Sensory and Motor Pathways

1. Sensory and Motor Pathways

2. Somatic Sensory Pathways • The 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; • Posterior Column Pathway to the Cortex • 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; • Corticospinal Tracts • 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)