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Information about Auditory System

The auditory system is the sensory system for the sense of hearing.

Ear

Main article: Ear

Outer ear

Main article: Outer ear
The folds of cartilage surrounding the ear canal are called the pinna. Sound waves are reflected and attenuated when they hit the pinna, and these changes provide additional information that will help the brain determine the direction from which the sounds came.

The sound waves enter the ear canal, a deceptively simple tube. The ear canal amplifies sounds that are between 3 and 12 kHz. At the far end of the ear canal is the eardrum (tympanum, or tympanic membrane), which marks the beginning of the middle ear.

Middle ear

Main article: Middle ear
Sound waves traveling through the ear canal will hit the tympanum, or eardrum. This wave information travels across the air-filled middle ear cavity via a series of delicate bones: the malleus (hammer), incus (anvil) and stapes (stirrup). These ossicles act as a lever and a teletype, converting the lower-pressure eardrum sound vibrations into higher-pressure sound vibrations at another, smaller membrane called the oval window. Higher pressure is necessary because the inner ear beyond the oval window contains fluid rather than air. The sound is not amplified uniformly across the ossicular chain. The auditory reflex of the middle ear muscles helps protect the inner ear from damage. The middle ear still contains the sound information in wave form; it is converted to nerve impulses in the cochlea.

Inner ear

Cochlea
Diagrammatic longitudinal section of the cochlea.
Main article: Inner ear
The inner ear consists of the cochlea and several non-auditory structures. The cochlea has three fluid-filled sections, and supports a fluid wave driven by pressure across the basilar membrane separating two of the sections. Strikingly, one section, called the cochlear duct or scala media, contains an extracellular fluid similar in composition to endolymph, which is usually found inside of cells.

The organ of Corti forms a ribbon of sensory epithelium which runs lengthwise down the entire cochlea. The hair cells of the organ of Corti transform the fluid waves into nerve signals. The journey of a billion nerves begins with this first step; from here further processing leads to a panoply of auditory reactions and sensations.

Hair cell

Main article: Hair cell
Hair cells are columnar cells, each with a bundle of 100-200 specialized cilia at the top, for which they are named. These cilia are the mechanosensors for hearing. Lightly resting atop the longest cilia is the tectorial membrane, which moves back and forth with each cycle of sound, tilting the cilia and allowing electric current into the hair cell (2).

Hair cells, like the photoreceptors of the eye, show a graded response, instead of the spikes typical of other neurons. These graded potentials are not bound by the “all or none” properties of an action potential.

At this point, one may ask how such a wiggle of a hair bundle triggers a difference in membrane potential. The current model is that cilia are attached to one another by “tip links”, structures which link the tips of one cilium to another. Stretching and compressing the tip links may open an ion channel and produce the receptor potential in the hair cell.

Neuron to hair cell relationship

There are far fewer hair cells than afferent nerve fibers in the cochlea. The nerve that innervates the cochlea is the vestibulocochlear nerve, or cranial nerve number VIII.

Neuronal dendrites innervate cochlear hair cells. The neurotransmitter itself is thought to be glutamate. At the presynaptic juncture, there is a distinct “presynaptic dense body” or ribbon. This dense body is surrounded by synaptic vesicles and is thought to aid in the fast release of neurotransmitter.

Efferent projections from the brain to the cochlea also play a role in the perception of sound. Efferent synapses occur on outer hair cells and on afferent dendrites under inner hair cells.

Central auditory system

This sound information, now re-encoded, travels down the auditory nerve, through parts of the brainstem (for example, the cochlear nucleus and inferior colliculus), further processed at each waypoint. The information eventually reaches the thalamus, and from there it is relayed to the cortex. In the human brain, the primary auditory cortex is located in the temporal lobe.

Associated anatomical structures include:

Cochlear nucleus

Main article: Cochlear nucleus


The cochlear nucleus is the first site of the neuronal processing of the newly converted “digital” data from the inner ear. This region is anatomically and physiologically spit into two regions, the dorsal cochlear nucleus (DCN), and ventral cochlear nucleus (VCN).

Trapezoid body

Main article: Trapezoid body


The Trapezoid body is a bundle of decussating fibers in the ventral pons that carry information used for binaural computations in the brainstem.

Superior olivary complex

Main article: superior olivary complex


The superior olivary complex is located in the pons, and receives projections predominantly from the anteroventral cochlear nucleus, although the posteroventral nucleus projects there as well, via the ventral acoustic stria.

Lateral lemniscus

Main article: lateral lemniscus

Inferior colliculi

Main article: inferior colliculus


The IC are located just below the visual processing centers known as the superior colliculi. The central nucleus of the IC is a nearly obligatory relay in the ascending auditory system, and most likely acts to integrate information (specifically regarding sound source localization from the SOC and dorsal cochlear nucleus) before sending it to the thalamus and cortex.

Medial Geniculate Nucleus

Main article: medial geniculate nucleus


The Medial Geniculate Nucleus is part of the thalamic relay system.

Primary auditory cortex

Main article: Primary auditory cortex


Primary Auditory Cortex is the first region of cerebral cortex to receive auditory input.

Perception of sound is associated with the right posterior superior temporal gyrus (STG). The superior temporal gyrus contains several important structures of the brain, including Brodmann areas 41 and 42, marking the location of the primary auditory cortex, the cortical region responsible for the sensation of basic characteristics of sound such as pitch and rhythm.

The auditory association area is located within the temporal lobe of the brain, in an area called the Wernicke's area, or area 22. This area, near the lateral cerebral sulcus, is an important region for the processing of acoustic signals so that they can be distinguished as speech, music, or noise.

Bibliography

Kandel, et al Principles of Neuroscience. Fourth ed. pp 591-624. Copyright 2000, by McGraw-Hill Co.

See also

External links

 •  • [ e]
Sensory system: Auditory and Vestibular systems
Outer earPinna (Helix, Antihelix, Tragus, Antitragus, Earlobe) • Ear canal
Middle earEardrum • Ossicles (Malleus, Incus & Stapes) • Stapedius • Tensor tympani • Eustachian tube (Torus tubarius)
Inner ear/LabyrinthBony labyrinth (Vestibule) • Membranous labyrinth
Oval window • Helicotrema • Round window
Cochlea: Spiral ganglion • Modiolus • Cochlear duct/scala media (Endolymph, Stria vascularis, Spiral ligament, Organ of Corti) • Scala vestibuli and Scala tympani (Perilymph)
Reissner's/vestibular membrane • Basilar membrane • Tectorial membrane
Organ of Corti: Hair cells • Stereocilia • Sulcus spiralis (externus, internus) • Limbus spiralis
Vestibular systemStatic/translations: Utricle (Macula) - Saccule (Macula, Endolymphatic sac, Endolymphatic duct) - Kinocilium - Otolith
Kinetic/rotations: Semicircular canals (Superior, Posterior, Horizontal) • Cupula • Ampullae (Crista ampullaris)
Brain (auditory)Cochlear nerve VIII → Cochlear nuclei → Superior olivary nuclei → Lateral lemniscus → Inferior colliculi → Medial geniculate nuclei → Primary auditory cortex
 •  • [ e]
Nervous system: Sensory systems/sense
Special sensesVisual system/Visual perception • Auditory system/Hearing • Chemoreception (Olfactory system/Olfaction • Gustatory system/Taste)
Somatosensory systemNociception • Thermoreception • Vestibular system • Mechanoreception (Pressure, Vibration, Proprioception)
OtherSensory receptor
sensory system: in this case, vision, for the visual system. ]]

A sensory system is a part of the nervous system responsible for processing sensory information.
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Hearing (or audition) is one of the traditional five senses, and refers to the ability to detect sound. In humans and other vertebrates, hearing is performed primarily by the auditory system: sound is detected by the ear and transduced into nerve impulses that are perceived
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outer ear is the most external portion of the ear. The outer ear includes the pinnae (also called auricle), the ear canal, and the very most superficial layer of the ear drum (also called the tympanic membrane).
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The outer ear is the external portion of the ear.

Pinna, or auricle

The visible part is called the pinna and functions to collect and focus sound waves. Many mammals can move the pinna (with the auriculares muscles) in order to focus their hearing in a certain direction
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The pinna (Latin for feather) is the visible part of the ear that resides outside of the head (this may also be referred to as the auricle or auricula).

Purpose

The purpose of the pinna is to collect sound.
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The ear canal (external auditory meatus, external acoustic meatus), is a tube running from the outer ear to the middle ear. The ear canal extends from the pinna to the eardrum and is about 26 mm in length and 7 mm in diameter.
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hertz (symbol: Hz) is the SI unit of frequency. Its base unit is cycle/s or s-1 (also called inverse seconds, reciprocal seconds). In English, hertz is used as both singular and plural.
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The tympanic membrane, colloquially known as the eardrum, is a thin membrane that separates the external ear from the middle ear. Its function is to transmit sound vibrations from the air, conducted through the external acoustic meatus to the ossicles inside the
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The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear.
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The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear.
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The tympanic membrane, colloquially known as the eardrum, is a thin membrane that separates the external ear from the middle ear. Its function is to transmit sound vibrations from the air, conducted through the external acoustic meatus to the ossicles inside the
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malleus or hammer is a hammer-shaped small bone or ossicle of the middle ear which connects with the incus and is attached to the inner surface of the eardrum. The word is Latin for hammer.
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For the record label, see Incus Records.


The incus or anvil is the anvil-shaped small bone or ossicle in the middle ear. It connects the malleus to the stapes. It was first described by Alessandro Achillin of Bologna.
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The stapes or stirrup is the stirrup-shaped small bone or ossicle in the middle ear which attaches the incus to the fenestra ovalis, the "oval window" which is adjacent to the vestibule of the inner ear. It is the smallest and lightest bone in the human body.
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The ossicles (also called auditory ossicles) are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea).
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The oval window (or vestibular window) is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear.

Vibrations arriving at the eardrum are transmitted via the interacting ossicles from the middle ear through the membrane of the
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The inner ear is the bony labyrinth, a system of passages comprising two main functional parts:
  • the organ of hearing, or cochlea
  • and the vestibular apparatus, the organ of balance that consists of three semicircular canals and the vestibule.

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The cochlea is the auditory portion of the inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along the partition separating fluid chambers in the coiled tapered tube of the cochlea.
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The basilar membrane within the cochlea of the inner ear is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani (see figure).
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The cochlear duct (or scala media) is an endolymph filled cavity inside the cochlea, located in between the scala tympani and the scala vestibuli, separated by the basilar membrane and Reissner's membrane (the vestibular membrane) respectively.
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Endolymph is the fluid contained in the membranous labyrinth of the inner ear.

It is also called Scarpa's fluid, after Antonio Scarpa.[1]

Composition


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Location Cochlea
Function Amplify sound waves and transduce auditory information to the Brain Stem

Morphology Unique (see text)
Presynaptic connections None
Postsynaptic connections
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cilium (plural cilia) is an organelle found in eukaryotic cells. Cilia are thin, tail-like projections extending approximately 5–10 micrometers outwards from the cell body.
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Hearing may refer to:
  • Hearing (sense), the sense by which sound is perceived
  • Hearing (person), a person who has hearing within normal parameters
  • Hearing (law), a legal proceeding before a court or other decision making body or officer

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The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain.
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The cochlear nerve (also auditory nerve) is part of the vestibulocochlear nerve, (or 8th cranial nerve) that is found in higher vertebrates. It is a sensory nerve, i.e.
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The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. Most sources consider the pons, medulla oblongata, and midbrain all to be part of the brainstem.
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The cochlear nuclei consist of:
  • (a) the dorsal cochlear nucleus, corresponding to the tuberculum acusticum on the dorso-lateral surface of the inferior peduncle; and
  • (b) the ventral or accessory cochlear nucleus

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The inferior colliculi (Latin, lower hill) together with the superior colliculi form the eminences of the corpora quadrigemina, and also part of the tectal region of the midbrain.
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For the computer game developer, see Thalamus Ltd.


The thalamus (from Greek θάλαμος = bedroom, chamber, IPA= /ˈθæləməs/) is a pair and symmetric part of the brain.
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