Sensory and motor pathways

1. Sensory and Motor
Pathways

2. Somatic Sensory Pathways
• consist of first-order, second-order, and third-
order neurons

3. Somatic Sensory Pathways
• The relative size of the area that the
somatosensory cortex represents a body part
are proportional to the number of specialized
sensory receptors

4. Somatic Sensory Pathways
Two Pathways;
1. Posterior Column Pathway to the Cortex
2. Spinothalamic Pathways to the Cortex

5. Posterior Column Pathway to the Cortex
• The nerve impulses for conscious
proprioception and most tactile sensations
ascend to the cortex.

6. Posterior Column Pathway to the Cortex
• The first neuron goes from the receptor to the
cord and ascends to the medulla

8. Posterior Column Pathway to the Cortex
• The second order neuron crosses in the
medulla and ascends to the thalamus

10. Posterior Column Pathway to the Cortex
• The third order neuron goes to the parietal
lobe

12. Posterior Column Pathway to the Cortex
• The posterior columns are damaged by B-12
deficiency

13. Anterolateral Pathways to the Cortex
• Carry mainly pain and temperature impulses

14. Anterolateral Pathways to the Cortex
• The first order neuron goes from the receptor
to the cord and releases substance P

16. Anterolateral Pathways to the Cortex
• The second order neuron crosses in the cord
and ascends to the thalamus (where we
become conscious of the pain)

18. Anterolateral Pathways to the Cortex
• The second order neuron ascends either via
the anterior or lateral spinothalamic tracts

20. Anterolateral Pathways to the Cortex
• The third order neuron goes to the parietal
lobe where we interpret the pain

22. Anterolateral Pathways to the Cortex
• Modulation of pain by the brain: release of
substance P is inhibited by descending
pathways that release enkephalins

23. Somatic Motor Pathways
• The primary motor area is the major control
region for initiation of voluntary movements

24. Somatic Motor Pathways
• Different muscles are not represented equally
in the motor cortex

25. Somatic Motor Pathways
• The degree of representation is proportional
to the number of motor units in a particular
muscle of the body

26. Somatic Motor Pathways
• Voluntary motor impulses are propagated
from the motor cortex to somatic efferent
neurons that innervate skeletal muscles via
the direct pathways

27. Somatic Motor Pathways
Direct pathways;
1. Corticospinal Tracts
2. Corticobulbar Tracts

28. Corticospinal Tracts
• They go from the primary motor cortex down
through the cerebral peduncles of the
midbrain

30. Corticospinal Tracts
• They cross in the medulla (if lateral) or in the
spinal cord (if anterior)

32. Corticospinal Tracts
• Then they run down the cord to the anterior
grey horn cells where the cell bodies of the
lower motor neuron lie

34. Corticospinal Tracts
• Lower motor neurons = somatic efferent
neurons

35. Corticospinal Tracts
• Efferent = Motor

36. Corticobulbar Tracts
• Axons of upper neurons run from the primary
motor cortex to the corticobulbar tracts in the
R. and L. cerebral peduncles of the midbrain

37. Corticobulbar Tracts
The tracts cross and the axons end in the motor
nuclei of nine cranial nerves (III, IV,V, VI, VII, IX,
X, XI, XII)

38. Thank you