Lecture 6 Flashcards
Location of cell bodies of LMN
anterior horn of spinal cord
Descibe considerations for muscle atrophy e.g. affect of damage to LMN
LMNs provide trophic influences on muscle, e.g. transmission of impulses and neuronal substances across synapses. Damage to LMN affect factors e.g. affect protein synthesis resulting in decrease muscle crossectional area. Weakness in muscle- lack of use and decreased size
Describe considerations for hyporeflexia e.g. affect of damage to LMN
Damage to LMN- absent stretch reflex responses (on motor side)
0 on deep tendon reflex scale
absent reflex
Describe tool to test reflexes (test for hyporeflexia)
Deep tendon reflex scale
1 on deep tendon reflex scale
decreased by present
2 on deep tendon reflex scale
normal
3 on deep tendon reflex scale
brisk but excessive
4 on deep tendon reflex scale
non-sustained clonus
5 on deep tendon reflex scale
Sustained clonus
Suggests hyporeflexia
(numbers on scale)
<2 on deep tendon reflex scale
Describe consideration of decreased tone
hypotonia- even at rest muscle receiving low levels of tonic stimulation. With LMN injuries, resting tone cannot get down to muscle
Describe how to test for tone and interpretation of testing
Move various joints through range of motion- test for resistance. Lack/absence of resistance to ROM with hypotonia, hyperextension of joints associated with decreased tone. Hypertonia- lots of resistance through ROM
How does foot drop affect gait?
- Excessive flexion of knee in swing on ipsilateral side
- Lack of ankle dorsi-flexion in swing on ipsi-lateral side
- Foot lands toe first and set down carefully
Name for gait assocaited with foot drop
‘high steppage gait’
Identify causes of LMN lesion
Injury or disease that affects any of the:
- Motor nuclei in anterior horn of grey mater of spinal cord
-ventral nerve roots (radiculopathy- damage to vental roots) as they come out through spinal cord
- spinal nerves (as travel through mixed nerve to muscle)
Describe polio
Virus that attacks cell bodies in anterior horn (primarily motor neurons), mostly irradicated worldwide with vaccine. Affects cell bodies in lumbar region of SC which innervate legs, typically symptoms involving lower limbs, sometimes thoracic region- affect intercostals activation- associated with iron lung device for breathing.
Describe typical age of people affected by polio
<5 years old
Describe polio types and prevalence
<10% people get neurological type e.g. affect cell bodies in anterior horn of grey mater.
~1% paralytic type which severely Affect LMN’s
Describe recovery from polio
Most people able to recovery, some people with neuological type may not (perminant paralysis)
Damage to spinal cord associated with lower motor neuron symptoms affect
lower motor neurons
Describe sources of spinal cord damage that affect LMN
- Spinal cord lesion- damaging cell bodies in anterior horn of spinal cord
- Disc herniation- damage to ventral roots as they leave intervertebral foramen by squeezing/impinging on them and prevent signal from traveling out
- Tumor- grows within spinal cord- if growing in anterior (ventral) part of spinal cord affects axons coming out, LMN symptoms of spinal cord at that level
Key consideration of spinal cord damage to LMN
Damage at one level likely to affect other levels of SC e.g. additional symptoms below injury in terms of motor function and sensory symptoms. However only LMN type symptoms at level of injury (associated with damage to LMN), LMN coming out from spinal cord below level of injury are intact and LMN coming out above the level of injury are also intact.
How can damage to ventral roots and spinal nerves occur?
Injury to ventral roots and spinal nerves can occur through compression, traction, laceration or entrapment- these prevent action potentials from going down
Describe upper motor neurons
cell bodies in motor cortex of brain (precentral gyrus), axons extend down through brain, brainstem and through spinal cord where they innervate LMN in spinal cord
Describe representation of primary motor cortex
somatotopic representation of motor nuclei in motor cortex, spatial organisation associated with different regions. Size of representation differs based on functionality e.g. large face and hand areas greater level of control for complex movements vs. small areas devoted to legs/trunk
Specifically specify where muscles of the body are represented somatotopically in the cortex
muscles of feet along the midline, travelling along the superior surface is the knee, then laterally the hip, trunk, upper and lower arms, lands and most laterally the face
Makes up primary motor cortex
precentral gyrus
Where most upper motor neurons reside
primary motor cortex
Corticospinal tracts
Bundles of axons from upper motor neurons travelling to spinal cord (made by white matter)
Describe the pathway of corticospinal tracts
Axons from cerebral cortex enter upper portions of white mater (corona radiata) in fan like apperance descend towards the internal capsule. Internal capsule continues into the midbrain cerebral peduncles through the basis pedunculi (white mater in ventral portion of cerebral peduncles), through the pons, and collect on ventral surface of medulla to form medullary pyraminds, where some fibres cross the midline via pyramidal decussation.
Identify these tracts
corticospinal and corticobulbar tracts
Identify this
posterior limb of internal capsule
Identify this
basis pedunculi
Identify this
pyramid
Identify this
lateral corticospinal tract (crossed)
Identify this
anterior corticospinal tract (uncrossed)
Identify this
pyramid
Identify this
pyramidal decussation
location of internal capsule
lateral to thalamus
Where lateral corticospinal tracts travel
lateral column of spinal cord
where anterior corticospinal tracts travel
anterior column of spinal cord
corticospinal tracts found in ____ of internal capsule
posterior limb
Orientation/appearance of internal capsule
u-shaped appearance pointing inwards
Identify three parts of internal capsule
anterior limb, genu- where turns (knee of internal capsule), posterior limb,
Identify this structure
Internal capsule
Identify this structure
putamen
Identify this structure
globus pallidus
Identify this structure
head of caudate
Identify this structure
thalamus
Identify this structure
anterior limb
Identify this structure
genu
Identify this structure
posterior limb
Identify the two corticospinal tracts and proportion
-lateral (85%- majorities of tracts)
- anterior (15%
lateral corticospinal tracts control ____
distal muscles of hands and feet, controls muscles of the contralateral side (crosses midline and control muscles on opposite side of the body)
Lateral corticospinal tracts terminate at _____
cervical and lumbo-sacral enlargments
Other name for corticospinal tracts
‘pyramidal tracts’
Describe the pathway of lateral corticospinal tract
tracts from cortex, through corona radiata, into internal capsule through midbrain through basis pedunculi until they get to cervicomedullary junction where they decussate (via pyramidal deccusation) to enter lateral white matter columns of spinal cord and travel to level of innervation and synapse on LMN
Level of cervicomedullary junction
sits at level of foramen magnum
site of origin of lateral corticospinal tracts
Primary motor cortex, and other frontal and parietal areas
Site of deccusation of lateral corticospinal tracts
pyramidal decessation at teh cervicomedullary junction
level of termination of lateral corticospinal tract
entire cord (predominately at cervical and lumbosacral enlargments)
Function of lateral corticospinal tracts
Movements of the contralateral limb
