1.7 Step 6. Position and orientation of the semicircular canals скачать в хорошем качестве

1.7 Step 6. Position and orientation of the semicircular canals

These videos have been excerpted from Netter’s Video Dissection Modules on Student Consult.  http://bit.ly/2oEt9CO Step 6 To locate the position and orientation of the semicircular canals and ducts, note that on the intact petrous ridge, there is a prominent arcuate eminence. This is made by the underlying anterior semicircular canal. On the other side, the bone of the eminence is shaved away to reveal the dense bone of both the anterior semicircular canal and the lateral semicircular canal along with the lumen for the semicircular duct, which is painted green. The position of the posterior semicircular canal can be exposed by shaving away the part of the posterior margin of the petrous ridge that is directly posterior to the anterior canal. With the temporal bone replaced in its normal position, note the orientation of the anterior and posterior semicircular canals. Key Terms • Semicircular canals: the three hollow bony arches of the osseous labyrinth N95 that contain the semicircular ducts N95. Like the ducts, their names are anterior, posterior and lateral. • Arcuate eminence: a prominence on the anterior slope of the petrous ridge of the temporal bone, indicating the position of the anterior semicircular canal N97 N92. • Anterior semicircular canal: the most anterior and superior of the three semicircular canals N95. It is a hollow arch with a thin, dense wall of bone. The canal houses the anterior semicircular duct N95 and protrudes upward to form the arcuate eminence on the petrous ridge. It lies in the same plane as the contralateral posterior semicircular canal N97. Its anterior end is dilated to accommodate the ampulla, and its posterior end joins the posterior canal to form a common bony limb. • Lateral semicircular canal: the bony canal that houses the lateral semicircular duct. It is also called the horizontal canal, which indicates its orientation. The outer surface of the canal protrudes into the middle ear cavity where it forms the prominence of the lateral semicircular canal; here it lies just dorsal to the bony prominence of the facial canal N94. In terms of the oval window (and footplate of the stapes) it is useful to remember that the ventral to dorsal sequence is: oval window facial canal lateral semicircular canal. It is the ampulla of the canal that lies above the oval window N95. • Posterior semicircular canal: the most posterior of the three semicircular canals. It is a hollow arch with a thin, dense wall of bone N95 that lies in the same plane as the petrous ridge. The canal houses the posterior semicircular duct and lies in the same plane as the contralateral anterior semicircular canal N97. Its inferior end is dilated to accommodate the ampulla, and its posterior end joins the anterior canal to form a common bony limb. • 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. • Temporal bone: the bone that occupies the temporal region of the skull. It is formed from three components: 1) a squamous part that forms a portion of the lateral wall of the cranial vault N6; 2) a tympanic part that forms a ring-like support for the tympanic membrane and forms the bony part of the external acoustic meatus; and 3) a petrous portion that forms a ridge between the middle and posterior cranial fossae. This part develops around the osseous labyrinth of the inner ear, around the internal carotid artery to form the carotid canal, around the facial nerve to form the facial canal and around parts of the middle ear to contribute to the walls of the tympanic cavity. Other important parts of the temporal bone are the styloid process and mastoid process. 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.