What are the three parts of the inner ear?

The ear is divided into three parts: outer ear, middle ear and inner ear.

If the inner ear is divided into three parts, it should be semicircular canal (semicircular canal+membranous semicircular canal), vestibule [vestibule+membranous vestibule (oval sac and balloon)] and cochlea (cochlea+membranous cochlear canal).

inner ear

The inner ear is located in the petrous part of the temporal bone and consists of two sets of nested pipes. Because of its bending direction and complex structure, it is called maze. The external labyrinthine is bony labyrinthine, and the membranous labyrinthine is nested in the bony labyrinthine (figure 18- 13). The fluid filled in the membranous labyrinth cavity is called endolymphatic, and the cavity between membranous labyrinth and bony labyrinth is filled with exolymphatic. Internal and external lymph nodes are not connected with each other, and have the functions of nourishing the inner ear and transmitting sound waves.

1. The bone labyrinth is divided into semicircular canal, vestibule and cochlea from back to front (Figure 18- 13). There are three semicircular canals, which are located at the posterolateral side and perpendicular to each other, and each semicircular canal forms an enlarged ampulla at the front connection. The cochlea is located on the anterior medial side and shaped like a snail shell. The cochlear canal of human bone revolves around the cochlear axis for one and a half times (figure 18- 13, 18- 14). The auditory canal is divided into upper and lower parts by the membranous canal. The upper part is called vestibular step and the lower part is called tympanic step, which communicate with each other through the cochlear foramen at the top of the cochlea. There is a round window between the bottom of the tympanic step and the tympanic cavity, which is closed by a film. The vestibule is located in the middle, which is an enlarged cavity connecting the semicircular canal and the vestibular step. The oval window between vestibule and tympanum is closed by the stapes base. The external lymph in the bone labyrinth may come from capillary blood in periosteum or cerebrospinal fluid in subretinal cavity of the ball.

2. The membranous labyrinth is divided into three parts: membranous semicircular canal, membranous vestibule (oval sac and balloon) and membranous cochlear canal, and the lumens are connected with each other (figure 18- 13). The wall mucosa of membranous semicircular canal, elliptic sac and balloon is generally composed of a single layer of flat epithelium and a thin layer of connective tissue under the epidermis, but the mucosa of ampulla, the side wall of elliptic sac and the front wall of balloon locally thickens into crista or plaque, which are called ampulla crista, elliptic sac spot and balloon spot respectively, and are all potential recipients. The membranous cochlear duct of human is also two and a half times around the cochlear axis, and its cross section is triangular (Figure 18- 14, 18- 15). The top wall of membranous cochlear canal is vestibular membrane, with a thin layer of connective tissue in the middle and a single layer of flat epithelium on both sides. The epithelium on the side wall of membranous cochlear duct is multi-layered columnar, which is called vascular stria because it contains blood vessels secreting lymph. Below the stria vascularis is a thickened periosteum called spiral ligament. The bottom wall of membranous cochlear duct is composed of medial bony spiral plate and lateral membranous spiral plate. The spiral plate of bone is formed by the outward extension of the bone tissue of the cochlear axis, and its initial periosteum thickens and protrudes into the membranous cochlear canal to form a spiral edge. Membrane spiral plate, also known as basement membrane, is connected with bone spiral plate on the inside and spiral ligament on the outside. The epithelium on the bottom wall of membranous cochlear duct thickens to form a spiral organ, which is an auditory receptor (figure 18- 15).