Physiology - UMN Lesions Flashcards
What makes up corticobulbar tracts?
Cranial nerves and brainstem motor nuclei
Which muscles are more likely to function after unilateral damage and why?
Proximal muscles (including forehead) This is because they receive information from both crossed and uncrossed fibres thereby they are more likely to function if one side is damaged because they will still receive input from the other functional side.
How many fibres decussate (and where). What happens to the other fibres that don’t decussate?
85% of fibres decussate at the medullary pyramids (pyramidal tract)
15% uncrossed fibres are ipsilateral
What does the lateral CST send signals to?
Distal and proximal muscle motor neuron pools
Where do most lateral CST axons synapse? Where do the others that do not synapse here go?
Most axons synapse on spinal interneurons which synapse on alpha motor neurons.
Small number of lateral CST synapse directly onto alpha motor neurons.
What is corticomotoneuronal axons and what is their function?
Small number of lateral CST synapse directly onto alpha motor neurons.
Contribute to the high level of fine distal control of digits
What is the rubrospinal tract?
Red nucleus to spinal cord
What is the function of the red nucleus?
Locomotion
Inter-joint coordination
What is the function of the superior colliculus (tectum)?
Input from visual pathway
Directs rapid orientation towards moving objects
Name the two parts of the reticular formation.
Pontine part
Medullary part
What is the function of the pontine part of the reticular formation?
Enhances anti-gravity reflexes (lower limb extensors, upper limb flexors)
What is the function of the medullary part of the reticular formation?
Suppresses reflexes to allow voluntary movement
What are the inputs to the vestibular nuclei?
Vestibular apparatus, neck proprioceptors, cerebellum
What are the outputs of the vestibular nuclei?
Postural reflexes, sense of head position
List the factors that define the primary motor cortex.
Cytoarchitectonics
High density of corticospinal cell bodies
Low threshold for electrically evoked movement
Somatotopic representation
How can we alter somatotopic representation and what is its organization with regards to different parts of the body?
Training allows for expansion of areas.
The area = type/amount used
Leg –> arm –> hand –> face
What are the functions of the primary motor cortex?
Voluntary motor commands
- Regulates muscle force
- Controls movement direction
What area is the primary motor cortex?
Area 4
Name the two parts of the secondary motor cortex and their locations.
Premotor cortex (PMC) - lateral area 6 Supplementary motor cortex (MCA) - medial area 6
How does the secondary motor cortex differ from the primary motor cortex?
Has a higher threshold for electrical stimulation
Less organized somatotopy
What is the functions of the SMA?
Initiation of movement, suppress unwanted movement, bimanual coordination
What is the function of the PMC?
Visual motor coordination, hand mouth coordination, mirror neurons
What are examples of UMN disorders.
Stroke (CVA), trauma, multiple sclerosis
Explain the characteristics of an UMN lesion.
Decrease in power Increase in tendon reflexes Increase in muscle tone Mild muscle atrophy (disuse) Extensor/Babinski plantar response
What does the clinical picture of an UMN depend on?
Time since injury
Location of injury
Describe the different clinical pictures seen with time since injury.
Immediate flaccid (hypotonic) paralysis Spasticity over hours to weeks
Describe the main signs of a cortical lesion.
UMN signs + language/perceptual/frontal abnormalities
Describe the main signs of a brainstem lesion.
UMN + cranial nerve deficits
Describe the signs of a spinal cord lesion.
UMN + sensory pathways (below lesion) + local nerve root
What happens if the injury is in the cortical/subcortical region vs brainstem vs spinal cord.
Subcortical/cortical region - flexed posture in upper limbs, extended in lower limbs
Brainstem: extreme postures depending on level
Spinal cord: below lesion - increased withdrawal reflex, increased autonomic reflexes. Innervated from lesion level = LMN defects
