What is a Summating potential?

What is a Summating potential?

This ‘summating potential’ (SP) is a d.c. change related to. the root-mean-square of the acoustic pressure, integrated over one or two. waves. It increases up to injurious sound pressure levels.

What is the resting potential of inner hair cells?

The hair cell has a resting potential between -45 and -60 mV relative to the fluid that bathes the basal end of the cell. At the resting potential, only a small fraction of the transduction channels are open.

What happens when an inner hair cell is depolarized?

Depolarization of the inner hair cell results in the activation of voltage-dependent ion channels located along the lateral cell membrane. These channels allow for the efflux of K+ from the cell and influx of Ca++. The influx of Ca++ activates glutamate release from the base of the cell.

What are the cochlear potentials?

There are two types of cochlear potentials : individual unit potentials recorded directly from a sensory cell or nerve cell, and compound potentials, recorded at a distance, reflecting the activity of several cells.

What is Summating potential of cochlea?

The cochlear summating potential (SP) to a tone is a baseline shift that persists for the duration of the burst. It is often considered the most enigmatic of cochlear potentials because its magnitude and polarity vary across frequency and level and its origins are uncertain.

What is the Endolymphatic potential?

The endolymphatic potential is a positive standing potential (70-100 mV) that can be measured from the scala media referenced to ground. The EP reflects flux of K+ ions through the stria vascularis into the scala media. The EP is generated by the combined action of multiple cells within the stria vascularis.

Are there hair cells in the semicircular canals?

Each of the three semicircular canals has at its base a bulbous expansion called the ampulla (Figure 14.7), which houses the sensory epithelium, or crista, that contains the hair cells.

Do cochlear hair cells have Kinocilium?

Unlike the hair cells of the crista ampullaris or the maculae of the saccule and utricle, hair cells of the cochlear duct do not possess kinocilia.

Why are hair cells depolarized?

When tension increases, the flow of ions across the membrane into the hair cell rises as well. Such influx of ions causes a depolarization of the cell, resulting in an electrical potential that ultimately leads to a signal for the auditory nerve and the brain.

What happens when hair cells bend?

Sensory cells, called hair cells, bend in the cochlea as the fluid is disrupted by the mechanical vibrations. This bending of the hair cells causes electrical signals to be sent to the brain by way of the auditory nerve.

What do outer hair cells do?

The outer hair cells mechanically amplify low-level sound that enters the cochlea. The amplification may be powered by the movement of their hair bundles, or by an electrically driven motility of their cell bodies. This so-called somatic electromotility amplifies sound in all land vertebrates.

What is an ECochG test?

Electrocochleography (ECochG) is another test that measures electrical activity that occurs in response to sound. During ECochG testing, electrical activity that is generated in the hearing portion of the inner ear called the cochlea is measured. Electrical activity from the hearing nerve is also recorded.

How do forensic scientists look at hair under a microscope?

The morphology under a microscope Forensic scientists view hair under a microscope to collect evidence based on the morphology. They usually study the hair’s scale pattern, its color, and the appearance of the medulla. An experienced forensic scientist can easily tell if the hair specimen is from humans or from animals.

What does the medulla look like under a microscope?

Medulla is the central core of hair which may or may not be present. It may be air-filled and, if so, will appear as a black or opaque structure under the transmitted light of the microscope. If the medulla is present, its structure may be continuous or fragmented.

What does the cortex look like under a microscope?

The cortex may contain air spaces called cortical fusi, pigment granules, and large oval-shaped structures referred to as ovoid bodies. Medulla is the central core of hair which may or may not be present. It may be air-filled and, if so, will appear as a black or opaque structure under the transmitted light of the microscope.

How is the SP response related to eh?

Changes in the SP response can reflect pressure differences between the scala media and the scala vestibuli, indicating excessive fluid pressure, thus deforming the basilar membrane toward the scala tympani, so that enhanced-amplitude SP is thought to reflect EH. SP/AP ratio is the most common parameter for diagnosis of EH.

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