Hair Cells: From Molecules to Function
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Conversion of a mechanical stimulus, such as sound, into an electrochemical signal. A thin, spike-like protrusion with an actin filament core that is generated on the leading edge of a motile animal cell. A filter that suppresses all frequencies above a certain point known as the cut-off frequency. The stem of a stereocilium that in electron micrographs is seen to be heavily stained by osmium, which probably indicates a dense concentration of protein. You can help keep your hair healthy by taking care of your overall health. Check with your doctor if you have questions on your hair’s growth and how it might be impacted by your health.
Chapter 34: Plant Structure, Growth, and Nutrition
As in other cellular systems, there is turnover of actin subunits, but the rate of actin turnover is relatively low (Zhang et al, 2012). This has led to a tip-turnover model in which actin monomers at the stereocilium tip (the barbed end of the actin filaments) turn over dynamically with F-actin, while the remaining F-actin is stable and not subject to turnover (Drummond et al. 2015; Narayanan et al. 2015). Mutation or deletion of the genes for plastin-1, fascin-2, and XIRP2 result in stereocilia degeneration, confirming their importance (McGrath et al. 2017).
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New findings pave the way for hearing loss therapies - EurekAlert
New findings pave the way for hearing loss therapies.
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This dense body is surrounded by synaptic vesicles and is thought to aid in the fast release of neurotransmitter. The role of the tectorial membrane in the cochlea helps us to understand this pattern. This membrane links the longest stereocilium of each OHC via otogelin, otogelin-like, and stereocilin proteins (Avan et al., 2019). When sound waves transmit from the perilymph to endolymph, they pass through the basilar membrane as traveling waves, converting vibration to the tectorial membrane via periodic compression at the top of the HC protein network. The relative displacement of both leads to radial fluid flow in a narrow space, a shearing motion, which results in stereocilia movement in the horizontal direction and finally causing stereocilia to tilt (Guinan, 2012).
Preventing Scalp Buildup
During a critical period of postnatal development of the altricial rodent cochlea, IHC transiently receive cholinergic innervation which is also mediated by α9α10 receptors (Fuchs, 1996; Glowatzki and Fuchs, 2000; Katz et al., 2004). During this period, comprising the first two weeks after birth, mice are deaf, but spontaneous electrical activity in the organ of Corti has been shown to occur. IHC are able to fire Ca2+ action potentials (Kros et al., 1998), driving neurons in the auditory pathway to respond rhythmically. This activity would be important for the normal maturation of synapses and circuits of the entire auditory pathway, and ceases after the onset of hearing (Kandler et al., 2009).
Seborrheic dermatitis causes the scalp and other skin areas to be dry, red, itchy, and flaky. An itchy scalp can be uncomfortable, but it is rarely a cause for concern. You might experience an itchy scalp because of an allergic reaction to a hair product or because the scalp is oily or dry. An oily scalp occurs when there is an overproduction and buildup of excess sebum on the scalp. A scalp detox is not a medical treatment, and there is limited research on its benefits. Meanwhile, “the goal of a serum is to target the hair follicle directly by delivering compounds that may allow for improved or optimal hair growth,” says Dr. Mirmirani.
The hair follicle is the part below the skin, and the hair shaft is what you see above your skin. The first involved a series of experiments where they used a virus to target the ERBB2 receptors in mice. For the second, the researchers genetically modified mice in an attempt to activate ERBB2. The last experiment saw them use two drugs that they knew could produce a response in ERBB2. Age or excessive exposure to loud noise can damage the cochlea, resulting in permanent hearing loss.
Structure of Hair
Several lines of evidence suggest that the MOC system has an important role in the protection from trauma produced by overly loud sounds. Moreover, the strength of this sound-evoked olivocochlear feedback pathway to the inner ear (in humans) is inversely correlated with the degree of hearing loss after acoustic trauma (Maison and Liberman, 2000). A transgenic mouse line was recently engineered carrying an enhanced MOC – OHC synapse due to an α9α10 receptor with increased gating properties (Taranda et al., 2009). Mutant mice exhibit higher tolerance to noise-induced trauma, further pinpointing to the participation of the MOC in protection of the inner ear. It is still unknown whether protection is due to reduced mechanical vibration of the sensory epithelium, or if Ca2+ entry through α9α10 produces downstream effects impacting on OHC function. Since hearing loss and tinnitus are a worldwide burden (Seidman and Standring, 2010), and exposure to loud sounds is one of the main underlying causes, the development of drugs that target α9α10 receptors has been recently suggested (Elgoyhen et al., 2009).
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Hearing Different Frequencies
An in-depth understanding of the underpinnings of how hearing takes place at the cellular and molecular level, will enable the development of more powerful tools for preventing and treating hearing loss. MOC neurons can fire at high frequencies in response to sound (Liberman and Brown, 1986); the louder the stimuli, the faster neurons fire. Inhibition of OHC is strongly dependent on the firing rate of these neurons, as transmitter release presents a robust enhancement when triggered at short succession (Ballestero et al., 2011). Recent data indicates that Ca2+ permeability of the α9α10 nicotinic receptors varies among species, being high in mammals and low in non-mammalian vertebrates, such as chicken (Lipovsek et al., 2012, 2014). Evolutionary analyses indicate that the mammalian α9α10 has been under strong selective pressure, acquiring non-synonymous substitutions in the coding regions of α9 and α10 (Franchini and Elgoyhen, 2006; Lipovsek et al., 2014). An increased Ca2+-permeable mammalian receptor might have been the phenotypic consequence of this evolutionary process.
Efferent modulation of the cochlear amplifier
In newborn mice, the top of each HC possesses dozens to hundreds of actin filament-based stereocilia of increasing height arranged in a stepped V or W shape (Figure 1). A true microtubule-based cilium that is about the same height as the tallest row of stereocilia, called the kinocilium, is found near the corner of this arrangement, i.e., on the non-neural side (Flock and Duvall, 1965; Sobkowicz et al., 1995). The stereocilia and kinocilium of each HC are collectively termed the hair bundle (Figure 1). Adjacent stereocilia are connected by several types of connecting protein including tip links, horizontal top connectors, shaft connectors, and ankle links (Goodyear et al., 2005). Similarly, the kinocilium and adjacent stereocilia are connected by kinocilial links, while in some HCs, the kinocilia are physically separated from stereocilia (Avan et al., 2019).
The effect of efferent modulation on IHCs is more clear-cut; hyperpolarization reduces transmitter release at the afferent synapse, allowing the central auditory system to attenuate or filter out those sound frequencies. This can improve detection of specific sound frequencies against background noise (the “cocktail party” effect) and also protects the cochlea from acoustic trauma (May and McQuone 1995; Lauer and May 2011; Fuente 2015). Developmentally, cholinergic efferents synapse onto both IHCs and OHCs prior to the onset of hearing (Simmons 2002). Efferent synapses develop first on IHCs, where they are initially excitatory due to an absence of Ca2+-activated K+ channels (SK channels); efferent synapses appear several days later (P6–P8) on OHCs (Roux et al. 2011).
However, it is still unclear whether kinocilia are present in these organoids. It is also interesting to explore whether mammalian HC regeneration is related to or even regulated by kinocilia. Thus, although kinocilia are promising therapeutic targets for genetic and acquired diseases, further studies are warranted to develop the treatment strategies. Cells with a lower resonant frequency have a lower density of BK channels and those channels are composed of subunits that result in slower activation of the channel.
You can do this by washing and brushing hair regularly, avoiding hair care products that contain harsh ingredients, reducing heat exposure from heat stylers, and covering hair when outdoors. When looking for an appropriate scalp detox product, you will want to choose products containing ingredients that assist in reducing inflammation, promote healthy cell turnover, and have antimicrobial and antifungal properties. This includes products that contain mainly natural ingredients like aloe vera, tea tree oil, rosemary oil, and bentonite clay. Clarifying shampoos are deep-cleaning shampoos advertised to remove hair product buildup, dead skin flakes, and excess oil. They should not be used daily and are not a replacement for regular shampoo. Pre-shampoo cleansers are applied to the hair and scalp before shampooing.
In addition to modulating the release of neurotransmitter, Ca2+ entry opens Ca2+-dependent K+ channels, which provide another avenue for K+ to enter the perilymph. Indeed, the interaction of Ca2+ influx and Ca2+-dependent K+ efflux can lead to electrical resonances that enhance the tuning of response properties within the inner ear (also explained in Box B in Chapter 14). In essence, the hair cell operates as two distinct compartments, each dominated by its own Nernst equilibrium potential for K+; this arrangement ensures that the hair cell's ionic gradient will not run down, even during prolonged stimulation. At the same time, compounds such as ethacrynic acid (see Box A), which selectively poison the ion-pumping cells of the stria vascularis, can cause the endocochlear potential to dissipate, resulting in a sensorineural hearing deficit.
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 axons under inner hair cells. The presynaptic terminal bouton is filled with vesicles containing acetylcholine and a neuropeptide called calcitonin gene-related peptide. The effects of these compounds vary; in some hair cells the acetylcholine hyperpolarizes the cell, which reduces the sensitivity of the cochlea locally. Mammalian sensory systems are vital for the interactions between organisms and their environment.
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