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Brain Stem

  1. 3 PARTS – medulla oblongata, pons & midbrain
  2. Brainstem occupies the posterior cranial fossa of the skull
  3. Has 3 broad functions –
    • Serves as a conduit for the ascending & descending tracts
    • Contains important reflex centers(RS.CVS)
    • Control of consciousness
    • Contains cranial nerves nuclei (CN3-CN12)
Brain stem in a midsagittal plane
 Dorsolateral aspect of the brain stem
Principal arteries of the brain stem (ventral view)

Medulla oblongata

External appearance
  • It’s conical in shape
  • Connects to the pons superiorly & to the spinal cord inferiorly
  • The junction between the MO & the spinal cord is at the origin of the 1st cervical spinal nerve (At the level of the foramen magnum)
  • Central canal expands in the upper half of the MO to form the 4th ventricle
 The anterior surface
  • On the anterior surface of the medulla is the anterior median fissure (Continuous with the AMF of the spinal cord)
  • On either side of the AMF, there are swellings called pyramids; in the lower part of the pyramids there’s decussation of the pyramids
  • Postero – lateral to the pyramids are the olives (Inferior olivary nuclei lies beneath them)
  • Nerve roots of the hypoglossal nerve (XII) emerges from the groove between the pyramids & olives
  • Posterior to the olives is the inferior cerebellar peduncle (Connects the MO to the cerebellum)
  • From the grove between the olives & the inferior cerebellar peduncle, emerge the nerve roots of:
    1. Glossopharyngeal (IX)
    2. Vagus (X)
    3. Accessory nerve (XI) – Cranial roots
The posterior surface
  • Superior half : Floor of the 4th ventricle (Lower part)
  • Inferior half : Possess posterior median sulcus (PMS)
  • On either side of the PMS there’s gracile tubercle
  • (Produced by underlying gracile nucleus)
  • Lateral to the gracile tubercle is the cuneate tubercle (Produced by underlying cuneate nucleus)

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Brain Stem Brain Stem Reviewed by Radiology Madeeasy on August 03, 2010 Rating: 5
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