10a Brainstem Pathways, Cranial Nerves & Reticular Formation

the brainstem is a conduit, what does this mean?

conduit = channel or tube

why is the brainstem's location unique?

it allows connections between areas above and below it

Information in the sensory and motor pathways must pass through the brain stem to get to other areas. CST, cerebellar pathways...

the brainstem is the origin point for:

1) medial UMN tracts

2) cranial nerve nuclei

3) reticular formation

why is damage to the brainstem fatal?

Because functions accomplished in this area are vital to survival. Such as the basic life support like pacing of the heart, and respiration. These are often called vegetative functions because they are compared to involuntary plant functions that deal with exchange of gases.

. Even when you are asleep, your brain stem is working.

WHICH IS THE MAIN ARTERY THAT PERFUSES THE PONS AND MIDBRAIN?

Anterior Spinal Artery

Basilar Artery

Vertebral Artery

B and C

Basilar artery

WHICH IS THE MAIN ARTERY THAT PERFUSES THE MEDULLA?

Anterior Spinal Artery

Basilar Artery

Vertebral Artery

A and C

both A and C

what is vertebrobasiliar artery ischemia?

kinking of the vertebral artery when the head is turned

- brain stem is at risk of reduced blood flow

- symptoms = dizziness, fainting, weak, vision disturbances

KNOW THE CRANIAL NERVES CHART WITH SENSORY/MOTOR AND FUCNTION

CN 1 and 2 and 8 are involved in special senses

CN 3, 4 & 6 supply extraocular muscles CN 6 innervates the lateral rectus, CN 4 is the superior oblique and CN 3 is the remaining eye muscles and sphincter pupillae causing narrowing of the pupil

5 supplies sensation to the face and muscles for mastication or chewing

7—is the motor of face, and sensation of taste in ant. 2/3 of tongue

9 controls muscles of neck and salivation and taste in posterior 1/3 of the tongue

10—is involved in many functions included control of the heart, lungs and visceral as well as control larynx and pharyngeal

11—innervates the traps and Sternocleidomastoid muscles coming from cervical levels 1-c5, as well as throat muscles

And finally

12—allows tongue movement

what are bulbar signs?

CN 9-12 somatic branches often affected together:

the 3 D's

- dysphagia: difficulty swallowing

- dysphonia: horse voice

- dysarthria: difficulty articulating words

**often injured together because they are very close together

visceral branch lesions are...

tachycardia and dyspnea

what cranial nerve would be affected with right homonymous hemianopia

CN II = optic nerve

what cranial nerve would be affected with left facial weakness

CN VII = facial nerve

what cranial nerve would be affected if their tongue deviates left

CN XII = hypoglossal nerve

Remember cranial nerves are the afferent and efferents of the head and neck. *except the vagus which wanders all around the neck, thorax and abdomen

As such they are bringing sensory input from the periphery into the CNS or they are sending motor output from the CNS to the periphery.

This is similar to how spinal nerves are afferents and efferent of the UE/LE's and trunk

CRANIAL NERVE AFFERENT PATHWAYS

do cranial nerve afferent pathways project bilaterally or unilaterally?

bilaterally

how are these pathways named

named by cranial nerve to destination

- olfactory cortical pathway (gustatory pathway)

- optic cortical pathway (visual pathway)

we are only focusing on 1 afferent path: CN 2 (optic nerve)

KNOW THE VISUAL PATHWAY PICTURE

the left side of the brain processes information from where?

right half of the visual field

- Right eye's nasal retinal field and left eye's temporal retinal field view the right visual field overall. This information projects to LEFT visual cortex.

- Nasal retinal fibers cross at chiasm

- Temporal retinal fibers stay ipsilateral

the right side of the brain processes information from where?

the left half of the visual field

The way the path works: the right side of your cortex processes information from the contralateral side (your left visual field).

Information from nasal retinal fields cross at optic chiasm. Information from temporal retinal fields do not

know the difference between visual field, nasal retina, and temporal retina

contralateral homonymous hemianopsia is a common presentation of what condition?

CVA (stroke)

MOTOR PATHWAYS

what are the motor pathways of the cranial nerves?

corticobulbar pathways

According to the general name cortico bulbar, where do you think the motor pathways originate and terminate?

start in the cortex and then head to the brainstem

the UMN of the corticobulbar pathways start where?

in the lateral part of the somatomotor cortex. *This is the "H" in HAL, the homunculus

The UMNs lead to various regions in the brain stem and synapse with LMNs in the cranial nerve nuclei. The LMNs are known as cranial nerves

what are the differences of cranial nerves vs spinal nerves

cranial nerves = LMN of the corticobulbar tract

spinal nerves = LMN of corticospinal tract

corticobulbar paths have _______ innervation

why is this important

bilateral innervation

- have a backup if issue on one side of cortex

***So for most paths: if you have a unilateral deficit in the cortex at the UMN level...you won't see a peripheral deficit....because the bilateral innervation coming from the other side of the cortex still innervates the nuclei and peripheral structures.

-if you have a unilateral deficit in LMN- this is when you will see unilateral deficit.

what cranial nerves do not follow bilateral innervation?

CN 7 and CN 12

terminology to know:

bilateral

unilateral

contralateral

ipsilateral

the UMN is at what level

the LMN is at what level

UMN = "supranuclear" level

LMN = "infranuclear" level

Most of the paths have bilateral UMN projections, meaning the UMN sends projections to both sides of the body.

However this is not true for the rule breakers: meaning these pathways may only project unilaterally- only go to one side. The side is usually the contralateral or opposite side from the origin

rulebreaker #1 = CN 12 (hypoglossal)

UMN only sends a unilateral projection to contralateral side of the body

If a person has trauma to the cortex that involves this UMN- we'll see deficits peripherally related to lack of innnervationn of the LMN onn the opposite side of the body

how do we test CN 12?

ask patient to stick out their tongue

if tongue deviates to the left side what does this mean

tongue deviating to left = lesion is on the left side

diagnosis= left side LMN lesion

Why is this LMN? Because if it was Right UMN lesion we would see other deficits from other UMNs. Such as Left facial drooping, and other deficts not shown in this photo, like left UE/LE weakness.

rule breaker #2 = CN 7 (facial nerve)

In this pathway, the UMN sends bilateral projections to the upper part of the face, while it only sends unilateral projection to the lower part of the face on the contralateral side.

Said a different way, the upper quarter of the face has bilateral innervation from the ipsilateral and contralateral cortex - giving the back up/or redundancy if one side fails.

The lower quarer of the face only has unilateral innervation from the contralateral cortex. If there is a dysfunction with the UMN, there is no redundancy for the lower quarter.

we have a redundant motor input for the upper part of the face but not for the lower part

what would an UMN lesion of CN 7 look like?

If we have an UMN lesion, or a supranuclear lesion, we'll see UMN signs in the lower left part of the face, but functionsn of the upper part of the face will still work because of the bilateral innervation.

what would a LMN lesion of CN 7 look like?

If we have an UMN lesion, or a supranuclear lesion, we'll see UMN signs in the lower left part of the face, but functionsn of the upper part of the face will still work because of the bilateral innervation.

UMN injury we see effects where?

LMN injurt we see effects where?

UMN injury: see effects on contralateral side, lower quarter only

LMN injury: see effects on same side, both upper and lower quarter (because redundancy from UMN is irrelevant. Final common pathway/LMN is not working)

when we test CN 7 we have the patient do what?

try to close both eyes and smile

if the patient:

left side of face = eye closed + smile

right side of face = not closed, not smiled

right sided LMN lesion with right LMN signs

if the patient:

closes both eyes

right side of face = smile

left side of face = no smile

left sided UMN lesion with right sided signs

LMN is lesion at nuclear level or below ON SAME SIDE.....

UMN is lesion in cortex or supranuclear ON Contralateral side of signs.

is bells palsy a LMN or UMN?

LMN problem

Which innervates sensation of the face?

CN 1

CN 5

CN 7

CN 9

CN 5

Which innervates the lateral rectus of the eye?

CN 3

CN 4

CN 6

CN 7

CN 6

Which of the following is TRUE regarding cranial nerve pathways?

Unilateral UMN injuries have disastrous results in these pathways

Unilateral UMN injuries show deficits in cranial nerve 5

Unilateral LMN injuries show deficits on the ipsilateral side

Unilateral LMN injuries show deficits on the contralateral side

C

RETICULAR FORMATION

what are the functions of the reticular nuclei

1) integrate

- sensory and cortical information

2) regulate

- attention & consciousness

- posture

- viscera

3) modulate

- nociceptive information

this is an ascending system that is conntected to consciousness, governing:

- alertness

- attention

- sleep

what does the reticular activating system do? (RAS)

what is important enough to alert cortex?

- primarily rostral midbrain

- encourages wakefullness and attention

- movement

if you have a lesion to the RAS =

constant sleep

what does the reticular inhibiting system do? (RIS)

what is important enough to alert cortex?

- primarily caudal midbrain to caudal medulla

- encourages sleep

- turn off lights, quietness

if you have a lesion to the RIS =

constant insomnia

how to activate RAS in clincal setting

- lights on

- upright position of head

- unpredictable tactile cues

- loud

how to activate RIS in clinical setting?

- lights off

- supine, head supported

- rocking, deep pressure

- white noise

chart on reticular nuclei

nucleus --> NT

VTA

PPN

locus ceruleus & medial zone

raphe nuclei

VTA --> dopamine

PPN --> acetylocholine

locus ceruleus & medial zone --> norepinephrine

raphe nuclei --> serotonin

Which of the following is found in the reticular formation?

Caudate nucleus

Nucleus gracilis

Pedunculoponine nucleus

Trigeminal nucleus

C

Which of the following excites the reticular activating system?

Lights on

Loud white noise

Supine with head on pillow

All of the above

A

Which of the following excites the reticular inhibitory system?

Gentle rhythmic rocking

Loud periodic verbal cues

Smells

Unpredictable tactile cues

A

Which of the following are extrapyramidal tracts?

Medial corticospinal tract

Vestibulospinal Tract

Spinocerebellar Tract

B and C

D