EXTRAPYRAMIDAL TRACTS & MOTOR NEURON LESIONS

EXTRAPYRAMIDAL TRACTS&

MOTOR NEURON LESIONS

Dr. SHAIKH MUJEEB AHMEDAssistant professor

AL MAAREFA COLLEGE

Learning Objectives

At the end of this lecture you should be able to:• List the extrapyramidal tracts.• Summarize the functions of extrapyramidal tracts.• describe the signs and symptoms caused by a lesion of the

spinal cord (fasciculus gracilis and fasciculus cuneatus, lateral corticospinal tract, and lateral spinothalamic tract).

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Overview of Motor System

Corticospinal tracts

Corticobulbar tracts

Bulbospinal tracts

Overview of Motor System

CNS influence the activity of skeletal muscle through two sets of neuron

• Upper motor neuron

• Lower motor neuron

PYRAMIDAL TRACTS •corticospinal tract

EXTRAPYRAMIDAL TRACTS-•Reticulospinal Olivospinal

•Vestibulospinal

•Tectospinal

•Rubrospinal tract

•Corticobulbar tract

•Corticorubral tract

Extrapyramidal tracts

• Definition: Extrapyramidal tracts are those motor pathways which may act as the alternative route for volitional impulses and which form the platform on which pyramidal system works skillfully Integrated at various level from cerebral cortex to spinal cord

• Cortical region controlling these tracts are area 8 and 6

Sp. c

ord

Med

ulla

Pons

Mid

Bra

inCerebral Cortex

Corti

cosp

inal

Tra

ct

Tect

ospi

nal T

ract

Rubr

ospi

nal T

ract

Vesti

bulo

spin

al T

ract

Retic

ulos

pina

l Tra

ct

SC RN

VN

RFM

RFP

Position of tracts in the spinal cord

Function of Extrapyramidal tract

• Cortinuclear fibre control movement of eyeball.• Other tract responsible for tone, posture(R.S. TRACT),

visiospinal reflex(T.S TRACT), equilibrium(V.S. TRACT) Control complex movement( co-ordinated movement)

• Exerts tonic inhibitory control over lower centers• Carry volitional impulse when pyramidal tract damage • The extrapyramidal system is responsible for

sustained postures, resting tone and patterned movements.

ATONIC ExtraPyramidal system

Pyramidal system

ROLE OF EXTRAPYRAMIDAL SYSTEM

Descending TractsTract Signal function

Corticospinal (pyramidal) Fine voluntary motor control of the limbs. The pathway also controls voluntary body posture

adjustments.

Rubrospinal Involved in involuntary adjustment of arm position in response to balance information; support of the body.

Reticulospinal (1) Pontine Regulates various involuntary motor activities and assists in balance (leg extensors). Some pattern

movements e.g. stepping

(2) Medullary Inhibits firing of spinal and cranial motor neurons, control of antigravity muscles.

Vestibulospinal (1) Medial It is responsible for adjusting posture to maintain balance (neck muscles).

(2) Lateral It is responsible for adjusting posture to maintain balance (body/lower limb).

Tectospinal Controls head and eye movements, Involved in involuntary adjustment of head position in response to

visual information.

Nerve pathways

Descending Pathways

Pathway Upper limb Lower limb

Cortico/-pyramidalThis Tract functions to modulate the activity of Alpha or Gamma Motor Neurons as directed by the Motor Cortex.

Rubro-spinal Stimulates flexors

Reticulo-spinalMedullary inhibits extensors and excites flexorsPontine excites extensors and inhibits flexors (Generally upper limb)

Vestibulo-spinalDoesn’t affect upper limbs but helps position head and neck in response to body tilting (medial)

Stimulates extensors (lateral)

Tecto-spinal Control of head, neck and eye movements.

Extrapyramidal disorders

• Lesions in the extrapyramidal tract cause various types of diskinesias or disorders of involuntary movement

• Parkinsonism • Chorea • Hemiballism • Athetosis • Dystonia Tardive dyskinesia

Parkinsonism

• Degeneration of extrapyramidal tract Characterized by

• Rigidity • Bradykinesia.• Tremors and • Postural deficits

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Components of motor neurons

• Upper motor neuron (corticospinal & corticobulbar).

Starts from motor cortex and ends in 1. Cranial nerve nucleus (corticobulbar).2. Anterior horn of spinal cord in opposite

side(corticospinal tracts).• Lower Motor NeuronStarts from anterior horn of spinal cord and ends in

appropriate muscle of the same side.eg. All peripheral motor nerves.

UPPER AND LOWER MOTOR NEURON

DIFFERENCE BETWEEN UPPER & LOWER MOTOR NEURON LESION

UMN LESION• Paralysis affect

movement rather than muscles

• Muscle wasting is only from disuse, therefore slight. Occasionally marked in chronic severe lesions.

• Spasticity of clasp-knife’ type. Muscles hypertonic.

LMN LESION• Individual muscle or group of muscles are affected.• Wasting pronounced.

• Flaccidity. Muscles hypotonic.

• Tendon reflexes increased. Clonus often present.

• Superficial reflexes diminished or modified. Abdominal reflex absent. Babinski’s sign +ve, Increased jaw jerk.

• Tendon reflexes diminished or absent.

• Superficial reflexes often unaltered.

Lesion of the right dorsal column at L1 produces what impairment?

Click for answer

Damage to the right dorsal column at L1 causes the absence of light touch, vibration, and position sensation in the right leg. Only fasciculus gracilis exists below T6.

Click for explanation

R L

Right Dorsal Column Lesion

Dorsal column lesionIpsilateral loss of light touch, vibration, and position sensegeneralized below the lesion level

Below T6 only the fasciculus gracilis is present.

R LDRG

L1

Common causes include MS, penetrating injuries, and compression from tumors.

Click to animate

Click for answer

Damage to the right lateral spinothalamic tract at L1 causes the absence of pain and temperature sensation in the left leg.

Click for explanation

Lesion of the right lateral spinothalamic tract at L1 produces what impairment?

R L

R LDRG

Lateral spinothalamic tract lesionContralateral loss of pain and temperature sense

Right Lateral Spinothalamic Tract Lesion

L1

Common causes include MS, penetrating injuries, and compression from tumors.

Click to animate

Lesion of the right lateral corticospinal tract at L1 produces what impairment?

Click for answer

Damage to the right lateral corticospinal tract at L1 causes upper motor neurons signs (weakness or paralysis, hyperreflexia, and hypertonia) in the right leg.

Click for explanation

R L

R L

UMN

Lateral corticospinal tract lesionIpsilateral upper motor neurons signsgeneralized below the lesion level

UMN signsWeakness (Spastic paralysis)Hyperreflexia (+ Babinski, clonus)Hypertonia

Right Lateral Corticospinal Tract Lesion

L1

Common causes include penetrating injuries, lateral compression from tumors, and MS.

Click to animate

Click for answer

Damage to the right dorsal columns at L1 causes the absence of light touch, vibration, and position sense in the right leg. Damage to the lateral corticospinal tract causes upper motor neuron signs in the right leg (Monoplegia), and damage to the lateral spinothalamic tract causes the absence of pain and temperature sensation in the left leg.

Click for explanation

Complete transection of the right half the spinal cord (Hemicord or Brown-Sequard syndrome) at L1 produces what impairments?

R L

R L

Hemicord Lesion (Brown-Sequard Syndrome)

Dorsal column lesionIpsilateral loss of light touch, vibration, and position sense

Lateral corticospinal tract lesionIpsilateral upper motor neurons signs

Lateral spinothalamic tract lesionContralateral loss of pain and temperature sense

Hemicord lesion

Build the lesion

L1

Common causes include penetrating injuries, lateral compression from tumors, and MS.

Click to animate

Hemicord Lesion (Brown-Sequard Syndrome)

Dorsal column lesionIpsilateral loss of light touch, vibration, and position sense

Lateral corticospinal tract lesionIpsilateral upper motor neurons signs

Lateral spinothalamic tract lesionContralateral loss of pain and temperature sense

UMN

Hemicord lesion

R L DRGDRG

L1

Click to animate