Lecture 12: Brainstem I

Question 1

What is similar about CN 3, 4, 6, 12?

Answer 1

• they are all motor axons

- they exit medially on the VENTRAL surface of brainstem

Question 2

What is similar about CN 5, 7, 8, 9 and 10

Answer 2

• they are all mixed nerves

- exit ventroLATERALLY

Question 3

Bulbar

Answer 3

involving the brainstem; “bulbar paralysis”

Question 4

Corticobulbar tract (corticonuclear)

Answer 4

-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

Question 5

Significance of Corticobulbar bilateral innervation (UMN neuron lesion)

Answer 5

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

Question 6

Significance of a lower motor neuron lesion

Answer 6

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

Question 7

Corticopontine tract

Answer 7

• 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)

Question 8

Crus Cerebri

Answer 8

anterior portion of the cerebral peduncle that contain the motor tracts

Question 9

What are the only nerves that don’t exit brainstem so to speak?

Answer 9

1, 2 and 12 (exits from hole in skull…misplaced spinal nerve)

Question 10

What 4 structures can be seen at level of Midbrain?

Answer 10

CN 3, 4 and Superior colliculus (Sight)/Inferior colliculus (hearing)
Remember, the colliculi lie DORSALLY, while all cranial nerves (save IV) come out ventrally

Question 11

What 4 CN can be seen exiting at level of Pons?

Answer 11

5-8

Question 12

What 4 CN can be seen at level of Medulla?

Answer 12

9-12

Question 13

What is contained in the cerebral peduncles?

Answer 13

• corticopontine axons
• corticobulbar axons
• corticospinal axons

Question 14

What will happen if you have a medial vasculature deficit in brain stem?

Answer 14

You will fuck up motor axons

Question 15

What will happen if you have a lateral vasculature deficit in brain stem?

Answer 15

You will fuck up mixed nerves

Question 16

What is only cranial nerve that exits dorsally from brainstem?

Answer 16

CN IV

-only completely crossed CN

Question 17

What is the interpeduncular fossa?

Answer 17

The space between the two CEREBRAL peduncles

Question 18

What will be the path that is taken by the corticospinal tract (lateral motor system)?

Answer 18

It courses ventrally and medially through the brainstem

Question 19

What happens if we lesion the corticospinal tract in the brainstem

Answer 19

Before decussation

Contralateral and below

Question 20

What happens if we lesion corticospinal tract in spinal cord?

Answer 20

After decussation

Ipsilateral and below

Question 21

Fasciculus

Answer 21

synonym for tract

Question 22

What are medial motor systems?

Answer 22

Located ventral-medial and is responsible for posture (the walking lecture)

Question 23

What happens when you lesion dorsal column in spinal cord?

Answer 23

Below decussation

Ipsilateral and below

Question 24

What happens when you lesion the medial lemniscus in brain stem?

Answer 24

Above decussation

Contralateral and below

Question 25

How does the orientation of medial lemniscus change as it ASCENDS the brainstem?

Answer 25

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

Question 26

How does Leg-arm orientation of medial lemniscus change as it ascends?

Answer 26

Goes from vertical (leg to arm, inferior to superior), to horizontal (leg to arm, lateral to medial)

Question 27

What happens when you lesion spinothalamic tract in spinal cord AND/OR brainstem?

Answer 27

Still contralateral and below the lesion

Question 28

Are the neurons of spinothalamic tract just going straight to thalamus? If not, why?

Answer 28

No -because some of spinothalamic tract go to nuclei of brainstem to relay effector information back down spinal cord to suppress pain signals

Question 29

Where does spinothalamic tract course?

Answer 29

Always laterally

Question 30

Where does descending hypothalamic course? Whats the significance?

Answer 30

With spinothalamic | Lesion of one lesions both…so you get pain and temperature deficits as well as horners syndrome together

Question 31

What is path of hypothalamic sympathetic fibers?

Answer 31

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

Question 32

What is the purpose of the medial longitudinal fasciculus (MLF)?

Answer 32

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

Question 33

Vestibular system

Answer 33

Allows you to sense head turning or head movement

Question 34

What will be found in every stem section in anatomy?

Answer 34

1. A long tract -corticospinal -dorsal column/medial lemniscus -spinothalamic/descending hypothalamic axons -MLF (medial longitudinal fasciculus) -central tegmental tract (upper medulla and above) 2. A cranial nerve nucleus or nerve 3. A trigeminal nucleus 4. A cerebellar Peduncle or fibers forming one ICP (inferior cerebellar peduncle) – medulla MCP – Pons SCP - Midbrain