Motor tracts

Fern WhiteHarvey Davies

Questions:

f.white@warwick.ac.ukharvey.davies@warwick.ac.uk

Motor tracts (Upper motor neurones)

Lateral corticospinal tract

Ventral corticospinal tract

Rubrospinal tract

Vestibulospinal tract

Reticulospinal 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.

Pyramidal and extrapyramidal 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?

What is the function of the corticobulbar tracts?

Extrapyramidal..

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!)

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.

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

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.

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