Organisation of the Brainstem and the Cranial Nerves Flashcards
04.10.2019
What is the brainstem?
The part of the CNS, exclusive of the cerebellum, that lies between the cerebrum and the spinal cord.
What are the components that make up the brainstem?
Midbrain
Pons
Medulla oblongata
Where do the brainstem structures sit in?
In the posterior cranial fossa
Structures on the posterior side of the brainstem
- 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))
What do radiologists refer to as the tectum?
Roof of the midbrain / dorsal region of the midbrain
Structures on the anterior side of the brainstem
- CN I (olfactory)
- CN II (optic nerve)
- pituitary stalk
- mammillary bodies
- CN III (oculomotor)
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Structures on the anterior side of the brainstem
- 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
Which CN emerges entirely from the pons?
CN V (trigeminal nerve) -> sensory nerve of the head and neck but also motor
Structures on the anterior side of the brainstem
- optic chiasm
- pituitary stalk (infundibulum)
- maxillary body
- CN3; CN5-12
- cerebral peduncles
- pyramids
- pyramidal decussation
Which CN emerges entirely from the pons?
CN V (trigeminal nerve) -> sensory nerve of the head and neck but also motor
Cranial nerves at the anterior side of the brainstem
- 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)
What are pyramidal and extrapyramidal symptoms?
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
What is the pyramidal decussation?
90-95% of nerve fibres cross over at the base of the medulla
Functional classification of cranial nerves
- General somatic afferent (GSA)
- sensation from skin and mucous membranes
- General visceral afferent (GVA)
- sensation from GI tract, heart, vessels & lungs
- General somatic efferent (GSE)
- muscles for eye & tongue movements
- General visceral efferent (GVE)
- preganglionic parasympathetic
- Special somatic afferent
- vision, hearing & equilibrium
- Special visceral afferent
- smell & taste
- Special visceral efferent
- muscles involved in chewing, facial expression, swallowing, vocal sounds & turning head
How does the brainstem develop?
Important:
motor = medial;
sensory = lateral
