Brainstem

Brainstem Stroke

• Knowing what we now know about spinal cord injuries, let’s imagine that our new patient has

actually had a rare brainstem stroke

• Because a lesion has occurred in a more caudal (or superior) location, we can imagine that damage

might be even greater compared to a spinal cord injury

• As we will learn though, the brainstem also houses structures necessary for important involuntary

functions

The Brainstem

• A required stop when transmitting signals

between the cerebrum and the spinal cord

• Located

• Inferior to the cerebrum

• Rostral to the spinal cord

• Anterior to the cerebellum

View of Ventral Brainstem and Cerebrum

• Although the structures of the brainstem look very

different, they transition into one another

• Can create difficulty in talking about structures independently

• Cranial nerves are also visible

Medulla

Importance:

• Critical center for cranial nerve

functions associated with:

• Sensory for hearing and balance (CN VIII)

• Swallowing and voice production (CN IX and CN X)

• Movement of the head (CN XI)

• Movement of the tongue (CN XII)

Nucleus is in the medulla

Reticular Formation

• A net-like formation of nuclei and neurons

• Stretches across various parts of the brainstem

• Includes ascending and descending tracts

• Involved in alertness, arousal, consciousness, and

sleep-wake cycles

• But speaking to the medullary reticular formation

• Autonomic control regulating blood flow and

heart rate

• One example of regulation is through the

baroreceptor reflex

Reticular

Formation

(cont.

• Medullary reticular

formation is also critical to

controlling respiration

• Part of the autonomic

regulatory system

• Based on feedback

regarding O2 and CO2

levels

• Integrates input from

the pons

Ascending

sensory

descending

motor

Damage to the

Reticular

Formation

• Among other concerns,

significant damage to the

reticular formation and the

ascending pathways from it

can lead to reduced

consciousness

• This may include hypersomnia,

coma, or death

Potential

Outcomes

of a Coma

States of Recovery and Patterns

External Structures of the Medulla

• Highlighting the pyramids and

pyramidal decussation

• Pyramids contain axon fibers of the

Corticospinal and Corticobulbar Tracts

• Smooth-flat region two thirds of the

way down the medulla is the pyramidal

decussation of the corticospinal tract

If there was damage approximately where

the star is, which side of the body (below the

neck) would be weak or paralyzed?

left side is damage before decuzation

If there was damage approximately where

the triangle is, which side of the body (below

the neck) would be weak or paralyzed?

left post decuzation

Moving up to the

Pons

• Between the medulla and

mesencephalon

• Bounded posteriorly by the cerebellum

• Importance:

• Ascending and descending

pathways

• Major connector to the

cerebellum

• Critical center for cranial nerves

• Respiratory center functions

Pons: The Cerebellar Peduncles

• Axon pathways into and out of the cerebellum

• Divided into 3 zones:

• Inferior cerebellar peduncles (input)

• Middle cerebellar peduncles (input)

• Superior cerebellar peduncles (output)

• Necessary for motor control circuit

Quick Detour to the Cerebellum

• Regulates movement in an indirect way for motor learning and motor coordination

• Consists of two large lateral hemispheres

• Cerebellar hemispheres are divided into an anterior and posterior lobe

Friedrich’s Ataxia

genetic, don’t realize they have it

Pons

• Connection point for cranial nerves for:

• Control of facial muscles for speech (CN VII)

• Movement of the mandible (CN V)

• Sensory inputs to the skin, oral muscosa, and mandibular region (CN V)

• Pontine respiratory region

• Pneumotaxic center

• Apneustic center

Respiratory Inputs from the Pons

• Additional image for

respiratory centers (right)

• Able to momentarily stop

or modify respiration

• Needed for both:

• Voluntary behaviors

• Non-vital reflexive

behaviors

Damage to

Pons

• Potential impacts on facial sensation, facial movement,

eye movement and more via the cranial nerves

• In rare cases, can lead to locked-in syndrome

Mesencephalon

(Midbrain)

Uppermost segment of the

brainstem, with diencephalon

above (rostrally)

• Bounded posteriorly by the

cerebellum

Mesencephalon

• Importance:

• Ascending and descending

pathways

• Center for cranial nerves (albeit

ones less associated with

communication or swallowing)

• Gray matter structures

associated with the cerebellum

and basal ganglia

A Special Case

for Sensation

• Auditory pathways of

the brainstem and

beyond

• Damage to brainstem

areas can lead to

deafness or more

complex auditory

processing difficulties

Brainstem Stroke Symptoms

Pons - damage tissue to the pons part of the brainstem

Jane is a 29 year old female who was recently involved in a car accident. She is no longer able to use her facial muscles and therefore cannot express emotions. She needs to now use an AAC device as she is no longer able to verbally communicate. Her lower extremities have also been impacted therefore sign language is not able to be used. Where is the lesion?

Cranial Nerves

How many cranial nerves are there?

Twelve pairs of nerves

While considered part of the PNS, for 10 pairs of them, they’re really part of

the following system:

Nucleus within the brainstem (CNS) →Nerve (PNS) →Peripheral Target

(Motor)

Nucleus within the brainstem (CNS) →Nerve (PNS) →Peripheral Target

(Sensory)

Exceptions for Cranial Nerves I and II

Cranial Nerves (Bolded specific for communication)

• Olfactory (CN I)

• Optic (CN II)

• Oculomotor (CN III)

• Trochlear (CN IV)

• Trigeminal (CN V)

• Abducens (CN VI)

• Facial (CN VII)

• Auditory-vestibular (CN VIII)

• Glossopharyngeal (CN IX)

• Vagus (CN X)

• Accessory (CN XI)

• Hypoglossal (CN XII)

Flattened Perspective

of the Brainstem

Revealing CN Nuclei

CN I – Olfactory

• Sensory: smell and discrimination of smell

• Links back to olfactory cortex and aspects of the temporal lobe

• Damage can lead to anosmia or hyposmia

CN II – Optic

• Sensory: vision

• Links back to primary visual cortex in the occipital lobe

• Damage can lead to visual field losses corresponding to the site of injury

• Optic neuropathy

• Glaucoma

CN III – Oculomotor

• Motor: Inferior oblique; superior, inferior, and medial rectus; and pupillary reflex

• Only somewhat associated with eye closing

CN IV – Trochlear

• Motor: Superior oblique (allows for downward/inward movement)

CN VI – Abducens

Motor: Lateral rectus (allows for outward/lateral movement)

CN V – Trigeminal

• Mixed nerve

• 3 branches

• Ophthalmic (V1)

• Maxillary (V2)

• Mandibular (V3)

• Sensory: Somatosensation from facial skin and oral/nasal linings (including the tongue)

• Motor: Mandibular division for the masseter, temporalis, and pterygoid muscles

Damage to CN V – Trigeminal

• Trigeminal neuralgia

• Sharp, intense pain on one side of the face

• Weakness in muscles for chewing (shown on

right)

• Neuropathy: Reduced or atypical sensations of

the face

weakness means asymmetry

Assess sensation of face skin, bilaterally

• Using a wisp of cotton, lightly touch face within all skin territories of V1, V2, &

V3, bilaterally

• Cranial Nerve V: Sensory (Typical)

• Cranial Nerve V: Sensory (Atypical

Test Motor Component of V

• Palpate master and temporalis while lightly clenching teeth

• Also, checking for deviation

• Cranial Nerve V: Motor (Typical)

• Cranial Nerve V: Motor (Atypical