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:
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.
The epididymis is a tube that connects a testicle to a vas deferens in the male reproductive system. It is present in all male reptiles, birds, and mammals. It is a single, narrow, tightly-coiled tube in adult humans, 6 to 7 meters in length connecting the efferent ducts from the rear of each testicle to its vas deferens.
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.
Cell adhesion is the process by which cells interact and attach to neighbouring cells through specialised molecules of the cell surface. This process can occur either through direct contact between cell surfaces such as cell junctions or indirect interaction, where cells attach to surrounding extracellular matrix, a gel-like structure containing molecules released by cells into spaces between them. Cells adhesion occurs from the interactions between cell-adhesion molecules (CAMs), transmembrane proteins located on the cell surface. Cell adhesion links cells in different ways and can be involved in signal transduction for cells to detect and respond to changes in the surroundings. Other cellular processes regulated by cell adhesion include cell migration and tissue development in multicellular organisms. Alterations in cell adhesion can disrupt important cellular processes and lead to a variety of diseases, including cancer and arthritis. Cell adhesion is also essential for infectious organisms, such as bacteria or viruses, to cause diseases.
The utricle and saccule are the two otolith organs in the vertebrate inner ear. They are part of the balancing system in the vestibule of the bony labyrinth. They use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation. The utricle detects linear accelerations and head-tilts in the horizontal plane. The word utricle comes from Latin uter 'leather bag'.
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.
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.
The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs and the auditory parts of the sensory system.
Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment.
Cell junctions are a class of cellular structures consisting of multiprotein complexes that provide contact or adhesion between neighboring cells or between a cell and the extracellular matrix in animals. They also maintain the paracellular barrier of epithelia and control paracellular transport. Cell junctions are especially abundant in epithelial tissues. Combined with cell adhesion molecules and extracellular matrix, cell junctions help hold animal cells together.
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 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.
