Pons and Medulla

What do the middle cerebral peduncles do?

connects pons to cerebellum

Right pons goes to which side of the cerebellum?

left

How to tell where you are in cross section by looking at middle cerebellar peduncles?

the larger they are, the farther down you are

What cranial nerves come off the pons?

5, 6, 7, 8

Where does CN V come off the pons?

cranial/lateral pons

Where do CNs VI, VII, VIII come off the pons?

pontomedullary junction

What cerebellar peduncles are seen in cross section of pons?

superior cerebllar peduncles @ dorsal aspect

middle cerebellar peduncles @ ventral lateral pons

The tegmentum of the pons is directly continuous with?

tegmentum of midbrain

What do both the tegmentum of pons + tegmentum of midbrain contain?

ascending sensory fibers + CN nuclei

What does the base of the pons contain?

descending motor fibers

pontine nuclei

Where does the pontine nuclei send info to and how?

motor fibers to cerebellum via middle cerebral peduncles

The 4th ventricle is dorsal to what in the pons?

tegmentum

What is the roof of the 4th ventricle @ level of pons?

superior + inferior medullary vellum of cerebellum

What is the floor of the 4th ventricle @ level of the pons?

facial colliculus in tegementum of pons

How can you tell where you are at in cross section of pons by looking at 4th ventricle?

the larger the 4th ventricle, the farther down you are

What is the trapezoid body?

decussating auditory fibers creating the intersection of tegmentum and base of pons

If you have small middle cerebral peduncles + small 4th ventricle, what half of the pons are you in?

Cranial half

Does CN V exit the pons in the cranial or caudal half?

cranial

What is the white matter of the superior medullary vellum?

decussating fascicles of CN IV

What are the orientation of the fibers in the base of the pons? What are they?

longitudinal fibers (run longitudinal): descending motor fibers

transverse fibers (run transverse): pontocerebellar fibers

The fibers that run longitudinal in the pons are cut how in cross section?

cut transverse/in cross section

The fibers that run transverse in the pons are cut how in cross section?

cut longitudinal

Where is the 4th ventricle the largest in the pons?

at the pontomedullary junction

What forms the facial colliculus?

internal genue of facial motor nucleus fibers

What kind of fibers does the facial motor nucleus have?

SVE fibers

What does damage to the facial motor nuclei cause?

ipsilateral, hemifacial, flaccid paralysis of face

hyperacusia

What is hyperacusis?

increased sensitivity to sound

What causes hyperacusia with damage to facial motor nucleus?

paralysis of stapedius

What does the stapedius do?

restricts movement of stapes

Compression of facial colliculus would affect what first? Then what?

affect CN VII fibers first, then CN VI

If compression of facial colliculus does damage CN VI, what would that look like?

esotropia (one eye nasal)

What can cause compression of facial colliculus?

4th ventricle tumors

cerebellar tumors

noncommunicating hydrocephalus

What is noncommunicating hydrocephalus?

hydrocephalus due to blockage of ventricles

What is common cause of noncommunicating hydrocephalus?

due to blockage of the 3 holes in the 4th ventricle, causing CSF back up

What does -tropia mean?

eye deviates in binocular vision

What does -phoria mean?

eye deviates in monocular vision

What is more common, a tropia or a phoria?

-phoria

Why is a -phoria not a problem?

eye corrects itself/moves into correct position

Corticospinal tract steps

1. 1º motor cortex send fibers into posterior limb between thalamus + globus pallidus

2. Run through crus cerebri of midbrain

3. Into base of pons

4. Into ventral medullary pyramids

5. Decussates in most caudal medulla

6. Runs in lateral column + into spinal cord

How are the descending motor fibers arranged as you move down the pons?

cranial: fibers are bundled close together

middle: fibers spread out

caudal: fibers bundled close together

What are corticpontine fibers? Where are they from/going to?

efferent copy

from cortex to pontine nuceli

What does efferent copy do?

Carries same info as corticospinal tract, tells pons what planned motor movement is

What do pontocerebllar fibers do?

tells cerebellum the motor plan

Summary of fibers in base of pons

decussated + non decussated pontocerebllar fibers

corticospinal tract

corticobulbar fiber

fibers to CNS

If you have spastic paralysis but all the cranial nerves are functioning, where is the lesion?

below the medulla

If you have spastic paralysis and CN damage, where is the lesion?

in the brainstem or brain

What does the cerebellum do?

unconscious proprioception

coordinates motor action + plan

The DCML does what kind off proprioception?

both conscious and unconscious

How does the cerebellum do unconscious proprioception?

via spinocerbellum tract

How many neurons does it take to get from limbs to cerebellum? Do they cross?

2 neurons, never cross

How many neurons does it take to get from limbs to sensory Cortex? do they cross?

3 neurons, 2nd one always crosses

What happens if you lose the cerebellum?

Cerebellar Ataxia:

dysdiadochokinesia (lose coordinated movement)

intention tremor @ beginning and end of voluntary movement

What are the 3 main structures of the medulla?

pyramid

olive

lateral funiculus

Where does the medullary pyramids run?

medial, entire length of medulla

What happens at the base of medullary pyramids?

motor fibers decussate

What/where is the anterior median fissure?

between the medullary pyramids

Where is the olive and where does it run?

lateral to pyramids, runs in only cranial half of medulla

What does the olive house?

inferior olivary nucleus

What/where is the anterior lateral sulcus?

between the pyramid + olive in medulla

Where is the lateral funiculus located?

lateral to olive

Where is the posterolateral sulcus of medulla?

between olive and lateral funiculus

Where are the vital centers located?

cranial half of medulla behind the olive

Where is the cardiovascular center located?

behind olive in cranial medulla

Where is the respiratory center located?

behind cardiovascular center in cranial medulla

What is the reticular formation?

sensory + motor nerve paths that run throughout entire medulla and into pons

What is the direction of anesthesia?

descending, so affects cortex first then moves downward

What is the direction of comas?

descending, so affects cortex first then moves downward

What is the floor of the 4th ventricle in the medulla?

medulla

What is the roof of 4th ventricle in cranial medulla?

cerebellum

What is roof of 4th ventricle in caudal medulla?

medulla

Where does the 4th ventricle look like a canal/is completely surrounded by medulla?

in caudal half of medulla

What cranial nerves exit at the medulla?

CN IX, X, XI, XII

What cranial nerves exit at the posterolateral sulcus?

CN IX, X, XI (bulbar root)

What cranial nerves exit at anterolateral sulcus?

CN XII

How does CN XII exit the medulla?

as ~10 rootlets @anterolateral sulcus

What is the only somatic/cranial nerve nucleus in the medulla?

CN XII

How does the size of the 4th ventricle change as you go down the medulla?

starts large and get smaller as you move down

What do the inferior cerebellar peduncles do?

connect medulla oblongata to cerebellum

What kind of nucleus is the inferior olivary nucleus?

motor nucleus

Inferior olivary nucleus sends its fibers to cerebellum through what?

through inferior cerebellar peduncles

As you move down the medulla what happens to size of olive? Size of inferior cerebellar peduncles?

olive starts medium size, grows, then get small until its gone

ICP starts medium size, grows, and then continually gets smaller

What is more medial, nucleus gracilis or cuneatus?

gracilis

What does nucleus gracilis do?

legs

What does nucleus cuneatus do?

arms

What does the nucleus cuneocerebllar do?

unconscious proprioception for arm synapses here and moves into ICP + into cerebllum

What nuclei can you see in caudal medulla?

nucleus gracilis, cuneatus, and cuneocerebllar

When is the 4th ventricle closed in cross section?

caudal medulla

Olive sends fibers where?

ipsalateral cortex

contralateral cerebellum

What do fibers from the olive synapse on? For what?

purkinje cells to form error detection system for motor

What group of nuclei are closest to midline?

somatic efferent nuclei

Where is the external genue of CN VII?

90º turn in facial canal to exit stylomastoid foramen

The superior cerebellar peduncles primary does what?

fibers from cerebellum to red nucleus, few input

The middle cerebellar peduncles does 100% what?

fibers from pons into cerebellum

The inferior cerebellar peduncles primary does what?

fibers from medulla into cerebellum, few output