Ch 6 Corticospinal Tract and Other Motor Pathways part 2

What is the most clinically important descending motor pathway?

Lateral Corticospinal Tract

What does the Lateral Corticospinal Tract control? Proximal or distal?

Voluntary movements of the extremities (distal movements) on the opposite side of the body

What is the most clinically important descending motor pathway?

Lateral Corticospinal Tract

What does the Lateral Corticospinal Tract control? Proximal or distal?

Voluntary movements of the extremities (distal movements) on the opposite side of the body

Lateral Corticospinal Tract: What its Fractionation?

• Ability to activate muscles independently of each other

• Fine motor tasks

Lateral Corticospinal Tract is a ___ neuron system/pathways: what are they?

• TWO

  • UMN and LMN

Corticospinal tract (CST) is alone is often used to describe what? What is it also known as?

• Lateral Corticosponal Tract

• Pyramidal Tract

Lateral Corticospinal Tract: Where of majority of Corticospinal axons originate?

Primary Motor Cortex (Area 4)

What is the Corticobulbar Tract?

Neurons from the CST that synapse on motor neurons CN in the brainstem to provide motor function to the face

Since function is similar to CST, and since it travels with CST to the brainstem, these 2 are what ?

These 2 tracts are sometimes described together??? Ask friends

Lateral Corticospinal Tract: After originating from the PMC, the CST descends through where and where does it exhibit?

• Internal Capsule

  • Posterior Limb

• Exhibits Somatotopy

Look at this

Lateral Corticospinal Tract: After descending through Internal Capsule, where does Lateral Corticospinal Tract descend and where does it exhibit?

• Through the Midbrain (Middle 1/3 of the Basis Pedunculi AKA Anterior Cerebral Peduncle)

• Exhibits Somatotopy

Lateral Corticospinal Tract: After descending through the Midbrain, where does Lateral Corticospinal Tract descend?

Ventral/Anterior Pons

Lateral Corticospinal Tract: After descending through the Pons, where does the Lateral Corticospinal Tract descend? Forms what?

Medulla >> form the medullary pyramid

At the inferior medulla, ~85-90% of the axons cross over to the contralateral side where?

Pyramidal Decussation

Lateral Corticospinal Tract: After descending through the medulla, where does the Lateral Corticospinal Tract descend?

Lateral portion of the SC

Lateral Corticospinal Tract: Where does the Lateral Corticospinal Tract enter and do what?

Anterior horn to synapse on LMN

What is the Lateral Corticospinal Tract responsible for? Give examples

• Movement of contralateral limbs

  • Left cortex controls right sided musculature of the body

  • Right cortex controls left sided musculature of the body

Where does the Rubrospinal Tract originate?

Red Nucleus of Midbrain

Where does Rubrospinal Tract cross over?

Contralateral side of ventral segmental decussation

Where does Rubrospinal tract descend?

Lateral SC to then enter the anterior horn to synapse on LMN

Where does Rubrospinal Tract end?

Cervical SC

What does the Rubrospinal tract control? What else about it, how does it contribute?

• Contralateral UE distal musculature

  • Small tract making minor contribution to muscle control

Anterior Corticospinal Tract: Origin and Site of Decussation and level of termination and function

• Origin: PMC and Supplementary Motor Area (Same as Lateral Corticospinal Tract)

• Site of Decussation: N/A

• Level of termination: Cervical and upper thoracic cord

• Function: Control of bilateral axial and girdle muscles (Proximal Muscles >> Neck and trunk )

Anterior Corticospinal Tract descent is the same as Lateral Corticospinal tract until what?

Pyramidal Decussation

Anterior Corticospinal Tract is formed by 10-15% of what?

10-15% of axons that do NOT cross at Pyramidal Decussation

Anterior Corticospinal Tract: After Pyramidal Decussation, Anterior Corticospinal Tract descends where?

Medial spinal cord to then enter the anterior horn to synapse on LMN

Where does Anterior Corticospinal Tract synapse while descending?

Ipsilateral and contralateral LMN (Bifurcates in anterior horn)

Anterior Corticospinal Tract ends where?

Thoracic cord

Anterior Corticospinal tract controls what? Give examples of what? Proximal or distal? Bilateral/contra lateral ?

• Voluntary movements of bilateral axial and girdle musculature (proximal muscles)

• Neck and trunk

Where does Lateral Vestibulospinal Tract (VST) Originate?

Lateral Vestibular Nucleus

Where does Lateral Vestibulospinal Tract (VST) descend after Lateral Vestibular Nucleus?

Ipsilaterally in Medial SC

Where does Lateral VST enter after descending ipsilaterally in medial SC and where does it run through? What is it involved in?

• Enters: Anterior Horn to Synapse on LMN

• Runs: Through Entire SC

• It’s involved in Balance

Where does Medial VST originate?

Medial and inferior vestibular nuclei (Upper Medulla)

Where does Medial VST descend after upper medulla?

bilaterally in the medial spinal cord (descends ipsilaterally and also crosses over to descend contralaterally)

Where does Medial VST enter and end after descending through upper medulla? What is it involved in?

• Enters: Anterior horn to synapse w LMN

• Ends upper thoracic SC

• Involved in positioning of head and neck

Vestibulospinal Tract: Level of Termination

• Medial VST: Cervical and Upper Thoracic Cord

• Lateral VST: Entire Cord

Vestibulospinal Tract: Site of Decussation

N/A

Pontine RST originates where?

Reticular formation on PONS

Medullary RST originates where?

Reticular Formation of Medulla

Both RST descends where?

Descends ipsilateral in the Medial SC

Where does RST Enter and Runs after descending down medial SC?

• Enters: Anterior horn to synapse on LMN

• Runs: Through entire SC

What is RST involved in?

Automatic posture and gait related movements

Reticulospinal Tract: Site of Decussation

N/A

Reticulospinal Tract: Level of Termination

Entire Cord

Tectospinal Tract: Origin and Site of Decussation

• Origin: Superior Colliculus (tectum of midbrain)

• Site of Decussation: Dorsal tegmental decussation in midbrain

Where does Tectospinal Tract descend after Dorsal Tegmental Decussation?

Medial SC to then enter the anterior horn to synapse on LMN

Where does Tectospinal Tract end?

Cervical SC

Tectospinal Tract: Function

Coordination of head and eye movement (uncertain in humans)

Review Question: Lesion of the Left Lateral Corticospinal tract at C3 produces what? In which cervical?

UMN Signs in the L arm and leg (C4 Myotome and below)

Summary of lateral motor systems and medial motor systems

Weakness can be caused by a lesion at what levels ? (4)

UMN Lesions Signs:

• YES: Weakness, Increase Reflexes and Tone

• No: Atrophy, Fasciculations

LMN Lesion Signs:

• YES: Weakness, Atrophy, Fasciculation

• NO: Decreased Reflexes and Tone

Trace the Lateral Corticopinal Tract :)

• Originates at PMC

  • Internal Capsule > Posterior Limb

  • Midbrain > Middle 1/3 of Basis Pedunculi

  • Ventral Anterior Pons

  • Medulla > Pyramidal Decussation

  • Lateral SC

• Enters anterior horn to synapse on LMN

Trace the Rubrospinal Tract :)

• Originates at Red Nucleus of Midbrain

  • Ventral Segmental Decussation (Contralateral)

  • Lateral SC

  • Enters Anterior Horn to synapse on LMN

• End at Cervical SC

Trace the Anterior Corticospinal Tract :)

• Originates at PMC and Supplementary Motor Cortex

  • Internal Capsule > Posterior Limb

  • Midbrain > Middle 1/3 of Basis Pedunculi

  • Ventral Anterior Pons

  • Medulla > Pyramidal Decussation (but doesn’t cross over)

  • Medial SC

  • Enters Anterior Horn to synapse on LMN

• Ends Thoracic Cord

Trace the Lateral Vestibular Nucleus (VST) :)

• Originates at Lateral Vestibular Nucleus

  • Descends Ipsilaterally in Medial SC

  • Enters Anterior Horn to Synapse w LMN

• Ends Through entire SC

Trace the Medial Vestibular Nucleus (VST) :)

• Originates at Medial and Inferior Vestibular Nuclei (Upper Medulla)

  • Descends Bilaterally in Medial SC

  • Enters Anterior Horn to Synapse w LMN

• Ends in Cervical and Upper Thoracic SC

Trace the Pontine and Medullary RST Tract :)

• Originates Pons (Pontine) and Medullary (Medulla)

  • Both Descend Ipsilaterally in Medial SC

  • Both Enter Anterior Horn to Synapse w LMN

• Ends Through Entire SC

Trace Tectospinal Tract :)

• Originates in Superior Colliculus

  • Dorsal Segmental Decussation

  • Medial SC

  • Enters Anterior Horn to Synapse on LMN

• Ends Cervical SC