Updated: 4/3/2017

Brainstem

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Overview
                
 
Introduction
  • The brainstem is composed of the midbrain, pons, and medulla
Brainstem Structures
Structure Cranial Nerves Comments

Midbrain (Mesencephalon)

  • Oculomotor nerve (CN III)
  • Trochlear nerve (CN IV)
  • Reticular activating system
    • involved in arousal and alertness
    • lesion can lead to coma
  • Superior colliculus
    • conjugate vertical gaze center
  • Inferior colliculus
    • auditory information processor
  • Parinaud's syndrome
    • due to compression of dorsal midbrain and pretectal area (e.g., pinealoma, hydrocephalus) 
      • lesions the superior colliculus
    • conjugate vertical gaze palsy

Pons (Metencephalon)

  • Trigeminal nerve (CN V)
  • Abducens nerve (CN VI)
  • Facial nerve (CN VII)
  • Vestibulocochlear nerve (CN VIII)
  • Medial longitudinal fasciculus
    • lesion leads to intranuclear ophthalmoplegia (INO)

Medulla (Myelencephalon)

  • Glossopharyngeal nerve (CN IX)
  • Vagus nerve (CN X)
  • Hypoglossal nerve (CN XII)
  • Vasomotor center
  • Respiratory center
  • Area postrema
    • incomplete blood-brain barrier
    • chemoreception of toxins
      • triggers nausea and vomiting
  • Medial lemniscus
    • formed by decussating fibers of the nucleus gracillis and cuneatus
  • Pyramids
    • contain corticospinal tracts
      • most decussate in the caudal medulla
  • Olives
    • send fibers through the inferior cerebellar peduncle
    • distinguishing feature of medulla
 

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Questions (3)
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(M1.NE.14.77) A 25-year-old male presents to his primary doctor with difficulty sleeping. On exam, he is noted to have impaired upgaze bilaterally, although the rest of his ocular movements are intact. On pupillary exam, both pupils accommodate, but do not react to light. What is the most likely cause of his symptoms? Tested Concept

QID: 106877
FIGURES:
1

Frontal lobe cavernoma

18%

(14/76)

2

Craniopharyngioma

20%

(15/76)

3

Pinealoma

50%

(38/76)

4

Melanoma with temporal lobe metastasis

4%

(3/76)

5

Spinal cord ependymoma

1%

(1/76)

M 1 E

Select Answer to see Preferred Response

(M1.NE.14.11) You are called to see a chemotherapy patient who is complaining of severe nausea. This patient is a 52-year-old male with acute lymphoblastic leukemia (ALL) who began his first cycle of chemotherapy 2 days ago. Which of the following structures is involved in the pathway responsible for this patient's nausea? Tested Concept

QID: 101675
1

Medulla oblongata

60%

(45/75)

2

Medial geniculate nucleus

3%

(2/75)

3

Lateral geniculate nucleus

1%

(1/75)

4

Posterior hypothalamus

11%

(8/75)

5

Ventral posterolateral nucleus

21%

(16/75)

M 1 D

Select Answer to see Preferred Response

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