Lecture 9: Brainstem and Cranial Nerves Flashcards
What is the brainstem made up of?
- midbrain
- pons
- medulla
What pathways pass through the brainstem?
ALL ascending and descending pathways
How is the cerebellum connected to the brainstem?
By 3 cerebellar peduncles (white fibre tracts)
Which cranial nerve nuclei are contained within the brainstem?
9 of the 12 pairs
III, IV, V, VI, VII, VIII, IX, X and XII
How are the pathways related to the brainstem?
- many of descending pathways synapse in brainstem nuclei before going to body
- many ascending pathways synapse here before going to the brain
- some start within nuclei of the brainstem
Describe the internal structure of the brainstem.
POSTERIOR –> ANTERIOR
- tectum (roof) sits behind relevant ventricular system depending on how far down the brainstem the section is
- ventricular system (e.g. cerebral aqueduct or 4th ventricle)
- tegmentum
- base
Name some visible structures from the posterior aspect of the brainstem.
- pineal gland
- superior colliculus
- inferior colliculus
- trochlear nerve (CN IV)
- dorsal columns
Why are there enlargements in the dorsal columns?
Cuneate and gracile pathways synapse here onto their nuclei (which contain cell bodies of secondary sensory nerves), (cross over to other side before going up to the brain) hence enlargement
What forms the roof of the 4th ventricle?
the cerebellum
What does the pineal gland do?
produces melatonin (important for sleep and circadian rythym)
What do the colliculi do?
Superior colliculus - involved in visual pathway
Inferior colliculus - involved in auditory pathway
Name some visible structures from the anterior aspect of the brainstem.
- optic chiasm
- pituitary stalk
- mammillary body
- cerebral peduncle
- medullary pyramids
- pyramidal decussation
What is the pyramidical decussation?
Point at which fibres from motor cortex cross over
What are the medullary pyramids?
contain corticospinal axons
What is the difference between an optic nerve and optic tract?
the optic tract has axons coming from both eyes whereas the optic nerve has axons from one eye
What are the descending tracts of the cerebral peduncles?
- corticospinal (muscles below head)
- corticobulbar (muscles of face and mastication)
What cranial nerves emerge at the midbrain level?
CN III (oculomotor) - emerges from anterior aspect - and CN IV (trochlear) - emerges from posterior aspect
What structures can you see on a midbrain transverse section?
- superior and inferior colliculi
- cerebral aqueduct
- cerebral peduncle
What cranial nerves emerge at the Pons level?
-CN V (trigeminal)
-CN VI (abducens)
-CN VII (facial)
-CN VIII (vestibulocochlear)
Emerging from or bringing info back to pontine nucleus
What is the difference between the open (upper) medulla and closed (lower) medulla?
In the open medulla there is no neural tissue surrounding the 4th ventricle because the cerebellum has been removed. However in the closed medulla the 4th moves anteriorly and is completely enclosed by neural tissue.
Which cranial nerves emerge from the medulla?
- CN IX (glossopharyngeal)
- CN X (vagus)
- CN XII (hypoglossal)
What is the central canal in the closed medulla continuous with?
the spinal cord central canal
What are the 2 arterial systems that supply blood to the CNS?
anterior and posterior
The anterior and posterior arterial systems are derived from which vessels?
ANTERIOR - internal carotid system
POSTERIOR - vertebral-basilar
What is the medulla (anatomically)?
Rostral continuation of spinal cord
What does the anterior surface of the medulla have?
pyramids (descending tracts)
What does the posterior surface of the medulla have?
Dorsal columns
How is the posterior surface of the medulla divided?
Into open and closed
How does the central canal change throughout the medulla?
The closed medulla has extension of central canal of spinal cord
Canal widens to form 4th ventricle in open medulla
Which motor pathway decussates in the lower medulla?
corticospinal tract
What are the different ways in which you can classify cranial nerve functions? (7 acronyms)
Have afferent and efferent functions: general somatic efferent (GSE) general visceral efferent (GVE) general visceral efferent (parasympathetic) general somatic afferent (GSA) general visceral afferent (GVA) special visceral efferent (SVE) special somatic afferent (SSA)
