to CSV + extracellular fluid.
- Endolymph: Fluid within Membranous Labyrinth. High K+; low Na+. Composition: similar to intracellular fluid. Critical role in signal transduction.
Inner Ear: Cochlea
- Cochlea: Snail shell-shaped bony structure, chambers in Cochlea: Vestibular Duct (Scala Vestibuli), Cochlear Duct, Tympanic Duct (Scala Tympani).
Organ of Corti
- Location: specialized cells and sensory receptors for auditory function.
- Function: Transduction of sound waves (vibration) into action potential (nerve impulse).
- Important Structures: Basilar Membrane (Organ of Corti attached here; flexible floor of Cochlear Duct), Hair Cell + Supporting Hair Cell (receptor cells), Stereocilia + Kinocilia (mechanoreceptors responding to vibration of sound waves), Tectorial Membrane (gelatinous, extends over hair cells, stationary).
Inner Ear: Transmission of Sound
- Vibrations travel through tympanic duct > Middle Ear > Inner Ear > Basilar Membrane.
- Basilar Membrane vibrates, creating friction/shearing force against Tectorial membrane > Stereocilia of Outer Hair Cells move.
- Towards tallest hair fibre = depolarization; Away from tallest hair fibre = hyperpolarization (no action potential).
Inner Ear: Transmission of Sound (cont.)
- Movement of Stapes pushes fluid (Endolymph) in Cochlear Duct.
- Causes Basilar Membrane to move up and down; Hair cells(Stereocilia) bend via shearing force with Tectorial Membrane.
- Opens K+ channels via TIP LINKS; K+ depolarizes cells (creates nerve impulses/action potential); Nerve impulse travels along Cochlear Nerve → Brain/CNS.
Inner Ear: Sound Interpretation
- Frequency: High Pitch = Base of Basilar Membrane (stiffer and shorter), Low Pitch = Apex (end or Helicotrema) of Basilar Membrane (flexible and longer). Example: Piano strings
- Amplitude: Loud sounds cause more hair cells to move (more nerve signal to brain).
Neurological Pathway of the Auditory System
- Basic Overview of Ascending Auditory Pathway: Sound Wave, Mechanical Ear Structures, Neurological Process (Brainstem Synapse, Thalamus Synapse, Cerebrum - Primary Cortex(sound processed and interpreted)).
- Terminology Review: Transduction (Conversion of Energy into another form), Ipsilateral (Same side), Contralateral (Opposite side).
Auditory Nerve Fibres and their Synapses
- Cochlear Nerve (CN VIII): Spiral Ganglion (outside Cochlear Duct within cochlea, collection of cell bodies from axons connected to Outer and Inner hair cells); Relaying auditory information from sensory hair cells to auditory system/circuits.
- Inner Hair Cells: Majority of axons from Inner hair cells (primary sensory cells of cochlea, responsible for relaying sound information to the brain).
- Outer Hair Cells: Primarily act as mechanical amplifiers and filter for background noises.
Brainstem Review
- Location where CN VIII enters brainstem: Pontomedullary Junction (between Pons and Medulla).
Auditory Nerve Fibres and their Synapses
- Afferent Pathway to Brain (Cochlear nerve joins with vestibular nerve --> CN VIII); Neurons from cochlear division of CN VIII synapse in cochlear nuclei (ventral and dorsal aspect); Majority of second-order neurons decussate (cross) to the contralateral side and travel to the inferior colliculus (primary pathway); Some neurons remain IPSILATERAL(secondary pathway); Third-order neurons travel to the medial geniculate nucleus of the thalamus.
Auditory Nerve Fibres and their Synapses (cont.)
- Spiral ganglion, Cochlear Division, superior olivary complex, lateral lemniscus, inferior colliculus, medial geniculate nucleus, auditory cortex. Auditory pathway to cerebral cortex.
- Mnemonic: ECOLI MA.
Vestibular System
-
Overview:
- What is the Vestibular System?
- Mechanical Ear Structures (where receptors are located and sensory stimulus is received)
- Neurological Pathway (complex) (where nerve signals synapse in CNS and are interpreted).
-
Sensory System:
- Motion
- Head position
- Spatial orientation
Vestibular System Functions
- Balance (maintains head & body movement) and posture
Mechanical Structures of the Vestibular System
- Review Inner Ear (Bony Labyrinth): Semicircular Canals, Vestibule.
- Review Inner Ear (Membranous Labyrinth): Semicircular Ducts, Utricle, Saccule, Ampullae
Inner Ear: Perilymph & Endolymph (Vestibular System)
- Perilymph: Fluid in space between bony and membranous labyrinths; Low K+, High Na+, similar to cerebrospinal fluid + extracellular
- Endolymph: Fluid within membranous labyrinth; High K+, low Na+, similar to intracellular
Vestibular System: Important Structures
- 3 bony semicircular canals with membranous semicircular ducts (contain endolymph);
- Anterior, Posterior, Horizontal; Perceive rotational movement.
- Vestibule: Utricle, Saccule; Perceive linear movement.
Receptor Organs: Semicircular Canal
- Ampulla: Enlargement at the base of semicircular ducts; contains Receptor Organs.
- Cristae Ampullaris (Crista): Hair cells (Stereocilia/Kinocilia) embedded here, create nerve impulse via cupula (gelatinous material surrounding cilia & cristae ampullaris).
Receptor Organs: Vestibule
- Utricle: Macula on floor, connected to semicircular ducts (horizontal planar movement, forward-backward acceleration).
- Saccule: Macula on medial wall, connected (vertical planar movement, gravitational forces).
How Receptors Function in Vestibular System: Semicircular Canal
- Hair cells function: nerve impulse (action potential) generated when cupula is shifted and causes cilia displacement.
- 3 Planes: detects rotational acceleration and balance in directional planes. (Anterior/Posterior/Horizontal)
Vestibular System: Rotational Acceleration + Balance
- Complimentary pairing of semicircular canals (right and left sides are oriented opposite—mirror orientation), depolarization of hair cells on one side = reciprocal hyperpolarization on the contralateral side.
Vestibular System: Linear Acceleration + Balance
- Otolith organs detect linear acceleration and gravity—detect motion.
- Hair cells of macula embedded within gelatinous otolith membrane, containing calcium carbonate crystals (otoconia/otoliths). Otolith membrane shifts in response to head movement = detecting linear acceleration & gravity.
Neurological Pathway of the Vestibular System
- Vestibular system pathways, peripheral to CNS (outside inner ear structure (vestibular ganglion)), vestibular ganglion (a collection of cell bodies from axons connected to receptor cells (ampulla, saccule, utricle)), relays information from vestibular sensory hair cells to areas within CNS.
Vestibular system Pathways: Vestibular Nuclear Complex
- Located in brainstem (between pons and medulla), adjacent to inferior cerebellar peduncle and cochlear nuclei
- 4 Vestibular nuclei; medial, lateral, inferior, superior nuclei are integration centers that receive afferents from inner ear, project to a variety of structures, and are parts of feedback loops.
Vestibular System Pathways: Vestibular Nuclear Complex (cont.)
- Receive vestibular nerve information; process information and relay signals; control of eye, head and body movements.
- Medial and Lateral vestibulospinal tracts. Medial vestibulospinal tract controls neck muscles; Lateral vestibulospinal tract controls proximal muscles.
- Connections to thalamus, cerebellum, visual pathways & higher-level cortex, and other areas of CNS.
Vestibular System Reflex Pathways
- 3 major reflex pathways (i) Vestibulo-ocular Reflex (VOR), (ii) Vestibulo-cervical Reflex, (iii) Vestibulo-spinal Reflex; each contributes crucial adjustments to maintain balance and spatial orientation during head and body movements. Adjusts eye movement to head movement.
Vestibular System Pathways: Reflex Pathway
- VOR: Connections in ascending tracts and Abducens, Trochlear, Oculomotor (CNIII)
- Vestibular nuclei process information and provide signals for vestibular reflexes;
- VOR (Vestibulo-ocular Reflex) keeps eyes fixed on the target when head turns—eyes turn reflexly in opposite direction to head rotation.
Vestibular System Pathways (overview for interest only)
- Vestibular nystagmus possible causes—caused by the vestibular system, objects moving in environment, or a lesion in the system vs. a normal nystagmus.
- Note:* Several slides in the presentation are labeled 'FOR INTEREST ONLY'. These sections provide supplementary details and are not a core study element for the auditory and vestibular systems.
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Description
Test your knowledge on the mechanical structures and functions of the auditory system. This quiz covers key concepts such as sound perception, frequency, inner ear roles, and the function of associated muscles. Enhance your understanding of how sound is processed in humans.
