3. Organisation of the brainstem and cranial nerves Flashcards
Define the brainstem
Part of the CNS, exclusive of the cerebellum, that lies between the cerebrum and the spinal cord
What are the three major divisions of the brainstem from the top to the bottom?
- Midbrain
- Pons
- Medulla Oblongata
How can you identify the roof of the midbrain?
- Area with four lumps
* Colliculi - “low lying hills”
What is the ventral floor of the 4th ventricle?
Pons
What is the pineal gland?
- One of the few midline structures (not bilateral like most others in the brainstem)
- Releases melatonin
- Regulation of circadian rhythm (24hr cycle)
- Can be entrained by light - skull too thick so trained with vision
What is the Superior Colliculus for?
Midbrain nucleus for coordination of eye and head movements at the same time
What is the Inferior Colliculus for?
Midbrain nucleus for auditory reflexes e.g. looking in the direction of a bang
Which cranial nerves emerge from the back of the brainstem
Only trochlear nerves (IV) - supplies superior oblique muscle of the eyes
Where are the dorsal columns involved in?
- Touch
- Proprioception (space perception)
- Sensory from lower limbs medial to sensory from upper limbs
Why is it easy to identify the pons?
Transverse fibres going across it
What structure is at the top of the midbrain?
Optic chiasm
What structure is immediately behind the optic chiasm?
Pituitary stalk (infundibulum)
What can you see behind the infundibulum?
Inferior part of the hypothalamus - mammillary bodies (part of limbic system)
What happens to mammillary bodies in chronic alcoholics?
- Becomes dark
* Neovascularisation
Which nerves emerge just above the the transverse fibres of the pons?
Oculomotor nerves (III)
What is the cerebral peduncle?
- Structure above the transverse fibres of the pons
- Main motor fibres coming from motor cortex to the spinal cord
- Also has structural role - holding cerebrum onto the brainstem
What does Pons mean, and what does it do?
- Pons = bridge
* Joins two halves of cerebellum together
Which nerves emerge from the lateral parts of the pons?
• Trigeminal (V) • Divide into: - Opthalmic - Maxillary - Mandibular
What is the function of the Trigeminal nerve?
- Touch and sensation throughout the head and neck
* Very small root next to large one as Trigeminal also has a motor function - mastication
Which nerves emerge below the pons (ponto-medullary junction) from medial to lateral?
- Abducens (VI) - supplies the lateral rectus muscle, causing abduction from midline
- Facial (VII) - innervates muscles involved in facial expression
- Vestibulocochlear (VIII) - balance and hearing
What is Bell’s Palsy?
- Dysfunction of facial nerves
- Loss of facial muscle tone
- May be due to post-infection inflammation
- Usually temporary
Which nerves emerge from the lateral medulla?
- Glossopharyngeal (IX) - sensory and motor innervation of tongue and pharynx
- Vagus (X) - main parasympathetic nerve that projects down into the viscera
- Accessory (XI) - supplies the sternocleidomastoid and trapezius
Which nerves emerge more anteriorly/medially from the medulla?
- Hypoglossal nerves (VII)
* Supplies the musculature of the tongue
Describe the pyramids of the medulla?
- Structures on the anterior surface of the medulla
- Continuation of corticospinal tracts
- Fibres come down from the cortex through the peduncles, behind the transverse fibres, and re-emerge as pyramids
- 90-95% of fibres cross over at “pyramidal decussation” at the base of the medulla - contralateral motor control
