Dr.K.Jaiganesh, MD

Professor of Physiology,

MGMC & RI

Motor System

Cerebral cortex

Ascending tracts- Sensory

Carrying up sensationsDescending tracts-Motor

Carrying down orders

Objectives

Descending tracts – Pathways & Functions

Applied aspects

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

Pyramidal system

1. Pyramidal system

a. Cortico spinal tract- LCST, VCST

b. Cortico bulbar 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

Cerebral cortex

30%

40%

30%

Cerebral cortex

30%30% 40%

Motor Homonculus

Left Right

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

Corticospinal

tract

Midbrain

Pons

Medulla

80% 20%

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 & LMN paralysis

UMN & LMN Lesion

Motor neuron

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