Pyramidal tracts

1. Motor systems and tracts,
Pyramidal tract
compiled by
András Csillag

2. Categorization of descending motor
pathways I
‘Classic’ categories
• voluntary, goal-oriented (pyramidal tract)
– corticospinal tract
– corticonuclear (corticobulbar) tract
• involuntary, stereotypic (extrapyramidal)
tracts
– reticulospinal, vestibulospinal, rubrospinal,
olivospinal, tectospinal tracts

3. Categorization of descending motor
pathways II
Modern categories:
• medial descending system
– vestibulospinal tract,
– reticulospinal tract
• lateral descending system
– corticospinal tract
– rubrospinal tract
postural control,
stabilization of head and
gaze
main inputs: visual,
labyrinthic,
proprioceptive, cerebellar
voluntary, organized
movements of face and
limbs
main inputs:
somatosensory, cortical,
basal ganglia, cerebellar

4. Functional classification of descending motor pathways

5. Principal descending motor tracts

6. Vestibulospinal tracts

9. Somatotopic organization of motor cortex

10. Course of the corticospinal tract
and its termination in the spinal cord
ACSP – anterior (uncrossed)
corticospinal tract
LCSP – lateral (crossed)
corticospinal tract

11. CA – anterior limb of IC
G – ‘knee’ (genu) of IC
CP – posterior limb of IC
G – representation of head
and face
A – representation of arm
B – representation of leg
Internal capsule
Arrangement of the fibres of pyramidal tract

12. Last-order premotor interneurons (LOPI) and
motor units of spinal cord

13. Postulated organization of locomotor
central pattern generator (CPG). V2a, Hb9,
and LC dI6 interneurons are postulated to
comprise the rhythm-generating core of the
locomotor CPG and receive descending input
from brain stem centers known to initiate
rhythmic locomotor activity in the spinal
cord. We propose that these cells provide
input onto the pattern-forming layer that includes
dI3, V2a, V0, Hb9 and TC dI6 cells.
Members of the pattern-forming layer make
direct connections onto motoneurons (MN).
Documented synaptic connectivity indicated
by solid lines, proposed synaptic connectivity
by dashed lines. Inhibitory terminal indicated
by black ball, excitatory terminal by
open triangle.
Jason Dyck, Guillermo M. Lanuza, and Simon Gosgnach, J Neurophysiol
107: 3256 –3266, 2012. nyomán
Central Pattern Generators, CPG
of spinal cord
Inhibitory synapse
Excitatory synapse
Rhythm generating inner zone
Pattern generating outer zone
MN – Motoneuron in ventral horn
dI3 – V2a – genetically determined
types of interneurons

14. Birinyi A. Habilitációs Tézisek, 2015
Last Order Premotor Interneurons (LOPI)
iLOPI - ipsilateral premotoric interneuron
cLOPI - contralateral premotoric interneuron

15. Birinyi A. Habilitációs Tézisek, 2015
Commissural interneurons of spinal cord
iCIN – ipsilateral commissural interneuron
cCIN – contralateral commissural interneuron
MN - motoneuron

16. Recurrent inhibition of motoneurons by
Renshaw cells
http://www.learnneurosurgery.com/

17. Types of interneurons in the spinal cord
Inhibitory interneuron of type Ia Inhibitory interneuron of Renshaw type
http://www.twitter.com/TheGaitGuys
Feed-forward
inhibition
Feedback (recurrent)
inhibition

18. Somatotopic organization of the major sensory and motor
pathways in the spinal cord