Brainstem

Question 0

Corona radiata

Answer 0

Motor axons forming the pyramidal tract descend:
1 ̊ motor cortex- Corona radiata- Internal capsule- Midbrain (cerebral crus)- Pons- Medulla oblongata (pyramids)- Spinal cord

Question 1

Brainstem composed of

Answer 1

Midbrain, pons, medulla

Axons from primary motor cortex passes down through the brainstem, decussate at medulla oblongata and enter spinal cord

Question 2

Mesencephalon derivatives:

Answer 2

Tectum
Tegmentum
Basis pedunculi (base)

Question 3

Tectum “Roof”

Answer 3

Quadrigeminal plate: 
• Superior colliculus x2 
• Inferior colliculus x2 
• (Colliculus = “small mound”) 
• Dorsal surface of cerebral aqueduct.

Question 4

Tegmentum

Answer 4

Located between tectum and base. 
• Ventral to cerebral aqueduct. 
• Dorsal to substantia nigra.  
Contains:  
• red nucleus 
• nucleus of CN III 
• nucleus of CN V 
• Reticular formation

Question 5

Red nucleus

Answer 5

Colour from high content of Fe (iron).
• Receives inputs from cerebral cortex and cerebellar nuclei.
• Gives rise to rubrospinal tract => controls flexor muscle tone.

Question 6

Substantia nigra

Answer 6

Brown colour due to high content of melanin.
• Projects to striatum (caudate nucleus + putamen) & thalamus.
• Death of dopaminergic cells => Parkinson’s disease => bradykinesia & hypokinesia (difficulty in initiating and performing voluntary movements)

Question 7

Basis pedunculi

Answer 7

Cerebral peduncle = tegmentum + basis pedunculi.

Contains corticospinal and corticopontine tracts

Question 8

Mesencephalon blood supply

Answer 8

• Posterior communicating artery
• Posterior cerebral artery
• Superior cerebellar artery

Question 9

Cerebral aqueduct

Answer 9

• Located between tectum and tegmentum.
• Surrounded by periaqueductal grey matter.
• Interconnects 3rd and 4th ventricles.
• Blockage = hydrocephalus.

Question 10

Pons “Bridge”

Answer 10

• Part of brainstem between medulla oblongata and midbrain.
• Base: contains corticospinal (descending motor) and corticopontine tracts.
• Tegmentum: contains cranial nerve nuclei, reticular nuclei, major ascending sensory pathways.
• Contains nuclei that mediate several auditory and balance functions.
• Input from vestibular system and communicates with cerebellum for balance.
• Sensory input from face and sends motor neurons to muscles of face for voluntary and involuntary facial expression.

Question 11

Pons blood supply and nerves

Answer 11

Supplied by basilar artery

Gives rise to CN V, VI, VII, VIII

Question 12

Medulla oblongata

Answer 12

• Pyramids contain corticospinal fibres primarily projecting from the primary motor cortex in the precentral gyrus.
• 90% of corticospinal fibres decussate (cross-over) in the caudal 1/3 of medulla oblongata to pass dorso-laterally to form the lateral corticospinal tract.

• 10% of corticospinal fibres don’t
decussate and form the anterior
corticospinal tract.