The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a

cranial nerve Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...

that transmits

sound In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the br ...

and equilibrium (balance) information from the

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...

to the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. Through olivocochlear fibers, it also transmits motor and modulatory information from the

superior olivary complex The superior olivary complex (SOC) or superior olive is a collection of brainstem nuclei that is located in pons, functions in multiple aspects of hearing and is an important component of the ascending and descending auditory pathways of the aud ...

in the brainstem to the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (cochlea), modiolus. A core component of the cochlea is the organ of Cort ...

Structure

The vestibulocochlear nerve consists mostly of

bipolar neuron A bipolar neuron, or bipolar cell, is a type of neuron characterized by having both an axon and a dendrite extending from the soma (cell body) in opposite directions. These neurons are predominantly found in the retina and olfactory system. The em ...

s and splits into two large divisions: the

cochlear nerve The cochlear nerve (also auditory nerve or acoustic nerve) is one of two parts of the vestibulocochlear nerve, a cranial nerve present in amniotes, the other part being the vestibular nerve. The cochlear nerve carries auditory sensory information ...

and the

vestibular nerve The vestibular nerve is one of the two branches of the vestibulocochlear nerve (the cochlear nerve being the other). In humans the vestibular nerve transmits sensory information from vestibular hair cells located in the two otolith organs (the u ...

. Cranial nerve 8, the vestibulocochlear nerve, goes to the middle portion of the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

called the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other mammals, lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...

(which then is largely composed of fibers going to the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

). The 8th cranial nerve runs between the base of the pons and

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

(the lower portion of the brainstem). This junction between the pons, medulla, and cerebellum that contains the 8th nerve is called the cerebellopontine angle. The vestibulocochlear nerve is accompanied by the

labyrinthine artery The labyrinthine artery (auditory artery, internal auditory artery) is a branch of either the anterior inferior cerebellar artery or the basilar artery. It accompanies the vestibulocochlear nerve (CN VIII) through the internal acoustic meatus. It ...

, which usually branches off from the

anterior inferior cerebellar artery The anterior inferior cerebellar artery (AICA) is one of three pairs of artery, arteries that supplies blood to the cerebellum. It arises from the basilar artery on each side at the level of the junction between the medulla oblongata and the pons ...

at the cerebellopontine angle, and then goes with the 7th nerve through the internal acoustic meatus to the internal ear. The cochlear nerve travels away from the

of the

where it starts as the spiral ganglia. Processes from the

organ of Corti The organ of Corti, or spiral organ, is the receptor organ for hearing and is located in the mammalian cochlea. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses' action potential. Trans ...

conduct afferent transmission to the spiral ganglia. It is the inner hair cells of the organ of Corti that are responsible for activation of afferent receptors in response to pressure waves reaching the

basilar membrane The basilar membrane is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani. The basilar membrane moves up and down ...

through the transduction of sound. The exact mechanism by which sound is transmitted by the

neurons A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

of the cochlear nerve is uncertain; the two competing theories are place theory and temporal theory. The vestibular nerve travels from the

vestibular system The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating motor coordination, movement with balance. Together with the cochlea, a part of the auditory sys ...

of the inner ear. The vestibular ganglion houses the cell bodies of the bipolar neurons and extends processes to five sensory organs. Three of these are the

cristae A crista (; : cristae) is a fold in the inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large amount of surface area for che ...

located in the ampullae of the semicircular canals. Hair cells of the cristae activate afferent receptors in response to rotational acceleration. The other two sensory organs supplied by the vestibular neurons are the maculae of the

saccule The saccule (Latin: sacculus) is a bed of sensory cells in the inner ear that detects linear acceleration and head tilting in the vertical plane, and converts these vibrations into electrical impulses to be interpreted by the brain. When the he ...

and utricle. Hair cells of the maculae in the utricle activate afferent receptors in response to linear acceleration, while hair cells of the maculae in the saccule respond to vertically directed linear force.

Development

The vestibulocochlear nerve is derived from the

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

nic otic placode.

Function

This is the

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

along which the sensory cells (the hair cells) of the inner ear transmit information to the

. It consists of the cochlear nerve, carrying details about

hearing Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory sci ...

, and the vestibular nerve, carrying information about

balance Balance may refer to: Common meanings * Balance (ability) in biomechanics * Balance (accounting) * Balance or weighing scale * Balance, as in equality (mathematics) or equilibrium Arts and entertainment Film * Balance (1983 film), ''Balance'' ( ...

and spatial orientation. It emerges from the pontomedullary junction and exits the inner

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

via the internal acoustic meatus in the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

. The vestibulocochlear nerve carries axons of type special somatic afferent.

Clinical significance

Symptoms of damage

Damage to the vestibulocochlear nerve may cause the following symptoms: *

hearing loss Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spo ...

vertigo Vertigo is a condition in which a person has the sensation that they are moving, or that objects around them are moving, when they are not. Often it feels like a spinning or swaying movement. It may be associated with nausea, vomiting, perspira ...

*false sense of motion *loss of equilibrium (in dark places) * nystagmus *

motion sickness Motion sickness occurs due to a difference between actual and expected motion. Symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Complications may rarely include ...

*gaze-evoked

tinnitus Tinnitus is a condition when a person hears a ringing sound or a different variety of sound when no corresponding external sound is present and other people cannot hear it. Nearly everyone experiences faint "normal tinnitus" in a completely ...

Examination

Examinations that can be done include the Rinne and

Weber test The Weber test is a screening test for hearing performed with a tuning fork. It can detect Unilateral hearing loss, unilateral (one-sided) conductive hearing loss (middle ear hearing loss) and unilateral sensorineural hearing loss (inner ear he ...

s. Rinne's test involves Rinne's Right and Left Test, since auditory acuity is equal in both ears. If

bone conduction Bone conduction is the conduction of sound to the inner ear primarily through the bones of the skull, allowing the hearer to perceive audio content even if the ear canal is blocked. Bone conduction transmission occurs constantly as sound waves vi ...

(BC) is more than air conduction (AC) (BC>AC) indicates Rinne Test is negative or abnormal. If AC>BC Rinne test is normal or positive. If BC>AC and Weber's test lateralizes to abnormal side then it is Conductive hearing loss. If AC>BC and Weber's test lateralizes to normal side then it concludes Sensorineural hearing loss. After pure-tone testing, if the AC and BC responses at all frequencies 500–8000 Hz are better than 25 dB HL, meaning 0-24 dB HL, the results are considered normal hearing sensitivity. If the AC and BC are worse than 25 dB HL at any one or more frequency between 500 and 8000 Hz, meaning 25+, and there is a no bigger difference between AC and BC beyond 10 dB at any frequency, there is a sensori-neural hearing loss present. If the BC responses are normal, 0-24 dB HL, and the AC are worse than 25 dB HL, as well as a 10 dB gap between the air and bone responses, a conductive hearing loss is present. The modified Hughson–Westlake method is used by many audiologists during testing. A battery of (1) otoscopy, to view the ear canal and tympanic membrane, (2) tympanometry, to assess the immittance of the tympanic membrane and how well it moves, (3) otoacoustic emissions, to measure the response of the outer hair cells located in the cochlea, (4) audiobooth pure-tone testing, to obtain thresholds to determine the type, severity, and pathology of the hearing loss present, and (5) speech tests, to measure the patients recognition and ability to repeat the speech heard, is all taken into consideration when diagnosing the pathology of the patient.

History

Etymology

Some older texts call the nerve the ''acoustic'' or ''auditory nerve'', but these terms have fallen out of widespread use because they fail to recognize the nerve's role in the vestibular system. ''Vestibulocochlear nerve'' is therefore preferred by most.

References

Additional images

File:Cranial endobasis of a 19-20 weeks foetus.JPG, Vestibulocochlear nerve File:Gray689.png, Superficial dissection of brain-stem. Ventral view. File:Gray705.png, Dissection showing the projection fibers of the cerebellum. File:Gray719.png, Hind- and mid-brains; postero-lateral view. File:Gray792.png, Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ. File:Gray922.png, Position of the right bony labyrinth of the ear in the skull, viewed from above. File:ThreeNeuronArc.png ,

Vestibulo-ocular reflex The vestibulo-ocular reflex (VOR) is a reflex that acts to stabilize Gaze (physiology), gaze during head movement, with eye movement due to activation of the vestibular system, it is also known as the cervico-ocular reflex. The reflex acts to im ...

File:Slide5nnn.JPG, Vestibulocochlear nerve

External links

* * () {{Authority control Cranial nerves Otorhinolaryngology Human head and neck Nervous system Neurology Nerves of the head and neck