Auditory and Vestibular Pathways: Anatomy

Auditory Pathway

The auditory pathway of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification begins with the external auditory canal External Auditory Canal Otitis Externa and includes the middle/ inner ear Inner ear The essential part of the hearing organ consists of two labyrinthine compartments: the bony labyrinthine and the membranous labyrinth. Ear: Anatomy and eventually the brainstem nuclei before sending final signals to the primary auditory cortex Primary auditory cortex The region of the cerebral cortex that receives the auditory radiation from the medial geniculate body. Cerebral Cortex: Anatomy in the temporal lobe Temporal lobe Lower lateral part of the cerebral hemisphere responsible for auditory, olfactory, and semantic processing. It is located inferior to the lateral fissure and anterior to the occipital lobe. Cerebral Cortex: Anatomy.

Peripheral components

• Outer ear Outer ear The outer part of the hearing system of the body. It includes the shell-like ear auricle which collects sound, and the external ear canal, the tympanic membrane, and the external ear cartilages. Ear: Anatomy:
  • Aurical (or pinna), auditory canal, and tympanic membrane Tympanic membrane An oval semitransparent membrane separating the external ear canal from the tympanic cavity. It contains three layers: the skin of the external ear canal; the core of radially and circularly arranged collagen fibers; and the mucosa of the middle ear. Ear: Anatomy
  • Directs sound waves to the tympanic membrane Tympanic membrane An oval semitransparent membrane separating the external ear canal from the tympanic cavity. It contains three layers: the skin of the external ear canal; the core of radially and circularly arranged collagen fibers; and the mucosa of the middle ear. Ear: Anatomy
• Middle ear Middle ear The space and structures directly internal to the tympanic membrane and external to the inner ear (labyrinth). Its major components include the auditory ossicles and the eustachian tube that connects the cavity of middle ear (tympanic cavity) to the upper part of the throat. Acute Otitis Media:
  • Begins at the tympanic membrane Tympanic membrane An oval semitransparent membrane separating the external ear canal from the tympanic cavity. It contains three layers: the skin of the external ear canal; the core of radially and circularly arranged collagen fibers; and the mucosa of the middle ear. Ear: Anatomy
  • Airspace with 3 ossicles (malleus, incus, stapes)
  • Conducts and concentrates sound
  • The stapes directs sound vibrations into the vestibule Vestibule An oval, bony chamber of the inner ear, part of the bony labyrinth. It is continuous with bony cochlea anteriorly, and semicircular canals posteriorly. The vestibule contains two communicating sacs (utricle and saccule) of the balancing apparatus. The oval window on its lateral wall is occupied by the base of the stapes of the middle ear. Ear: Anatomy of the inner ear Inner ear The essential part of the hearing organ consists of two labyrinthine compartments: the bony labyrinthine and the membranous labyrinth. Ear: Anatomy through the oval window
• Inner ear Inner ear The essential part of the hearing organ consists of two labyrinthine compartments: the bony labyrinthine and the membranous labyrinth. Ear: Anatomy:
  • Vibrations from the stapes are transferred to the perilymph in the scala vestibuli in the cochlea Cochlea The part of the inner ear (labyrinth) that is concerned with hearing. It forms the anterior part of the labyrinth, as a snail-like structure that is situated almost horizontally anterior to the vestibular labyrinth. Ear: Anatomy →
  • The vibrating perilymph pushes down on the vestibular membrane (which separates the scala vestibuli from the scala media) → 
  • Causes vibration Vibration A continuing periodic change in displacement with respect to a fixed reference. Neurological Examination of endolymph Endolymph The lymph fluid found in the membranous labyrinth of the ear. Vertigo in the scala media → 
  • Causes vibration Vibration A continuing periodic change in displacement with respect to a fixed reference. Neurological Examination of the basilar membrane (separating the scala media from the scala tympani) →
  • As the basilar membrane vibrates up and down, the hair cells (which have mechanoreceptors) resting on top of the membrane move up and down.
  • The stereocilia on top of the hair cells are anchored to the tectorial membrane.
  • As the hair cells move, the stereocilia are bent back and forth by the tectorial membrane. 
  • Bending of the stereocilia of the inner hair cells opens a mechanically gated ion channel, allowing in a quick burst of K⁺ from the surrounding endolymph Endolymph The lymph fluid found in the membranous labyrinth of the ear. Vertigo →
  • Causes the hair cell to depolarize, effectively converting the sound vibrations into auditory nerve signals:
    • Loud sounds produce vigorous vibrations → 
    • Activate more hair cells over a broader area of the basilar membrane
  • The signal is then passed to the cochlear branch of cranial nerve VIII (CN VIII), also known as the auditory nerve.
  • Tonotopy of basilar membrane: low frequency heard at apex and high frequency heard at base
    • Signals received from the apex (distal) are interpreted as low pitch.
    • Signals received from the base (proximal) are interpreted as high pitch.

Central components

Afferent Afferent Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology fibers in CN VIII convey information from the organ of Corti → auditory nuclei in the brainstem. The signal passes through brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification nuclei in the following order:

• Cochlear nuclei: located at the dorsolateral side of the brainstem at the pontomedullary junction
• Superior olivary nuclei: located in the pons Pons The front part of the hindbrain (rhombencephalon) that lies between the medulla and the midbrain (mesencephalon) ventral to the cerebellum. It is composed of two parts, the dorsal and the ventral. The pons serves as a relay station for neural pathways between the cerebellum to the cerebrum. Brain Stem: Anatomy
  • Sends signals back to the ear via CN V and CN VII efferent Efferent Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology fibers, which control the middle ear Middle ear The space and structures directly internal to the tympanic membrane and external to the inner ear (labyrinth). Its major components include the auditory ossicles and the eustachian tube that connects the cavity of middle ear (tympanic cavity) to the upper part of the throat. Acute Otitis Media muscles and cochlear tuning
  • Compares signals from the right and left to identify the direction of the sound
• Lateral lemniscal nuclei: tract of axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology in the brainstem carrying auditory information to the inferior colliculus Inferior colliculus The posterior pair of the quadrigeminal bodies which contain centers for auditory function. Brain Stem: Anatomy of the midbrain Midbrain The middle of the three primitive cerebral vesicles of the embryonic brain. Without further subdivision, midbrain develops into a short, constricted portion connecting the pons and the diencephalon. Midbrain contains two major parts, the dorsal tectum mesencephali and the ventral tegmentum mesencephali, housing components of auditory, visual, and other sensorimotor systems. Brain Stem: Anatomy
• Inferior colliculus Inferior colliculus The posterior pair of the quadrigeminal bodies which contain centers for auditory function. Brain Stem: Anatomy: located in the midbrain Midbrain The middle of the three primitive cerebral vesicles of the embryonic brain. Without further subdivision, midbrain develops into a short, constricted portion connecting the pons and the diencephalon. Midbrain contains two major parts, the dorsal tectum mesencephali and the ventral tegmentum mesencephali, housing components of auditory, visual, and other sensorimotor systems. Brain Stem: Anatomy
  • Processes fluctuations in pitch (important in understanding speech)
  • Helps locate the origin of the sound in space
  • Involved in the startle response (rapidly turning the head in response to sudden noise)
• Medial geniculate body of the thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus: Anatomy: part of thalamic relay system
• Auditory cortex: located in the anterior and posterior transverse temporal areas
  • Conscious perception Perception The process by which the nature and meaning of sensory stimuli are recognized and interpreted. Psychiatric Assessment of sound
  • Information processing

Circuitry of pathway

Outer ear Outer ear The outer part of the hearing system of the body. It includes the shell-like ear auricle which collects sound, and the external ear canal, the tympanic membrane, and the external ear cartilages. Ear: Anatomy → inner ear Inner ear The essential part of the hearing organ consists of two labyrinthine compartments: the bony labyrinthine and the membranous labyrinth. Ear: Anatomy → depolarization Depolarization Membrane Potential of hair cells in the cochlea Cochlea The part of the inner ear (labyrinth) that is concerned with hearing. It forms the anterior part of the labyrinth, as a snail-like structure that is situated almost horizontally anterior to the vestibular labyrinth. Ear: Anatomy → both the ipsilateral and contralateral superior olivary nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles → lateral lemniscus → inferior colliculus Inferior colliculus The posterior pair of the quadrigeminal bodies which contain centers for auditory function. Brain Stem: Anatomy → medial geniculate bodies Geniculate Bodies Part of the diencephalon inferior to the caudal end of the dorsal thalamus. Includes the lateral geniculate body which relays visual impulses from the optic tract to the calcarine cortex, and the medial geniculate body which relays auditory impulses from the lateral lemniscus to the auditory cortex. Thalamus: Anatomy of the thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus: Anatomy → auditory cortex of temporal lobe Temporal lobe Lower lateral part of the cerebral hemisphere responsible for auditory, olfactory, and semantic processing. It is located inferior to the lateral fissure and anterior to the occipital lobe. Cerebral Cortex: Anatomy

Vestibular Pathway

The vestibular pathway of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification begins with the utricle and saccule, with additional input from the semicircular canals. Information eventually reaches the brainstem nuclei before sending final signals to the thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus: Anatomy and cerebellum Cerebellum The cerebellum, Latin for “little brain,” is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum: Anatomy.

Functions of the vestibular pathway

The primary function of the vestibular system is to help the body maintain equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy as it relates to balance and coordination Coordination Cerebellar Disorders.

• Types of equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy:
  • Static equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy: perception Perception The process by which the nature and meaning of sensory stimuli are recognized and interpreted. Psychiatric Assessment of head orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment while stationary
  • Dynamic equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy: perception Perception The process by which the nature and meaning of sensory stimuli are recognized and interpreted. Psychiatric Assessment of motion and acceleration:
    • Linear acceleration
    • Angular acceleration
• The vestibular system monitors the orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment of the body with respect to gravity. 
• Stimulates the vestibulospinal tracts to elicit compensatory movements
• Head position relative to gravity (static equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy and linear acceleration) is sensed by the 2 otolith organs Otolith Organs Vertigo, the utricle and saccule:
  • Utricle: oriented horizontally
  • Saccule: oriented vertically
• Angular acceleration of the head is sensed by the 3 semicircular canals.

Physiology of the vestibular apparatus

Hair cells in the utricle, saccule, and semicircular canals are displaced based on their position relative to gravity, leading to depolarization Depolarization Membrane Potential and stimulation of the vestibular portion of CN VIII.

• Macula Macula An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. Eye: Anatomy:
  • Groups of hair cells and supporting cells in the saccule and utricle:
    • Macula Macula An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. Eye: Anatomy sacculi: lies almost vertically on the saccule wall
    • Macula Macula An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. Eye: Anatomy utriculi: lies almost horizontally on the utricle floor
  • Otolithic membrane:
    • A gelatinous membrane that sits atop the macula Macula An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. Eye: Anatomy
    • Stereocilia of hair cells are embedded within.
    • Contains calcium carbonate Calcium carbonate Carbonic acid calcium salt. An odorless, tasteless powder or crystal that occurs in nature. It is used therapeutically as a phosphate buffer in hemodialysis patients and as a calcium supplement. Hypocalcemia deposits called otoliths, which make the otolithic membrane top-heavy and generate inertia
  • Detects linear acceleration
• Crista ampullaris:
  • Groups of hair cells and supporting cells in the ampulla of the semicircular canals
  • Cupula:
    • A gelatinous membrane overlying the hair cells
    • Stereocilia of the hair cells are embedded within.
    • Connected to the roof of the ampulla, loosely anchoring it
  • Detects angular acceleration
• Both the macula Macula An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. Eye: Anatomy and crista ampullaris are surrounded by endolymph Endolymph The lymph fluid found in the membranous labyrinth of the ear. Vertigo.
• Process:
  • Head movement causes movement of the otolithic membrane and/or cupula relative to the underlying macula Macula An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. Eye: Anatomy/crista ampullaris (due to gravity and inertia) → 
  • Bends stereocilia of the hair cells → 
  • Opens mechanically-gated ion channels Channels The Cell: Cell Membrane → 
  • Burst of K⁺ influx → 
  • Depolarization Depolarization Membrane Potential of the hair cell
  • Impulses are transmitted via the vestibular branch of CN VIII
• Different head orientations and movements cause varying stimulation of the macula Macula An oval area in the retina, 3 to 5 mm in diameter, usually located temporal to the posterior pole of the eye and slightly below the level of the optic disk. It is characterized by the presence of a yellow pigment diffusely permeating the inner layers, contains the fovea centralis in its center, and provides the best phototropic visual acuity. It is devoid of retinal blood vessels, except in its periphery, and receives nourishment from the choriocapillaris of the choroid. Eye: Anatomy and crista ampullaris on the right and left sides, which are interpreted by the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification.

Neural pathway within the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification

The base of the hair cells synapses with sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology fibers in the vestibular branch of CN VIII. Cranial nerve VIII enters the brainstem at the pontomedullary junction (at the cerebellopontine angle Cerebellopontine angle Junction between the cerebellum and the pons. Acoustic Neuroma) and then sends fibers to the vestibular nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles and flocculonodular lobe Flocculonodular lobe Cerebellum: Anatomy in the cerebellum Cerebellum The cerebellum, Latin for “little brain,” is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum: Anatomy:

Vestibular nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles:

• Includes superior, lateral, inferior, and medial portions
• Receives the majority of afferents from CN VIII
• Sends fibers to:
  • The flocculonodular lobe Flocculonodular lobe Cerebellum: Anatomy of the cerebellum Cerebellum The cerebellum, Latin for “little brain,” is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum: Anatomy, which helps coordinate:
    • Smooth-tracking eye movements
    • Postural adjustments
  • The ascending medial longitudinal fasciculus Medial Longitudinal Fasciculus Internuclear Ophthalmoplegia ( MLF MLF Internuclear Ophthalmoplegia) (a nerve tract) → brainstem nuclei for cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. The 12 Cranial Nerves: Overview and Functions that control eye movement (CN III, IV, and VI)
  • Nuclei for CN XI that control movement of the head and neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess
  • Lateral and medial vestibulospinal tracts:
    • Descending motor tracts Motor tracts Spinal Cord: Anatomy
    • Have axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology that terminate at all spinal levels
    • Innervate axial Axial Computed Tomography (CT) (e.g., intercostal, neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess, and back) and extensor muscles important for maintaining balance and equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy
  • Thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus: Anatomy: related to conscious perception Perception The process by which the nature and meaning of sensory stimuli are recognized and interpreted. Psychiatric Assessment of equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy
• Almost all efferent Efferent Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology output from the vestibular nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles is reflexive (i.e., very difficult to voluntarily inhibit).

Flocculonodular lobe Flocculonodular lobe Cerebellum: Anatomy

• Located in the cerebellum Cerebellum The cerebellum, Latin for “little brain,” is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum: Anatomy
• Synapses with fibers leading to the:
  • Vestibular nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles (helps coordinate smooth-tracking eye movements)
  • Fastigial nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles (provides information regarding skeletal muscle and spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: Anatomy activity necessary to coordinate vestibular responses)

Vestibular pathway outputs

Clinical Relevance

• Acoustic neuroma Acoustic neuroma Acoustic neuroma, also referred to as vestibular schwannoma, is a benign tumor arising from Schwann cells of the vestibular component of the cranial nerve VIII. Acoustic neuroma forms within the internal auditory meatus and extends into the cerebellopontine angle. Acoustic Neuroma: an acoustic neuroma Acoustic neuroma Acoustic neuroma, also referred to as vestibular schwannoma, is a benign tumor arising from Schwann cells of the vestibular component of the cranial nerve VIII. Acoustic neuroma forms within the internal auditory meatus and extends into the cerebellopontine angle. Acoustic Neuroma is a benign Benign Fibroadenoma tumor Tumor Inflammation of Schwann cells that involves the cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. The 12 Cranial Nerves: Overview and Functions within the cranium Cranium The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy. Acoustic neuromas most frequently affect the vestibular branch of CN VIII. Acoustic neuromas often present with hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss and tinnitus Tinnitus A nonspecific symptom of hearing disorder characterized by the sensation of buzzing, ringing, clicking, pulsations, and other noises in the ear. Objective tinnitus refers to noises generated from within the ear or adjacent structures that can be heard by other individuals. The term subjective tinnitus is used when the sound is audible only to the affected individual. Tinnitus may occur as a manifestation of cochlear diseases; vestibulocochlear nerve diseases; intracranial hypertension; craniocerebral trauma; and other conditions. Cranial Nerve Palsies. Treatment is with surgical removal.
• Hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss: hearing impairments are classified into conductive hearing loss Conductive hearing loss Hearing loss due to interference with the mechanical reception or amplification of sound to the cochlea. The interference is in the outer or middle ear involving the ear canal; tympanic membrane; or ear ossicles. Hearing Loss and sensorineural hearing loss Sensorineural hearing loss Hearing loss resulting from damage to the cochlea and the sensorineural elements which lie internally beyond the oval and round windows. These elements include the auditory nerve and its connections in the brainstem. Hearing Loss. Conductive hearing loss Conductive hearing loss Hearing loss due to interference with the mechanical reception or amplification of sound to the cochlea. The interference is in the outer or middle ear involving the ear canal; tympanic membrane; or ear ossicles. Hearing Loss comes about when there is a problem transferring sound waves anywhere along the pathway from the outer ear Outer ear The outer part of the hearing system of the body. It includes the shell-like ear auricle which collects sound, and the external ear canal, the tympanic membrane, and the external ear cartilages. Ear: Anatomy, the tympanic membrane Tympanic membrane An oval semitransparent membrane separating the external ear canal from the tympanic cavity. It contains three layers: the skin of the external ear canal; the core of radially and circularly arranged collagen fibers; and the mucosa of the middle ear. Ear: Anatomy, or middle ear Middle ear The space and structures directly internal to the tympanic membrane and external to the inner ear (labyrinth). Its major components include the auditory ossicles and the eustachian tube that connects the cavity of middle ear (tympanic cavity) to the upper part of the throat. Acute Otitis Media. In cases of sensorineural hearing loss Sensorineural hearing loss Hearing loss resulting from damage to the cochlea and the sensorineural elements which lie internally beyond the oval and round windows. These elements include the auditory nerve and its connections in the brainstem. Hearing Loss, there is an error Error Refers to any act of commission (doing something wrong) or omission (failing to do something right) that exposes patients to potentially hazardous situations. Disclosure of Information in the transmission of auditory stimuli from the cochlea Cochlea The part of the inner ear (labyrinth) that is concerned with hearing. It forms the anterior part of the labyrinth, as a snail-like structure that is situated almost horizontally anterior to the vestibular labyrinth. Ear: Anatomy to the auditory nuclei.
• Vertigo Vertigo Vertigo is defined as the perceived sensation of rotational motion while remaining still. A very common complaint in primary care and the ER, vertigo is more frequently experienced by women and its prevalence increases with age. Vertigo is classified into peripheral or central based on its etiology. Vertigo: the sensation of movement between oneself and the surroundings when no movement is actually occurring. Vertigo Vertigo Vertigo is defined as the perceived sensation of rotational motion while remaining still. A very common complaint in primary care and the ER, vertigo is more frequently experienced by women and its prevalence increases with age. Vertigo is classified into peripheral or central based on its etiology. Vertigo is not limited to a feeling of rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays (spinning); other forms include upward lifting, swaying, rocking, and unsystematic movement. Vertigo Vertigo Vertigo is defined as the perceived sensation of rotational motion while remaining still. A very common complaint in primary care and the ER, vertigo is more frequently experienced by women and its prevalence increases with age. Vertigo is classified into peripheral or central based on its etiology. Vertigo most often occurs due to problems within the semicircular canals.