Intro to Brainstem Flashcards
3 main functions of the brainstem
conduit, integrative, cranial nerve home (III-XII)
Classic divisions of the brainstem
Midbrain, Pons, Medulla
Longitudinal divisions of the brainstem
from ventral to dorsal –> Basis, tegmentum, Tectum (“roof”)
Medial and lateral divisions of brainstem
- Alar plate (dorsal; sensory)– separated by septum limitans
- basal plate (ventral)
- pneumonic: ASsBM
Conduit function of brainstem
transit and processing stations for ascending and descending pathways to and from cerebrum, cerebellum and spinal cord
Integrative function of brainstem
- “Keeps you alive!”: integrative functions like consciousness, sleep wake cycle, muscle tone, posture, respiratory and CV control
- found thanks to reticular formation
Midbrain main distinguishing features
cerebral peduncles, interpeduncular fossa
- also see mammillary bodies (above; part of hypothalamus not brainstem)
Medulla features
- Ventral: pyramids (medial), olive (lateral)
Pons features
pontine protuberance, middle cerebellar peduncles (laterally)
Dorsal surface features
- Midbrain: superior/inferior colliculi with 3rd ventricle above
- Pons: superior/middle/inferior cerebrllar peduncle
- Medulla:
tract
bundle of axons in CNS
nerve
bundle of axons in PNS
Peduncle
collection of tracts that travel together from one part of brain to another
How many peduncles
1- cerebral
3- cerebellar (superior, inferior, middle)
Cerebral Peduncle
Information going from cerebrum to spinal cord, pons, and CN nuclei
Superior Cerebellar Peduncle
- Info from anterior spinocerebellar tract to cerebellum
- mostly info from cerebellum to red nucleus and thalamus (VA/VL)
Inferior Cerebellar Peduncle
- into cerebellum (posterior spinocerebellar tract and olive)
- Information going back and forth between cerebellum and vestibular nucleus
Middle Cerebellar Peduncle
information from Cerebral cortex–> PONS –> Cerebellum
Major distinguishing feature midbrain
Dorsal: sup/inf canaiculi
Ventral: cerebral peduncles
Pons distinguishng features
D: cerebellum
V: Pons
Distinguishing features of rostral medulla
D: ICP
V: inferior olive, pyramids
distinguishing features of caudal medulla
D: nucleus cuneatus/gracilis
V: pyramids (and their decussation)
Corticospinal tract
Motor; Decussates at base of medulla
Dorsal Column Medial Lemniscus
- Fine touch/vibration, proprioception
- Decussates mid medulla then becomes medial lemniscus
Anerolateral System (Spinothalamic)
- Pain/temp
- Decussates at level of spinal cord
Most long tract lesions in brainstem will be _______ and most cranial nerve signs will be _______ to the lesion
1) contralateral
2) ipsilateral
Cranial Nerve locations
- Midbrain: 3, 4
- Pons: 5, 6, 7, 8
- Medulla 9, 10, 11, 12
(LR6SO4)3
all occulomotor muscles innervated by CN III except lateral rectus (6) and superior oblique (4)
CN VII
Motor – muscles of facial expression
Sensory – taste ant 2/3
CN V
Motor: muscles of mastication
CN VIII
l
CN IX
l
CN X
Vagus
CN XI
Accessory nerve
Location of CN NUCLEI
Midbrain: III, IV, edinger westphal nucleus
Pons: V, VI, VII, VIII (cochlear and vestibular nuclei)
Medulla: IX, X, XII, spinal nucleus of V (pain/temp)
Nuclei of CN V
mesencephalic, primary motor nucleus, main sensory nucleus, spinal nucleus (in pons/medulla?)
CN VIII nuclei
cochlear nucleus and vestibuilar nucleus – both in Pons
Superior vs inferior caniculus
Inferior has “capsule”
Pupillary light reflex
shining light in one eye will cause pupillary constriction in both eyes
Pupillary light reflex
shining light in one eye will cause pupillary constriction in both eyes
MLF
midlongitudinal faniculus
- coordinates eye movements with head movements
- CN nuclei 3, 4, 6, 8
- also involves cerebellum, medial vestibulospinal tract (too coordinate neck muscles too)
Vagal Pathways
Dorsal motor nucleus X, Nucleus ambigusou, solitary nucleus
Gag reflex
touch wall fo 1 side fo pharynx elicits bilateral gagging response (tests sensory fibers of IX and nucleus ambiguous of X)
Jaw Jerk Reflex
Downward tapping of jaw causes bilateral contraction of masseter
- Afferent mesencephalic nucleus of V
- Efferent = main motor nucleus of V
Corneal Blink Reflex
Cornea touched by foreign object –> both eyes blink
- Afferent= spinal nucleus of V
- Efferent = motor nucleus of VII
Which CN get innervation from bilateral UMN
3, 4, 5, 6, upper of 7, Nucleus ambiguous
which CN innervation from contralateral UMN
lower of 7, hypoglossal (12)
All LMN are ipsilateral onto targets except for which?
CN IV
corticospinal tract
carries info from cerebrum to spinal cord
corticopontine tract
carries info from cerebrum to pons
corticobulbar tract
carries info from cerebrum to cranial nerves
Middle cerebellar peduncle
carries information from Cerebral cortex –> Pons –> Cerebellum
Inferior cerebellar peduncle
carries info from posterior spinocerebellar tract and inferior olive to cerebellum; carries info between cerebellum and vestibular nucelsu both ways
superior cerebellar peduncle
carries info from cerebellum to red nucleus/thalamus; carries info from anterior spinocerebellar tract to cerebellum
midline medial motor nuclei
3, 4, 6, 12
Dorsal motor nucleus of X
preganglionic parasympathetic vagal neurons to heart and thoracic and abdominal viscera
Nucleus ambiguous
motor vagal neurons to muscles of pharynx, larynx (swallowing, phonation, movement of uvula, gagging). Also contains motor fibers to stylopharyngeus muscle which helps in phonation and swallowing but not gagging
gag reflex
afferent (IX sensory fibers)
Efferent (X nucleus ambiguous)
which CN get bilateral innervation from corticobulbar tract
3, 4, 5, 6, upper of 7, N. ambiguous
CN with contralateral UMN innervation from corticobulbar tract
lower of 7, hypoglossal (12) (note 12 has minor ipsilateral contribution but dominated by contralateral)
