Brainstem & Cranial Nerves Flashcards
(42 cards)
Three regions of the Brainstem
1 midbrain
2 pons
3 medulla
Basic functions of the Brainstem
1 cranial nerve function
- similar to lower motor & sensory neurons in spinal cord
2 conduit
- ascending and descending tracts
3 integration
- mostly by reticular formation
Midbrain
Dorsal surface
▪ superior & inferior colliculi
▪ superior cerebellar peduncle
Ventral surface
▪ cerebral peduncles
CN rootlets
▪ CN III (oculomotor)
➢ ventral surface, between cerebral peduncles
▪ CN IV (trochlear)
➢ dorsal surface at junction of pons & midbrain
▪ (only CN on dorsal surface)
Pons
Dorsal surface
▪ middle cerebellar peduncle
➢ superior cerebellar peduncle forms roof of 4th ventricle
Ventral surface
▪ swelling of basal pons
CN rootlets
▪ at midpons
➢ CN V (trigeminal)
▪ at junction of medulla and pons
▪ from medial to lateral
➢ CN VI (abducens)
➢ CN VII (facial)
➢ CN VIII (vestibulocochlear)
Medulla
Dorsal surface
▪ obex
➢ where 4th ventricle narrows into central canal
▪ inferior cerebellar peduncle
Ventral surface
▪ olive
▪ pyramids
▪ pyramidal decussation
➢ interrupts anterior fissure of spinal cord
➢ site of cerebrospinal tract crossing
CN rootlets
▪ CNs IX, X, & XII (glossopharyngeal, vagus, & hypoglossal
Three anterior/posterior regions
1 Tectum: most posterior layer
▪ primarily in midbrain
- contains superior & inferior colliculi
2 Tegmentum: middle layer
- contains most brainstem nuclei
3 Basis: anterior layer
- contains tracts
▪ e.g., cerebral peduncle, pyramids
In general, sensory nuclei are more _______ & motor are more _______
Lateral; medial
Oculomotor nucleus (CN III)
Located in rostral midbrain
▪ ventral edge of periaqueductal gray
Function (all ipsilateral)
▪ supplies eyelid (eyelid elevator)
▪ ocular muscles
➢ superior rectus
➢ medial rectus
➢ inferior oblique
➢ inferior rectus
Damage to CN III
▪ lateral strabismus
▪ cannot move eye medially
▪ vertical eye movements impaired
▪ diplopia
➢ double vision (due to misaligned eyes)
▪ ptosis
➢ drooping of eyelid
Edinger-Westphal nucleus (subdivision of oculomotor nucleus)(CN III)
Located in rostral midbrain
Function
▪ parasympathetic control of pupillary sphincter & ciliary muscle
➢ pupil constriction & focus (near vision)
Damage
▪ mydriasis
➢ dilated pupil, does not react to light (failed pupillary light reflex)
➢ cannot focus near vision
Substantia nigra
Located in rostral midbrain
Function
▪ site of dopamine production (compact part)
▪ functional part of basal ganglia
➢ initiating/coordinating/modifying movements and muscle tone
Damage (see basal ganglia notes)
▪ Parkinsonism type of hypokinetic disorder
Red nucleus
Located in rostral midbrain
Function
▪ coordinating motor movement via cerebral cortex/cerebellar connections
▪ origin of rubrospinal tract….facilitates flexor musculature (predominate UE)
➢ fibers project (contralateral) to all spinal levels but predominate in cervical region
(prox UE)…thus flexor spasticity of UE
Damage to red nucleus
▪ isolated lesion to red nucleus or rubrospinal tract is rare
▪ lesion rostral to red nucleus
➢ contribute to decorticate rigidity
▪ flexion of elbows, wrists & fingers
▪ extension & internal rotation of legs
▪ lesion caudal to red nucleus
➢ contribute to decerebrate rigidity
▪ extension of arms & legs (esp. elbow)
▪ internal rotation of both arms & legs
▪ cerebellar signs may also be associated with red nucleus damage
Trochlear nucleus (CN IV)
Located in caudal midbrain near midline
▪ only cranial nerve to emerge from dorsal surface
Function
▪ motor control of contralateral superior oblique
Damage
▪ less noticeable than other regions controlling eye movements
➢ diplopia while attempting to move eye down & laterally
Mescencephalic nucleus of trigeminal (CN V)
Located from rostral pons to midbrain
▪ not a true nucleus
▪ is a sensory ganglion embedded in brainstem
Function
▪ proprioceptive information from jaw (and teeth)
▪ primary sensory information for jaw jerk reflex
➢ tapping chin causes mouth to close (vis masseter, mostly)
Damage
▪ loss of jaw jerk reflex
Trigeminal motor nucleus (CN V)
Located mid-pons
Function
▪ motor neurons for muscles of mastication
▪ masseter, temporalis, medial/lateral pterygoids
➢ other minor inputs to tensor tympani, mylohyoid, & anterior belly of digastric
Damage
▪ unilateral lesions to nucleus have NO observable effect on chewing
➢ due to bilateral innervation
▪ exception is tensor tympani
Trigeminal main sensory nucleus (CN V)
➢ aka – principal sensory nucleus of V
Located in mid-pons
▪ rostral of facial motor nucleus
Function
▪ somatosensory & conscious proprioceptive inputs from the face & head
➢ information decussates here & joins medial side of medial lemniscus
▪ minor: some oral cavity information remains uncrossed (dorsal trigeminothalamic tract)
Damage
▪ ipsilateral loss of touch sensation from face
Abducens nucleus (CN VI)
Located in caudal pons
▪ closer to the midline (because it is a motor nucleus)
▪ surrounded by genu of facial nerve
➢ visible as facial colliculus on the floor of the 4th ventricle
Function
▪ supplies the ipsilateral lateral rectus m.
▪ causes abduction of the eye
Damage
▪ medial strabismus
➢ ipsilateral eye deviates slightly medially while gazing straight ahead
▪ as a result of the now-unopposed medial rectus m.
➢ may be able to get affected eye to midposition – but not past
Facial motor nucleus (CN VII)
Located in caudal pons
Function
▪ somatic motor output
➢ muscles of facial expression
▪ bilateral to upper face
▪ unilateral to lower face
➢ stapedius (in middle ear)
Damage
▪ hemiplegia of ipsilateral face
➢ note: compare this to UMN damage (e.g., corticobulbar fibers) which paralyzes
the mid- and lower- contralateral face
Cochlear nucleus (CN VIII)
Located in the caudal pons near the medulla/pons junction
▪ dorsolateral extreme
Function
▪ receives auditory information from the cochlear division of VIII (auditory n.)
➢ hearing
Damage
▪ may cause loss of specific frequencies from the ipsilateral ear
Vestibular nuclei (vestibular portion of VIII)
Located mid-medulla to mid-pons
▪ 4 separate nuclei
Function
▪ receive input from vestibule & semicircular ducts
➢ head position, movement, & rotation
➢ primary sensors for VOR
➢ primary contributor to medial & lateral vestibulospinal tracts
Damage
▪ vertigo, nystagmus, nausea/vomitting
Nucleus of the solitary tract (CNs VII, IX, & X)(facial, glossopharyngeal, & vagus)
Located from medulla to caudal pons
Function
▪ major visceral sensory system of the brainstem
➢ taste
➢ blood pressure & chemical sensation (from carotid sinus & aortic bodies)
➢ status of GI & cardiopulmonary systems
▪ e.g., lung stretch, dryness of mucous membranes
Damage
▪ loss of ipsilateral taste (esp. rostral end of NTS)
▪ increased heart rate (caudal end of NTS
Dorsal motor nucleus of the vagus (CN X)
Located in medulla
Function
▪ visceral motor output (90% of parasympathetic fibers)
➢ parasympathetic output to thoracic & abdominal regions
▪ are preganglionic neurons
Damage
▪ ?loss of GI tract motility; cardiopulmonary problems
Nucleus ambiguus
Located through medulla
Function – split innervation: both branchial motor & visceral motor (parasympathetic)
▪ branchial motor component
➢ CNs IX & X (glossopharyngeal & vagus)
➢ damage = difficulty swallowing (dysphagia) & speaking (dysphonia)
▪ visceral motor component
➢ CN X (vagus)
➢ cardioinhibitory neurons
▪ decreases cardiac output (e.g., during sudden blood pressure increases)
▪ damage = increased resting heart rate
