3.descending tracts kjg
TRANSCRIPT
Cerebral cortex
Ascending tracts- Sensory
Carrying up sensationsDescending tracts-Motor
Carrying down orders
Descending Tracts
1. Pyramidal system
Cortico spinal tract- LCST, VCST
Cortico bulbar tract
2. Extra pyramidal system
Cortically Originated EPS
Sub Cortically Originated EPS
Rubro spinal tract
Vestibulo spinal tract
Reticulo spinal tract
Tectospinal tract
Olivospinal tract
Corticospinal tract
(Pyramidal tract)
Site of Origin
Primary motor area 4,6 (30%)
Pre motor (30%)
Primary Somato sensory cortex (40%)
Originate from
Giant cells of Betz (3%)
Other areas (97%)
(layer 5)
Origin
Course & termination
Descend via “corona radiata”
Converge via “internal capsule”
[occupy genu & anterior 2/3 of posterior limb]
Pass via middle 3rd
of “cerebral peduncle”
Broken into discrete bundles by “pontine nuclei”
At lower border of “pons” – reorganised into a
compact bundle
Forms pyramid on anterior “medulla”
80% crossed 20% uncrossed
Synapses with antr.horn Disappear at
cells of spinal cord thoracic level
LCST VCST
Functions of CST
VCST controls gross voluntary
movements [walking, climbing]
LCST controls voluntary fine skilled
movements [writing, drawing]
Facilitates superficial reflexes
Facilitates muscle tone
Effect of lesion of CST during
its course
Motor areas of cortex – Monoplegia
Corona radiata – Monoplegia
Internal capsule – Contralateral hemiplegia
Brain stem – above decussation – Contralateral hemiplegia
Upper part of mid brain – Cont. hemiplegia &
ipsilateral III N palsy (Weber’s syndrome)
Pons – Cont. hemiplegia & ipsilateral VI N palsy
(Raymond’s syndrome)
Cont. hemiplegia & ipsilateral VII N palsy
(Millard Gubler syndrome)
Medulla – Cont.hemiplegia & ipsilat. XII N palsy.
Lateral corticospinal tract – Ipsilateral UMN type of palsy
Above C5 – Both upper & lower limbs
Below T1 – Only lower limbs
Effects of lesion of CST -
Hemiplegia
Paralysis of one half of the body
Lesion in the internal capsule of the
opposite side
Impairment of voluntary movements
Impairment of skilled movements
Increased muscle tone – spasticity
clasp knife rigidity
Exaggerated tendon reflexes
Loss of superficial reflexes
Appearance of pathological reflexes
( Babinski’s sign)
UMN Lesion LMN Lesion
Muscle bulk Disuse atrophy Wasting
Muscle tone (spasticity) (flaccidity)
Superficial
reflexes
Lost Lost
Deep reflexes Exaggerated Lost
Plantar reflex Babinski’s sign Normal
Clonus Present Absent
Cause Damage to motor
tracts above the
anterior horn cell
Damage to the
anterior horn
cells and below
UMN & LMN Lesion
Corticobulbar (or)
Corticonuclear tract
Origin: motor cortex
Termination: cell bodies of cranial nerves
Course: Descend along with pyramidal tract & cross to
opp. side throughout the brain stem & synapse with
cranial nuclei
Function: This acts as UMN for 3,4,5,6,7,9,10, 11,12th
cranial nerves
Lesion: These nerves are affected in bulbar paralysis
Extrapyramidal System
All motor pathways not part of the pyramidal system
Includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts
These motor pathways are complex and multisynaptic, and regulate:
Axial muscles that maintain balance and posture
Muscles controlling coarse movement of the proximal portions of limbs
Head, neck, and eye movement
Origin area – 8,6,4,3,1,2,5,7,24
Tracts –
Cortico-nigral
c.pallidal
c.striatal
c.rubral
c.pontine
c.thalamic
c.subthalamic
c.hypothalamic
c.tegmental
EPS – CO EPS
EPS – Sub COEPS
Rubro spinal tract
Tectospinal tract
Vestibulo spinal tract
Reticulo spinal tract
Olivospinal tract
Rubrospinal Tract
Origin: Red nucleus in midbrain
Course: Fibres cross to opposite side in tegmentum as Forel’s decussation & descend thro’ reticular formation of pons & medulla to the spinal cord
Termination: Anterior horn cells
Function: Facilitatory influence on muscle tone
Tectospinal tract
Origin: Superior colliculus of midbrain
Course: Cross in tegmentum as Meynerts decussation
Descend through Reticular formation of pons and
medulla
Termination: Terminates on anterior horn cells
Function: Co ordinate retinal impulses with body
movements
Ventral Vestibulospinal tract
Origin: Arises in vestibular nucleus (Deiter’s nucleus)
in lower pons
Course: Descends through medulla to spinal cord
lateral to pyramidal tract
Termination: Terminates on anterior horn cells
Extend upto upper thoracic segments
Lateral Vestibulospinal tract
Origin: Deiter’s nucleus
Course: Descends thro’ medulla in spinal cord, lying
anterior to rubrospinal tract
Termination: Terminates on antr. horn cells
Function:
These form a pathway for impulses from cerebellum
& labyrinth to spinal cord
Regulate Muscle tone & equilibrium
Reticulo spinal tract
Origin: Reticular formation of Pons and medulla
Termination: Terminates on antr. horn cells
Function: Pontine - Facilitatory
Medullary – Inhibitory
Facilitate /Inhibit the effect of stimulation of pyramidal tract
Olivospinal tract
Origin: Inferior olivary nucleus
Course: Thalamus – Inferior olivary nucleus –
spinal cord (Tract of Helweg)
Function: Movements arising due to
proprioception
Differences between pyramidal & EPS
Features Pyramidal tract Extra pyramidal tract
Development New Old
Myelination Starts at birth &
stops by 2 years
Starts before birth
Onset of function After 2 years From birth
Synapses 1 or 2 Polysynaptic
Functions Fine skilled
movements
Gross movements
Conduction rate Slow Fast
Control of body parts Upper limb Lower limb
Nature of fibres Facilitatory Facilitatory & inhibitory
Effect of damage Flaccid paralysis
(pure pyramidal)
Spastic paralysis