Motor tracts Fern White Harvey Davies Questions: f.white@warwick.ac.uk harvey.davies@warwick.ac.uk Medullary: Suppresses extensor reflex Projects bilaterally to all spinal cord Loss leads to spasticity in UMN lesions Pons Facilitates extensor reflex Ipsilateral projection

Motor tracts (Upper motor neurones) Lateral corticospinal tract Ventral corticospinal tract Rubrospinal tract Vestibulospinal tract Reticulospinal tracts Upper motorneurones project to the spinal cord via DESCENDING TRACTS where they then exert influence on spinal lower motorneurones in the reflex arcs. Upper motor neuron cell body situated in primary motor cortextravels down through internal capsule  Axon decussates (crosses sides) at pyramids (lower medulla) Descend in contralateral lateral corticospinal tract Synapses with lower motor neuron in ventral grey horn Ventral corticospinal tracts don’t deccusate at pyramids- 10% decend ispsilateral side Alpha motor neurons – extrafusal fibres Gama motor neurons – Intrafusal fibres

Pyramidal and extrapyramidal tracts… PYRAMIDAL: First order neurones originate in the cortex. Also referred to as the CORTICOSPINAL & CORTICOBULBAR TRACTS - they extend from the cortex all the way through to the spinal cord. Named as the tracts pass through the pyramids of the medulla. EXTRAPYRAMIDAL: First order neurones are more diverse in terms of their origins and pathways… It is functionally difficult to separate the different tracts, so they are lumped together in terms of signs and symptoms.

What is the function of the corticobulbar tracts? Corticospinal tracts Initiate and regulate voluntary skilled movements by innervating α and γ motorneurones in the spinal cord Provide the CONSCIOUS VOLUNTARY CONTROL of all skeletal muscles. Decussate at the level of the medulla. The Tracts are for the main part CROSSED, hence limb movements are controlled by the contralateral cerebral cortex. Function? Lateral corticospinal tract = main pyramidal motor fibre tract (80-90%) Ventral corticospinal tract = secondary pyramidal motor fibres (~10%) The corticobulbar tract conducts impulses from the brain to the cranial nerves. These nerves control the muscles of the face and neck and are involved in facial expression, mastication, swallowing, and other functions. NB: a- motor neurons Innervate extrafusal muscle fibres Large myelinated axons g-motor neurons Innervate intrafusal muscle fibres of the muscle spindle Smaller diameter neurons What is the function of the corticobulbar tracts?

Extrapyramidal.. VESTIBULOSPINAL: Maintain balance and posture. Excites extensor LMN and inhibits flexor LMN. Originates in the VESTIBULAR NUCLEI of the PONS and MEDULLA. The tract is UNCROSSED and remains ipsilateral to the site of origin TECTOSPINAL: Function: Associated with reflex postural responses to visual stimuli. Originates in the SUPERIOR COLLICULUS, and travels in the spinal cord in the lateral white column. The tract DECUSSATES close to the LEVEL of ORIGIN. RETICULOSPINAL: Modulate muscle activity/tone; Modulate sympathetic activity; Control emotional movement of muscles of facial expression (Patients can smile even if they have bilateral corticobulbar lesions to CN VII!) Involuntary reflexes and movement, and modulation of movement (i.e. coordination) - compared to pyramidal, which directly innervate motor neurons of the spinal cord or brainstem. RUBROSPINAL: Regulates α and γ motorneurones. Excite flexor LMN, Inhibit extensor LMN. Route by which the cortex and cerebellum target reflexes. Originates in the RED NUCLEUS and DECUSSATES at the level of origin (ventral tegmental region) within the MIDBRAIN.

Describe the cranial nerve motor supply from the cortex Bilateral supply from cortex Innervation comes from corticobulbar/corticonuclear neurons Main UMN innervation is contralateral . So cortex damage results in weakness but not total paralysis. Can then recover as ipsilateral UMNs compensate. Exception is unilateral supply to CNVII to the lower face. Decussation occurs at synapse on to CN LMN in the brain stem. NB: Reticulospinal tracts control emotional movement of muscles of facial expression, so patients can still smile even if they have bilateral corticobulbar lesions to CN VII.

What are the signs of Upper motor neuron lesions? Spastic paralysis Hyper-reflexia No muscle wasting Extensor plantar response

Lesions of pyramidal tracts - tests Babinski sign: On testing the Big toe is dorsally flexed and other toes fan outward on scratching the sole of foot. Absent superficial abdominal reflexes: Abdominal muscles fail to contract when abdomen is scratched. This is due to a loss of tonic pyramidal (corticospinal) drive. Loss of fine-skilled movement Clonus: rhythmic involuntary oscillation of a joint. BABINSKI: On testing the Big toe is dorsally flexed and other toes fan outward on scratching the sole of foot. Normal response is plantar flexion of all toes. THIS IS YOUR GIVEAWAY INDICATION OF A PYRAMIDAL SIGN. If you see this there is upper motorneurone damage at the level of the pyramidal system. Loss of fine-skilled movement: This is because the pyramidal tracts carry the commands for voluntary movement e.g. walking, running away from danger etc. If the system is not intact, performing such functions is compromised. N.B. some voluntary control is possible through other descending tracts.

What are the signs of Lower motor neuron lesions? Flaccid paralysis Hyporeflexia Muscle wasting Fasciculation's

Upper & Lower Motor Neurons When deducing which motor neuron symptoms will be observed, think about the level of the damage and the tracts/neurons involved

Clinical Problems Spinal cord hemisection can lead to both upper and lower motor neuron signs in different parts of the body

Clinical Problems Spinal cord hemisection can lead to both upper and lower motor neuron signs in different parts of the body