pyramidal 2012 pdf
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OB J ECTIVES :
1. Enumerate the tracts that constitute thepyramidal system.
2. Trace the pathway of the pyramidal tracts.
3. Locate the position of the lateral and anteriorcorticospinal tracts in a section of thespinal cord.
4. Differentiate an upper motor vs. a lowermotor neuron lesion.
5. Describe briefly the other descending tracts.
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MOTOR SYSTEM
1.PYRAMIDAL SYSTEM= the primary control of voluntary movement thru:a. corticospinalb. corticobulbar pathways
2. EXTRAPYRAMIDAL SYSTEMa. Basal Ganglia (nuclei)b. Cerebellum
supporting role in the production of well-coordinated movements
= influence lower motor neurons indirectlythrough modulation of the cerebral cortex &brainstem
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Cerebral cortexAssociation areas Premotor areas Motor area
(Desire to move) (program) (commands)
BASAL GANGLIAInitiation & Postural Adjustment
Posterior LobeCEREBELLUM
(Coordination) Ant. Lobe FNL BRAINSTEM CENTERS (Supraspinal Reflex Activity)
Vestibular Receptors (Equilibrium)
Intrafusal Stretch Receptors Extrafusal Contractile Fibers
VOLUNTARY MUSCLES
LOWER MOTOR NEURONS (Commands)
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TRACT
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PYRA MIDA L TRA CT
• longest & largestdescending fiber tract(hu m an CNS)
• concerned with voluntary,discrete, skilledmovements; control ofmuscles involved inspeech & vocalization
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• passthrough themedullarypyramids
PYRA MIDA L TRA CT
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PYRA MIDA L TRA CT
• CORTICOSPINAL TRACT Lateral CST
Anterior or Ventral CST
• CORTICOBULBAR TRACT
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PYRA MIDA L TRA CT
Fibers arise from the following areas:
1/3 of axons – precentral gyrus(BA 4) Primary Motor Cortex
* 10% or 3% of CST- Pyramidal Cells of Betz
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ANTERIORHORN CELLS
of BETZ
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PYRA MIDA L TRA CT
Fibers arise from the following areas:
1/3 of axons – precentral gyrus(BA 4) Primary Motor Cortex
1/3 of axons – postcentral gyrus (BA 3,1,2) Primary Sensory Cortex
1/3 of axons – Premotor/ SecondaryMotor Cortex (BA 6 )& some from frontaleye fields (BA 8)
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SENSORIMOTOR CORTEX
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MOTOR HOMUNCUL US
the body has asomatotopicrepresentation
on the PRIMARYMOTOR andPREMOTORCORTEX
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SUPPL EMENTARY MOTOR A REA
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Desc end ing Pathw ays :A natom ical Organizat ion
SERIES OF NEURONS:• 1ST ORDER NEURON
- cel l body in cerebral cor tex
• 2ND ORDER NEURON- in ternunc ial neuron in an te r io r g ray co lumn of SC- shor t axon
• 3RD ORDER NEURON (LMN or
FINAL COMMON PATHWAY)- an ter io r g ray c o lum n o f SC- axon inn ervates skeleta l m us cles throug h anter ior
roo t o f sp ina l nerve
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Desc end ing Pathw ays :A natom ical Organizat ion
SERIES OF NEURONS:• 1ST ORDER NEURON
- ce l l bod y in cerebral cor tex • 2ND ORDER NEURON
- in ternunc ial neuron in an ter io r g ray co lum n of SC- shor t axon
• 3RD ORDER NEURON (LMN or FINAL COMMONPATHWAY)
- an ter io r g ray c o lum n of SC- axon inn ervates skeleta l m us cles throu gh anter ior
root of s pinal nerve
* Some axons of 1 st order neurons terminate directly on 3 rd
order neurons (as in reflex arcs)
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PYRA MIDA L TRA CT
• CORTICOSPINAL TRACT Lateral
Anterior or Ventral CST
• CORTICOBULBAR TRACT
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•
CEREBRAL CORTEX (or ig in)- 1 s t o rde r neuron
• CORONA RADIATA
• INTERNAL CAPSULE
(po s ter ior l imb )
• CEREBRAL PEDUNCLES(mid d le 3/5)
• PONS (break up in to fasc ic les)
• PYRAMIDS (up per m edul la)
• PYRAMIDAL DECUSSATION(caudal m edul la)
CORTICOSPINALTRACT
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• CEREBRAL CORTEX (or ig in)- 1 s t o rde r neuron
• CORONA RADIATA
• INTERNAL CAPSULE (po s ter ior l imb )
• CEREBRAL PEDUNCLES(mid d le 3/5)
• PONS (break up in to fasc ic les)
• PYRAMIDS (up per m edul la)
• PYRAMIDAL DECUSSATION(caudal m edul la)
CORTICOSPINALTRACT
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PYRA MIDA L TRA CT
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• 75 - 90%crossed LATERAL CST
– term inate: ant . grayco lum n of a ll sp ina lcord segments
• 10 - 15%uncrossed ANTERIOR CST
– eventu al ly crossbefore term inat ingon an ter io r horncel ls in cervical &upper thorac icreg ions
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Term inat ion ofPYRA MIDA L TRA CT FIB ERS
Cervical spinal cord level 55%Thoracic level 20%Lumbar / Sacral level 25%
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The cortisospinal tracts are NOT thesole pathway for serving voluntarymovement rather they form thepathway that confers SPEED and
AGILITY to voluntary movements. Theyare believed to control the prime movermuscles while the other descending
tracts are important in controllingsimple basic movements.
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UPPER MOTOR NEURON VS.
L OWER MOTOR NEURON PA RA L YSIS
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UMN
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LMN
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POINTS TO REMEMB ER:
• The pyramidal tract is used commonly byphysicians and refer SPECIFICALLY to theCORTICOSPINAL TRACT.
• The pyramidal tracts normally tend to INCREASE
muscle tone while the extrapyramidal tractsINHIBIT muscle tone.
• In clinical practice, it is rare to have an organiclesion that is restricted only to the pyramidal oronly to the extrapyramidal tracts. Usually BOTHsets of tracts are affected to a variable extentproducing both groups of clinical signs.
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UPPER MOTORNEURON
Paresis
NO muscle atrophy
Spasticity
Hyperreflexia
Clonus
Babinski
loss of certain superficialreflexes:
a. Superficial abdominalb. Cremasteric reflex
LOWER MOTORNEURON
Complete paralysis
WITH muscle atrophy
Flaccidity
Arreflexia
NO clonus
NO Babinski
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UPPER MOTORNEURON
Paresis
NO muscle atrophy
Spasticity
Hyperreflexia
Clonus
Babinski (Extensor Plantar Reflex)
loss of certain superficialreflexes:
a. Superficial abdominalb. Cremasteric reflex
LOWER MOTORNEURON
Complete paralysis
WITH muscle atrophy
Flaccidity
Arreflexia
NO clonus
NO Babinski
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CORTICOB ULB A R TRA CT
Arise from FACE region of primarymotor cortex (BA 4), BA 6 andBA 3,1 & 2
Project : motor nuclei of CNs
III,IV,V,VI,VII,IX,X,XI & XII: parts of reticular formation
(co r t icoret icular f ibers)in pons & medulla
: sensory relay nuclei (gracil is ,cun eatus , senso ry t r igeminalnuc le i, & n ucleus o f sol i taryfasciculus)
Projections are BILATERAL – innervationsfrom BOTH contra & ipsilateral cortex
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CORTICOB ULB A R TRA CT
Project : motor nuclei of CNsIII,IV,V,VI,VII,IX,X,XI & XII
: parts of reticular formation(co r t icoret icular f ibers)in pons & medulla
: sensory relay nuclei (gracil is ,cu neatus , senso ry t r igeminalnuc le i, & n ucleus o f sol i taryfasciculus)
Projections are BILATERAL :
innervations from BOTHcontra & ipsilateral cortex
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The shaded areas of the face show the distribution of facial musclesparalyzed after a supranuclear lesion of the corticobulbar tract &
after a lower motor neuron lesion of the facial nerve
FACIALMOTOR
NUCLEUS
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PERIPHERAL FACIALPARALYSIS (BELL’S PALSY)
* LMN LESION
FACIALMOTOR
NUCLEUS
BELL’S PALSY
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BELL’S PALSY (Perip h eral Facial Paralys is)
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PRA CTICE # 1 :
• CASE SCENARIO: A post-stroke patientwith inability to move the left half of theface but can still wrinkle botheyebrows.
• TYPE OF LESION?• WHERE IS THE LESION?
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PRA CTICE # 2 :
• CASE SCENARIO: A patient uponwaking up in the morning is unable tomove the entire RIGHT half of his face.
• PHHx: had chicken pox 2 weeks prior• TYPE OF LESION?• DIAGNOSIS?• WHERE IS THE LESION?• PROGNOSIS?
FACIAL
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CENTRAL FACIALPARALYSIS
* UMN LESION
PERIPHERAL FACIALPARALYSIS
(BELL’S PALSY) * LMN LESION
FACIALMOTOR
NUCLEUS
HYPOGLOSSAL
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HYPOGLOSSALNUCLEUS
Corticobulbarprojectionsare largelyCONTRALATERAL
LEFT RIGHT
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PRA CTICE # 3 :
• CASE SCENARIO: The resident notedthat the tongue of a post-stroke patientis atrophied and deviated to the LEFT.
• TYPE OF LESION?• WHERE IS THE LESION?
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PRA CTICE # 4 :
• CASE SCENARIO: The resident notedthat the tongue of a post-stroke patientis NOT atrophied and deviated to theLEFT.
• TYPE OF LESION?• WHERE IS THE LESION?
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OTHER DESCENDING TRA CTSI. MIDBRAINA. Tectospinal and TectobulbarB. Rubrospinal tractC. Interstitiospinal tract
II. PONS/MEDULLAA. Vestibulospinal tracts
1. LATERAL VESTIBULOSPINAL2. MEDIAL VESTIBULOSPINAL
B. Reticulospinal tracts1. PONTINE RETICULOSPINAL TRACT2. MEDULLARY RETICULOSPINAL TRACT
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OTHER DESCENDING TRA CTS
I. MIDBRAINA. Tectospinal and
Tectobulbar
ORIGIN : superior colliculus
FIBERS : cross in dorsal tegmentaldecussation (midbrain)
- incorporated > MLF(m edullary level)
OTHER DESCENDING TRA CTS:
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Tecto sp inal and Tecto bu lbar
TERMINATE: anterior gray column (Rexed lam in ae VI,VII & VIII)in upper cervical segmentsof the spinal cord
FUNCTION: mediate reflex posturalmovements in responseto visual & auditory stimuli(head turning and eye
movements)
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OTHER DESCENDING
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O SC GTRACTS: MIDB RA IN
B. Rubrospinal tractORIGIN : red nucleus (level of
sup erio r co l l i cu lus )
FIBERS : cross immediately inthe ventral tegmentaldecussation > descenddown (bra ins tem) > enterlateral funiculus of SC
TERMINATE: internuncialneurons (anterior graycolumn)
FUNCTION: influence tonecontrol in flexor musclegroups
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OTHER DESCENDING TRA CTS: MIDB RA IN
C. Interstitiospinal tract- or ig in : interstitialnucleus of CAJAL- uncrossed
- forms part of MLF- terminate: anteriorhorn of upper cervicallevels of the SC inlaminae VII and VIII- function: modulatesreflex postural movementsin response to visual &vestibular stimuli
OTHERDESCENDINGTRA CTS
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OTHER DESCENDING TRA CTS
II. PONS/MEDULLAA. Vestibulospinal tract
1.LATERAL VESTIBULOSPINALORIGIN: lateral vestibular nucleus
> descends in anterolateral funiculusand terminates in Rexed laminae VII& VIII on alpha and gamma motorneurons from cervical & lumbosacrallevels
AFFERENTS: vestibular nerve andcerebellum
FUNCTION: for maintenance of uprightposture and balance (excitesextensor motor neurons innervatingneck, back, forelimb and hindlimbmuscles)
*UNCROSSED
OTHERDESCENDINGTRA CTS
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OTHER DESCENDING TRA CTS
2. MEDIAL VESTIBULOSOPINAL
ORIGIN : medial vestibular nucleus >
descends in MLF > anterior funiculusof SC (as far as m idtho racic level )
terminates in same laminae as lateral
vestibulospinal tract (Rexed laminaeVII & VIII)
AFFERENTS : primary vestibular& cerebellar
FUNCTION : maintains upright posture(exc i t es neck & backmo tor neurons )
* BOTH CROSSED A ND UNCROSSED
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OTHERDESCENDINGTRA CTS
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OTHER DESCENDING TRA CTS
B. Reticulospinal tracts
1. PONTINE (MEDIAL)RETICULOSPINAL TRACT
- almost entirely IPSILATERAL- descends chiefly in anterior
funiculus of SC (all cord levels,laminae VII & VIII)
- facilitatory to extensormotor neurons
2. MEDULLARY (LATERAL)RETICULOSPINAL TRACT
- fibers project BILATERALLY
to spinal levels- descend both IPSI/CONTRAin lateral funiculus of SC (allcord levels, laminae VII & IX)
- inhibitory to extensormotor neurons
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OTHERDESCENDINGTRA CTS
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OTHER DESCENDING TRA CTS
Medullary ReticulospinalTract :
- provide a pathway bywhich the hypothalamuscan control thesympathetic outflow &sacral parasympatheticoutflow
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Thank you
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REFERENCES :
1. Gilman and Newman. Manter andGatz’s Essentials of ClinicalNeuroanatomy and Neurophysiology,10 th ed., 2003
2. Snell. Clinical Neuroanatomy forMedical Students, 7 th ed., 2010
3. Lansang et al., Modules inNeuroanatomy