Tracts that indirectly influence LMNs:
Cortico-ponto-cerebellar
tract
Cerebello-rubro-thalamocortical tract
Corticorubrospinal tr
Inferior olivary nucleus
Cerbral cortex communicates with
contralateral cerebellum
-Afferent
-Cerebellum learning about muscles
Cerebellum indirectly influences motor
control
-Efferent
-Feedback
In cats
Descending pyramidal:




Skilled voluntary movements; piano, typing.
Terminate on motor and sensory neurons, motor is more important.
Effects concentrated on UMNs in hands, otherwise lots of interneurons.
Little effect on posture and background muscle tone.
MOTOR
Corticospinal tract:
LCST
-All SC levels
-Innervates limbs
VCST
-Only to thoracic lvls
-Innervates axial musc.
-Decussates @ lvl of
termination in anterior
white commissure
Corticobulbar tract:
-Cerebral cortex
-White matter of cerebral cortex
-Internal capsule
-Cerebral crus
-Basilar pons
-Pyramid
-Pyramidal decussation (X)
-Lateral column of cord
-Gray matter of cord
terminates on LMNs (in ventral/anterior
horn) or interneurons. CONTRA
- Dorsal CST more significant than ventral CST.
-Cerebral cortex
-White matter of cerebral cortex
-Internal capsule
-Cerebral crus (X)
-Basilar pons (X)
-Pyramid (X)
Terminate bilaterally on all levels of brainstem
(bulb)
-Facial motor nuclei get contralateral
corticobulbar input only.
Somatotopy: Legs are
Lateral in LCST & ST.
DCML is organized as you
are (hands at side – arms
outside, legs inside)
LLS
C U
TT
DCML
LCST
SLTC
SL
T C
ST
Lesions:
LMN lesions = lowered!
muscle mass, muscle tone, reflexes, downgoing toes (no Babinski)
UMN lesions = up!
muscle tone, DTRs, toes up (+ Babinski)
Other supraspinal descending:



Maintain posture, muscle tone, gross muscle activities.
Excitatory and in hibitory effects on LMN balance eachother.
B/C NO direct connection between cerebellum & LMNs
Vestibulospinal tract
Reticulospinal tract (RST)
(medial and lateral)
CEREBELLAR
Raphe spinal tract
Medial longitudinal
fasciculusMLF
(med. vestibulospinal tr.)
-Runs w/ VST
-posture & balance
-MS pts = diplopia
Intersegmental fibers: In spinal cord are essential for coordinating spinal reflexes that involve multiple
Fasciculus Proprius
cord segments.
Septomarginal tract
Fasciculus interfascicularis
Cerebellum influences LMNs; upright
posture, balance. Gymnastics, diving.
Descending autonomics.
Cerebellum influences LMNs; posture,
muscle tone. Segmental spinal cord
integration; walking, running. SOMATIC
motor control.
Modulates pain by mimicing opium
alkaloids.
Medullary reticular formation origin.
Terminates in substantia gelatinosa.
Coordinates head and eye movements
related to equilibrium.
Ascending to CN III, IV, VI nuclei.
Descending to cervical levels of ventral horn.
Input from vestibular nuclei.
Damage to MLF causes lack of coordination
of eye movements.
- intranuclear opthalmoplegia
damage to MLF
incoordination of eye movements,
esp medial- lateral
ipsilateral eye can’t move past
midline
Immediately surrounds the gray matter.
Ascends and descends, fibers vary in length.
Descending branches of large diameter
dorsal root primary afferents.
Descending branches of large diameter
dorsal root primary afferents.
ASCENDING:
Spinocerebellar:
-Large diameter 1’ afferents, unconscious proprioception, sensory,
intimate association with motor control.
-Medial division dorsal root
2 Neurons!
Dorsal spinocerebellar tract:
DSCT
Cuneocerebellar tract:
CCT
Ventral spinocerebellar tract:
VSCT
1’ lower extremity input
1’ cell body in DRG
1’ axons in fasciculus gracilis
2’ cell body in Clark’s nuclues
Uncrossed
Ipsilateral input to cerebellum
ICP
1’ upper extremity input
1’ cell body in DRG
1’ axons in fasciculus cuneatus
2’ cell body lat cuneate nucleus
Uncrossed
Ipsilateral input to cerebellum
ICP
1’ lower extremity input
1’ cell body in DRG
1’ axons in fasciculus gracilis
2’ cell body base of ventral horn
Crosses and recrosses
Primarily ipsilateral input to cerebellum
SCP
Ascending
SENSORY
Anterolateral Ascending:
Spinothalamic:
3 Neurons!
Raphe runs w/ ST (PAIN)
Spinoreticular
Spinotectal
Dorsolateral Ascending:
Dorsal column medial
leminiscus
3 Neurons!
F. gracilis – input from mid
thoracic and below
F. cuneatus – input from mid
thoracic and above
Lesions:
ST: Loss of Pain & Temp / 2 segments below lesion / CONTRA
DCML: Loss of discriminative touch, conscious proprioception & vibration /
Below level of lesion / IPSI if in SC & CONTRA if above nuc g/c
Consious awareness of pain and
temperature.
1’ input from small afferent fibers associated
with free nerve endings.
1’ cell body in DRG
Enters through the lateral division of the
dorsal root.
Ascend 1-2 segments in Lissauer’s tract.
2’ cell body in ipsilateral dorsal horn
Decussation in ventral white commissure
3’ thalamus (CONTRA)
Indirect transmission of pain.
Ascending reticular activation system and
level of consiousness.
Alternate route to cerebellum and
brainstem.
Conscious awareness of discriminative
touch, pressure, proprioception, vibration.
1’ input from large afferent fibers associated
with sensory receptors.
1’ cell body in DRG
Enters through the medial division of dorsal
horn
2’ cell body in cuneate or gracilis nucleus
Decussation in internal arcuate fibers of
medial leminiscus
3’ thalamus