The organ of hearing and balance.

Vestibule-cochlear organ(organum vestibulocochleare) in the process of evolution in animals arose as a complexly structured organ of balance (vestibule), perceiving the position of the body (head) during its movement in space, and the organ of hearing. The organ of balance in the form of a primitively structured formation (static bubble) appears in invertebrates. In fish, due to the complexity of their motor functions, first one and then the second semicircular canal is formed. In terrestrial vertebrates with their complex movements, an apparatus was formed, which in humans is represented by the vestibule and three semicircular canals located in three mutually perpendicular planes and perceiving not only the position of the body in space and its movements in a straight line, but also the movements (turns) of the body, head in any plane.

The organ of hearing in aquatic vertebrates is poorly developed. With the emergence of vertebrates on land, the organ of hearing underwent progressive development and was formed largely due to the restructuring of the gill apparatus. Along with the sound-perceiving apparatus, related to the inner ear, a sound-conducting apparatus appeared, including the middle ear (the tympanic cavity with its auditory ossicles, the auditory tube). The outer ear with its sound-catching device, the auricle, was formed, mobile and turning towards the sound in many mammals. Subcortical and cortical hearing centers appeared, reaching their highest development in the cerebral cortex in humans, where not only the analysis of nerve impulses coming to the brain from the organ of hearing is performed, but also abstract "sound" thinking associated with the features of the second signal system.

The vestibulocochlear organ is divided into three parts, closely related anatomically and functionally: the outer, middle and inner ear. The outer ear includes the auricle and the external auditory canal, the middle ear includes the tympanic cavity with the auditory ossicles, with the mammillary cells and the auditory (Eustachian) tube. The inner ear has the most complex structure, in which the bony and membranous labyrinths are distinguished, forming the actual organ of hearing and the organ of balance (vestibular organ), located only in the inner ear. The outer, middle ear and part of the inner (cochlea) belong to the organ of hearing. The organ of balance (vestibular) is located only in the inner ear.

Vessels and nerves of the vestibulocochlear organ. The vestibulocochlear organ (the organ of hearing and balance) is supplied with blood from several sources. Branches from the external carotid artery system approach the outer ear: the anterior auricular branches from the superficial temporal artery, the auricular branch from the occipital artery, and the posterior auricular artery.The deep auricular artery branches from the maxillary artery in the walls of the external auditory canal. The same artery is involved in the blood supply of the eardrum, which also receives blood from the arteries that supply the mucous membrane of the tympanic cavity. As a result, two vascular networks are formed in the membrane: one in the skin layer, the other in the mucous membrane.

Venous blood from the outer ear flows through the veins of the same name into the submandibular vein, into the external jugular vein.

In the mucous membrane of the tympanic cavity there is a vascular network formed by branches of several arteries.

The walls of the auditory tube are supplied with blood by the anterior tympanic artery and the pharyngeal branches of the ascending pharyngeal artery, as well as the petrosal branch of the middle meningeal artery.The artery of the pterygoid canal (a branch of the maxillary artery) gives off branches to the auditory tube.

The veins of the middle ear accompany the arteries of the same name and flow into the pharyngeal venous plexus, into the meningeal veins (tributaries of the internal jugular vein) and into the retromandibular vein.

The artery of the labyrinthine (a. labyrinthi - a branch of the basilar artery) approaches the inner ear, accompanying the vestibulocochlear nerve and giving off branches to the vestibule, semicircular canals and cochlea. Venous blood from the inner ear flows through the vein of the same name into the superior petrosal sinus, as well as through the vein of the cochlear canal and the vein of the vestibular aqueduct, located in the canals of the same name and opening into the inferior petrosal sinus or directly into the internal jugular vein.

Lymph from the outer and middle ear flows into the mammillary, parotid, deep cervical - internal jugular, and also into the retropharyngeal (from the auditory tube) lymph nodes.

The nerves of the organ of hearing and balance originate from several sources. The outer ear receives sensory innervation from the great auricular, vagus, and auriculotemporal nerves. Branches from the auriculotemporal and vagus nerves, as well as from the tympanic plexus of the cavity of the same name, approach the tympanic membrane. In the mucous membrane of the tympanic cavity there is a tympanic plexus (plexus tympanicus), formed by the branches of the tympanic nerve (n. tympanicus - a branch of the glossopharyngeal nerve), a connecting branch of the facial nerve with the tympanic plexus, and sympathetic fibers of the carotid-tympanic nerves (from the internal carotid plexus). The tympanic plexus continues in the mucous membrane of the auditory tube, where branches from the pharyngeal plexus also penetrate. The chorda tympanicus passes through the tympanic cavity in transit and does not participate in its innervation. The muscles attached to the auditory ossicles receive innervation from different sources: the stapedius muscle - from the facial nerve, the muscle that tenses the tympanic membrane - the branch of the same name from the mandibular nerve.