Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4606_Библиотеки_им_академика_М_И_Перельмана
.pdf
Chapter 1
https://t.me/medicina_free
The Anatomy oftheVestibular System
Rafaelda CostaMonsanto, HenriqueFurlanPauna, andSebahattinCureoglu
Introduction
The inner ear consists of bony and membranous structures. The bone forms around
the membranous labyrinth during fetal development and reaches its nal form and
size around 16weeks of gestational age. The membranous labyrinth is housed in a
densely packed bone, considered to be the hardest bone in the human body, which
is the otic capsule. Galen, in the second century AD, named the inner ear “the labyrinth,” considering the complexity of its anatomical structure [1]. In the nineteenth
century, the function of the vestibular labyrinth was only found to be related to balance and not to hearing. Marie Jean-Pierre Flourens was the rst author to report
that the semicircular canals were part of the balance system rather than the auditory
system [2]. In her experimental studies, she observed that the destruction of pigeons’
semicircular canals affected their postural equilibrium and their ability to y while
not signicantly affecting their hearing.
The bony vestibular labyrinth delineates the semicircular canals and the vestibule. Each of the three semicircular canals is perpendicular to the others (Fig.1.1).
Within these areas are uid-lled compartments (endolymphatic and
R. da CostaMonsanto (*) · S. Cureoglu
Otopathology Laboratory, Department of Otolaryngology, Head and Neck Surgery, University
of Minnesota, Minneapolis, MN, USA
e-mail: rdacosta@umn.edu; cureo003@umn.edu
H. F. Pauna
Departamento de Otorrinolaringologia, Hospital Universitário Cajuru, Pontifícia Universidade
Católica do Paraná (PUC-PR), Curitiba, Paraná, Brazil
© The Author(s), under exclusive license to Springer Nature
Switzerland AG 2023
B. T. Crane et al. (eds.), Disorders of the Vestibular System,
https://doi.org/10.1007/978-3-031-40524-2_1
1
2
vestibular aqueduct)
Posterior
Anterior
https://t.me/medicina_free
Superior
semicircular
canal
Lateral
semicircular
canal
Crus
communis
Posterior
semicircular
canal
R. da CostaMonsanto et al.
Utricle
Saccule
Endolymphatic
sac
Posterior
cranial fossa
Fig. 1.1 Bony and membranous anatomy of the vestibular labyrinth
Endolymphatic
duct (within the
Cochlea
(basal turn)
Cochlear
aqueduct
perilymphatic), one of which has a potassium-rich uid (endolymph) and the other
a sodium-rich uid (perilymph). There are several openings in the bony labyrinth,
including the small foramina (through which bundles of the vestibular nerve enter
the vestibule), the vestibular aqueduct (that houses the endolymphatic duct), and the
oval window.
Balance System
The vestibular system is divided into two main categories: the central system, which
includes the brain, cerebellum, and brainstem, and the peripheral system, which
includes the vestibular organs and their pathways to the brainstem. This system as a
whole is responsible for maintaining balance, stability, and spatial orientation.
The vestibular organs consist of the semicircular canals, the utricle, and the saccule (Fig.1.2). The semicircular canals are largely responsible for detecting angular
accelerations, while the utricle and the saccule detect linear accelerations (including
gravity).
The saccule is a attened sac that lies on the medial wall of the vestibule (Figs.1.2
and 1.3). It is directly attached to the wall of the utricle superiorly; however, no connection exists between these two structures. Its macula is in a vertical position. The
Superior canal
P
ule
1 The Anatomy oftheVestibular System
https://t.me/medicina_free
3
osterior
Utricle
canal
Vestib
Saccule
Fig. 1.2 Relative positions of the membranous structures of the vestibular portion of the human
inner ear
saccule communicates with the cochlear duct (ductus reuniens; Fig.1.1) and the
endolymphatic sinus (saccular duct). The utricle is an oval-shaped tube that lies
superior to the saccule on the medial wall of the vestibule (Figs.1.2, 1.4, 1.5, and
1.6). The utricular duct arises from the inferior part through a cleft-shaped opening
to enter the endolymphatic duct. At the cleft-shaped opening, there is a thickened
portion that forms the utriculo-endolymphatic (Bast’s) valve, which is responsible
4
a
a
https://t.me/medicina_free
R. da CostaMonsanto et al.
b
Fig. 1.3 Two sections of human temporal bones showing the saccular macula. (a) The vertical
disposition of the sensory epithelium is shown in light microscopy (4×, Hematoxylin and Eosin).
(b) The saccular macula seen in differential contrast interference microscopy showing structural
differences between vestibular hair cell types I (1) and II (2)
b
c
Fig. 1.4 A representative human temporal bone section showing important landmarks. (a)
Panoram of the external, middle, and inner ears (1×; Hematoxylin and Eosin). (b) and (c) The
crista ampullaris and macula of the utricle, which had been marked in (a) in squares. 1: External
auditory canal; 2: Tympanic membrane; 3: Malleus; 4: Incus (short process); 5: Middle ear (epitympanum level); 6: Aditus ad antrum; 7: Facial nerve (tympanic portion); 8: Cochlea; 9: Utricle;
10: Lateral semicircular canal; and 11: Internal auditory canal
for controlling the endolymphatic volume (Fig.1.6) [3, 4]. As opposed to the saccule, the macula of the utricle lies in the horizontal plane.
Each inner ear has three semicircular canals that are perpendicular to each other
(Figs.1.1, 1.2, and 1.4). The arrangement of the canals allows them to detect head
rotation in multiple directions. The head movements result in displacement of the
endolymph inside the ducts, which plays an important role in the physiology of balance. When considering the semicircular canals from both ears, it can be observed
that some canals are in the same plane (left superior and right posterior; left posterior and right superior; and left and right lateral canals) (Fig.1.5). The angle arrangements of the semicircular canals allow them to reconstruct the three-dimensional
1 The Anatomy oftheVestibular System
https://t.me/medicina_free
5
Left
posterior
canal
Right
superior
canal
Left and right
superior canal
30˚
Left
superior
canal
Right
posterior
canal
Fig. 1.5 Schematic gure showing the relative planes of the semicircular canals. These planes are
important to provide to the central nervous system information on head rotation, as contralateral
canals in the same plane provide antagonistic information to the central vestibular system
Fig. 1.6 A representative
human temporal bone
section of the crista
ampullaris of the lateral
semicircular canal showing
vestibular hair cells as well
as transitional and dark
cells
angular forces acting on the head. The ducts of the semicircular canals communicate with the utricle via ve openings, one of which is the common crus, which
consists of the union of the non-ampullated ends of the superior and posterior canals.
The sensory epithelium of the vestibule shares structural and functional similarities with the cochlea [5]. In the vestibular apparatus, the sensory epithelium can be
found in the form of maculae (utricle and saccule) and cristae (ampulla of the semicircular canals). Each macula is divided by a central curved zone termed striola,
where hair-bundle polarization reverses. The polarization is in the direction toward
6
https://t.me/medicina_free
the striola in the utricle, and away from the striola in the saccule. In the cristae, the
hair cell polarization is away from the utricle in the superior and posterior canals,
and toward the utricle in the lateral canal.
Similarly to the organ of Corti in the cochlea, the vestibular sensory epithelium
contains two different types of hair cells (Figs.1.3, 1.4, and 1.6). Type I vestibular
cells are ask-shaped and have a large nucleus, while type II cells are cylindrical in
shape. At birth, the cristae have a higher density of hair cells as compared with the
saccule and utricle. Each vestibular hair cell has cilia emerging from its apical portion. The cilia of the vestibular cells are quite different from their cochlear pairs: in
the cochlea, the kinocilium is rudimentary, and there is a much larger number of
stereocilia. In vestibular hair cells, a single, well-developed kinocilium emerges from
the basal body of the cell at the periphery of the bundle. The exact function of the
kinocilia is unknown, but it seems to establish the direction of mechanical sensitivity.
The stereocilia tend to be shorter in type I hair cells as compared to type II cells. A
single kinocilium emerges from the basal body of the cell at the periphery of the
bundle. Stereocilia movement toward the kinocilium results in an excitatory stimulus, while displacements away from the kinocilium result in an inhibitory stimulus.
The cilia of the hair cells are embedded in a gelatinous substance, the otolithic
membrane (saccule and utricle), and the cupulae (semicircular canals). Although
the precise composition of these is unknown, it is known that they contain acid
mucopolysaccharides. In the otolithic membrane of the saccule and utricle, there is
an otoconial layer, which contains crystals composed of calcium carbonate and
other ions.
At the base of the crista ampullaris and utricular/saccular maculae, two different
types of cells are identied: transitional cells and dark cells (Fig.1.6). Dark cells are
distinguished from the surrounding cells by their characteristics: (1) intimate contact
with melanin granules and (2) nuclei positioned high and close to the endolymphatic
space that is intensely stained by Hematoxylin and Eosin. Transitional cells are
cuboid cells located in between the vestibular hair cells and the dark cell epithelium.
These cells are cuboid, are not associated with melanin granules, and have large,
round nuclei located at the center of the cell body. Although the exact role of these
cells is still under debate, it seems that they have similar roles as the stria vascularis
in the cochlea, with dark cells being related to the strial marginal cells and transitional cells to the intermediate strial cells. It was demonstrated that dark and transitional cells have ionic transport mechanisms that contribute to the maintenance of
the high potassium levels in the endolymph and to endolymph production [6–9].
R. da CostaMonsanto et al.
Endolymphatic Sac andDuct
The endolymphatic sac lies within the layers of the dura mater of the posterior fossa,
on the posterior surface of the petrous bone. It is connected to the endolymphatic
system by the endolymphatic duct, which lies in a bony canal called the vestibular
aqueduct (Figs.1.1 and 1.7).
1 The Anatomy oftheVestibular System
https://t.me/medicina_free
Fig. 1.7 Histological anatomy of the human temporal bone (panoram). The squared area represents the utriculo-endolymphatic valve, which controls the outux of endolymph from the saccule
(9) to the endolymphatic duct and sinus (12). 1: External auditory canal and tympanic membrane;
2: Malleus; 3: Incus (long process); 4: Stapes (footplate, oval window); 5: Protympanum and opening of the Eustachian Tube; 6: Tensor tympani muscle; 7: Facial nerve; 8: Saccule; 9: Utricle; 10:
Lateral semicircular canal; 11: Posterior semicircular canal; 12: Endolymphatic duct; 13: Cochlea;
14: Internal auditory canal
7
Histologically, the endolymphatic duct is lined by squamous and cuboidal cells.
The endolymphatic sac has an uneven surface with folds and crypts, in which
degenerated cells and otoconia can be found.
Some authors divide the endolymphatic sac into three different parts. The proximal part lies within a bony niche; the intermediate part lies partly in a bony niche
and partly between layers of the dura mater; its epithelial lining has tall cylindrical
cells that are arranged in papillae and crypts. The distal part is embedded within
layers of the dura mater; its epithelium is cuboidal. In the lumen of the endolymphatic sac, products of cellular and otoconial degeneration can be found interspersed
with free-oating macrophages. The presence of these macrophages suggests that
the sac is involved with the immune response [10]. Additionally, the sac seems to be
involved in the regulation of endolymph through cytochemical mechanisms. It has
been demonstrated that the endolymphatic sac expresses receptors for vasopressin
and aquaporin 2 [11].
Innervation
Two distinct nerves can be found in the internal auditory canal that relate to vestibular function. The superior vestibular nerve receives bers from the cristae of the
superior and lateral semicircular canals, from the macula of the utricle, and from the
8
a
https://t.me/medicina_free
R. da CostaMonsanto et al.
b
Fig. 1.8 (a) Representative human temporal bone section showing the facial (3) and superior
vestibular (4) nerves within the internal auditory canal. The squared area in (a) is shown at a higher
magnication in (b) showing Scarpa ganglion cells of the superior vestibular nerve within the
internal auditory canal. 1: Internal auditory canal; 2: Cochlea; 3: Facial nerve (intrameatal and
tympanic portions); 4: Superior vestibular nerve traveling from the internal auditory canal toward
the utricle and crista ampullaris of the lateral canal; 5: Utricle; 6: Lateral semicircular canal; 7:
Posterior semicircular canal; 8: Middle ear cleft
anterosuperior portion of the macula of the saccule. The inferior vestibular nerve
receives bers from the cristae of the posterior semicircular canal and most of the
saccular macula.
The vestibular afferent neurons have their cell bodies in Scarpa’s ganglion, which
sends a peripheral axon toward the vestibular sense organs and a central axon to the
vestibular nuclei in the brainstem (Fig.1.8). At birth, humans have an average of
22,000 cells in Scarpa’s ganglion [12].
The axons of the vestibular afferents are myelinated and heterogeneous in caliber. Large bers give rise to calyceal terminals that embrace the hair cells, while
smaller bers end in small bouton-type terminals [13].
Efferent vestibular system bers were also identied in experimental studies.
They are located ventromedial to the ventral portion of the lateral vestibular nucleus.
The efferent neurons seem to be cholinergic and produce other neurotransmitters
and neuromodulators. After emerging from the brainstem, vestibular efferent bers
travel along the cochlear efferent bers in the vestibular nerve trunk as far as the
saccular ganglion, at which point they diverge at almost right angles to each organ.
The bers then supply the maculae and cristae. When activated, these efferent bers
result in a complex mix of excitatory and inhibitory effects on the responses of vestibular afferents.
In the central nervous system, the vestibular nerve bers connect to the four vestibular nuclei on the oor of the IV ventricle. These nuclei contact the oculomotor
centers (nuclei of the III, IV, and VI cranial nerves) through the medial longitudinal
fasciculus and reach centers in the neck and along the spinal cord (vestibulospinal
tracts).
Common
Basilar
artery
1 The Anatomy oftheVestibular System
https://t.me/medicina_free
9
The main function of the vestibular system is to inform the central nervous system of the position and movements of the head and the body. This implies on correcting the eye movements to keep them in harmony with the body movements.
The vestibular system is extensively controlled by the cerebellum, which sends
bers to all the vestibular nuclei. The maintenance of the body’s equilibrium
depends fundamentally on three systems: the eyes, the proprioceptive receptors, and
the vestibular organs. It is well known, clinically, that to maintain body balance, at
least two of these systems must be normal. It is now known that there are tracts arising from the oculomotor centers and from areas of the brain that process proprioceptive information and that bring information to the vestibular nuclei. These nuclei,
therefore, are the integrators of the body balance system [14–16].
Vascular Supply
The arterial supply to the membranous labyrinth is comprised of branches that also
supply the bony labyrinth and the middle ear cleft. However, only some of these
branches penetrate the endosteal layer of the bony labyrinth to supply the membranous structures.
The anterior inferior cerebellar artery gives rise to the labyrinthine artery and the
subarcuate artery before taking a recurrent course to the cerebellum (Fig.1.9). The
labyrinthine artery divides into the common cochlear artery and the anterior vestibular artery. The common cochlear artery divides into the main cochlear and vestibulocochlear branches. The vestibulocochlear artery branches into the posterior
vestibular artery and the cochlear ramus. Of these branches, the anterior vestibular
Anterior inferior
cerebellar
artery
Labyrinthine
artery
cochlear
artery
Fig. 1.9 Sketch showing the principal arteries of the inner ear
Main
cochlear
artery
artery
Cochlear ramus
artery
Anterior
vestibular
artery
Vestibulocochlear
Arteries of
the canals
Posterior
vestibular
artery
10
Anterior
Vein of vestibular
Posterior
aqueduct
https://t.me/medicina_free
R. da CostaMonsanto et al.
Vestibulocochlear
vein
spiral
Anterior
vein
Fig. 1.10 Sketch showing the venous drainage system of the human labyrinth
spiral
vein
vestibular
vein
Common
modiolar
vein
the round
Vein at
cochlear
Vein of
window
aqueduct
Veins of
the canals
Posterior
vestibular
vein
artery supplies: (1) the macula of the utricle; (2) a small part of the macula of the
saccule; (3) the cristae and membranous canals of the superior and lateral semicircular canals; and (4) the superior surfaces of the utricle and saccule. The posterior
vestibular artery supplies the macula of the saccule, the crista, and the inferior surfaces of the utricle and saccule.
Regarding venous drainage (Fig.1.10), the anterior vestibular vein carries blood
from the utricle and the ampullae of the superior and lateral canals. The posterior
vestibular vein drains the saccule, ampulla of the posterior canal, and basal end of
the cochlea. The semicircular canals are drained by vessels that pass toward their
utricular ends to form the vein of the vestibular aqueduct, which accompanies the
endolymphatic duct and drains into the lateral venous sinus.
References
1. Hawkins JE, Schacht J.Sketches of otohistory. Part 8: The emergence of vestibular science.
Audiol Neurootol. 2005;10(4):185–90. https://doi.org/10.1159/000085076.
2. Yildirim FB, Sarikcioglu L.Marie Jean Pierre Flourens (1794–1867): an extraordinary scientist of his time. J Neurol Neurosurg Psychiatry. 2007;78(8):852. https://doi.org/10.1136/
jnnp.2007.118380.
3. Hofman R, Segenhout JM, Buytaert JAN, Dirckx JJJ, Wit HP. Morphology and function
of Bast’s valve: additional insight in its functioning using 3D-reconstruction. Eur Arch
Otorhinolaryngol. 2008;265(2):153–7.
4. da Costa MR, Pauna HF, Kwon G, etal. A 3-dimensional analysis of the endolymph drainage system in Meniere’s disease. Laryngoscope. 2017;127(5):E170–5. https://doi.org/10.1002/
lary.26155.
https://doi.org/10.1007/s00405- 007- 0424- 8.
Соседние файлы в папке Библиотека им академика М.И. Перельмана