17 Step 8 Vestibular and cochlear aqueducts endolymphatic duct and sac

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These videos have been excerpted from Netter’s Video Dissection Modules on Student Consult. • http://bit.ly/2oEt9CO • Step 8 • This is a left temporal bone. On the back side of the petrous ridge, posterior to the internal acoustic meatus, look for a slight change in the contour or an indentation that marks the position of the endolymphatic sac. The vestibular aqueduct containing the endolymphatic duct connects with the sac and opens into the sac beneath this ridge. • The final structure on the posterior slope of the petrous ridge is a notch directly inferior to the internal acoustic meatus. This notch marks the intracranial opening of the cochlear aqueduct. This provides a potential route of communication between the perilymph in the scala tympani and the CSF in the cranial cavity. • Key Terms • • Petrous ridge: the ridge of bone that protrudes into the cranial cavity and separates the middle cranial fossa from the posterior cranial fossa N13. The anterior slope of the ridge is marked by grooves for the greater N43 N125 and lesser petrosal nerves and a depression for the trigeminal ganglion N86. It has a groove for the superior petrosal sinus N106 and an elevation (arcuate eminence) that marks the position of the anterior semicircular canal N97 N92. The crest of the ridge is an attachment line for the tentorium cerebelli. The back slope of the petrous ridge has the internal acoustic meatus and an aperture for the vestibular aqueduct N13, where the endolymphatic duct emerges to become confluent with the endolymphatic sac N96. The posterior inferior margin of the ridge is where the inferior petrosal sinus is located and where the intracranial opening of the cochlear aqueduct is located. • • Internal acoustic meatus: a canal in the temporal bone of the skull that transmits the vestibulocochlear and facial nerves and the labyrinthine artery. Its entrance is near the center of the posterior slope of the temporal bone. It is about one cm in length and ends at the beginning of the facial canal. N8 N13 • • Endolymphatic duct: a small diameter duct that is formed in the vestibule of the inner ear by the merging of two small tubes from the utricle and saccule N96. The duct occupies the vestibular aqueduct and emerges on the posterior slope of the petrous ridge N97, where it becomes confluent with the endolymphatic sac. The sac and duct appear to absorb and secrete endolymph and additionally have phagocytic and immunodefensive functions. • • Endolymphatic sac: the dilated end of the endolymphatic duct, which lies in a shallow concavity on the posterior slope of the petrous ridge, posterior and inferior to the internal acoustic meatus N96 N97. The sac and duct appear to absorb and secrete endolymph and additionally have phagocytic and immunodefensive functions. • • Vestibular aqueduct: the channel in the petrous portion of the temporal bone that houses the endolymphatic duct N96. • • Cochlear aqueduct: a channel that connects, or potentially connects, the perilymphatic fluid-filled scala tympani of the inner ear with the subarachnoid space of the cranial cavity N96. The channel also contains a labyrinthine vein. The intracranial opening of the aqueduct is marked by a notch that is directly inferior to the internal acoustic meatus and over the medial part of the opening of the jugular foramen N13. The aqueduct provides a potential pathway for the spread of infections of the inner ear to the cranial cavity. • • Scala tympani: the perilymphatic fluid-filled space in the cochlea that is inferior to the basilar membrane N96. It is also internal to the membrane of the round window and communicates with the scala vestibuli at a point in the cochlear apex called the helicotrema N95. • • Cerebrospinal fluid (CSF): a clear fluid which is produced by the choroid plexus N110 and fills the ventricles of the brain. It circulates through the interventricular foramina to fill the subarachnoid space that surrounds the brain and spinal cord and then returns to the blood via arachnoid granulations that protrude into the dural venous sinuses N103. The brain floats in the CSF, and the fluid acts as a cushion. • • ABOUT: • The project was made possible by several very dedicated faculty and staff at University of North Carolina, Chapel Hill--especially O.W. Henson and Noelle A. Granger--and partner schools, and by a grant from the Fund for the Improvement of Post-Secondary Education of the US Department of Education. This channel includes over 400 short videos highlighting the steps in a full-body human dissection in the gross anatomy lab. Each step is narrated and key structures labeled.

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