Inner Ear- Bony Labryinth

Question 1

Why is it called the “bony labryinth”?

Answer 1

It is made up of many passages and channels, forming a maze to support and protect the organs and nerves inside.

Question 2

What is the Osseus Vestibule? What does it look like?

Answer 2

Forms the central portion of the bony labryinth, it is continuous with the semicircular canals and with the cochlea. It is ovoid in shape.

Question 3

What is contained in the lateral wall of the Osseus Vestibule? In the medial wall?

Answer 3

The lateral wall contains the oval window, connecting it to the middle ear. The medial wall contains the opening of the vestibular aqueduct.

Question 4

Why is the Osseus Vestibule considered to be part of the vestibular portion of the inner ear?

Answer 4

It houses the Utricle in the Elliptical recess, and Saccule in the Spherical recess, both of which have vestibular functions.

Question 5

What are the two distinct depressions in the Osseus Vestibule?

Answer 5

The Elliptical recess which contains the Utricle, and the Spherical recess which contains the Saccule.

Question 6

What is the Vestibular aqueduct?

Answer 6

The bony channel in the Osseus Vestibule that contains the endolymphatic duct.

Question 7

What is the course of the Endolymphatic duct?

Answer 7

Courses from wall of the vestibule to the endolymphatic sac, located on the posterior surface of the temporal bone (in layers of dura mater in cranial cavity).

Question 8

What are the Osseus Semicircular Canals?

Answer 8

Three semicircular canals that contain a dilation/ampulla where the canal joins the vestibule.

Question 9

What are the three semicircular canals? Which two join to form a common crus?

Answer 9

The Superior (Anterior), Posterior, and Lateral (Horizontal) semicircular canals. The Superior (Anterior) and Posterior canals join to form common crus that opens into the vestibule.

Question 10

How many openings are formed by the semicircular canals into the vestibule?

Answer 10

Five- each has two openings, with the superior and posterior joining at one common crus.

Question 11

What is the Osseus Cochlea? How many turns does it have, and how large are these turns?

Answer 11

The “snail shell” portion that is located in the petrous portion of the temporal bone medial to the tympanic cavity. It turns around itself 2 and 5/8 times, with larger turns at the base than at the apex in the middle.

Question 12

What is the Modiolus? What is it continuous with?

Answer 12

Located in Osseus Cochlea, a central, perforated bony core that accommodates nerve fibers from hair cells, as well as blood vessels. It is the central structure around which the cochlea is wrapped. It is continuous with the IAM at the medial end.

Question 13

What is the Osseus spiral lamina? What is it composed of?

Answer 13

A shelf like structure that winds around the Modiolus from base to apex. Composed of two thin plates between which auditory nerve fibers pass from hair cells in the cochlea to the spiral ganglion to form the auditory nerve.

Question 14

What are the perforations in the Osseus spiral lamina that accommodate nerve fibers called?

Answer 14

Habenula perforata!

Question 15

Where is the Osseus spiral lamina narrowest?

Answer 15

More so at the apex than at the base.

Question 16

What does the lower shelf of the Osseus spiral lamina serve as? The upper shelf?

Answer 16

The lower is the support point for the connector for the inner aspect of the basilar membrane. The upper is continuous with the spiral limbus, which serves as an attachment/support point for the tectorial membrane.

Question 17

What does the Osseus spiral lamina divide the cochlea into?

Answer 17

The scala vestibuli (superior) and the scala tympani (inferior)- further divided by scala media (cochlear duct).

Question 18

What are the three openings of the bony cochlea?

Answer 18

Oval window, Round window, and Osseus Cochlear aqueduct.

Question 19

What is the purpose of the Oval window? Where is it located?

Answer 19

It interacts with the stapes of the middle ear and opens into the scala vestibuli. It is the more superior of the two windows.

Question 20

What is the purpose of the Round window? Where is it located?

Answer 20

It opens into the scala tympani, and is covered by a membrane that retains cochlear fluids within the cochlea. It is inferior to the Oval window.

Question 21

Where is the Promontory located?

Answer 21

Between the Oval and Round windows.

Question 22

What is the Ossues Cochlear aqueduct? Where is it located?

Answer 22

It contains perilymph (osseus fluid), and allows transfer of cerebrospinal fluid. It courses from the basal turn of the scala tympani (near round window) to the subarachnoid space near the jugular fossa.

Question 23

What is the Helicotrema? Where is it located?

Answer 23

The ONLY point of communication between the scala vestibuli and the scala tympani. It is located at the apex of the cochlea.

Question 24

What is the Hamulus? Where is it located?

Answer 24

Assists in forming the boundary of the helicotrema. It is the hook like process formed by the termination of the spiral lamina.

Question 25

What is the Internal Auditory Meatus? (IAM)

Answer 25

A bony canal that houses Facial, Auditory, and Vestibular nerves and a portion of the basilar artery. It carries these nerve bundles from the brainstem to the cochlea.

Question 26

What can the IAM be divided into when viewed at the opening where the nerve fibers begin their ascent to the brainstem? What lies within these divisions?

Answer 26

Four quadrants.

1. Upper left (Superior anterior): contains the facial nerve (7up)
2. Lower left (Inferior anterior): inferior to facial nerve is auditory (cochlear) portion of 8th nerve (coke)
3. Upper right (Superior posterior): contains nerve fibers from superior vestibular branch of 8th nerve (Skinny Vanilla)
4. Lower right (Inferior posterior): contains nerve fibers from inferior vestibular branch of the 8th nerve (Iced Vanilla)
5. Lower right (Inferior posterior):

Question 27

What are the three main parts of the “bony labryinth”?

Answer 27

Osseus vestibule, Osseus Semicircular canals, and Osseus Cochlea