corticospinal tracts.pptx

gives detailed information concerning the corticospinal tracts

1. Corticospinal tracts Future life savers presentation

2. introduction The corticospinal tract also called the pyramidal tract is one of the descending tracts sending motor information from the cortex to the spinal cord. It provides voluntary motor fibers using the lower motor neurons. The corticospinal tract are the pathway concerned with voluntary, discrete, skilled movements, especially those of the distal part of the limb. Pyramidal tracts are considered with ; Corticospinal tracts – supplies the musculature of the axial skeleton Corticobulbar tracts – supplies the musculature of the head and neck

3. Corticobulbar tracts / corticonuclear tracts Corticonuclear fibers otherwise called as Corticobulbar tract. That Motor Cranial Nuclei (Particularly 4, 7, 12) This is a pathway that begins in the cerebral cortex and ends in the brain stem. Bulbar means pertaining to the brainstem where all motor cranial nuclei are located. • Throughout the brainstem, the corticobulbar fibers are crossing to reach the motor cranial nuclei of the opposite side

4. GROWTH OF CORTICOSPINAL TRACT IN FETUS: MYELINATION :- The myelination of the pyramidal fibers is incomplete at birth & gradually progresses in Cranio-caudal (from head to feet) direction and thereby progressively gaining functionality. Most of the myelination complete by 2 years of the age. Myelination commences between postnatal days 10-12. Myelinate largely during the 1st & 2nd years after birth. It progressively slowly in Cranio-caudal direction up to 12the year of the age. The rate of extension of corticospinal axons are not constant.

5. ORIGIN OF CORTICOSPINAL TRACT Fibers of the corticospinal tract arise as axons of pyramidal cells situated in the 5th layer of the cerebral cortex. 1/3rd of the fibers originate primary motor cortex (Area 4). 1/3rd originate from the Secondary motor cortex (Area 6). 1/3rd originate from the Primary Somatosensory cortex (post central gyrus) (Area 3, 1 and 2).

6. COURSE OF THE CORTICOSPINAL TRACT

7. • These descending fibers converge in the Corona radiata to reach Internal capsule. (Located between the Thalamus and the basal ganglia) • IN THE INTERNAL CAPSULE: then pass through the posterior limb of the Internal capsule. Where they occupy in the genu and the anterior 2/3rd of the posterior limb The motor fibers passes through the posterior limb of the internal capsule where they are organized in the sequence of “fibers of UPPER EXTREMITY, TRUNK, LOWER EXTREMITY”. This is clinically important, as the internal capsule is particularly susceptible to compression from hemorrhagic bleeds, known as a capsular stroke‘.

8. COURSE OF THE CORTICOSPINAL TRACT cont … IN THE MIDBRAIN: The tract then continues through the middle 3/5th of the (Crus cerebri of Cerebral peduncle) or basis pedunculi of the midbrain ventral to the substantia nigra. The middle fifth carries the pyramidal tract and medial frontopontine and lateral temporopontine fibers.

9. COURSE OF THE CORTICOSPINAL TRACT cont … IN THE PONS: And then passes through the base (Basilar part) of the pons. In the pons the corticospinal tracts are become scattered. IN MEDULLA OBLONGATA : While coming out of the pons, the scattered corticospinal fibers are reunited and enter the medulla as a thick bundle. The bundles are become grouped together in the upper part of medulla & along the anterior border to form a swelling known as the pyramid or Medulla Oblongatary Pyramids (Cervicomedullary Junction) (hence the alternative name pyramidal tract).

10. COURSE OF THE CORTICOSPINAL TRACT cont … The majority of the fibers cross (Decussate) to the opposite side & enter the lateral white column as the Lateral Corticospinal Tract of spinal cord. The remaining fibers about do not cross in the decussation & enter the anterior white column as Anterior corticospinal tract of spinal cord.

11. LATERAL CORTICOSPINAL TRACT They decussate at the caudal of the medulla oblongata and descend to the posterior part of the lateral white column . It extend throughout the spinal cord. At each segment some fibers leave the tract, turn inward and end round the anterior grey horn cells (Motor neurons) either directly or through interneuron's. They are also called as “CROSSED CORTICOSPINAL TRACT • The Lateral Corticospinal Tract (Betz cells fibers) descend in the Lateral funiculus of the spinal cord to terminate mainly in the lumbosacral region of the spinal cord.

12. TERMINATION OF THE LATERAL CORTICOSPINAL TRACT: • It terminates via Interneurons on ventral horn motor neurons and sensory neurons of the dorsal horn till the lumbosacral region of the spinal cord.

13. ANTERIOR CORTICOSPINAL TRACT In the caudal of the medulla they do not decussate but instead enter the anterior white column of the spinal cord. They are also called as “UNCROSSED CORTICOSPINAL TRACT ”. The Anterior Corticospinal Tract descend in the Anterior funiculus of the spinal cord to terminate mainly in the anterior horn grey matter of the cervical and upper thoracic spinal cord levels . Near their termination, fibres of the anterior corticospinal tract cross the midline (decussate to the opposite side) to end round the anterior horn cells of the opposite side & instead synapse directly with lower motorneurons .

14. Functions of corticospinal tracts The corticospinal tract has many functions which include the, Control of afferent inputs :– (These fibers that originate from the sensory cortex (somatosensory cortex) terminate in the dorsal horn of the spinal cord where they synapse with interneurons that receive input from somatosensory receptors and are thought to regulate information peripheral receptors within the spinal cord ). Spinal reflexes :– (the 1st order afferent sensory fibers transmitting sensory information from the muscle spindles also from synapses with the inhibitory interneurons (that synapse with the Lateral corticospinal tract) to mediate reflex activity.

15. MOTOR NEURON ACTIVITY LATERAL CORTICOSPINAL TRACT This mediates the execution of rapid, skilled, voluntary and Fine movements of the distal musculature of upper and lower limbs . i.e ., The intrinsic and extrinsic muscles of the hand and foot, especially the muscles of the hand ANTERIOR CORTICOSPINAL TRACT Control of Axial muscles (Neck, Shoulder, and Trunk) Proximal upper limb (girdle) musculature. And they are associated with the maintenance of upright posture.