Brain Stem

3 PARTS – medulla oblongata, pons & midbrain Brainstem occupies the posterior cranial fossa of the skull Has 3 broad functions – ...

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 1^st cervical spinal nerve (At the level of the foramen magnum)
• Central canal expands in the upper half of the MO to form the 4^th 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 4^th 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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