Supraspinal Motor Control
Alpha motor
Neuron
Muscle fibers
+
-
Renshaw cell
The Motor Unit
Flexor-Crossed Extensor Reflex
Long Spinal Reflexes
Inputs: vestibular, neck proprioceptors
Organized by circuits of propriospinal neurons
Muscle
Forebrain
Brain
Stem
Alpha Motor Neuron
"lower motor neuron"
Spinal cord circuitry
Multisegmental
Long spinal
Flexor/crossed extensor
Segmental
Reciprocal innervation
Myotatic
Motor unit
M1S1Posterior
ParietalPrefrontal
Thalamus
VLc VLo
Cerebellum
Spin
ocere
bella
r Tr.
Inf.
Olive
Vest.
Nuc.
Retic.
Form.
Red
Nuc.
Vest.
Spinal
Tr.
Retic.
Spinal
Tr.
Rubro
Spinal
Tr.
Cortico-
Spinal
Tr.
Cere
bella
r Loop
Basal G
anglia
Loop
Pons
Sup. & Inf.
Colliculi
Tecto-
Spinal
Tr.
SMA
PMA
Caudate
Putamen
N. Accumbens
Globus pallidus
Substantia nigra
Subthalamic nuc.
Primary motor andPremotor cortex
Brain stem
Motor systems of spinal cord
and brain stem
Interneurons
Motor neurons
Basal ganglia
Cerebellum
Thalamus
Skeletal muscle
Limbs and Trunk Head
Intermediate zone Reticular formation
Ventral hornCranial nerve
motor nuclei
Spinal cord Brainstem
Lawrence and Kuypers
The Three Major Descending Pathways
“Upper motor neurons” “Long motor tracts”
Vestib.Nuclei
Reticularformation
RedNuc.
Cerebral cortex
MidbrainTectumVentromedial
brainstempathway
Lateral brainstempathway
Corticospinalpathway
Tectospinal Vestibulospinal Reticulospinal Rubrospinal Corticospinal
Corticobulbar
(Pyramidal)
Tracts
Targeted muscle
groups
Axial Girdle/proximal
(upper limb)
All
The Three Major Descending Pathways
“Upper motor neurons”
“Long motor tracts”
Spinal termination of
the red nucleus
Tracer injected in contralateral
RN (midbrain) of the cat
Lateral brainstem
pathway
(rubrospinal tract)
DescendingAscending
Ventromedial
brainstem
pathway
Control of trunk,
axial muscles impaired
(↓ anti-gravity posture,
difficulty righting)
Bilateral pyramidotomy
(eliminate CST input)
Left lateral brainstem lesion
(eliminate rubrospinal
influence on left)
Lateral brainstem intact Eliminate lateral brainstem
Cerebral cortex
Red nucleus
Medulla
Pons
Midbrain
Thalamus
Superior colliculus
Vestibular nuclei
Reticular nuclei
Vestibulospinal Tr.
Reticulospinal Tr.
Corticospinal Tr. Rubrospinal Tr.
Tectospinal Tr.
MidlineLeft Right
Descending Motor Pathways
Decorticate
rigidity
Cut here
Decerebrate
rigidityCut hereVestib.Nuclei
Reticularformation
RedNuc.
+ Extensors + Flexors
Cerebralcortex
Spinal cord
MidbrainTectum
Ventromedialbrainstempathway
Lateral brainstempathway
Corticospinalpathway
Hemiplegia Paraplegia Quadriplegia
-plegia = paralysis -paresis = weakness
Disease of muscle, lower motor neuron Flaccid Paralysis
Damage to long motor tracts (UMN) Spastic paralysis
Long Motor Tract Signs
Spasticity
Weakness
Clonus
Babinski sign
Hypertonia
Hyperreflexia
Positive Babinski sign(following lesions to the pyramidal tract)
Thought to reflect a flexor withdrawal reflex that is normally
suppressed by the corticospinal tract
1
sec
Stimulation of site
A
Stimulation of site
B
Ia firing rate
Medial
reticular
formation
Lateral
reticular
formation
Normally under cortical inhibition
Gamma
motor
neurons
Gamma
motor
neurons
+ +
Clonus
Hyperreflexia due to increased excitability of and/or MN
Alpha motor
Neuron
Muscle fibers
+
-
Renshaw cell
The Motor Unit
Tract Tracing With Chemical Tracers
Horseradish peroxidase (and its enzymatic reaction products)
travel in both the retrograde and anterograde directions
Inject retrograde tracer
near (injured) terminals
Retrograde axonal
transport
Labeled cell soma
Inject anterograde
tracer near (or in) somata
Anterograde axonal
transport
Labeled synaptic
terminals
Electrophysiological Tract Tracing
Orthodromic Conduction
Antidromic and Orthodromic Spikes
?Possible Target
Nucleus
Stimulus PulseRecord
1
ms
Shock
Latency 1 ms
Short, constant latency Follows high frequency stimulation
Antidromic Invasion
B
Soma
Axon
Terminals
OrthodromicAntidromic
Conduction Direction
A Shock
Tract Tracing by A/D Invasion
Collision
The Critical Interval Test
Collision Test
?
Stimulus PulseRecord
Orthodromic Antidromic
Stimulator
Out
A/D stim
A/D latency
Orthodromic
spike
Response intermittent
Collision occuring
No A/D spike
Collision every time
Critical interval
1
2
3
4 TimeSpontaneous or evoked orthodromic spike triggers oscilloscope
and, after a variable delay, triggers the A/D stimulator
Variable
Delay
Oscilloscope
A/D spike
Measurement of Conduction Velocity
Soma Axon Terminals
Record
S1
L
A/D Latency 1 A/D Latency 2
T = Lat. 2 - Lat. 1 Conduction Velocity = T
L
S2