Organisation of the Brainstem and the Cranial Nerves

Question 1

What is the brainstem?

Answer 1

The part of the CNS, exclusive of the cerebellum, that lies between the cerebrum and the spinal cord.

Question 2

What are the components that make up the brainstem?

Answer 2

Midbrain
Pons
Medulla oblongata

Question 3

Where do the brainstem structures sit in?

Answer 3

In the posterior cranial fossa

Question 4

Structures on the posterior side of the brainstem

Answer 4

• pineal gland (midline, only one, important for circadian rhythm, melatonin)
• superior colliculus (two, coordinated neck and eye movements)
• inferior collicului (auditory reflex -> look towards and assess)
• trochlear nerve (CNIV, supplies one of the eye muscles: superior oblique muscle)
• 4th ventricle at the level of the pons
• dorsal columns at the level of the medulla, responsible for touch and proprioception (medial: gracilis (leg), lateral cuneate (upper arm))

Question 5

What do radiologists refer to as the tectum?

Answer 5

Roof of the midbrain / dorsal region of the midbrain

Question 6

Structures on the anterior side of the brainstem

Answer 6

• CN I (olfactory)
• CN II (optic nerve)
• pituitary stalk
• mammillary bodies
• CN III (oculomotor)
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Question 7

Structures on the anterior side of the brainstem

Answer 7

• optic chiasm
• pituitary stalk (infundibulum)
• maxillary body
• CNIII (oculomotor)
• cerebral peduncles
• CN6 (abducens) -> medial at pontomedullary junction
• CN7 (facial) -> more lateral at pm-junction
• CN8 (vestibulocochlear) -> further lateral at pmj
• CN9 (glossopharyngeal) -> at medulla
• CN10 (vagus) -> at medulla
• CN11 (accessory) -> at medulla
• CN12 (hypogolossal nerve)
• pyramids

Question 8

Which CN emerges entirely from the pons?

Answer 8

CN V (trigeminal nerve) -> sensory nerve of the head and neck but also motor

Question 9

Structures on the anterior side of the brainstem

Answer 9

• optic chiasm
• pituitary stalk (infundibulum)
• maxillary body
• CN3; CN5-12
• cerebral peduncles
• pyramids
• pyramidal decussation

Question 10

Which CN emerges entirely from the pons?

Answer 10

CN V (trigeminal nerve) -> sensory nerve of the head and neck but also motor

Question 11

Cranial nerves at the anterior side of the brainstem

Answer 11

• CNIII (oculomotor)
• CN6 (abducens) -> medial at pontomedullary junction
• CN7 (facial) -> more lateral at pm-junction
• CN8 (vestibulocochlear) -> further lateral at pmj
• CN9 (glossopharyngeal) -> at medulla
• CN10 (vagus) -> at medulla
• CN11 (accessory) -> at medulla
• CN12 (hypogolossal nerve)

Question 12

What are pyramidal and extrapyramidal symptoms?

Answer 12

If you have a motor problem:

• pyramidal if it Is down to the corticospinal tract
• extrapyramidal if it is down to the cerebellum or other parts in motor control

Question 13

What is the pyramidal decussation?

Answer 13

90-95% of nerve fibres cross over at the base of the medulla

Question 14

Functional classification of cranial nerves

Answer 14

1. General somatic afferent (GSA)
   
   • sensation from skin and mucous membranes
2. General visceral afferent (GVA)
   
   • sensation from GI tract, heart, vessels & lungs
3. General somatic efferent (GSE)
   
   • muscles for eye & tongue movements
4. General visceral efferent (GVE)
   
   • preganglionic parasympathetic
5. Special somatic afferent
   
   • vision, hearing & equilibrium
6. Special visceral afferent
   
   • smell & taste
7. Special visceral efferent
   
   • muscles involved in chewing, facial expression, swallowing, vocal sounds & turning head

Question 15

How does the brainstem develop?

Answer 15

Important:
motor = medial;
sensory = lateral

Question 16

internal structure of the midbrain

Answer 16

= “Mickey Mouse”

Question 17

What are the important structures in the midbrain?

Answer 17

• inferior colliculus
• cerebral aqueduct
• substantia nigra
• cerebral peduncle

Question 18

What are the important structures in the pons?

Answer 18

• 4th ventricle
• middle cereberral peduncle
• transverse fibers

Question 19

What are the important structures in the medulla?

Answer 19

• 4th ventricle
• inferior olivary nucleus
• Pyramids

Question 20

What are important structures in the lower medulla?

Answer 20

• dorsal columns
• central canal
• pyramidal decussation

Question 21

Lateral Medullary Syndrome

Answer 21

=> Thrombosis of vertebral artery or PICA

Question 22

What are the symptoms of lateral medullary syndrome?

Answer 22

• Vertigo
• Ipsilateral cerebellar ataxia
• Ipsilateral loss of pain/thermal sense (face)
• Horner’s syndrome
• Hoarseness, difficulty in swallowing
• Contralateral loss of pain/thermal sense (trunk and limbs)

Question 23

Which cranial nerves are sensory, motor and both?

Answer 23

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