Lecture 12: Brainstem I Flashcards
What is similar about CN 3, 4, 6, 12?
- they are all motor axons
- they exit medially on the VENTRAL surface of brainstem
What is similar about CN 5, 7, 8, 9 and 10
- they are all mixed nerves
- exit ventroLATERALLY
Bulbar
involving the brainstem; “bulbar paralysis”
Corticobulbar tract (corticonuclear)
-connects cortex to brainstem
Goes from M1 internal capsule cerebral peduncle LMN of the cranial nerves
Function: UMN that controls muscle of face, head and neck
Bilaterally innervates muscles that shut eye and wrinkle forehead of CN7
Bilateral innervation of all muscles except for 7 and XII
Significance of Corticobulbar bilateral innervation (UMN neuron lesion)
A lesion to a single corticobulbar neuron will not result in weakness (ipsilateral and contralateral) of muscles that shut eye and wrinkle forehead (for facial nerve) nor weakness in other CN motor neurons
Example: forehead and levator palpebrae would be spared on both sides of face if one corticobulbar axon is lesioned but CONTRALATERAL lower face would experience weakness
Significance of a lower motor neuron lesion
Unlike a corticobulbar lesion, in which only the lower half of the contralateral face is weakened, a LMN lesion would cause the ENTIRE IPSILATERAL face to be weakened
Bell’s palsy
Corticopontine tract
- motor fibers that stretch from all major subdivisions of cerebral cortex to nuclei of CN V, VII and XII
- terminates in pontine nuclei of V, VII and XII (as the name suggests)
Crus Cerebri
anterior portion of the cerebral peduncle that contain the motor tracts
What are the only nerves that don’t exit brainstem so to speak?
1, 2 and 12 (exits from hole in skull…misplaced spinal nerve)
What 4 structures can be seen at level of Midbrain?
CN 3, 4 and Superior colliculus (Sight)/Inferior colliculus (hearing)
Remember, the colliculi lie DORSALLY, while all cranial nerves (save IV) come out ventrally
What 4 CN can be seen exiting at level of Pons?
5-8
What 4 CN can be seen at level of Medulla?
9-12
What is contained in the cerebral peduncles?
- corticopontine axons
- corticobulbar axons
- corticospinal axons
What will happen if you have a medial vasculature deficit in brain stem?
You will fuck up motor axons
What will happen if you have a lateral vasculature deficit in brain stem?
You will fuck up mixed nerves
What is only cranial nerve that exits dorsally from brainstem?
CN IV
-only completely crossed CN
What is the interpeduncular fossa?
The space between the two CEREBRAL peduncles
What will be the path that is taken by the corticospinal tract (lateral motor system)?
It courses ventrally and medially through the brainstem
What happens if we lesion the corticospinal tract in the brainstem
Before decussation
Contralateral and below
What happens if we lesion corticospinal tract in spinal cord?
After decussation
Ipsilateral and below
Fasciculus
synonym for tract
What are medial motor systems?
Located ventral-medial and is responsible for posture (the walking lecture)
What happens when you lesion dorsal column in spinal cord?
Below decussation
Ipsilateral and below
What happens when you lesion the medial lemniscus in brain stem?
Above decussation
Contralateral and below
How does the orientation of medial lemniscus change as it ASCENDS the brainstem?
It moves medial to lateral from medulla up to midbrain
Therefore, vasculature supply lesions, depending at which segment, will differently affect the medial lemniscus
-medial blood supply lesion and medulla will fuck up proprioception and vibration
-medial blood supply lesion at midbrain will not touch proprioception and vibration
How does Leg-arm orientation of medial lemniscus change as it ascends?
Goes from vertical (leg to arm, inferior to superior), to horizontal (leg to arm, lateral to medial)
What happens when you lesion spinothalamic tract in spinal cord AND/OR brainstem?
Still contralateral and below the lesion
Are the neurons of spinothalamic tract just going straight to thalamus? If not, why?
No
-because some of spinothalamic tract go to nuclei of brainstem to relay effector information back down spinal cord to suppress pain signals
Where does spinothalamic tract course?
Always laterally
Where does descending hypothalamic course? Whats the significance?
With spinothalamic
Lesion of one lesions both…so you get pain and temperature deficits as well as horners syndrome together
What is path of hypothalamic sympathetic fibers?
Goes from autonomic regulatory nuclei of hypothalamus T1-L2 From T1 and T2 goes to T1 nerve root Inferior Cervical (stellate ganglion) superior cervical ganglion carotid plexus pupillary dilator muscle, superior tarsal muscle and sweat glands
What is the purpose of the medial longitudinal fasciculus (MLF)?
Links the vestibular nuclei and centers for conjugate gaze with the abducens, trochlear and oculomotr (particularly 3 and 6)
-so that you ABduct and ADduct eyes concomitantly
Vestibular system
Allows you to sense head turning or head movement
What will be found in every stem section in anatomy?
- A long tract
-corticospinal
-dorsal column/medial lemniscus
-spinothalamic/descending hypothalamic axons
-MLF (medial longitudinal fasciculus)
-central tegmental tract (upper medulla and above) - A cranial nerve nucleus or nerve
- A trigeminal nucleus
- A cerebellar Peduncle or fibers forming one
ICP (inferior cerebellar peduncle) – medulla
MCP – Pons
SCP - Midbrain
