Tip link

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Pictures G-N show the tip links connecting the stereocilia. The Tailchaser mutation does not affect formation of interstereocilial links.png
Pictures G-N show the tip links connecting the stereocilia.

Tip links are extracellular filaments that connect stereocilia to each other or to the kinocilium in the hair cells of the inner ear. [1] [2] Mechanotransduction is thought to occur at the site of the tip links, which connect to spring-gated ion channels. [3] These channels are cation-selective transduction channels that allow potassium and calcium ions to enter the hair cell from the endolymph that bathes its apical end. When the hair cells are deflected toward the kinocilium, depolarization occurs; when deflection is away from the kinocilium, hyperpolarization occurs. The tip link is made of two different cadherin molecules, protocadherin 15 and cadherin 23. [4] It has been found that the tip links are relatively stiff, so it is thought that there has to be something else in the hair cells that is stretchy which allows the stereocilia to move back and forth. [5]

It is hypothesized that the tip link is attached to the myosin motor which moves along actin filaments. [6]

See also

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The inner ear 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 temporal bone of the skull with a system of passages comprising two main functional parts:

Cochlea Snail-shaped part of inner ear involved in hearing

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. A core component of the cochlea is the Organ of Corti, the sensory organ of hearing, which is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea.

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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 in response to incoming sound waves, which are converted to traveling waves on the basilar membrane.

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Utricle (ear) Membranous labyrinth in the vestibule of ear

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The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves vertically, the sensory cells of the saccule are disturbed and the neurons connected to them begin transmitting impulses to the brain. These impulses travel along the vestibular portion of the eighth cranial nerve to the vestibular nuclei in the brainstem.

Organ of Corti Receptor organ for hearing

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. Transduction occurs through vibrations of structures in the inner ear causing displacement of cochlear fluid and movement of hair cells at the organ of Corti to produce electrochemical signals.

Auditory system Sensory system used for hearing

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Hair cell

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Stereocilia (inner ear)

In the inner ear, stereocilia are the mechanosensing organelles of hair cells, which respond to fluid motion in numerous types of animals for various functions, including hearing and balance. They are about 10–50 micrometers in length and share some similar features of microvilli. The hair cells turn the fluid pressure and other mechanical stimuli into electric stimuli via the many microvilli that make up stereocilia rods. Stereocilia exist in the auditory and vestibular systems.

A kinocilium is a special type of cilium on the apex of hair cells located in the sensory epithelium of the vertebrate inner ear.


Stereocilia are non-motile apical modifications of the cell. They are distinct from cilia and microvilli, but closely related to the latter.

The saccule is the smaller sized vestibular sac ; it is globular in form, and lies in the recessus sphæricus near the opening of the scala vestibuli of the cochlea. Its anterior part exhibits an oval thickening, the macula of saccule, to which are distributed the saccular filaments of the acoustic nerve.

Mechanosensation is the transduction of mechanical stimuli into neural signals. Mechanosensation provides the basis for the senses of light touch, hearing, proprioception, and pain. Mechanoreceptors found in the skin, called cutaneous mechanoreceptors, are responsible for the sense of touch. Tiny cells in the inner ear, called hair cells, are responsible for hearing and balance. States of neuropathic pain, such as hyperalgesia and allodynia, are also directly related to mechanosensation. A wide array of elements are involved in the process of mechanosensation, many of which are still not fully understood.

The cochlear amplifier is a positive feedback mechanism within the cochlea that provides acute sensitivity in the mammalian auditory system. The main component of the cochlear amplifier is the outer hair cell (OHC) which increases the amplitude and frequency selectivity of sound vibrations using electromechanical feedback.

The neuronal encoding of sound is the representation of auditory sensation and perception in the nervous system.

TRPN is a member of the transient receptor potential channel family of ion channels, which is a diverse group of proteins thought to be involved in mechanoreception. The TRPN gene was given the name no mechanoreceptor potential C (nompC) when it was first discovered in fruit flies, hence the N in TRPN. Since its discovery in fruit flies, TRPN homologs have been discovered and characterized in worms, frogs, and zebrafish.

A. James Hudspeth

A. James Hudspeth is the F.M. Kirby Professor at Rockefeller University, where he is director of the F.M. Kirby Center for Sensory Neuroscience. His laboratory studies the physiological basis of hearing.


  1. Pickles JO, Comis SD, Osborne MP. 1984.Cross-links between stereocilia in the guinea pig organ of Corti, and their possible relation to sensory transduction. Hearing Research 15:103-112.
  2. Scott T. Brady; George J. Siegel; Robert Wayne Albers; Donald Lowell Price (2012). Basic Neurochemistry: Principles of Molecular, Cellular and Medical Neurobiology. Academic Press. p. 920. ISBN   978-0-12-374947-5.
  3. David J. Aidley (3 September 1998). The Physiology of Excitable Cells. Cambridge University Press. pp. 248–. ISBN   978-0-521-57421-1.
  4. Lewin GR, Moshourab R. 2004. Mechanosensation and pain. Journal of Neurobiology 61:30-44
  5. Corey, D. Harvard University. Phone Interview. 19 November 2008.
  6. Howard, J.; Hudspeth, A. J. (1987). "Mechanical relaxation of the hair bundle mediates adaptation in mechanoelectrical transduction by the bullfrog's saccular hair cell". Proceedings of the National Academy of Sciences of the United States of America. 84 (9): 3064–3068. doi: 10.1073/pnas.84.9.3064 . PMC   304803 . PMID   3495007.