Motor tracts

Neuroanatomy presentation on motor tracts.

1. MOTOR TRACTS Naresh Mullaguri MD Resident Physician PGY3 Department of Neurology University of Missouri

2. LEARNING PLAN Cerebral areas of Motor control Corticospinal tracts C orticobulbar tracts (largely covered under Brainstem nuclei) Rubrospinal tracts Reticulospinal tracts Vestibulospinal tracts Tectospinal tracts

3. MOTOR CORTEX

4. PREMOTOR AREAS

5. https:// youtu.be /9BaWBGRVxp8

6. CORTICOSPINAL TRACTS Aka Pyramidal tract Contains Axons and cell bodies present in the motor cortex of the Brain Originates from the Pyramidal cells of Betz – Layer V of Primary Motor cortex (30%), Premotor area and supplementary Motor area(30%) and Somatic sensory area (40%)

7. MOTOR HOMUNCULUS

8. FACTS ABOUT CORTICOSPINAL TRACTS Lateral CST: Crossed, Lateral funicuus , terminate in the Internuncial Neurons of the Spinal grey matter, some fibers end directly on the AH cells, Throughout the length of the cord Uncrossed Pyramidal fibers, about 10%, anterior funiculus and run until mid thoracic level, Cross the other side at the appropriate spinal segment and terminate in the same way as the lateral CST Unmyeinated at birth, Myelinates from 2 nd week after birth to 2 years of age, small and large fibers. Senile degeneration of the large fibers leading to shaky movements.

9. Extrapyramidal tracts Motor pathways act as an alternative route for volitional impulses and which form the platform on which the pyramidal system works skillfully. Integrated at various levels from cerebral cortex to spinal cord Cortical areas controlling these tracts are areas 6 and 8

10. Types Rubrospinal tract Reticulospinal tract Olivospinal tract Vestibulospinal tract Tectospinal tract Medial Longitudinal Fasciculus

11. FUNCTIONS These tracts responsible for maintenance of TONE, POSTURE, VISUOSPINAL REFLEX, EQUILIBRIUM Control complex movements, Acts as alternate route of Pyramidal tract. Exerts tonic inhibitory control over the lower centers

12. Rubrospinal tract

13. RED NUCLEUS Prominent structure in the rostral midbrain just dorsal to substantia nigra . High in Iron content and is more vascular than the surrounding tissue Most important efferent projection is to the contralateral spinal cord i.e., Rubrospinal tract Course: Dorsally to pons and ventral to the lateral reticular nuclei of the Medulla. Then enters the lateral white column of the spinal cord and terminate in the internuncial neurons at the base of the anterior horn cells Extension: Cervical cord receives max. number of fibers. In Humans this tract do not extend beyond thoracic segments Facilitatory influence over the flexor muscle tone, Acts as alternate route to the Pyramidal tract.

14. RETICULOSPINAL TRACT Divided into Medial and Lateral tracts MEDIAL RETICULOSPINAL TRACT(Pontine Reticular Tract) Origin from Pontine reticular formation from Reticularis pontis oralis and Reticularis Pontis Caudalis Runs ipsilateral through Longitudinal Fasciculus Medial part of the anterior funiculus in the Spinal cord Terminates ipsilaterally at all spinal levels

15. Lateral Reticulospinal fibers(Medullary Reticulospinal tract) Origin from Medullary reticular formation – Nucleus reticularis gigantocellularis Some fibers cross and rest of them remain ipsilaterally Descend in the anterior part of the lateral funiculus Terminate in the internuncial neurons of the anterior horn of the Spinal cord

16. Functions CORTICO_RETICULOSPINAL PATHWAY Integrates information from the motor systems to coordinate automatic movements of locomotion and posture (antigravity muscles) Facilitates and inhibits voluntary movement, influences MUSCLE TONE Conveys autonomic fibers from higher centers Modulates pain impulses MRST: Facilitate voluntary control and reflex movements, control of Muscle tone through Gamma Neurons, Favors expiration and facilitates Vasoconstriction LRST: Inhibits voluntary control and reflex movements, Decrease muscle tone, favors inspiration and responsible for vasodilatation.

17. OLIVOSPINAL TRACT Also called Bulbospinal tract or tract of Helweg Course: Arise in the inferior Olivary nucleus Enter anterior part of the Lateral funiculus  Terminate in the anterior horn cells of Spinal cord Found in Cervical region only Function: Reflex movements arising from proprioception, existence is doubtful.

18. TECTOSPINAL TRACT Origin: Superior colliculus of the midbrain Fibers cross in the Dorsal tegmental decussation (Decussation of Meynert ) which is ventral to the Cerebral aqueduct Descend to the anterior white funiculus and terminate in the anterior horn of the spinal cord Function: Control head and arm movements (posture control) in response to visual and auditory stimuli

19. Vestibulospinal Tracts Two types Medial Vestibulospinal Tract : Medial Vestibular nucleus in Medulla  Descend upto upper thoracic spinal segment  Enter uncrossed into Anterior white funiculus and terminate in the anterior horn cell Function: Concerned with adjustment of head and body during angular and linear acceleration and conjugate horizontal eye movements, integration of eye and neck movements. Lateral Vestibulospinal tract: Lateral Vestibular nucleus (Dieter’s Nucleus) in medulla on both sides  Tract descend throughout the spinal cord length Run uncrossed in the anterior white funiculus and terminate in the anterior horn cell of the spinal cord. Function: Essentially the same as the Anterior Reticulospinal tract with facilitatory influence on reflex spinal activities and Spinal mechanisms underlying Muscle tone. Facilitates extensor muscles and inhibit flexor muscles. Maintenance of balance.

20. Medial Longitudinal Fasciculus Extends from midbrain downwards. Fibers take origin from Vestibular nuclei, Reticular formation, superior colliculus , Interstitial nucleus of cajal , Posterior commissure and has connections to CN III, IV, VI, VII, VIII, XII Anterior horn cells of the Neck Function: Hormonious movements of the eyes and Neck

21. VESTIBULOSPINAL SYSTEM

22. LATERAL VESTIBULOSPINAL SYSTEM

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