Descending Motor Systems Flashcards
What is the route of motor neurons from motor cortex to medulla?
The axons travel throug hthe cerebral peduncles of the midbrain and through the base of the pons and form the pyramids of the medulla.
Which funiculus do the descending motor fibers course through?
Lateral
Where do the long projecting axons leave the funiculus and terminate?
The ventral horn, on motor neurons or interneurons (which synapse on motor neurons)
What segment of the spinal cord do most fibers terminate?
cervical
What is the function of the corticalspinal tract?
To provide voluntary cortical drive to spinal motor systems to induce conscious movement.
How are the fibers positioned within the lateral funiculus?
Sacral fibers are most lateral and cervical fibers are most medial.
How are most axons in the corticospinal tract located in relation to the spinal motor neurons?
Ipsilateral, known as the lateral corticospinal tract
Which side of the cortex do fibers in the lateral corticospinal tract originate from?
Contralateral
What are signs of upper motor neuron disease?
spastic paralysis, increased muscle stretch reflexes (deep tendon reflexes), clonus, Babinski’s sign, clasp-knife response to passive movements, lack of muscle atrophy except for disuse atrophy.
What is the most prominent impairment attributed to lesions involving uppre motor neuron lesions?
Weakness
What is paresis?
Voluntary muscle weakness
What is Plegia?
Complete loss of motor control
Define spasticity
an increase in muscle tone resulting from increase sensitivity of the muscle stretch reflex
Define clonus
Rapid beating of an extremity such as hand or foot when one of the muscles controlling it is placed under rapid and sustain tension
Define Babinski’s sign
Reflex extension and flaring of the toes in response to scraping the lateral margin of the sole of the foot
Clasp knife phenomenon
increase in resistance to passive manipulation during the initial period of manipulation follwed by a sudden decrease or disappearance of resistance as the manipulation proceeds
What side is innervation of muscle from motor neurons?
ipsilateral
What are signs of lower motor neuron lesions?
Decreased muscle stretch reflexes, flacid paralysis of muscles supplied by dmaged neuron, eventual atrophy of muscles dur to loss of trophic influence of anterior horn cells on muscle fibers, fibrllation and fasciulations are signs of muscles undergoing early stages of atrophy.
What is atrophy?
wasting away of muscle mass, it is a profound and important sign of lower motor neuron disease
What are fasciculations?
An involuntary twitching of a motor unit, frequently the result of muscle denervation
Where is the decussation that forms the corticospinal tract?
The caudal mdulla, known as the pyamidal decussation
What will a motor cortex lesion cause?
An upper motor neuron deficit on the contralateral side of the body
What will a upper motor neuron spinal cord lesion result in?
ipsilateral upper motor neuron deficit
What will a lower motor neuron lesion cause?
An ipsilateral lower motor neuron lesion
Upper and lower motor neuron damage on strength
Upper-decreased, lower-decreased
Upper and Lower motor neuron damage on muscle tone
Upper-increased, lower-decreased
Upper and lower motor neuron lesion on deep tendon reflexes
Upper-increased, lower-decreased
Upper and lower motor neuron lesions on atrophy
upper-mild, lower-pronounced
Fasciculations, upper or lower motor neuron lesion?
Lower
Clonus-upper or lower motor neuron lesion?
upper
Babinski’s sign-upper or lower motor neuron lesion?
upper
What is the anterior corticospinal tract?
the 10% of axons which do not cross in the pyramids, many of these fibers cross in the anterior white commissure at the level of termination. May be involved in control of neck and shoulder movements. May end in cerical and thoracic segments.
Where is the rubrospinal tract origin?
The red nucleus, in the midbrain
What is the function of the rubrospinal tract?
to excite flexor motor neurons
What is the organization and course of the rubrospinal tract?
Contralateral to origin, crossing in the midbrain, travels in the lateral funiculus of the cord
Where is the vestibulospinal tract origin?
The vestibular nuclei in the midbrain
What is the function of the vestibulospinal tract?
It facilitates extensor and flexor motor neurons. May be important for mediation of postural adjustment and head movements
What is the organization and course through the vestibulo spinal tract?
Ipsilateral to origin, travels in anterior region of lateral funiculus and anterior funiculus
Where is the origin of the reticulospinal tract?
The reticular formation in the pons and medulla
What is the function of the reticulospinal tract?
Facilitates extensor and flexor motor neurons
What is the organization of the reticulospinal cord?
Majority are ipsilateral to origin, travels in anterior region of the lateral funiculus
What is the origin of the tectospinal tract?
The superior colliculi, midbrain
What is the function of the tectospinal tract?
presumed to mediate reflex postural movements in response to visual and auditory stimuli
What the organization and course of the tectospinal tract?
Iti s contralateral to the orgiin and travels in the anterior funiculus
What is the result of complete transection of the spinal cord?
Immediately after, sensation ad voluntary movement are lost below the level of the lesion. If at C3 or above, respiration stops (phrenic nucleus for innervaion of diaphragm is at C3-5)
What is the result of partial transecion of the spinal cord
some ascendin and desceding pathways are affected
What is Brown-Sequard Syndrome?
Hemisection of the cord, paralysis and loss of tactile discrimination are detected no the side of the lesion and pain and temperature is lost on the side opposite the lesion
What is syringomyelia?
A cavitation around and near the central canal of the spinal cord, typically interfers with crossing of spinothalamic tract, therefore results in suspended sensory loss at level of lesion
