Motor System Flashcards
An UPPER MOTOR LESION of CN 7 will cause what?
What is a likely cause of this lesion?
contralateral paralysis of the LOWER face
(upper face spared)
- STROKE
A LOWER MOTOR LESION of CN 7 (or Cranial nuclei) will cause what? What is a likely cause of this lesion?
ipsilateral paralysis of UPPER & LOWER side of face –> CANNOT CLOSE EYE (orbicularis oculi is non-functioning)
- BELL’S PALSY
so cut Cn 7 on left = left side of face wiped out (upper & lower)
What is a motor unit?
Muscle fiber & everything it innervates
What is an upper motor neuron?
anything above the Anterior Horn cells
but below the cerebellum, basal ganglia, and Association Cortex
What is the size principle? What is the order of the units?
test
There is a proportional increase in the muscle contraction
- LMN’s are recruited in order of size & force**
SS - FR - FF
Where does the Lateral Corticospinal tract located in the internal capsule? Where is the corticobulbar tract in the internal capsule?
(TEST)
- Posterior Limb of the INTERNAL CAPSULE (PL)
2. GENU = Corticobulbar
Where does the CST originate from?
- Motor cortex
- Adjacent areas
- Sensory cortex (somatosensory)
Where does the CST terminate?
- SPINAL CORD (anterior horn cells)
- BRAINSTEM
- Association cortex
- Basal ganglia, thalamus, RT, sensory nuclei
Where is the Corticobulbar tract in the internal capsule?
GENU of the internal capsule (the bend)
Where does the Corticobulbar tract terminate? (2 areas)
- terminates on INTERNEURONS of the RETICULAR FORMATION
- some on SPINAL MOTOR NEURONS
Which Cranial nerves does the Corticobulbar tract innervate? Which does it NOT innervate?
- 5,7,9,10,12
5 & 12 have more contralateral contribution (so opposite would be affected?)
- CN 3,4,6 of the eye are NOT innervated by Corticobulbar tract
What structures are innervated by the MEDIAL column of the LMN of the spinal cord? LATERAL?
What is dorsally places? Ventrally?
- AXIAL (leg/trunk)
- ARM - distal limb muscles
= SOMATOTOPIC org.
- DORSAL = flexor
- VENTRAL = extensor
What do LMN’s release?
acetylcholine
What are corticospinal/corticobulbar neurons referred as?
UPPER MOTOR NEURON
What are neurons of the brainstem & spinal cord?
LOWER MOTOR NEURONS
Distinguish between the following three muscle units:
- S-units
- slow twitch
- ALOT of mitochondria & capillaries
- not fatigueable
- small force
- RED MUSCLE fibers - FR-units
- fast twitch
- WHITE fibers
- moderate force
- fatigue resistant - FF-units (only fatiguable unit)
- fast twitch
- WHITE fibers
- LARGE force
- fatigueable***
LMN’s are found in the white matter or the grey matter of the spinal cord? Which areas of the spinal cord have grey matter enlargement?
GREY MATTER
- CERVICAL (arm) & LUMBOSACRAL (leg)
What is the firing pattern of LMN’s dependent on?
INTERNEURONS
What is the transmitter in Corticospinal tract? Is it excitatory or inhibitory?
- GLUTAMATE
2. Excitatory
What are the 3 control systems for LMN’s?
- Descending Pathway
- Higher cortical centers
- Basal Ganglia & Cerebellum**
Fibers in the CST are JUST localized in the MOTOR cortex. TRUE OR FALSE?
FALSE
- they are in adjacent cortex & sensory cortex as well
Where does the CST originate from?
- Primary motor cortex
- Adjacent Frontal Motor
- Parietal areas
(somatosensory)
CST descends through what?
POSTERIOR LIMB of the Internal Capsule
If you lesion the PL, will this lead to ipsilateral loss or contralateral loss? What tract will be affected if you lesion the GENU of the internal capsule?
- CST in PL (fine motion)
- CONTRALATERAL loss
(this is similar to a stroke)
- Corticobulbar Tract
Where does the CST decussate?
Medullary Pyramids
- most fibers = LATERAL corticospinal tract*
What will occur if you lesion a PYRAMID before the CST crosses? What about a lesion in the spinal cord?
PYRAMID = OPPOSITE SIDE
SPINAL CORD = same side***
(fine motor movement affected)
If you lesion the cerebellum, association cortex, or basal ganglia, will there be WEAKNESS?
NO
-
Weakness only occurs in lesion of which 2 neurons?
UPPER MOTOR NEURONS +
LOWER MOTOR NEURONS
(anterior horn cells)
What are the symptoms of a LOWER MOTOR NEURON lesion?
- Flaccid paralysis
- Hyporeflexivity
- Fasciculations
* ATROPHY
What are the symptoms of an UPPER MOTOR NEURON lesion?
- Spasticity
- Exaggerated reflexes
- Hemiplegia
-STROKE!!!
The motor neurons of Cranial nerves, sensory relay nuclei, & RT is which tract?
CORTICOBULBAR
- anterior to CST tract
Where does the cortibulbar tract end?
Interneurons of the RETICULAR FORMATION
Which nerves receive no direct corticobulbar innervation?
3,4,6
controlled instead by MLF
A contralateral loss of the RIGHT lower face muscles would be indicative of what?
LEFT STROKE (or lesion of the cortex) CN 7
An ipsilateral loss of the whole LEFT face would be indicative of what?
Bell’s Palsy
lesion CN7 or the nucleus
What modulates the motor cortex?
- Association Cortex
- Basal Ganglia
- Cerebellum
(modulate via UPPER MOTOR NEURONS)
