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Descending Tracts
(Motor or Efferent Tracts)
1)Pyramidal (Corticospinal) Tracts
2)Extrapyramidal tracts
Specific Learning Objectives
At the end of session the students should be
able to :
•Enumerate the descending tracts.
•Des...
1)Pyramidal (Corticospinal) Tracts :
i)Lateral Corticospinal tract
(Crossed Pyramidal tract).
ii)Anterior Corticospinal tr...
2)Extrapyramidal tracts:
i)Rubrospinal tract
ii)Tectospinal & Tectobulbar tracts
iii)Reticulospinal Tracts:
a)Medial or Po...
Corticospinal tracts –
Pyramidal tracts
and corticobulbar tract
Introduction:
Longest tract –
Extends – Motor cortex to last segment of
spinal cord.
Present only in higher vertebrates & ...
Composition:
Tracts on each side – One million nerve fibres.
Myelinated -60%,unmyelinated 40%.
Most of myelinated fibres a...
Origin:-
1.Primary motor cortex (area 4 ) – 30% (3% -
large pyramidal cells- Betz cells )
2.Premotor cortex (area 6 ) & ar...
Most impressive fibres from Giant Pyramidal
cells called as Betz cells (number 34,000)
i.e only 3% of the total fibres (my...
Motor cortex
Internal capsule
Ant.
Post.
C.N.
Thala.
Mid brain
Pons
Medulla
SP.Cord
Corona
radiata
Post limb
Cerebral
pedu...
Motor cortex
Internal capsule
Corticobulbar fibers
Decussasion of pyramids
Ant. corticospinal
Lat. Cortico spinal
Ant. Mot...
Inputs of motor cortex :-
• Somatosensory, visual and auditory cortex
• Motor cortex of opposite side
•Thalamic sensory nu...
Course :-
Genu & post limb of Internal capsule
Middle 3/5 of crus cerebri – face medially & legs
laterally, fibers to III,...
Fibres in 1)Primary motor area(Precentral
gyrus) are arranged Upside down.
Toes –At the top,
Trunk – Middle &
Head - Below...
3)Internal capsule:
Corticonuclear (corticobulbar) fibres – genu
Corticospinal fibres - Ant 2/3rd
of post limb.
Plane of f...
4)Midbrain:
Corticobulbar fibres end on motor nuclei of
III & IV Cranial nerves of same & opposite
side.
Remaining fibres ...
5)Pons:
Pyramidal fibres - most ventral part in front of
Trapezium.
Tract broken up into scattered bundles by
Nuclei Ponti...
6)Medulla:
Upper medulla: Scattered corticospinal fibres
reunite, occupy most ventral part forms a
bulge - Pyramid.
Lower ...
7)Spinal cord –
It extends throughout the cord & at each
spinal segment,some fibres leave the tract,
turn inward & end rou...
Fibers ending in each segment turn medially
Directly on α- motor
neurons -10%
Innervating distal
groups of limb muscles
Th...
Termination :-
Cervical region – 55%
Thoracic region – 20%
Lumbosacral region – 25%
Direct / ventral / uncrossed corticospinal tract
-15 to 20 % fibers without crossing in medulla
-directly descend in ant. ...
Significance –
Lateral & Anterior Corticospinal Tracts
indicates that certain muscles in the
body must have bilateral cont...
To cerebellum
Collaterals of corticospinal tract
• To cortex for lat inhibition –
sharpness of boundaries.
• To
Red n. → r...
Corticobulbar pathways :-
Formed by the fibers leaving corticospinal tract in
the brain stem and ending in the nuclei of t...
Functions of pyramidal tracts:-
1. Lat.CST –Controls voluntary, rapid, skillful
movements of fingers & hands of
contralate...
3.Forms part of pathway for superficial
reflexes such as cremasteric,abdominal &
plantar reflex.
4.Modify sensory input
So...
5.Sensory motor co-ordination –
Somatosensory feedback to the motor
cortex helps to control the precision of
muscle contra...
6.Most of the CST fibres end on α motor
neurons.
But some fibres end on γ motor neurons.They
a)help in adjusting the lengt...
7.Corticobulbar /corticonuclear tracts are
responsible for voluntary control of muscles of
(head & neck) i.e larynx, phary...
Ant. CST–
Supplementary motor area thr Ant CST
controls bilateral postural movements.
Along with Premotor area provides fi...
Applied aspects :-
1.Phylogenetically, ant. CST is older
Lat. CST - in human beings and few vertebrates
2.Myelination is c...
Damage to motor control system - Stroke or
apoplexy (sudden attack of paralysis).
Paralysis - (Loss of power of muscle gro...
Damage to motor cortex alone - Hypotonia.
Cause -Primary motor cortex exerts
continous tonic stimulatory effect on motor
n...
Accessory pathways normally inhibit
Vestibular & Reticular brain stem nuclei.
When the inhibition is gone they become
spon...
Monoplegia - primary motor cortex
hemiplegia - internal capsule
quadriplegia or paraplegia – brain stem
paraplegia - spina...
Lower motor neuron lesion –
Results also in Paralysis but it is Flaccid
paralysis.
Clinical picture in Pyramidal tract les...
Upper motor neuron lesion :-
•Increased muscle tone - Hypertonia.
•Resistance to passive movements -Rigidity.
Rigidity - c...
•Superficial reflexes are absent.
Plantar reflex →Babinski’s sign positive.
•Deep /tendon reflexes are Exaggerated.
•Clonu...
Toes down
(flexion)
Fanning
of toes
Normal plantar response Extensor plantar response
(Babinski sign)
Lower motor neuron lesion :
•Decreased muscle tone – Hypotonia.
•No rigidity but flaccid paralysis.
• Atrophy prominent (m...
•Individual muscles of same side are
affected.e.g:Poliomyletis.
•Trophic changes are seen.
Lesion to cranial nerve nuclei(LMN) –
Bulbar palsy.
Lesion to Corticonuclear tracts – (UMN)
Pseudobulbar palsy →Weakness o...
LMNP UMNP
Site of
lesion
α- or cranial
motor neuron
Neurons forming
descending tracts
Muscles
Involved
-single muscle on
t...
Planter reflex – lost only if
S1 is affected
LMNP UMNP
Tendon jerks – lost Exaggerated,
clonus+
Muscle atrophy – marked wa...
Motor area for face
Supranuclear lesion (UMN)
Facial nerve n.
Facial paralysis
Facial nerve
Corticobulbar tract
Pyramidal tract by Sunita.M.Tiwale,Prof. Dept of physiology,D.Y.Patil Medical college, Kolhapur
Pyramidal tract by Sunita.M.Tiwale,Prof. Dept of physiology,D.Y.Patil Medical college, Kolhapur
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Pyramidal tract by Sunita.M.Tiwale,Prof. Dept of physiology,D.Y.Patil Medical college, Kolhapur

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Specific Learning Objectives:
At the end of session the students should be able to :
Enumerate the descending tracts.
Describe the origin, course, termination, collaterals of Pyramidal tract.
Describe the functions of the pyramidal tract.


Veröffentlicht in: Gesundheit & Medizin
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Pyramidal tract by Sunita.M.Tiwale,Prof. Dept of physiology,D.Y.Patil Medical college, Kolhapur

  1. 1. Descending Tracts (Motor or Efferent Tracts) 1)Pyramidal (Corticospinal) Tracts 2)Extrapyramidal tracts
  2. 2. Specific Learning Objectives At the end of session the students should be able to : •Enumerate the descending tracts. •Describe the origin, course, termination, collaterals of Pyramidal tract. •Describe the functions of the pyramidal tract.
  3. 3. 1)Pyramidal (Corticospinal) Tracts : i)Lateral Corticospinal tract (Crossed Pyramidal tract). ii)Anterior Corticospinal tract (Uncrossed Pyramidal tract).
  4. 4. 2)Extrapyramidal tracts: i)Rubrospinal tract ii)Tectospinal & Tectobulbar tracts iii)Reticulospinal Tracts: a)Medial or Pontine b)Lateral or Medullary iv)Vestibulospinal tract v)Medial longitudinal fasciculus
  5. 5. Corticospinal tracts – Pyramidal tracts and corticobulbar tract
  6. 6. Introduction: Longest tract – Extends – Motor cortex to last segment of spinal cord. Present only in higher vertebrates & man where cerebrum has developed. So we are superior to other animals.
  7. 7. Composition: Tracts on each side – One million nerve fibres. Myelinated -60%,unmyelinated 40%. Most of myelinated fibres are of small diameter so the tract is slow conducting.
  8. 8. Origin:- 1.Primary motor cortex (area 4 ) – 30% (3% - large pyramidal cells- Betz cells ) 2.Premotor cortex (area 6 ) & area 8 - 30% 3.Somatosensory cortex (SI & SII) (3,1,2 & 40) parietal lobe association areas (5,7) – 40%
  9. 9. Most impressive fibres from Giant Pyramidal cells called as Betz cells (number 34,000) i.e only 3% of the total fibres (myelinated but of large diameter) so (fast conducting). Remaining 97 % fibres of small diameter conduct i) background tonic signals to the motor areas of the cord, ii)Feedback signals from cortex to incoming sensory signals to control their intensities.
  10. 10. Motor cortex Internal capsule Ant. Post. C.N. Thala. Mid brain Pons Medulla SP.Cord Corona radiata Post limb Cerebral peduncles Long. fasciculi Pyramids decussation Lat. CST Ant.CST III, IV V, VI, VII IX,XI,XII
  11. 11. Motor cortex Internal capsule Corticobulbar fibers Decussasion of pyramids Ant. corticospinal Lat. Cortico spinal Ant. Motor fibers
  12. 12. Inputs of motor cortex :- • Somatosensory, visual and auditory cortex • Motor cortex of opposite side •Thalamic sensory nuclei • Basal ganglia & cerebellum through thalamus • Intralaminar nuclei
  13. 13. Course :- Genu & post limb of Internal capsule Middle 3/5 of crus cerebri – face medially & legs laterally, fibers to III, IV Longitudinal fasciculi in pons, fibers to V, VI, VII Pyramids in upper part of medulla, fibers to IX, XI, XII Corona radiata in subcortical areas 80% cross Lat. CST 20% - uncrossed In lower part of medulla Ant. CST In the spinal cord
  14. 14. Fibres in 1)Primary motor area(Precentral gyrus) are arranged Upside down. Toes –At the top, Trunk – Middle & Head - Below. Motor homonculus. 2)Corona radiata – Fan shaped. Projection type of fibres.
  15. 15. 3)Internal capsule: Corticonuclear (corticobulbar) fibres – genu Corticospinal fibres - Ant 2/3rd of post limb. Plane of fibres rotates from coronal to right angle so Head fibres come ant & med while Leg fibres lie posterior & lateral.
  16. 16. 4)Midbrain: Corticobulbar fibres end on motor nuclei of III & IV Cranial nerves of same & opposite side. Remaining fibres occupy middle 3/5th of the Crus cerebri or Cerebral peduncle. Medial 1/5th carries Fronto pontine & lateral 1/5th Temporo pontine fibres.
  17. 17. 5)Pons: Pyramidal fibres - most ventral part in front of Trapezium. Tract broken up into scattered bundles by Nuclei Pontis & crossing fibres of Middle cerebellar pedencle.
  18. 18. 6)Medulla: Upper medulla: Scattered corticospinal fibres reunite, occupy most ventral part forms a bulge - Pyramid. Lower medulla: 80 to 85 % fibres decussate, cross to opposite side enter lateral white column & descend down as Lateral Corticospinal Tract.
  19. 19. 7)Spinal cord – It extends throughout the cord & at each spinal segment,some fibres leave the tract, turn inward & end round the Ant horn cells(motor neurons) either directly or through interneurons. Excites flexor motor neurons & inhibits extensor motor neurons of digits. So plantar reflex is Plantar flexion response.
  20. 20. Fibers ending in each segment turn medially Directly on α- motor neurons -10% Innervating distal groups of limb muscles Through interneurons Fibers arising from somatosensory cortex end on Dorsal horn cells
  21. 21. Termination :- Cervical region – 55% Thoracic region – 20% Lumbosacral region – 25%
  22. 22. Direct / ventral / uncrossed corticospinal tract -15 to 20 % fibers without crossing in medulla -directly descend in ant. white column near median fissure as Anterior Corticospinal Tract. -Origin - supplementary motor areas - Extend up to mid thoracic region -Termination - on the interneurons of the same side or of the opposite side - Function - Control of axial muscles on both sides.
  23. 23. Significance – Lateral & Anterior Corticospinal Tracts indicates that certain muscles in the body must have bilateral control from both cerebral hemisphere e.g – Respiratory muscles.
  24. 24. To cerebellum Collaterals of corticospinal tract • To cortex for lat inhibition – sharpness of boundaries. • To Red n. → rubrospinal Reticular n. → reticulospinal Vestibular n. → vestibulospinal Pontine n. → pontocerebellar Olivary n. → olivocerebellar Caudate and lentiform nuclei,
  25. 25. Corticobulbar pathways :- Formed by the fibers leaving corticospinal tract in the brain stem and ending in the nuclei of the motor cranial nerves on opposite side Mid brain – III, IV Pons – V, VI, VII, VIII Medulla – IX, X, XI, XII Functions – control vol. movement of muscles of larynx, pharynx, palate, face, jaw and eyes.
  26. 26. Functions of pyramidal tracts:- 1. Lat.CST –Controls voluntary, rapid, skillful movements of fingers & hands of contralateral side. Signals coming from Primary motor cortex excites a pattern of muscle activity. 2.Premotor area – develops a motor image of total muscle movement to be performed. Then sends signals to primary motor area to exite the pattern of muscle activity.
  27. 27. 3.Forms part of pathway for superficial reflexes such as cremasteric,abdominal & plantar reflex. 4.Modify sensory input Some of the fibres of the tract end presynaptically on axon terminals of afferent neurons or dendrites or cell bodies & thus affect afferent system.
  28. 28. 5.Sensory motor co-ordination – Somatosensory feedback to the motor cortex helps to control the precision of muscle contraction.
  29. 29. 6.Most of the CST fibres end on α motor neurons. But some fibres end on γ motor neurons.They a)help in adjusting the length & excitation of the extrafusal fibres & b)also saves the energy of brain for further stimulation of extrafusal fibres for damping of movement.
  30. 30. 7.Corticobulbar /corticonuclear tracts are responsible for voluntary control of muscles of (head & neck) i.e larynx, pharynx, palate, upper & lower jaw, eye etc.
  31. 31. Ant. CST– Supplementary motor area thr Ant CST controls bilateral postural movements. Along with Premotor area provides fixation movements of different segments of the body, positional movements of the head & eyes. i.e background for finer motor control of arms & hands. e.g –bilateral grasping movements of hands while climbing.
  32. 32. Applied aspects :- 1.Phylogenetically, ant. CST is older Lat. CST - in human beings and few vertebrates 2.Myelination is complete after the age of 2 yrs. 3.Cortical neurons & certain brain stem nuclei with their axons activate lower motor neurons-Upper motor neurons. 4.Cranial nerve nuclei, Spinal motor neurons /Ant horn cells with their axons activate directly skeletal muscles -Lower motor neurons.
  33. 33. Damage to motor control system - Stroke or apoplexy (sudden attack of paralysis). Paralysis - (Loss of power of muscle group due to absence of contraction of those muscles →loss of movement). Cause – i)Ruptured blood vessel -Haemorrage in brain. ii)Thrombosis of one of the major arteries supplying the brain. Commonest site is when CST passes through the internal capsule.
  34. 34. Damage to motor cortex alone - Hypotonia. Cause -Primary motor cortex exerts continous tonic stimulatory effect on motor neurons of spinal cord. But lesions of motor cortex involve not only the Primary motor cortex but also adjacent cortical areas & deeper structures of cerebrum (basal ganglia) - Damage to Accessory pathways.
  35. 35. Accessory pathways normally inhibit Vestibular & Reticular brain stem nuclei. When the inhibition is gone they become spontaneously active & cause excessive stimulation of spinal motor neurons →excessive/spastic tone in the involved muscle areas of the body → Results in muscle spasm or muscle spasticity on opposite side of the body - Upper motor neuron lesion.
  36. 36. Monoplegia - primary motor cortex hemiplegia - internal capsule quadriplegia or paraplegia – brain stem paraplegia - spinal cord at thoracic level
  37. 37. Lower motor neuron lesion – Results also in Paralysis but it is Flaccid paralysis. Clinical picture in Pyramidal tract lesions - Lesion above the level of sp. Cord – effects on opposite side of body. Lesion in the spinal cord – effects on the same side. Impairment of voluntary, skilled movements.
  38. 38. Upper motor neuron lesion :- •Increased muscle tone - Hypertonia. •Resistance to passive movements -Rigidity. Rigidity - clasp knife (Spasticity), lead pipe or Cogwheel rigidity. •Group of muscles of opp side affected. e.g:Flexors & extensors. So associated movements affected. •No atrophy (wasting of muscle).
  39. 39. •Superficial reflexes are absent. Plantar reflex →Babinski’s sign positive. •Deep /tendon reflexes are Exaggerated. •Clonus. •No tropic changes.
  40. 40. Toes down (flexion) Fanning of toes Normal plantar response Extensor plantar response (Babinski sign)
  41. 41. Lower motor neuron lesion : •Decreased muscle tone – Hypotonia. •No rigidity but flaccid paralysis. • Atrophy prominent (marked wasting of muscles). •Superficial reflexes absent. •Deep reflexes absent.
  42. 42. •Individual muscles of same side are affected.e.g:Poliomyletis. •Trophic changes are seen.
  43. 43. Lesion to cranial nerve nuclei(LMN) – Bulbar palsy. Lesion to Corticonuclear tracts – (UMN) Pseudobulbar palsy →Weakness or paralysis of the muscles of pharynx, larynx, palate, jaw & eye etc.
  44. 44. LMNP UMNP Site of lesion α- or cranial motor neuron Neurons forming descending tracts Muscles Involved -single muscle on the same side Groups of muscles on opposite side Vol. movements lost lost Tone of involved muscles - flaccidity Clasp-knife rigidity, spastic paralysis
  45. 45. Planter reflex – lost only if S1 is affected LMNP UMNP Tendon jerks – lost Exaggerated, clonus+ Muscle atrophy – marked wasting absent Superficial reflexes – lost lost Babinski’s +ve
  46. 46. Motor area for face Supranuclear lesion (UMN) Facial nerve n. Facial paralysis Facial nerve Corticobulbar tract

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