1. MOTOR SYSTEM
Dr Csáki Ágnes
2014

2. CNS cortex Macroscopically the following parts could be separated:
Hemispheres (cortex + basal ganglia)
Diencephalon (thalamus, hypothalamus)
Brainstem – midbrain (mesencephalon)
- pons
- medula oblongata
Cerebellum
Spinal cord
diencephalon
brainstem
cerebellum

3. Motor system Spinal reflexes
Pyramidal system (corticospinal tract - execution)
Extrapyramidal system (cerebellum, basal ganglia)
Brainstem (less important in humans)
The cortex (corticospinal tract) and the spinal cord (spinal reflexes) has the major roles in voluntary movements. If any of them is damaged, voluntary movements become impossible (paresis)
The cortex usually does not exert a direct control over the spinal motoneurons, rather only modifies spinal reflexes indirectly to reach the desired movement.
Cerebellum and the system of basal ganglia mostly influence the activity of the corticospinal tract via the secondary and supplementer motor cortex. Cerebellum is responsible for fine adjustments, while the ganglia in planning and initiating the movements, but not for executing. Their damage will usually not lead to paresis.

4. Reflex arc

5. Corticospinal (Pyramidal) Tract
Direct pathway.
CROSSED and uncrossed
Clinically the most important descending tract is the crossed corticospinal tr. (tr. corticospinalis cruciatus). Damage will lead to paresis (loss of voluntary movements).

6. Pyramidal Tract Could be simplified to two neurons:
upper motoneuron
Could be simplified to two neurons:
- upper (cortical) motoneuron
lower (spinal) motoneuron (reflexes!)
The axon of upper motoneuron form the pyramidal tract. Most of the descending fibers cross in the pyramid of medulla. The minority of the fibers (mostly those, that will supply the muscles of the trunk) stay uncrossed. Axons terminate – usually through interneurons – on the lower motoneurons.
The axon of spinal neurons reach the skeletal muscles via spinal and peripheral nerves. Contribute to the spinal reflexes as well (final common pathway).
corticospinal tr.
lower motoneuron

7. Pyramidal Tract General tendency:
upper motoneuron
General tendency:
muscles of the distal part of extremity receive fibers only from the opposite side of the cortex through the crossed corticospinal tr.
muscles of the trunk and most muscles supplied by cranial nerves receive innervation from both side of the cortex (extra defense)
corticospinal tr.
lower motoneuron
primary motor cortex
Brodmann: 4,6

8. (sensory and motor functions of lower extremity)
cerebri anterior
(sensory and motor functions of lower extremity)
cerebri posterior
(vision, storing memory)

9. (sensory and motor functions of lower extremity)
a. carotis interna
cerebri anterior
(sensory and motor functions of lower extremity)
cerebri media
(sensory and motor functions of upper extremity, speech)
cerebri posterior
(vision, storing memory)
a. basilaris
a. vertebralis

10. Cerebellum Functions pedunculus cerebelli sup. diencephalon
Communicates with other structures via the 3 cerebellar peduncules. Collect information from spinal cord, brainstem, cortex etc.
The main function of the cerebellum is the fine adjustments and automatic correction of movements. The main output tract runs to cortex and influences the motor movements at cortical level.
diencephalon
mesencephalon
cerebellum
pons
medulla oblongata
pedunculus cerebelli med.
spinal cord
pedunculus cerebelli inf.
Interbrain

11. Telencephalon: basal ganglia
Islands of gray matter embedded in the white matter of telencephalon under the cortex. Their main function is related to the motor system: to plan and to initiate a certain desired movement.
Diseases of the basal ganglia system (substantia nigra) include the Parkinson-syndrome: progressive hypo motility, slow movement initiation, tremor. Specific cause: loss of dopaminerg neurons in substantia nigra.
lateral ventricle
caudate n.
claustrum
thalamus
lentiform n
Interbrain

12. Ascending (right) and Descending (left) Tracts of the Spinal Cord12

13. crossed corticospinal tr.
gracile and cuneate tr.
crossed corticospinal tr.
spinothalamic tr.
other motor tracts

14. Brown-Séquard Syndrome
In case of hemidissection of the spinal cord (Brown-Séquard syndrome) heat, pain and basic touch information is lost under the damage on the opposite side.
In case of hemidissection of the spinal cord (Brown-Séquard syndrome) epicritical sensitivity is lost under the damage on the same side.
In case of hemidissection of the spinal cord (Brown-Séquard syndrome) paresis is under the damage on the same side.

15. Paresis Central paresis
cell body or axon of upper motoneuron is damaged (usually contralateral cortical, or ipsilateral spinal cord injury)
effects mostly the distal muscles of the extremity,
muscles of the trunk and cranial nerves (except VII and XII) are often intact
reflexes usually stronger, liberated, increased tone of the muscles
atrophy of muscle is slow
no regeneration
Peripheral paresis
cell body or axon of lower motoneuron is damaged (spinal cord or peripheral nerve injury)
paresis on the side of the damage, can effect muscles of the trunk and cranial nerves
no reflexes (afferent part damaged too), hypotonia
quick atrophy
fairly good possibility for regeneration if the peripheral nerve is damaged

16. Rami, spinal nerve and ganglion
dorsal root
senory fibers
spinal nerve
mixed fibers
ventral root
motor fibers

17. Spinal nerves dorsal ramus -mixed ventral ramus - mixed
rearrangements
plexus
grey communicating branch
white communicating branch

18. Dermatomes
segmental pain,
segmental symptoms

19. Spinal nerves
- plexuses

22. Literature Szentagothai J, Réthelyi M: Funkcionális anatómia, 1989
Pictures from Sobota: Atlas of Human Anatomy, 20th edition, Urban and Schwarzenberger, 1993
Goldberg Stephen: Clinical Neuroanatomy Made Ridiculously Simple, 25th edition, MedMaster Inc., Miami, Florida, 1997