3. 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
4. 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
5.
6.
7.
8. 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
9.
10.
11. Constituted by crossed fibers
Descends in the lateral white funiculus of
opposite side
These fibers terminate in the internuncial
neurons 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
12. 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
13. 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
14. 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
15. UMN :- neurons giving origin to pyramidal
tract
LMN :- AH cells along with their neuron
constitutes LMN
16. 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
17. 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 ..
18. Descendings tracts other than pyramidal
tract are called extra pyramidal tracts
› Rubrospinal tract
› Vestibulospinal tract
› Reticulospinal tract
› Tectospinal tract
› Olivospinal tract
› Medial longitudinal fasciculus
19.
20.
21.
22. 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
23. 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
24.
25.
26.
27. 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
28.
29.
30. 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
31. 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 .
32. 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
33. Fibres orginates from medullary reticular
formation (gigantocellular) , descends
mostly uncrossed in the lateral funiculi
and terminates in same way as pontine
RS tract
34.
35. 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
36. Pontine and medullary nuclei functions
opposite to one another in controlling
› Muscle tone
› Respiration
› Vascular caliber
› Antigravity muscles posture
37. 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
38. Originates from inferior olivary nucleus
Descends uncrossed and terminates in
AH cells
May control reflex muscle activity
Tract is of doubtful existence
39.
40. 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
41.
42.
43.
44. Upper Motor Neuron paralysis :- paralysis
of UM neurons
Lower Motor Neuron Paralysis :- paralysis
of LM neurons
45.
46.
47. 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