Motor Tracts PDF

MOTOR TRACTS BIO336 Audrey Forbes-Cardinali, D.C. Mercyhurst University  THE LONG MOTOR TRACTS Tracts that descend from the cerebral cortex to the spinal cord. The control contralateral movement They are influenced by feed-back loops involving basal nuclei, cerebellum, thal...

MOTOR TRACTS BIO336 Audrey Forbes-Cardinali, D.C. Mercyhurst University  THE LONG MOTOR TRACTS Tracts that descend from the cerebral cortex to the spinal cord. The control contralateral movement They are influenced by feed-back loops involving basal nuclei, cerebellum, thalamus and pons Involve 2 neurons: Upper Motor Neurons and Lower Motor Neurons UMN: Cortex to Spinal cord LMN: Spinal cord to muscles These tracts run in either the lateral white columns or anterior white columns of the spinal cord Lateral corticospinal tract Anterior corticospinal tract  U P P E R M OTO R N E U RO N S Have their origin primarily in the primary motor cortex Some being in the premotor area Are arranged in a somatotopic distribution Are large pyramidal neurons (type of multipolar neurons) found in layer V of the cortex  UPPER MOTOR NEURON AXONS IN THE CEREBRUM As the axons leave the cortex they enter the corona radiata Corona radiata – radiating crown. These axons ascend to or descend from the cortex, sometimes known as projection fibers. Not only UMNs From here, they form the internal capsule as they pass between the thalami and the basal nuclei The internal capsule has an anterior limb, a genu and a posterior limb Anterior limb is between the… Posterior limb is between the… https://meetingarchive.ami.org/2021/wp-content/uploads/2021/07/Jiyu-Kelly-Lim- I1_Relative_po.jpg  INTERNAL CAPSULE http://neuroanatomy.ca/horizontals.html  INTERNAL CAPSULE http://neuroanatomy.ca/coronals.html  INTERNAL CAPSULE The somatotopic distribution is maintained in the internal capsule! MOTO R TRACTS IN THE MIDBRAIN Corticospinal Tracts condense in the midbrain and becomes the crus cerebri (AKA cerebral peduncles) “Legs of the brain” Anterior to the substantia nigra CRUS CEREBRI MOTOR TRACTS IN THE PONS Corticospinal fibers descend from the crus cerebri and travel through the basilar portion of the pons  M OTO R TRAC TS IN TH E M ED U LLA O B LO N G ATA Corticospinal fibers in the pons coalesce as they approach the pontomedullary junction and form the pyramids). ~85% of the fibers decussate at the pyramidal decussation and become the lateral corticospinal tract Remaining 15% become the anterior corticospinal tract  MOTOR TRACTS IN THE SPINAL CORD The anterior corticospinal tracts courses inferiorly in the anterior white columns (anterior funiculus). At the segmental spinal levels, the fibers will synapse ipsilaterally and contralaterally with LMNs. These will control trunk and girdle musculature around the upper extremity The lateral corticospinal tract courses inferiorly through the contralateral lateral white column. At the appropriate level, axons will enter the anterior grey horn and synapse with lower motor neurons. A somatotopic distribution is present in this tract. Axons coursing to the lower extremity are on the periphery, while axons coursing to the distal parts of the upper extremity are more central within the spinal cord. MOTOR TRACTS IN THE SPINAL CORD MOTOR TRACTS IN THE SPINAL CORD  OTHER MOTOR TRACTS Corticobulbar tract – Runs parallel to the corticospinal tracts but only reaches the brainstem. Responsible for innervations of muscles of head and neck. Rubrospinal tract – Begins in midbrain from red nucleus. Decussates within midbrain. Responsible for control of contralateral muscles*. Tectospinal tract – Beings in superior colliculus and decussates within midbrain. Controls head and eye movements. Vestibulospinal tract – Begins in Vestibular nuclei in brainstem (Pons and medulla). Decussates within spinal cord. Controls muscles positioning head and neck, and balance. Reticulospinal tract – Begins in reticular formation. Helps control gait and posture. OTHER MOTOR TRACTS