(16) blood suppy

Medial Striate Artery (from ACA)

Target: Anterior Limb of the internal capsule(ALIC).

Clinical Fact: The most famous branch here is Heubner’s Artery

• Damage here can cause personality changes or complex motor planning issues because it hits fibers heading to the frontal lobe

Lenticulostriate Arteries (from MCA)-internal capsule

Target: Anterior Limb (ALIC) and the Posterior Limb (PLIC).

Clinical Fact: These are often called the "Arteries of Stroke."

• They are very thin and prone to bursting in people with high blood pressure (hemorrhagic stroke) or clogging (ischemic stroke)

Internal Carotid Artery (Direct Branches)— internal capsule

Target: The Genu (the "knee" or bend of the capsule).

Clinical Fact: The Genu contains the Corticobulbar tract (muscles of the face and tongue)

• A stroke here specifically causes facial drooping and speech issues

Anterior Choroidal Artery (from ICA)—internal capsule

Target: Posterior Limb (PLIC) and the Retrolenticular part.

Clinical Fact: This is a "silent killer" artery

• Because the PLIC contains the Corticospinal Tract (body movement) and the Somatosensory Tract (feeling), a stroke here causes a "Pure Motor" or "Sensorimotor" stroke———-

• total weakness and numbness on the opposite side

Which artery supplies the Anterior Limb (ALIC) via its medial striate branches?

Anterior Cerebral Artery (ACA).

Lenticulostriate arteries arise from which major vessel?

Middle Cerebral Artery (MCA)

A stroke in the Anterior Choroidal Artery would primarily damage the:

Posterior Limb (PLIC)

Which part of the internal capsule is supplied directly by the Internal Carotid?

Genu

Which artery would likely be involved if a patient has only facial weakness?

Direct branches of the Internal Carotid

• (supplying the Genu)

Quadrigeminal Artery (from PCA)

provides crucial lateral branches to the Crus Cerebri

• If this is blocked, it can affect the Lateral part of the CST (the Leg fibers)

Posterior Choroidal Arteries (from PCA)

supply the crus cerebri

Weber Syndrome

blood supply to the Crus Cerebri is compromised

• causes Contralateral Hemiparesis (weakness of the opposite arm and leg)

• Oculomotor Nerve (CN III) (right next to the crus cerebri so it is often damaged)

Weber Syndrome result

patient has a "down and out" eye on the same side as the stroke

• but weakness on the opposite side of the body

what supplus the pons

Branches of the basilar

"Locked-In" Syndrome

Cause: A massive stroke or blockage of the Basilar Artery

Result: The CST is destroyed on both the left and right

• The patient is completely paralyzed from the neck down (quadriplegia) and cannot speak (corticobulbar loss)

Why is a patient still fully conscious in Locked-in Syndrome?

Because the "Tegmentum" (the back of the pons) is supplied by different vessels

• the patient remains fully conscious and can usually still move their eyes vertically (controlled by the Midbrain)

what supplies the medulla

anterior spinal artery

Medial Medullary Syndrome

the Anterior Spinal Artery is blocked

• Contralateral Hemiparesis

• Contralateral Loss of Proprioception/Vibration

• Ipsilateral Tongue Weakness: Because the CN XII (Hypoglossal) nerve fibers exit right through this area

Why would you have contralateral loss when there is damage to the medulla?

This is where the fibers primarily cross

• the pyramids are located here

What is the Pyramidal Decussation?

site where 85–90% of fibers cross: These become the Lateral Corticospinal Tract

• 10–15% do NOT cross: These become the Anterior Corticospinal Tract

Why is it said that "only CST fibers remain" after the decussation?

Because all Corticobulbar fibers have already exited to hit brainstem nuclei

• finbers for face and tongue movements have left so all that is left are fibers for body movments

If a patient has a lesion below the decussation, which side of the body is affected?

Ipsilateral (same) side

• fibers are still on their "home" side

• If you damage the left side of the brain, the signal hasn't crossed yet, so the Right side of the body is affected (Contralateral)

If a patient has a brainstem tumor above the medulla, is the weakness opposite or same-side?

Opposite side (Contralateral)

A stab wound to the Right side of the Spinal Cord causes weakness on which side?

Right side (Ipsilateral)

A stroke in the Right Internal Capsule causes weakness on which side?

Left side (Contralateral)

Where do the CST fibers physically terminate?

Ventral Horn of the spinal cord gray matter

At the point of Termination, what cell does the CST synapse with?

Lower Motor Neuron (Alpha Motor Neuron)

What is the course of the Corticospinal Tract?

1. Corona Radiata

2. Internal Capsule

3. Midbrain

4. Pons

5. Medulla

6. The Decussation

7. Spinal cord

Medial Motor Pools (The Center)

control your Proximal muscles (shoulders, hips) and Axial muscles (back, neck, trunk)

Lateral Motor Pools (The Edges)

control your Distal muscles (elbows, wrists, and especially fingers and toes)

Anterior CST → Medial Pools

Anterior CST (which didn't cross in the medulla) stays near the midline of the cord to talk to the Medial motor pools

• This is why it controls your core and posture.

Lateral CST → Lateral Pools

Lateral CST (which crossed in the medulla) travels in the side of the cord to talk to the Lateral motor pools

• This is why it controls your hands and feet

What kind of movements do the midline (medial) pools control?

Bilateral/Axial movements (walking, swimming, standing up)

What kind of movements do the lateral pools control?

Skilled, peripheral movements (fine motor skills of the hands)

What is the primary permanent deficit of a "pure" pyramidal lesion?

Loss of fractionated finger movements (dexterity)

• can not move fingers IND

• ONLY damage to the pyramids

Why can a patient still walk after a "pure" pyramidal lesion?

Because Extrapyramidal tracts (Vestibulo/Reticulospinal) are still intact

• they can pick up the slack

Does a pure pyramidal lesion cause Spasticity or Hypotonia?

It causes Hypotonia

• (the spasticity comes from damaging "other" tracts)

Why are real-world stroke symptoms more "extensive" than pure pyramidal lesions?

Strokes usually damage the CST plus surrounding tracts (like Corticoreticular)

Which tract is the "backup" for gross arm movement when the CST is gone?

Rubrospinal tract

Extrapyramidal system as a bulldozer (it can move big things and get you from A to B) and the Corticospinal tract as a scalpel (it's for precise, delicate work)

If you lose the scalpel, you can't perform surgery, but you can still move the dirt!

Decorticate Posturing

Lesion: Occurs ABOVE the Midbrain

• Corticospinal Tract (CST) is cut (The "brakes" from the cortex are gone)

• Rubrospinal Tract is still intact

Result: * Arms Flexed:

• The Rubrospinal tract's main job is to flex the arms

• Without cortical inhibition, it goes into overdrive, pulling the arms toward the chest (the "core")

Decerebrate Posturing

Lesion: Occurs BELOW the Midbrain

• Both the Corticospinal Tract AND the Rubrospinal Tract are cut

• Vestibulospinal and Reticulospinal tracts (in the Pons/Medulla) are the only ones left

Result: Arms Extended/ Legs Extended

• Since the "flexor" (Rubrospinal) is gone, the "extensor" tracts take over completely

Which posture has a worse prognosis?

Decerebrate (it indicates deeper brainstem damage)

• near the centers that control breathing and heart rate

Abnormal Flexion to pain

decorticate

Extensor Response to pain

decerebrate

If a patient shifts from Decorticate to Decerebrate, what does it mean?

brain is herniating (the damage is moving down the brainstem)