Motor system

Neuroanatomy

1. Motor System
•Lower motor neuronal control;
•Upper motor neuronal control.
by Dr. M. Kornieieva

2. Central Nervous System

3. The Lower Motor System
SKELETAL MUSCLE CONTRACTION is
initiated by “lower” motor neurons in the spinal
cord and brainstem.
Cell Bodies in the:
1) Ventral horn of the spinal
cord gray matter;
2) Motor nuclei of the cranial
nerves in the brainstem
Axons: passdirectly to skeletal muscles
αmotor neurons
Control of movement:
1
2
3
4

4. Lower Motor Neuron –Spinal Cord
αmotor neurons

5. Lower Motor Neuron –Brainstem
α motor neurons
The term “lower” regarding neurons indicates
relation to muscle rather then level of localization.

6. Motor Neuronal Pools
MCS
LCS

7. γ-Motor neuron
Specialized muscle fibers
(sensory receptors -spindles)
Sensory axons 1a
Send information about length of
the muscle to the SC and BS
Muscle spindles in
striated muscle
α-Motor
neuron
Extrafusal
fibers
Contraction

8. Myotatic (stretch) reflex
Ia

9. Myotatic (stretch) reflex

10. Golgi Tendon Organs
Localization –musculartendon
Structure–network of nerve endings
interdigitating with collagen fibers
Activation–tension of muscle contraction
Function–suppression of the related
⍺-motor neuron output
Negative feedback system

11. Golgi Tendon Organs
Works via the inhibitory interneuron

12. Flexion-
withdrawal
(crossed
extensor)
reflex

13. Spinal Cord Circuitry and Locomotion
Central pattern generator
(in spinal cord)
Stance phase
Swing phase
Mesencephalic
locomotorregion
Speed

14. Lower Motor Neuron Syndrome
•Muscle atrophy
•Fibrillations and fasciculations
•Muscle paralysis (loss of volitional control) or paresis
(profound weakness)
•Areflexia(loss of myotacticreflexes)
•Profound reduction in muscle tone

15. Upper Motor Neuronal
Control of Movement

16. Upper Motor system
•Encoding of movement intention
•Expression of emotions (facial
expression, posture)
•Skilled motor behavior
Motor cortex:
Brainstem:
•Settings of posture
•Setting the gain of reflexes

17. Somatotopy in the spinal cord (LMN)
Lateral white matter
(axons from motor cortex)
Medial white matter
(axons from brainstem)
UMN
Parallel pathways
bilateral contralateral

18. Parallel
pathways:

19. Primary Motor Cortex
Lateral view Medial view

20. Primary Motor Cortex
Large motor neurons in the
layer 5 called the Betz cells.
Betz cells give rise to corticospinal and
corticobulbartracts => lower motor circuits.
Precentral gyrus

21. Somatotopy in the
Motor Cortex
What exactly is represented here?
•movements (not muscles!) or movement intentions
•multiple dimensions of movements (force, direction,
amplitude)
•movements that engage hand, lower face and hand-to-
mouth coordination
•skilled manual behavior in central person space
•lesions impair “fractionated” finger/facial movements
(i.e. manual and facial skills)

22. Encoding of Movement Intention
in Central Space in M1

23. Mosaic organization
Medial part Lateral part
Premotor Cortex
monkey
L
M

24. Brainstem Upper Motor Neurons
L/M
Vestibulo-
spinal tracts
Adjustment of position
of body regarding the
position of the head
Feedback operation
on posture
Anticipate adjustment
of posture
Forebrain
Spinal cord
Ready..
Set…

25. Reticular Formation

26. Pyramidal tracts
1)Corticospinal tract
2) Corticobulbar tract
Cortex
α-motor neuron
Cortex
Basal ganglia
Red nucleus
Reticular formation
Olivarynucleus

27. The Corticospinaland
Corticobulbarp/w
s
Internal capsule

28. The Corticospinaland Corticobulbartracts
Corticopontine
tract
Opposite
cerebellar
hemisphere
Cerebellar
peduncle
All parts of
motor cortex

29. The Corticospinaland Corticobulbartracts
Midbrain
Pons
Cerebral
peduncles
of midbrain
Pontine nuclei
Lower pons
Upper Medulla
Cortico-
spinal
tract
Medullary
Pyramids
Corticobulbar, -pontine, -
spinal fibers
Caudal medulla
Decussation of the pyramids

30. The CorticospinalPathway
90-95%
5-10 %

31. Control of Facial Expression
Facial nerve, VII
Lower motor neuron
UMN

32. Emotional
Motor
System
Primary Motor Cortex
Somatosensory Cortex
Supplementary motor cortex
Cingulate motor cortex
Pyramidal smile
Emotional smile

33. Speech Motor System

34. Red nucleus
Olivary nucleus Lat. vestibular nucleus
Superior
colliculus
Reticular
formation
Paracentral gray

35. Extrapyramidal tracts
1.Rubrospinaltract
2.Pontine reticulospinaltract
3.Medullaryreticulospinal tract
4.Lateral vestibulospinal tract
5.Tectospinaltract
Look for details at Clinical Neuroanatomy 7
th
ed. by R. Snell (pp.157-160)
541
23

36. Upper Motor Neuron Syndrome