| Hair cell | |
|---|---|
 |
|
| Location | Cochlea |
| Function | Amplify sound waves and transduce auditory information to the Brain Stem |
| Morphology | Unique (see text) |
| Presynaptic connections | None |
| Postsynaptic connections | Via auditory nerve to vestibulocochlear nerve to inferior colliculus |
| Gray's | subject #232 1057 |
Hair cells are the sensory receptors of both the auditory system and the vestibular system in all vertebrates. 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 brain stem (or brainstem) is the lower part of the Brain, adjoining and structurally continuous with the Spinal cord. The term morphology in Biology refers to the outward appearance ( Shape, Structure, Colour, Pattern) of an Organism The cochlear nerve (also auditory nerve or VIIIth nerve) is part of the Vestibulocochlear nerve, (or 8th Cranial nerve) that is found in higher The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve Cranial nerves, and is responsible for transmitting sound The inferior colliculi ( Latin, lower hills) together with the superior colliculi form the eminences of the Corpora quadrigemina, and also part the Peripheral organs of the Special senses the organs of Taste ( Peripheral gustatory or In a Sensory system, a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of an Organism. The auditory system is the Sensory system for the sense of hearing. The vestibular system, which is a contributor to our balance system and our sense of spatial orientation is the sensory system that provides the dominant input about movement and Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes In mammals, the auditory hair cells are located within the organ of Corti on a thin basilar membrane in the cochlea of the inner ear. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands The organ of Corti (or spiral organ) is the organ in the Inner ear of Mammals that contains auditory sensory cells or " Hair cells " 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 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 ear is the sense organ that detects Sounds The Vertebrate ear shows a common biology from Fish to Humans with variations They derive their name from the tufts of stereocilia that protrude from the apical surface of the cell, a structure known as the hair bundle, into the scala media, a fluid-filled tube within the cochlea. Stereocilia are apical modifications of the cell which are distinct from Microvilli and Cilia. The cochlear duct (or scala media) is an Endolymph filled cavity inside the Cochlea, located in between the Scala tympani and the Scala Mammalian cochlear hair cells come in two anatomically and functionally distinct types: the outer and inner hair cells. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Hair cells are the Sensory receptors of both the Auditory system and the Vestibular system in all Vertebrates. Hair cells are the Sensory receptors of both the Auditory system and the Vestibular system in all Vertebrates. Damage to these hair cells results in decreased hearing sensitivity, i. e. sensorineural hearing loss. Sensorineural hearing loss is a type of Hearing loss in which the root cause lies in the Vestibulocochlear nerve ( Cranial nerve VIII the inner Ear
Contents |
Hair bundles as sound detectors and amplifiers
Research of the past decades has shown that outer hair cells do not send neural signals to the brain, but that they mechanically amplify low-level sound that enters the cochlea. 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 amplification may be powered by movement of their hair bundles, or by an electrically driven motility of their cell bodies. The inner hair cells transform the sound vibrations in the fluids of the cochlea into electrical signals that are then relayed via the auditory nerve to the auditory brainstem and to the auditory cortex. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies The cochlear nerve (also auditory nerve or VIIIth nerve) is part of the Vestibulocochlear nerve, (or 8th Cranial nerve) that is found in higher The brain stem (or brainstem) is the lower part of the Brain, adjoining and structurally continuous with the Spinal cord. The primary auditory cortex is the region of the Brain that is responsible for processing of auditory ( Sound) information
Results in recent years further indicate that mammals apparently have conserved an evolutionarily earlier type of hair-cell motility. This so-called hair-bundle motility amplifies sound in all non-mammalian land vertebrates. It is effected by the closing mechanism of the mechanical sensory ion channels at the tips of the hair bundles. Thus, the same hair-bundle mechanism that detects sound vibrations also actively “vibrates back” and thereby mechanically amplifies weak incoming sound.
Inner hair cells – from sound to nerve signal
The deflection of the hair-cell stereocilia opens mechanically gated ion channels that allow any small, positively charged ions (primarily potassium and calcium) to enter the cell. Stereocilia are apical modifications of the cell which are distinct from Microvilli and Cilia. Stretch-activated or stretch-gated ion channels are Ion channels which open their Pores in response to mechanical deformation of a Neuron 's Ion channels are pore-forming Proteins that help establish and control the small Voltage Gradient across the Plasma membrane of all living Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Unlike many other electrically active cells, the hair cell itself does not fire an action potential. In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal Instead, the influx of positive ions from the endolymph in Scala media depolarizes the cell, resulting in a receptor potential. Receptor potential, a type of graded potential is the Transmembrane potential difference of a Sensory receptor. This receptor potential opens voltage gated calcium channels; calcium ions then enter the cell and trigger the release of neurotransmitters at the basal end of the cell. Voltage-dependent calcium channels (VDCC are a group of voltage-gated Ion channels found in excitable cells ( e See Chemical synapse for an introduction to concepts and terminology used in this article The basal lamina is a layer of extracellular matrix on which Epithelium sits and which is secreted by the epithelial cells The neurotransmitters diffuse across the narrow space between the hair cell and a nerve terminal, where they then bind to receptors and thus trigger action potentials in the nerve. See Chemical synapse for an introduction to concepts and terminology used in this article In Biochemistry, a receptor is a Protein molecule embedded in either the Plasma membrane or Cytoplasm of a cell to which a mobile signaling In this way, the mechanical sound signal is converted into an electrical nerve signal. The repolarization in the hair cell is done in a special manner. The perilymph in Scala tympani has a very low concentration of positive ions. The electrochemical gradient makes the positive ions flow through channels to the perilymph.
Hair cells chronically leak Ca+2. This leakage causes a tonic release of neurotransmitter to the synapses. It is thought that this tonic release is what allows the hair cells to respond so quickly in response to mechanical stimuli. The quickness of the hair cell response may also be due to that fact that it can increase the amount of neurotransmitter release in response to a change as little as 100 μV in membrane potential. [1]
Outer hair cells – acoustical pre-amplifiers
In mammalian outer hair cells, the receptor potential triggers active vibrations of the cell body. This so-called somatic electromotility consists of oscillations of the cell’s length, which occur at the frequency of the incoming sound and in a stable phase relation. Outer hair cells have evolved only in mammals. They have not improved hearing sensitivity, which reaches similarly exquisite values also in other classes of vertebrates. But they have extended the hearing range from about 11 kHz (maximum in some birds) to about 200 kHz (maximum in some marine mammals). They have also improved frequency selectivity (frequency discrimination), which is of particular benefit for humans, because it enabled sophisticated speech and music.
The molecular biology of hair cells has seen considerable progress in recent years, with the identification of the motor protein (prestin) that underlies somatic electromotility in the outer hair cells. Motor proteins are a class of Molecular motors that are able to move along the surface of a suitable substrate Prestin is the Motor protein of the outer hair cells of the inner ear of the Mammalian Cochlea. Santos-Sacchi et al. have shown that prestin's function is dependent on chloride channel signalling and that it is compromised by the common marine pesticide tri-butyl tin. Organotin compounds or stannanes are Chemical compounds based on Tin with Hydrocarbon substituents Because this class of pollutant bioconcentrates up the food chain, the effect is pronounced in top marine predators such as Orcas and toothed whales. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at ftudruinsubstance is lost The Orca or Killer Whale ( Orcinus orca) less commonly Blackfish or Seawolf, is the largest species of the Oceanic dolphin family The toothed whales ( Systematic name Odontoceti) form a Suborder of the Cetaceans including sperm whales beaked whales orca dolphins [2]
Neural connection
Neurons of the auditory or vestibulocochlear nerve (the VIIIth cranial nerve) innervate cochlear and vestibular hair cells. The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve Cranial nerves, and is responsible for transmitting sound Cranial nerves are Nerves that emerge directly from the Brain stem in contrast to Spinal nerves which emerge from segments of the Spinal cord. [3] The neurotransmitter released by hair cells to stimulate the dendrites of afferent neurons is thought to be glutamate. Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its 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.
Nerve fiber innervation is much more dense for inner hair cells than for outer hair cells. A single inner hair cell is innervated by numerous nerve fibers, whereas a single nerve fiber innervates many outer hair cells. Inner hair cell nerve fibers are also very heavily myelinated, which is in contrast to the unmyelinated outer hair cell nerve fibers.
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 (towards the brain) dendrites under inner hair cells. The presynaptic terminal bouton is filled with vesicles containing acetylcholine and a neuropeptide called Calcitonin gene-related peptide (CGRP). The Chemical compound acetylcholine (often abbreviated ACh) is a Neurotransmitter in both the Peripheral nervous system (PNS and Central Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the Calcitonin gene related peptide (CGRP is derived with Calcitonin, from the CT/CGRP gene located on Chromosome 11. The effects of these compounds varies, in some hair cells the acetylcholine hyperpolarized the cell, which reduces the sensitivity of the cochlea locally.
Additional images
 The lamina reticularis and subjacent structures. |
 Inner ear illustration showing semicircular canal, hair cells, ampulla, cupula, vestibular nerve, & fluid |
References
- ^ Chan DK, Hudspeth AJ (2005 Feb). "Ca2+ current-driven nonlinear amplification by the mammalian cochlea in vitro. ". Nature Neuroscience 8 (2): 149—155. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 15643426.
- ^ Santos-Sacchi Joseph, Song Lei, Zheng Jiefu,Nuttall Alfred L (2006-04-12). "Control of Mammalian Cochlear Amplification by Chloride Anions". Journal of Neuroscience 26 (15): 3992-3998. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16611815.
- ^ [Cranial Nerve VIII. Vestibulocochlear Nerve]. Meddean. Retrieved on 2008-06-04. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 781 BC - The first historic Solar eclipse is recorded in China.
- Manley GA, Popper AN, Fay RR (2004). Evolution of the Vertebrate Auditory System. New York: Springer-Verlag.
- Kandel ER, Schwartz JH, Jessell TM (2000). Eric Richard Kandel (born November 7, 1929) is a Psychiatrist, a neuroscientist and Professor of Biochemistry Principles of Neural Science, 4th ed. First published in 1981 by Elsevier, Principles of Neural Science is a Neuroscience Textbook edited by Eric R , New York: McGraw-Hill, 590-594. ISBN 0-8385-7701-6.
- Coffin A, Kelley M, Manley GA, Popper AN. "Evolution of sensory hair cells". pp 55-94 in Manley et al
- Manley GA. "Advances and perspectives in the study of the evolution of the vertebrate auditory system". pp. 360—368 in Manley et al
- Fettiplace R, Hackney CM (2006). "The sensory and motor roles of auditory hair cells". Nat. Rev. Neurosci. 7 (1): 19-29. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16371947.
External links
- Hair Cells at the University of Montpellier
- Dancing OHC video Yale Ear Lab
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic