Alternative mechanism/route for voluntary and reflex motor activity. Form platform on which Pyramidal system work skillfully.

1. EXTRAPYRAMIDAL TRACTS
Motor fibers arising from cortical &
subcortical areas of brain descending
outside the corticospinal tract,
»-- reaching sp.cord.
»-- Ending on α or γ motor neurons.motor neurons.
»--ipsilat. or contralat.
»--Multichannel system

2. Extra Pyramidal System
1.Rubrospinal
2.Tectospinal
3.Lat. Vestibulospinal
4.Medial vestibulospinal
5.Pontine reticulospinal
6.Medullary reticulospinal
RRTV

5. Some peculiarities of individual
tract
• Rubrospinal –
- Red nucleus
- crossed
- located in lat. White column
- part of lat. motor system
- extend up to mid tho. Level
- facilitatory to flexors of wrist
- do not control fine
movements of hand & fingers.

6. •Tectospinal – crossed
- from sup. colliculus
- lower cervical region
- control reflex postural
movements in response to
visual & auditory stimuli or
visually guided move. of head

7. Reticulospinal tracts :
Support the body against gravity.
Two group of nuclei: Pontine & Medullary.
Function antagonistically to each other.
Pontine excites the antigravity muscles.
Medullary inhibit the antigravity muscles.

8. Pontine
reticulospinal
tract
Medullary
reticulospinal
tract
Pontine reticular N.
Crossed and
uncrossed fibers
Ant. white column
Inhibit γ-motor neurons
of extensors of body
Maintain body posture
Facilitate γ-motor
neurons of extensors of
body
Medullary reticular.N.

9. Medullary reticulospinal – Inhibitory input to
-- γ Motor neuron
-- bilateral
-- Extensors of proximal muscles of limb.
Cerebral cortex via reticular formation sends
inhibitory output from Medullary reti spinal
tract to γ Motor neurons.
Cerebellum also sends inhibitory drive
via this tract.
Function:Inhibits the antigravity in certain
portions of the body to perform special motor
activities.

10. • Normally, inhibitory control
of medullary reticulospinal
tract is prominent on the
muscle tone

11. Vestibulospinal tracts :
Works in association with Pontine reticular
nuclei (Pontine reticulospinal tract) to excite
antigravity muscles.
Without the support of vestibular nuclei the
pontine reticular system loses much of its
excitation of axial antigravity muscles.
Function :Controls selectively excitatory
signals to different antigravity muscle to
maintain equilibrium in response to signals
from vestibular apparatus.

12. Medial vestibulospinal Lat. vestibulospinal
Medial vestibular N.
Semicircular canals
Rotation of head
Ant. White column
Uncrossed fibers
Through out the length of sp. cord
Facilitation of extensors and inhibition of flexors
Linear acceleration
Utricle, saccule
Lat. vesti. N.
Uncrossed fibers
Lat White column
α-motor neurons

13. cortex
Med. Ret. formation
Red n.
putamenC.N.
S.N.
Pontine. Ret. formationS.C.
Vesti. N.
cerebellum
+ α
+ α
- γ
+ γ
-γ
+ γ + α
Midline

14. Functions of E.P.S.
1. Alternative channel for voluntary and
reflex activity.
2. Coarse movements of trunk & whole
limb.
3. Background posture.
4. Changing tone of muscle for smooth
& purposeful movements.

15. FUNCTIONS OF EPS
• Control of tone, posture and equilibrium.
• Control of complex movements (automatic
associated movements) of the body and
limbs.
• Cortex exerts tonic inhibitory control over
lower centers through these tracts. So
damage to these tracts→ Rigidity of
muscle (release phenomena).

16. Pyramidal system Extrapyramidal system
Origin
Myelination
Course
Main control
controlled
muscle
Functions
Effects of
lesion
subcortical
During iu life
polysynaptic
Lower extremity
Postural muscles,
Proximal jts
Gross movements
hypertonia
Cortical
After birth
Monosynaptic
Upper extremity
Flexors of hand &
fingers , distal jts
Skilled movements
hypotonia

17. Applied aspect :
1)Decerebrate rigidity.
2)Ischaemic decerebration.
Decerebrate rigidity : Transection at
midcollicular level of midbrain.

18. Rigidity in antigravity muscles (neck, trunk &
extensors of legs.
Cause :Blockage of strong inhibitory input
from cortex, red nuclei & basal ganglia to
medullary reticular nuclei.
So medullary reticular sys less effective
(nonfunctional) as depending solely upon
cerebello bulbar connections for its inhibtory
drive on spinal motor neurons.

19. Over excitation of pontine reticular
system(few fibres damaged).
Also the sensory influx while going to ARAS
gives collaterals to Pontine reticular nuclei
so facilitatory effect remains on γ motor
activity which leads to rigidity.
Hence called γ rigidity.

21. 2)Ischaemic decerebration : α rigidity
Both carotid & basilar arteries are tied so
excitation from Pontine reticular nuclei is
blocked, still rigidity appears.
Cause is over excitation of Vestibular
nuclei through vestibulospinal tract which
directly influences α motoneurons.