Neuroanatomy Draw It To Know It

160 Neuroanatomy: Draw It to Know It

Know-It Points

Major Sensory Projections

■ Th e leg fi bers of the medial lemniscus originate in
the gracile nucleus of the medulla.
■ Th e arm fi bers of the medial lemniscus originate in
the cuneate nucleus of the medulla.
■ Th e gracile nucleus lies medial to the cuneate nucleus.
■ Within the internal arcuate decussation, the leg fi bers
shift anterior to the arm fi bers.
■ As the medial lemniscus ascends the brainstem, the
arm fi bers shift medial to the leg fi bers.

■ Th e arm and leg fi bers project to the ventroposterior

lateral thalamic nucleus.

■ Th e facial fi bers project to the ventroposterior medial

thalamic nucleus.

■ Th e leg, arm, and face fi bers project from medial to

lateral along the posterior paracentral g yrus and

p o s t c e n t r a l g y r u s.

Major Motor Projections

■ Th e leg, arm, and face fi bers originate from medial
to lateral along the anterior paracentral g yrus and
precentral g yrus.
■ Th e descending fi bers bundle in the internal
capsule from anterior to posterior as face, arm,
and leg fi bers.

■ Th e motor fi ber arrangement in the brainstem, from

medial to lateral, is the face, arm, and leg fi bers.

■ During the corticospinal tract decussation at the

medullo-cervical junction, the arm and leg fi bers shift

so that despite the decussation, the arm fi bers remain

medial to the leg fi b e r s.

Midbrain Syndromes ( Advanced )

■ Weber’s syndrome results from injury to the
paramedian midbrain.
■ Weber’s syndrome is a syndrome of ipsilateral
third nerve palsy and contralateral face and body
weakness.
■ Benedikt’s syndrome results from injury to the red
nucleus and neighboring third nerve fi bers.

■ Benedikt’s syndrome is a syndrome of ipsilateral third

nerve palsy and contralateral choreiform movements.

■ Claude’s syndrome results from injury to the post-

decussation superior cerebellar fi bers and

neighboring third nerve fi bers.

■ Claude’s syndrome is a syndrome of ipsilateral third

nerve palsy and contralateral ataxia.

Pontine Syndromes ( Advanced )

■ Locked-in syndrome results from injury to the
pontine basis and ventral paramedian pontine
tegmentum.
■ In locked-in syndrome, there is:

• Damage to the descending corticospinal and
  corticonuclear tracts


• Preservation of most of the reticular formation


• Destruction of the exiting facial motor nerve fi bers
  
  
  • Destruction of the paramedian pontine reticular
    formation (the PPRF)
  
  
  • Spared third nerve innervation of the levator palpebrae
    ■ Dysarthria-clumsy hand syndrome is due to restricted
    paramedian pontine injury.
    ■ Dysarthria-clumsy hand syndrome is a syndrome of
    contralateral face and upper extremity weakness with
    preserved lower extremity strength.