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FasciculusGracilis: (T7down)present allthroughout thespinal cord
FasciculusCuneatus: (T6up)situated laterallyin the upperthoracic andcervicalsegments of the
cord
Septumseparates thesefasciculi
Sense musclespindles and
tendon organs
horn, internuncialneurons andanterior horncellsintersegmentalreflex
Long ascendingfibers: alsoinvolved inintersegmentalreflex but ascendas the fasciculusgracilis andcuneatus
Ipsilateralascent!!!
internal arcuatefibers, cross themedian plane at
the great sensorydecussation at
the inferior/caudal
half of themedulla)
Fibers ascend asthe MEDIALLEMNISCUS
PosteriorSpinocerebellar
UnconsciousMuscle JointSense
Feedback controlfor motorperformance
Musclespindles,
tendon organsand joint
receptors of thetrunk andlower limbs
Posterior rootganglion
in sacral, lumbar
and lowerthoracic levels
(axons enteringthe spinal cord
from the posteriorroots of the lower
lumbar andsacral segments
ascend in the
posterior whitecolumn until they
reach L3/L4,where they enter
the nucleusdorsalis)
Nucleus Dorsalis(ClarkesColumn)
Lamina VII
Axons enter thelateral whitecolumn and
ascendipsilaterally to the
medulla
--- NONE Cerebellarcortex via the
inferiorcerebellar
peduncles(terminate asmossy fibers)
Information isused by
cerebellar cortexin the
coordination oflimb movements
and maintenanceof posture
AnteriorSpinocerebellar
Double-crossingfibers
UnconsciousMuscle JointSense
Information fromskin and
Musclespindles,
tendon organs
and jointreceptors of the
upper and
Posterior rootganglion
in lumbar and
sacral segments
Nucleus Dorsalis(ClarkesColumn)
Majority of axons:cross to opposite
--- Axons of N2 crossto contralateral
side at the
nucleus dorsalisat the same level
of entry
Cerebellarcortex via the
superior
cerebellarpeduncles
(terminate as
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Comparatorbetween action ofinhibitory &excitatory inputsto spinal motorneurons andinterneurons
superficial fascia
Providecerebellum withinformation aboutthe state of motorneuron excitation
lower limbs,skin and
superficialfascia
side and ascendcontralaterally
BUT these axonscross back in the
cerebellum
Minority of axons:ascend
ipsilaterally in thelateral white
column
The same fiberscross back to
original side in thecerebellum
mossy fibers)
Cuneocerebellar
Fibers of thefasciculus
cuneatus thatproceed to thecerebelluminstead of BA 312
UnconsciousMuscle JointSense
Musclespindles,
tendon organsand joint
receptors of theupper limband upper
part of thorax
Posterior rootganglion
in cervical andupper thoracic
region
Lateral/AccessoryNucleus
Cuneatus ofmedulla
Axons leave forthe cerebellum as
the posteriorexternal arcuate
fibers
--- NONE Cerebellarcortex via the
inferiorcerebellar
peduncles(terminate asmossy fibers)
Spinotectal Afferentinformation forspinovisual
reflexes bringsabout movementof eyes and headtoward source ofstimulation
Posterior rootganglion
Unknown
But fibers cross
median plane atthe same level ofentry
--- N2 fibers crossthe median plane
SuperiorColliculus of
Midbrain
Spinoreticular Influences level ofconsciousness
Responsible forspread of painsensationthroughout brain
Posterior rootganglion
Unknown
Axons ascend inlateral white
columns mixedwith the spinal
lemniscus
Most fibersremain
UNCROSSED
ReticularFormation in themedulla, ponsand midbrain
Spino-olivary Information fromcutaneous andproprioceptiveorgans
Posterior rootganglion
Unknown but inposterior gray
column
Axons ascend inthe contralateral
anterolateral
white column ofthe cord
Inferior OlivaryNuclei (Medulla)
Axons crossmidline back
toward inferiorcerebellar
peduncle onsame side of
entry into the cord
N2 fibers crossthe midline
N3 fibers crossmidline back
toward originalside
Cerebellarcortex via the
inferiorcerebellarpeduncles
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VisceralSensory
Information fromthorax andabdomen
Visceral pain:Caused by
ischemia,chemicaldamage, spasmof smooth muscleand distension
Pain andstretch
receptorendings in
viscera
Visceralafferent fibersusually takepart in reflex
activity
Posterior rootganglion
N2 in posterior orlateral gray
columns
Axons arebelieved to join
the spinothalamictracts as they
ascend
Ventralposterolateralnucleus of the
thalamus
SomestheticArea (BA 312) ofcerebral cortex(post-central
gyrus)
NOTES:
In the thalamus, the lateral spinothalamic tract is joined by the posterior white
column pathway (fasciculus gracilis and cuneatus) which mediates position-vibration sensem simple touch and conscious proprioception
FIBERS for position-vibration sense will NOT GO TO GRAY MATTER butwill terminate in the posterior columns (fasciculus gracilis and cuneatus)
The periaqueductal gray area is where pain is masked (area of painmodulation)
LESIONSMIDLINE LESIONS in the SPINOTHALAMIC TRACTS cause BILATERALDEFICITS because fibers cross at the ventral gray commissure!!! Cervical
fibers are in the medial aspect while sacral fibers are in the most lateral
aspect of the tracts so upper body is usually affected by these lesions
Before entry to the thalamus, the MEDIAL LEMNISCUS and the LATERALSPINOTHALAMIC TRACT are almost joined. It is only in the VPLN thatthere is COMPLETE FUSION OF THESE TWO TRACTS!!!
CEREBELLAR LESIONS always manifest on the ipsilateral side!!!
Lesions at POSTERIOR FOSSA LEVEL: ipsilateral head and contralateral
body deficits loss of pain and temperature sensations!
THALAMIC SYNDROME: Loss of all modalities of sensation on thecontralesional side!!!
General Somatosensory System: Sensory tracts for anterior part of the faceAscending Tract Sensation
ConveyedReceptor N1 N2 N3 Decussation(s) Destination (N4)
From CNV1,CNV2, CNV3 ofTrigeminalNerve
Pain &temperature fromthe anterior partof the head
Free nerveendings
IpsilateralSemilunar
(Gasserian)Ganglion
Ipsilateral MainSensory Nucleusof the 5
thcranial
nerve (sensorynucleus of the
trigeminal)
Ventralposteromedialnucleus of the
thalamus
SomestheticArea (BA 312) ofcerebral cortex(post-central
gyrus)
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Direct Activation Pathway: Motor tracts for the initiation and control of voluntary muscle activity Pyramidal TractsDescending
TractMovement Controlled N1
(Cerebral Cortex)N2
(Spinal Cord)N3
(Lower MotorNeuron)
Decussation(s) Branches
CorticospinalTract
Voluntary, discrete &skilled movements,
especially those of thedistal part of the limbs
Majority of fibers aremyelinated and arerelatively SMALL, SLOW-CONDUCTING fibers
Form the pathway that
confers speed and agilityto voluntary movements used in performingrapid, skilled movements
Pyramidal (BETZ)cells in the 5
thlayer
of the cortex in BA4
Fiber origins:1/3: from BA 41/3: from BA 61/3: from BA 312
Descending fibersconverge on the
corona radiata
Posterior limbofinternal capsule
Middle 3/5 of basispedunculi of the
midbrain
Tract is broken inthe pons by the
transversepontocerebellar
fibers
Fibers regroup inthe anterior of the
medulla as thepyramids
2/3 of fibers cross
midline at thedecussation of
pyramids and enterthe lateral whitecolumns to form
lateralcorticospinal tract
Internuncialneurons
Alpha motor andGamma motor
neurons in anteriorhorn cells
Largestcorticospinal fibers
can synapsedirectly with themotor neurons
Act on all motorneuron pools but
especially on lateralportions of theventral horns
(which then controlthe distal muscles
of the arm andhand)
Fibers ventralhorn cells
via glutamate(excitatory)
But ventral horncell axons
muscle fibers viaACh
Junction of themedulla and spinal
cord at thedecussation of the
pyramids
Lesion abovedecussation
contralateral deficit
Lesion below
decussation ipsilateral deficit
Anteriorcorticospinal tract(those uncrossed at
the pyramidaldecussation) cross
over at the level ofdestination
(1) Early fibers thatreturn to the
cortex to inhibitactivity in theadjacent corticalregions
(2) Branches to thecaudate andlentiform nuclei,red nuclei, and
the olivary nucleiand the reticularformation keep thesubcorticalregions informedabout corticalmotor activity
Once alerted,subcortical regions
can send their ownnervous sinals tothe alpha andgamma motorneurons by otherdescendingpathways
CorticobulbarTract
Innervate voluntarymuscles of the larynx,pharynx, etc
Supranuclear fibers
occupy a more
Internuncialneurons
Brainstem motornuclei of cranial
nerves
Same level as exit
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Indirect Activation Pathway: Motor tracts for involuntary muscle control of posture, coordination and equilibrium Extrapyramidal TractsDescending
TractMovement Controlled N1 N2
(Spinal Cord)N3
(Lower MotorNeuron)
Decussation(s) Branches
Medial Indirect Activation Pathways
MedullaryReticulospinalTracts
Depends ondescendingstimuation formsupretentorialmotor structures
Inhibition of extensormotor neurons
Excitation of flexors
Inhibition of tendonreflexes
Hypothalamus controlssympathetic & SACRAL
parasympathetic outflows
Inhibitory Area ofthe ReticularFormation in the
Ventromedial Partof the Caudal
Medulla(lower medulla)
descend in lateralwhite column
Medial interneurons Posterolateral partof anterior hornalpha and gamma
motor neurons
Crosses over atvarious levels Give off multiplebranches as theydescend
TectospinalTracts
Reflex posturalmovements in responseto visual stimuli
Superior Colliculusof Midbrain
cross midline soonafter origin
descends throughthe anterior white
columns close toanterior median
fissure
does not extendbelow the cervical
levels
Internuncialneurons in anteriorgray column in the
upper cervicalsegments
Anteromedialportion of anteriorhorn on both alphaand gamma motor
neurons
Cross midline soonafter origin
?
VestibulospinalTracts
Excitation of extensormotor neurons
Inhibit flexors
Maintains balance
Lateral VestibularNuclei
(beneath the floorof the 4th
ventricle)
descendsuncrossed through
medulla in theanterior white
column
Medial interneuronsof the anterior gray
column
Anteromedialportion of anterior
horn on both alphaand gamma motorneurons
Most descenduncrossed
Receive input frominner ear through
vestibular nerveand from thecerebellum
Lateral Indirect Activation Pathways
PontineReticulospinalTracts
Excitation of extensormotor neurons
ExcitatoryDorsolateral
Reticular Formation
Lateralinterneurons
Anteromedialportion of anteriorhorn on both alpha
Descenduncrossed in themedial part of the
Multiple branchesas they descend
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Cerebellar Afferent Fibers
Cerebellar Afferent Fibers from the Cortex- Important in control of voluntary movements- Information on initiation of movement transmitted from cerebral cortex to the cerebellum so that movement can be monitored and
muscle adjustments can be made
Pathway Origin Cerebellar
Afferent fibers
(from the
cortex)
Descends
through
Terminates where? Further pathway Function
Corticopontocerebellar
Pathway
Nerve cells in thefrontal, parietal,
temporal, & occipital
lobes of cerebral cortex
Corticopontinefibers
coronaradiata
and
internal
capsule
pontine nuclei andmossy fibers to
cerebellar cortex
Pontine nuclei give rise totransverse fibers of the pons
(will cross the midline and
enter opposite cerebellar
hemisphere as the middle
cerebellar peduncle)
Converyscontrol form
cerebral cortex
Cerebro-
olivocerebellar Pathway
Nerve cells in the
frontal, parietal,temporal, & occipital
lobes of cerebral cortex
Cortico-olivary
fibers
corona
radiataand
internal
capsule
Terminate
bilaterally on theinferior olivary
nuclei
Inferior olivarynuclei give rise
to fibers that will cross themidline & enter opposite
cerebellar hemisphere
through inferior cerebellar
peduncle (these fibers
terminate as climbing fibers in
the cerebellar cortex)
Converys
control formcerebral cortex
Cerebroretic
ulocerebellarPathway
Nerve cells from
sensorimotor areas ofcerebral cortex
Corticoreticula
r fibers
Reticular formation
on the same &opposite side in the
pons and medulla
Cell in reticular formation give
rise to reticulocerebellarfibers and will enter the
cerebellar hemisphere on the
same side through inferior
and middle cerebellar
peduncles
Converys
control formcerebral cortex