Tracts originating from the brain and

descending in to spinal cord

These tracts are concerned with various

motor activities of body

Two groups

› Pyramidal tract

› Extra pyramidal tract

Aka corticospinal tract

Contains axons of cell bodies present in

motor cortex of brain.

Pyramidal cells of Betz

Origin :- 30% from primary motor cortex (Area 4)

30% from premotor area and supplementary

motor cortex

40% from the somatic sensory area

The fibers descend as a part of corona radiata

Then pass through the posterior limb of internal capsule

Then downwards through the brainstem

Forming pyramids in the medulla

At the lower part of medulla 90% of the fibers decussate in the midline to reach opposite side

Forming two separate tracts from here

Constituted by crossed fibers

Descends in the lateral white funiculus of opposite side

These fibers terminate in the internuncialneurons of spinal grey matter.

Internuncial neurons synapse with motor neurons in anterior horn cells

Some fibers end directly on the AH cells

Axons of AH cells supply skeletal muscle through spinal nerve

Formed by the uncrossed pyramidal

fibers

They descend thro ant white funiculi on

same side

They reach only till mid thoracic region

On reaching appropriate spinal segment

they cross to the opposite side

Terminate in the same way as lateral

corticospinal tract

In brainstem some fibres terminate in

motor nuclei of cranial nerve

They cross to opposite side at various

levels of brainstem depending upon the

nuclei

Which supply muscles of face

Both the anterior and lateral

corticospinal tracts ultimately innevate

opposite side of the body

i.e Fibres from the right lobe of cerebral

cortex terminate on the left AH cells

UMN :- neurons giving origin to pyramidal

tract

LMN :- AH cells along with their neuron

constitutes LMN

Fibres of CS tract are unmyelinated at

birth

Myelination begins at 2nd week after birth

and completes at 2years of age

Contains large fibres and small fibres

Large fibres disappear at old age

leading to shaky movements

Cerebral cortex controls voluntary

movements of the body thro CS tract

Lesion produce paralysis of concerned

muscle group

Sends collateral to other motor control

systems like basal ganglia , cerebellum ..

Descendings tracts other than pyramidal

tract are called extra pyramidal tracts

› Rubrospinal tract

› Vestibulospinal tract

› Reticulospinal tract

› Tectospinal tract

› Olivospinal tract

› Medial longitudinal fasciculus

Origin:- arises from nucleus magnocellularis or red nucleus in midbrain

Course :- fibres cross to the opposite side in the lower part of tegmentum of midbrain

After that follows a course similar to lateral CS tract

Termination :- on the interneurons along with CS tract

Facilitates flexor muscles and inhibit

extensor muscles

Red nucleus receives corticorubral fibres

from ipsilateral motor cortex

Cortico-rubro-spinal tract acts as a

alternate route of pyramidal tract

Reaches only upper three cervical

segments

Lateral Vestibulospinal Tract:- origin from

lateral vestibular nucleus (deiter’s) at

lower pons

fibres are somatotopically arranged in

this nucleus

Course :- tract is uncrossed and lies in the

ant funiculi

They terminate on alpha and gamma

motor neuron thro interneuron

Vestibular nucleus receives afferents

from vestibular apparatus mainly from

utricle

Adjustment of postural muscles to linear

acceleration

Facilitates extensor muscles and inhibits

flexor muscle

Maintenance of balance

Fibres originates from medial vestibular nucleus

Descends thro the anterior funiculi and mostly uncrossed

Fibres ends in AH cells either directly or thro interneuron

Receives inputs from vestibular apparatus mainly from semicircular canals

Controls movements of head with respect to auditory and visual stimuli .

Two divisions

Medial – pontine Reticulospinal tract

Lateral – medullary Reticulospinal tract

pontine Reticulospinal tract:- arises from

medial pontine reticular formation and

descends mostly uncrossed and

terminates in alpha & gamma motor

neurons in spinal cord thro interneurons

Fibres orginates from medullary reticular

formation (gigantocellular) , descends

mostly uncrossed in the lateral funiculi

and terminates in same way as pontine

RS tract

Reticular formation Receives afferents

from cortex

Forming cortico-reticulospinal pathway

Control of movements and muscle tone

Also convey autonomic fibres from

higher center to spinal cord

Pontine and medullary nuclei functions

opposite to one another in controlling

› Muscle tone

› Respiration

› Vascular caliber

› Antigravity muscles posture

Fibres originates from superior colliculi

Fibres cross the midline at tegmentum of

midbrain (dorsal tegmental decussation)

And descends thro anterior funiculi

Terminates in AH cells of upper cerviccal

levels

Functions :- turning head and moving

arms in response to visual or other stimuli

Originates from inferior olivary nucleus

Descends uncrossed and terminates in

AH cells

May control reflex muscle activity

Tract is of doubtful existence

Extends from midbrain downwards

Fibres takes origin from

› Vestibular nuclei

› Reticular formation

› Superior colliculus

› Interstitial nucleus of cajal

› Posteriior commisure

› Has connection Cranial nerves 3, 4, 6, 7 , 8, 12

AH cells of muscles of neck

Function :- harmonius movement of eye

and neck

Upper Motor Neuron paralysis :- paralysis

of UM neurons

Lower Motor Neuron Paralysis :- paralysis

of LM neurons

Monoplegia :- paralysis of all muscles of

one limb

Hemiplegia :- paralysis of one half of

body

Paraplegia :- paralysis of both lower

limbs

Quadriplegia :- paralysis of all four limbs