Brainstem Flashcards
What makes up the brainstem?
- (moving superior to inferior:) midbrain, pons, medulla
- the cerebellum is NOT considered to be part of the brainstem
Which cranial nerve nuclei are found in the brainstem? What other major matrix of neurons is found in the brainstem?
- the nuclei for cranial nerves III-XII
- the reticular formation is also found here (this deals with consciousness, pain perception, and regulation of cardiovascular and respiratory systems)
- (brainstem also deals with movement, posture, and muscle tone)
Which cerebellar peduncles connect each part of the brainstem to the cerebellum?
- superior: midbrain
- middle: pons
- inferior: medulla
What major features are found on the dorsal side of the brainstem?
- medulla: the continuation of the dorsal columns and their termination into the nucleus gracilis (medial) and nucleus cuneatus (lateral); CSF apertures (Magendie and Luschka)
- midbrain: superior (visual) and inferior (auditory) colliculi; origin of trochlear nerve (CN IV) right beneath the inferior colliculus
What major features are found on the ventral side of the brainstem?
- medulla: pyramids running along the ventral median fissure, decussation of the pyramids; olives
- pons: pontocerebellar fibers (pontine nuclei to contralateral cerebellum)
- midbrain: crus cerebri and cerebral peduncles
What major internal structures are found in the medulla?
- caudally: dorsal horn of spinal cord becomes the trigeminal sensory nucleus (afferents from the head go here)
- mid-medulla: contains the internal arcuate fibers and the medial lemniscus of the dorsal column pathway
- rostrally: the ventricular system and the medulla’s cerebellar connections arise; olivary nuclei; nuclei of CNs (V, VII,) IX, X, XI, XII (major one is vestibular nuclei and the medial longitudinal fasciculus)
What major internal structures are found in the pons?
- pontine nuclei (a crucial relay between the cerebrum and cerebellum)
- trapezoid body (acoustic fibers from cochlear nuclei) and the ascending lateral lemniscus (terminates at the inferior colliculus in the midbrain)
- part of tegmentum: contains nuclei for CNs V, VI, VII, VIII
What major internal structures are found in the midbrain?
- dorsal portion: tectum; ventral portion: tegmentum
- tectum has inferior and superior colliculi (collectively known as the corpora quadrigemina)
- cerebral aqueduct and the periaqueductal grey
- nuclei for CNs III, IV, V
- tegmentum has the red nucleus, substania nigra, and the crus cerebri
Where does the inferior colliculus project to? What about the superior colliculus?
- inferior colliculus receives input from the lateral lemniscus (carries acoustic fibers from cochlear nuclei) and projects to the medial geniculate nucleus (MGN) of the thalamus and then to the auditory cortex in temporal lobe
- superior colliculus has several afferents and efferents; major efferent projections are to the lateral geniculate nucleus (LGN) of thalamus and to the tectospinal tract for the visuospinal reflexes
What is the reticular formation?
- a complex matrix of neurons that extends throughout the brainstem that deals with regulation of consciousness, the cardiovascular system, and the respiratory system
- it also deals with muscle tone via the reticulospinal tracts
What is the reticular activating system?
- these are efferents originating from the reticular system that project into the thalamus, resulting in stimulation of the cerebral cortex and heightened arousal
What are Raphe nuclei?
- these are special nuclei found within the reticular formation; most of these use serotonin (5-HT) as their NT and play a role in mood, cognition, and sleep
- some have long axons that descend into the spinal cord and release enkephalin here (to modify nociception; the analgesic system)
Which type of cranial nerves originate in the brainstem? Which type terminates in the brainstem?
- motor cranial nerves originate in the brainstem cranial nerve nuclei
- sensory cranial nerves terminate in the brainstem cranial nerve nuclei
Which centers/structures of the brainstem generate descending tracts to the spinal cord?
- the reticular formation (reticulospinal tract)
- the red nucleus (rubrospinal tract)
- the vestibular nuclei (vestibulospinal tract)
What will a unilateral brainstem lesion result in?
- ipsilateral cranial nerve dysfunction
- contralateral spastic hemiparesis, hyperreflexia, Babinksi positive (this assumes the lesion is before the decussation of the pyramids)
- contralateral hemisensory loss (dorsal columns decussate in brainstem, spinothalamic tracts are already crossed over)
- ipsilateral incoordination
- (note that the facial hemiplegia will be ipsilateral because these fibers deal with the cranial nerve nuclei)
