What are upper motor neurons?
projection neurons from the primary motor cortex to the ventral horn
Function of UMNs?
modulate LMN activity
What are lower motor neurons?
final effectors/ motor neurons
Where are the cell bodies of somatic LMNs found?
ventral horn of spinal cord
Where are the cell bodies of autonomic LMNs found?
- ParaNS = motor nucleus
- SymNS = lateral horn of spinal cord)
What two neuronal populations influence LMNs?
UMNs and segmental afferents of PCML tract
Describe how a spinal reflex occurs?
sensory afferents send a branch to interneurons in spinal laminae which activate efferents in the ventral horn of the segment
What type of LMN fibers active extrafusal fibers (skeletal muscle)?
Alpha fibers
What type of LMN fibers active intrafusal fibers (muscle spindles)?
Gamma fibers
What happens to muscle spindles when UMN modulation is lost?
Muscle spindles become more sensitive = muscle weakness & spastic movements
How is the Ventral horn topographically arranged?
What spinal levels innervated the upper extremities?
C4-T1
What spinal levels innervated the lower extremities?
L1-S2
What is flaccid paralysis?
LMN lesion resulting in complete loss of motor innervation to a muscle
What are the 5 types of LMN lesion findings?
- flaccid paralysis
- areflexia
- atonia
- atrophy
- fasciculations
What is atonia?
Loss of Gamma motor neuron activity = loss of muscle tone
What is atrophy?
loss of muscle mass due to lack of innervation
What are fasciculations?
twitching d/t increased sensitivity of motor end plates b/c of lesion to LMN
Damage to the ventral horn impairs what?
LMNs only
Damage to nerve roots (radiculopathy) causes what type of nerve impairment?
weakened motor and decrease sensory in a region
DTRs may +/-
Damage to peripheral nerves (neuropathy) causes what?
weakness & paraesthesia in specific muscle groups
What is Poliomyolitis?
Destruction of LMNs in the ventral horn by the poliovirus
What are the signs of poliomyolitis?
- fever
- myalgia
- Loss of muscle tone & reflexes with normal dermatome testing
- Negative Hx for polio vaccine
Where does the corticospinal tract start?
Primary motor cortex
What is the course of the corticospinal tract?
- primary motor cortex
- internal capsule of cerebrum
- cerebral peduncles (midbrain)
- anterior/rostral pons
- medullary pyramids –> decussates
- lateral CST (contralateral)
*anterior CST is different
Does the lateral or anterior corticospinal tract crossover in the pyramidal decussation
Lateral corticospinal tract
When do the “uncrossed” fibers of the anterior corticospinal tract crossover?
at the targeted spinal level
The lateral corticospinal tract accounts for how much of the total fibers of the corticospinal UMNs?
85%; important for thinking about injuries
Where is the lateral corticospinal tract located in the spinal column?
Posterior lateral funiculus, posterior to the ventral horn
Where in the spinal column is the anterior corticospinal tract located?
Anterior funiculus along the anterior median fissure
Is damage to the anterior corticospinal tract typically obvious?
No because it contain very few UMN fiber = minor modulator effect
What are the 7 clinical presentations of a UMN lesion?
- spastic paralysis/paresis
- hypertonia
- hyperreflexia
- clonus
- rigidity
- disuse atrophy
- babinksis reflexes
What is spastic paralysis/paresis?
Velocity-dependent increase in resistance to passive movement, (typically in a specific direction
What is hypertonia?
increased resting muscle tone due to loss of inhibitor signalling
What is hyperreflexia?
increase in reflex due to loss of inhibition from UMNs
What is clonus?
rapid series of alternating muscle contractions in response to a sudden stretch
Does a UMN or LMN lesion cause a more serve a form of atrophy?
LMN causes more serve form
What is a + Babinski’s reflex?
extension of hallux when planter surface is stroked (normal is to curl hallux)
What are common causes of corticospinal tract lesions?
cerebrovascular accidents and spinal cord traumas (i.e. whiplash)
How would a lesion of the R medullary pyramid above the decussation present?
Loss of UMN modulation on the LEFT SIDE = hypertonia, hyperreflexia, clonus, etc
How would a right-sided lesion below the decussation present?
UMN loss on to right side = clonus, hypertonia, hyperreflexia, etc on right
Why is a unilateral lesion in the medullary pyramids more serve than a lesion below the decussation
lesion above decussation = complete loss of UMNs to the contralateral side
Lesion below decussation = 85% loss of UMNs to the ipsilateral side & 15% loss of UMNs to the contralateral side
What muscles are controlled by the lateral corticospinal tract?
skeletal muscle of the extremities
What muscles are supplied by the anterior corticospinal tract?
axial (trunk) mucles
Damage to the L ACA would result in loss of UMNs to what?
The contralateral LE > UE
Damage to the R MCA would result in loss of UMNs to what?
The face and UE > LE
Damage to the posterior limb of the internal capsule would damage what arteries and present how?
Lenticular/thalamostriatal arteries that supply the Lentiform nucleus = complete contralateral hemiparesis
What is spinal shock?
Trauma to the spinal cord that results in LMNs s&s that recover in 1-2wks
* can cause spastic paresis
What is cerebral palsy?
group of CNS disorders characterized by aberrant muscle control & posture
What are the 4 main types of Cerebral palsy?
- spastic (cerebral cortex)
- dyskinetic (basal ganglia)
- ataxic (cerebellum)
- mixed (multiple areas)
how is the type of cerebral palsy diagnosed?
By clinical presentations = indicated affected brain regions
Clinical features of Amyotrophic lateral sclerosis (ALS)
mixed UMN & LMN signs
What is the function of the reticulospinal tract?
Pontine activation of the antigravity reflexes when in erect positions
What is the medullary reticulospinal pathway?
mediates cortical inhibitor control of reflexes
Where does the rubrospinal tract originate from?
Red nucleus of the midbrain (in the tegmentum)
What type of voluntary movement is controlled by rubrospinal tract?
flexor movement
What nucleus originates in the superior colliculus and coordinates head and eye movements
tectospinal tract (originates in tectum)
What tract maintains postures against gravity and UE/LE extensors?
Vestibulospinal tract from vestibular cortex
