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Brain Stem

Comparison of the different levels of the pons

The midbrain
  • 2 cm in length
  • It connects the pons & the cerebellum with the forebrain
  • It’s traversed by a narrow channel called cerebral aqueduct (Filled with CSF)
The anterior surface
  • There’s a deep depression in the midline (Inter peduncular fossa)
  • Inter peduncular fossa is bounded on either side by the crus cerebri
  • Many blood vessels perforate the floor of the IPF & it’s called the posterior perforated substance
  • Occulomotor nerve emerges from the groove on the medial side of the crus cerebri
The posterior surface
  • There are 4 colliculi (2 superior & 2 inferior)
  • Superior colliculi : Centers for visual reflexes
  • Inferior colliculi : Lower auditory centers
  • In the midline below the inferior colliculi, the trochlear nerve emerges
  • The lateral surface : Superior & inferior brachia ascend in an antero – lateral direction
  • Superior brachium : Connects superior colliculus to the lateral geniculate body (Nuclei of the thalamus) & the optic tract
  • Inferior brachium : Connects inferior colliculus to the medial geniculate body (Nuclei if the thalamus)

Internal structure of the midbrain is considered at 2 levels
  • The mid brain has 2 lateral halves : Cerebral peduncles
  • Cerebral peduncles are divided into 2 parts by substantia nigra (Pigmented band of grey matter)
    1. Anterior part : Crus cerebri
    2. Posterior part : Tegmentum
  • There’s a narrow cavity in the midline : Cerebral aqueduct (Connects 3rd & 4th ventricles)
    1. It’s lined by ependyma
    2. It’s surrounded by the central grey matter
  • Tectum : part of the midbrain posterior to the cerebral aqueduct
  • Tectum has superior & inferior colliculi

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Brain Stem Brain Stem Reviewed by Radiology Madeeasy on August 04, 2010 Rating: 5
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