Neuro: Cortiospinal Motor System: Dip And Weak Flashcards
What are the two consecutive neurons in the Corticospinal motor system?
Upper motor neuron and lower motor neuron
Where is the UMN located?
Pre central gyrus
Where is the LMN located
Ventral/anterior horn
LMN project to muscle from the ventral horn via ____ ____
Peripheral nerves
Neuroanatomical pathway:
- UMN cell bodies in PrecentralGyrus.
- Axons descend through Cerebrum in a white
matter tract called the Internal Capsule. - Axons continue to descend through brainstem levels, including through the Pyramids of Medulla.
- Most UMN axons cross the midline to the
opposite side at the Pyramidal Decussation in Medulla. - UMN axons continue to descend down Lateral CorticospinalTract (LCST) until they reach their target level of the spinal cord, i,e, their target LMNs.
- Axons exit the LCST and terminate (synapse) on LMN in Anterior (Ventral) Horn.
- LMN projects out anterior (ventral) roots and via peripheral nerve to muscle.
The precentral gurus is the _____ cortex
Motor cortex
UMN damage at the pre central gurus: possible pathologies
-Amyotrophic lateral sclerosis
-Cerebral palsy(hypoxia/ ischemia)
-Ischemic stroke
UMN damage at the pyramidal decussation: possible pathologies
-Brain stem infarcts(UMN axons)
-mass growing
UMN damage at the spinal cord: possible pathologies
-white matter disease
-injury/infarct/mass
LMN damage can occur at
Spinal cord, muscle, neuromuscular junction, peripheral nerves
If the corticospinal tract is damaged superior to pyramidal decussation produces
Limb paresis or paralysis on side contra lateral to the lesion
Lateral corticospinal tract damage inferior to the pyramidal decussation produces
Paresis or paralysis on side ipsilateral to the lesion
Damage to the pyramidal decussation produces
Bilateral paresis or paralysis
Damage only to the ventral/anterior horns typically produces
Segmental pattern of weakness
Damage only to the lateral corticospinal tract produces a
Level-down pattern of weakness
Rating of neurological exams
5 / 5 Normal strength, can overcome resistance from examiner
4 / 5 Limited ability to overcome resistance
3 / 5 Movement does not overcome resistance, but can overcome gravity
2 / 5 Movement does not overcome gravity or resistance (horizontal only)
1 / 5 Muscle contraction visible without movement
0 / 5 No contraction, no movement
Stretch reflex or deep tendon reflex rating in neuro exam
4 / 4 Clonus, (rapid alternating contractions, e.g. flexion / extension)
3 / 4 Brisk (slightly excessive in magnitude or speed)
2 / 4 Normal***
1 / 4 Trace (barely detectable)
0 / 4 Absent reflex
The patellar reflex is mediated by ____ _____
Muscle spindles
patellar reflex pathway
① Tap on patellar tendon creates mild stretch in quadriceps muscles.
② Stretch detected by sensory neuron
fibers wrapped around spindle muscle
fibers.
③ Sensory neuron fires, releases
excitatory neurotransmitter on
motorneuronthat activates
contraction of quadriceps muscles.
Stretch reflex can also be activated by ______ stretch by the examiner which activates _____ ____.
Passive, muscle spindles
Sensory arc for muscle spindles
Stretching muscle spindle fibers activate sensory neurons that are wrapped around muscle fibers
Motor arc for muscle spindles
Sensory fibers form excitatory synapses on alpha motor neurons to activate muscle contraction and movement
the patellar reflex tests which spinal cord level?
L4
The shoulder reflex tests which spinal cord level
C5
The brachioradialis reflex tests which spinal cord level
C5-C6
The triceps reflex tests for which spinal cord level
C7
What are the four most common stretch reflex tests
Biceps
Brachioradialis
Triceps
Knee jerk(patellar)
LMN lesion signs -
Strength:
Muscle tone:
Stretch reflexes:
Atrophy:
Other signs:
Strength:decreased
Muscle tone: decreased
Stretch reflexes:decreased
Atrophy: severe
Other signs: fasciculation’s
UMN lesion signs
Strength
Muscle tone
Stretch reflexes
Atrophy
Other signs
Strength: decreased
Muscle tone: increased
Stretch reflexes:increased
Atrophy:mild
Other signs: clonus, pathological reflex (babinski)
Fasciculation definition
Spontaneous contractions of groups of muscle fibers visible as muscle twitches
Clonus definition
A series of alternating and opposite muscle group contractions in response to muscle stretch by the examiner
Exaggerated response to passive stretch stimulus
What is babinkski’s sign
Foot extends and toes fan out in response to touching the bottom of foot
-normal response is toe flexion
LMN signs are described as ____ weakness
Flaccid weakness
UMN signs are described as ___ weakness
Spastic
If both LMNs and UMNs are damaged, patient shows ___ signs
LMN
LMN must be _____ for UMN signs to occur
Intact
The exaggerated reflexes of UMN lesions signs is due to
LMN trying to compensate for the lack of stimulus from UMN
If there is a lesion on the entire pre central gurus on the patients left side:
Where is the weakness
UMN or LMN
Where is the weakness: right side
UMN
If there is a lesion on the internal capsule on the patients right side:
Where is the weakness:
UMN or LMN:
Left side
UMN
If there is a lesion in the corticospinal tract in the brain stem, patient’s left side:
Where is the weakness:
UMN or LMN:
Right side
UMN
If there is a lesion on the pyramidal decussation at the midline:
Where is the weakness:
UMN or LMN:
Bilateral
UMN
A lesions at the lateral corticospinal tract @ C5, patients right side:
Where is the weakness:
UMN or LMN:
Segmental or level-down Pattern:
Right side
UMN
Level-down
A lesion on the anterior horn @ C5, patient’s right
Where is the weakness:
UMN or LMN:
Segmental or level-down Pattern:
Right side
LMN
Segmental
A lesion or neuropathy on the peripheral nerves would cause:
- mixed motor and sensory deficits
-Nerve conduction testing, hand-held device
lesion of the neuromuscular junction disorder would cause____ _____ issues
pure motor
What is Myasthenia Gravis?
Neuromuscular junction disorder
Antibodies vs Nicotinic Ach receptors, “fatigue able weakness”
What is Lambert-Eaton disorder?
Neuromuscular junction disorder
Antibodies vs Ca++ channels
Pattern: weakness can improve with activity
