Inner ear, also called labyrinth of the ear

Anatomical Position and Structure    seo gold coast,
The inner ear is located within the petrous a part of the temporal bone. It lies between the center ear and the internal acoustic meatus, which lie laterally and medially respectively. The inner ear has two predominant additives – the bony labyrinth and membranous labyrinth.

Bony labyrinth – consists of a series of bony cavities within the petrous part of the temporal bone. It is composed of the cochlea, vestibule and 3 semi-circular canals. All these structures are coated internally with periosteum and incorporate a fluid called perilymph.
Membranous labyrinth – lies inside the bony labyrinth. It consists of the cochlear duct, semi-round ducts, utricle and the saccule. The membranous labyrinth is filled with fluid known as endolymph.
The inner ear has openings into the center ear, both included by way of membranes. The oval window lies among the center ear and the vestibule, even as the spherical window separates the middle ear from the scala tympani (a part of the cochlear duct).

Bony Labyrinth
The bony labyrinth is a sequence of bony cavities inside the petrous a part of the temporal bone. It includes three elements – the cochlea, vestibule and the three semi-circular canals.

Vestibule

The vestibule is the valuable a part of the bony labyrinth. It is separated from the center ear through the oval window, and communicates anteriorly with the cochlea and posteriorly with the semi-round canals.

Two parts of the membranous labyrinth; the saccule and utricle, are placed in the vestibule.

Cochlea

The cochlea houses the cochlea duct of the membranous labyrinth – the auditory a part of the inner ear. It twists upon itself around a central portion of bone known as the modiolus, producing a cone shape which points in an anterolateral path. Branches from the cochlear part of the vestibulocochlear (VIII) nerve are located at the bottom of the modiolus.

Extending outwards from the modiolus is a ledge of bone referred to as spiral lamina, which attaches to the cochlear duct, holding it in function. The presence of the cochlear duct creates perilymph-filled chambers above and under:

Scala vestibuli: Located superiorly to the cochlear duct. As its name shows, it is non-stop with the vestibule.
Scala tympani: Located inferiorly to the cochlear duct. It terminates at the round window.
Semi-round Canals

There are three semi-round canals: anterior, lateral and posterior. They include the semi-round ducts, that are responsible for stability (along with the utricle and saccule).

The canals are situated superoposterior to the vestibule, at right angles to every other. They have a swelling at one give up, called the ampulla.

By TeachMeSeries Ltd (2021)

Fig 2 – The three elements of the bony labyrinth.

Membranous Labyrinth
The membranous labyrinth is a continuous machine of ducts full of endolymph. It lies in the bony labyrinth, surrounded with the aid of perilymph. It consists of the cochlear duct, three semi-round ducts, saccule and the utricle.

The cochlear duct is situated in the cochlea and is the organ of listening to. The semi-round ducts, saccule and utricle are the organs of balance (also known as the vestibular apparatus).

Cochlear Duct

The cochlear duct is located in the bony scaffolding of the cochlea. It is held in location by way of the spiral lamina. The presence of the duct creates canals above and underneath it – the scala vestibuli and scala tympani respectively. The cochlear duct can be described as having a triangular form:

Lateral wall – Formed by means of thickened periosteum, known as the spiral ligament.
Roof – Formed with the aid of a membrane which separates the cochlear duct from the scala vestibuli, called the Reissner’s membrane.
Floor – Formed by a membrane which separates the cochlear duct from the scala tympani, known as the basilar membrane.
The basilar membrane homes the epithelial cells of hearing – the Organ of Corti. A more distinctive description of the Organ of Corti is past the scope of this newsletter.

By TeachMeSeries Ltd (2021)
Fig 1.2 – Structure of the cochlea, and borders of the cochlear duct.
Fig three – Structure of the cochlea, and borders of the cochlear duct.

Saccule and Utricle

The saccule and utricle are two membranous sacs located inside the vestibule. They are organs of balance which come across motion or acceleration of the pinnacle in the vertical and horizontal planes, respectively.

The utricle is the larger of the 2, receiving the 3 semi-round ducts. The saccule is globular in shape and receives the cochlear duct.

Endolymph drains from the saccule and utricle into the endolymphatic duct. The duct travels thru the vestibular aqueduct to the posterior component of the petrous a part of the temporal bone. Here, the duct expands to a sac wherein endolymph may be secreted and absorbed.

Semi-round Ducts

The semi-round ducts are located within the semi-circular canals, and share their orientation. Upon movement of the pinnacle, the go with the flow of endolymph in the ducts changes velocity and/or course. Sensory receptors within the ampullae of the semi-circular canals detect this alteration, and send indicators to the brain, allowing for the processing of stability.

By TeachMeSeries Ltd (2021)
Fig 1.1 – The additives of the membranous labyrinth.
Fig four – The additives of the membranous labyrinth.

 

Vasculature
By TeachMeSeries Ltd (2021)
Fig 1.Four – The labyrinthine artery arising from the basilary artery
Fig 5 – The labyrinthine artery springing up from the basilary artery

The bony labyrinth and membranous labyrinth have distinctive arterial components. The bony labyrinth receives its blood deliver from three arteries, which additionally deliver the encompassing temporal bone:

Anterior tympanic branch (from maxillary artery).
Petrosal branch (from center meningeal artery).
Stylomastoid branch (from posterior auricular artery).
The membranous labyrinth is provided via the labyrinthine artery, a department of the inferior cerebellar artery (or, from time to time, the basilar artery). It divides into three branches:

Cochlear branch – supplies the cochlear duct.
Vestibular branches (x2) – deliver the vestibular apparatus.
Venous drainage of the inner ear is through the labyrinthine vein, which empties into the sigmoid sinus or inferior petrosal sinus.

Innervation
The inner ear is innervated by means of the vestibulocochlear nerve (CN VIII). It enters the internal ear via the internal acoustic meatus, wherein it divides into the vestibular nerve (accountable for stability) and the cochlear nerve (liable for hearing):

Vestibular nerve – enlarges to form the vestibular ganglion, which then splits into superior and inferior elements to supply the utricle, saccule and three semi-circular ducts.
Cochlear nerve – enters at the base of the modiolus and its branches bypass through the lamina to supply the receptors of the Organ of Corti.
The facial nerve, CN VII, also passes thru the inner ear, however does now not innervate any of the systems gift.

Clinical Relevance: Meniere’s Disease
Meniere’s disorder is a ailment of the inner ear, characterized with the aid of episodes of vertigo, low-pitched tinnitus, and hearing loss.

The signs and symptoms are concept to be resulting from an extra accumulation of endolymph in the membranous labyrinth, causing revolutionary distension of the ducts. The resulting pressure fluctuations harm the skinny membranes of the ear that discover balance and sound.

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