Utricle Health Dictionary

The ear is concerned with two functions. The more evident is that of the sense of hearing; the other is the sense of equilibration and of motion. The organ is divided into three parts:

(1) the external ear, consisting of the auricle on the surface of the head, and the tube which leads inwards to the drum; (2) the middle ear, separated from the former by the tympanic membrane or drum, and from the internal ear by two other membranes, but communicating with the throat by the Eustachian tube; and (3) the internal ear, comprising the complicated labyrinth from which runs the vestibulocochlear nerve into the brain.

External ear The auricle or pinna consists of a framework of elastic cartilage covered by skin, the lobule at the lower end being a small mass of fat. From the bottom of the concha the external auditory (or acoustic) meatus runs inwards for 25 mm (1 inch), to end blindly at the drum. The outer half of the passage is surrounded by cartilage, lined by skin, on which are placed ?ne hairs pointing outwards, and glands secreting a small amount of wax. In the inner half, the skin is smooth and lies directly upon the temporal bone, in the substance of which the whole hearing apparatus is enclosed.

Middle ear The tympanic membrane, forming the drum, is stretched completely across the end of the passage. It is about 8 mm (one-third of an inch) across, very thin, and white or pale pink in colour, so that it is partly transparent and some of the contents of the middle ear shine through it. The cavity of the middle ear is about 8 mm (one-third of an inch) wide and 4 mm (one-sixth of an inch) in depth from the tympanic membrane to the inner wall of bone. Its important contents are three small bones – the malleus (hammer), incus (anvil) and stapes (stirrup) – collectively known as the auditory ossicles, with two minute muscles which regulate their movements, and the chorda tympani nerve which runs across the cavity. These three bones form a chain across the middle ear, connecting the drum with the internal ear. Their function is to convert the air-waves, which strike upon the drum, into mechanical movements which can affect the ?uid in the inner ear.

The middle ear has two connections which are of great importance as regards disease (see EAR, DISEASES OF). In front, it communicates by a passage 37 mm (1.5 inches) long – the Eustachian (or auditory) tube – with the upper part of the throat, behind the nose; behind and above, it opens into a cavity known as the mastoid antrum. The Eustachian tube admits air from the throat, and so keeps the pressure on both sides of the drum fairly equal.

Internal ear This consists of a complex system of hollows in the substance of the temporal bone enclosing a membranous duplicate. Between the membrane and the bone is a ?uid known as perilymph, while the membrane is distended by another collection of ?uid known as endolymph. This membranous labyrinth, as it is called, consists of two parts. The hinder part, comprising a sac (the utricle) and three short semicircular canals opening at each end into it, is the part concerned with the balancing sense; the forward part consists of another small bag (the saccule), and of a still more important part, the cochlear duct, and is the part concerned with hearing. In the cochlear duct is placed the spiral organ of Corti, on which sound-waves are ?nally received and by which the sounds are communicated to the cochlear nerve, a branch of the vestibulocochlear nerve, which ends in ?laments to this organ of Corti. The essential parts in the organ of Corti are a double row of rods and several rows of cells furnished with ?ne hairs of varying length which respond to di?ering sound frequencies.

The act of hearing When sound-waves in the air reach the ear, the drum is alternately pressed in and pulled out, in consequence of which a to-and-fro movement is communicated to the chain of ossicles. The foot of the stapes communicates these movements to the perilymph. Finally these motions reach the delicate ?laments placed in the organ of Corti, and so affect the auditory nerve, which conveys impressions to the centre in the brain.... ear

The collective term for the convoluted structures of the inner ear.

The first part of the labyrinth is the cochlea, which contains the mechanism of hearing.

Situated behind the cochlea are 2 sacs (the saccule and the utricle) and 3 fluid-filled semicircular canals, all of which are concerned with balance.... labyrinth

(BPPV) a common cause of vertigo in which the patient complains of brief episodes of rotatory vertigo precipitated by sudden head movements. It is thought to be due to microscopic debris derived from the *otoliths of the utricle and displaced into one of the semicircular canals, most commonly the posterior semicircular canal. The debris is most commonly thought to be free in the canal (canalithiasis; see canalith) but can be attached to the *cupula (cupulolithiasis; see cupulolith). Diagnosis is by performing a *Dix–Hallpike test. Treatment is with a predetermined set of head movements to move the debris from the semicircular canal (see Epley particle repositioning manoeuvre; Semont liberatory manoeuvre; Brandt-Daroff exercises). Surgery is occasionally used to occlude the relevant semicircular canal, cut the *singular nerve or vestibular nerves, or perform a *labyrinthectomy. Drugs are generally ineffective in the treatment of this condition.... benign paroxysmal positional vertigo

n. a particle derived from *otoliths in the *utricle of the inner ear, displaced from its normal site and located within the canal portion of one of the semicircular canals. Canaliths are implicated in *benign paroxysmal positional vertigo.... canalith

n. a particle derived from *otoliths in the *utricle of the inner ear, displaced from its normal site and attached to the *cupula within the ampullary portion of one of the semicircular canals. Cupuloliths are implicated in *benign paroxysmal positional vertigo.... cupulolith

n. (pl. maculae) a small anatomical area that is distinguishable from the surrounding tissue. The macula lutea is the yellow spot on the retina at the back of the eye, which surrounds the greatest concentration of cones (see fovea). Maculae occur in the saccule and utricle of the inner ear (see illustration). Tilting of the head causes the otoliths to bend the hair cells, which send impulses to the brain via the vestibular nerve. See also labyrinth.... macula

(otoconium) n. one of the small particles of calcium carbonate associated with a macula in the *saccule or *utricle of the inner ear.... otolith

n. a sac or pouch. The saccus endolymphaticus is the small sac connected to the saccule and utricle of the inner ear by the *endolymphatic duct.... saccus

those parts of the inner ear involved with balance. They comprise the *semicircular canals, *saccule and *utricle. See ear; vestibular system.... vestibular apparatus

the division of the *vestibulocochlear nerve that carries impulses from the semicircular canals, utricle, and saccule of the inner ear to the brain, conveying information about the body’s posture and movements in space and allowing coordination and balance.... vestibular nerve

n. (in anatomy) a cavity situated at the entrance to a hollow part. The vestibule of the ear is the cavity of the bony *labyrinth that contains the *saccule and *utricle – the organs of equilibrium. —vestibullar adj.... vestibule