1. Sensory and Motor Pathways

2. Cross Section of Spinal Cord

3. Ascending and Descending Tracts/Pathways
= sensory
= motor

4. Sensory Nerve Tracts
Each pathway involved with different categories of sensory information
First half of word indicates “origin”, second half indicates “destination”

5. Spinocerebellar--periphery of lateral and dorsal columns
Dorsal Column System
proprioception, fine-touch, two point discrimination, pressure
Anteriolateral System —Spinothalamic Tracts: somatic sensory information from cutaneous receptors to Thalamus
pain, pressure, crude touch, temperature
Spinocerebellar--periphery of lateral and dorsal columns
proprioception to cerebellum

6. Anterolateral System: Spinothalamic Tract
Anterior portion: crude touch/pressure
Lateral portion: pain and temp
Contralatteral
Decussates in spinal cord
Three neuron system
Primary neuron (1st order) : from receptor to posterior horn of spinal cord
Synapse with interneurons
Secondary neuron (2nd order): cross to opposite side, enter spinothalamic tract, ascend to thalamus
Tertiary neuron (3rd order): thalamus to somatic sensory cortex

7. Spinothalamic -- Anteriolateral Tracts
Anterior portion: crude touch/pressure
Lateral portion: pain and temp
Contralateral
Decussates in spinal cord
3 neuron system
Primary neuron (1st order) : from receptor to posterior horn of spinal cord
Synapse with interneurons
Secondary neuron (2nd order): cross to opposite side, enter spinothalamic tract, ascend to thalamus
Tertiary neuron (3rd order): thalamus to somatic sensory cortex

8. Dorsal-Column (Medial-Lemniscal) System
Carries sensations of: fine touch, two-point discrimination,
proprioception, vibration to cerebrum, and cerebellum
Contralatteral
Decussates in medulla
3 neurons
Primary neurons have cell bodies in dorsal root ganglion.
Axons enter spinal cord and ascend to the medulla oblongata without decussating where they synapse with secondary neurons.
Secondary neurons in medulla:
axons decussate and ascend to thalamus
Tertiary neurons:
project to somatic sensory cortex

9. fine touch, two-point discrimination, Contralatteral
Dorsal Column
fine touch, two-point discrimination,
Contralatteral
Decussates in medulla
3 neurons
Primary neurons have cell bodies in
dorsal root ganglion.
Axons enter spinal cord and ascend to the medulla oblongata without decussating where they synapse with secondary neurons.
Secondary neurons in medulla:
axons decussate and ascend to thalamus
Tertiary neurons:
project to somatic sensory cortex

10. Spinocerebellar System
Carries proprioceptive information to cerebellum, most of which is unconscious
Actual movements monitored and compared to cerebral information representing intended movement
Posterior and anterior spinocerebellar tracts
Ipsilatteral=“same side”
Does not decussate

11. Spinocerebellar tracts:
proprioceptive to cerebellum
Posterior and anterior spinocerebellar tracts
Ipsilatteral=“same side”
Does not decussate
2 neurons
Primary neuron from receptor to spinal cord
Cell body in posterior root ganglion
Secondary neurons from spinal cord to
cerebellar cortex

12. Descending Pathways Two functions: Somatic and Visceral motor control
Through both excitation and inhibition
Modification of sensation:
cortex may reduce the conscious perception of sensations

13. Descending Pathways through spinal cord white matter
Corticospinal (pyramidal)—within dorsal and anterior columns
voluntary movements
Indirect Pathways
involuntary movement, upright posture, balance, walking, reflexive movements of head and neck in response to visual and auditory stimuli

14. The Descending Pathways
Direct pathways (pyramidal system): maintenance of muscle tone, controlling speed and precision of skilled movements
Indirect pathways (extrapyramidal system): less precise movements.

15. Direct Pathways (pyramidal System) Corticospinal tracts

16. Skeletal Muscle Control
Motor system:
maintains posture and balance; moves limbs, trunk, head, eyes; facial expression, speech.
Reflexes and voluntary movement
Two neurons: upper and lower
Upper motor neurons:
Arise in cortex connect to lower motor neurons (sometimes with an interneuron)
Lower motor neurons:
axons leave the CNS, extend through PNS to skeletal muscles.
Cell bodies in anterior horns of spinal cord and in cranial nerve nuclei of brainstem

17. Direct Pathways
Control muscle tone and conscious fine, skilled movements in the face and distal limbs
Direct synapse of upper motor neurons of cerebral cortex with lower motor neurons in brainstem or spinal cord
Contralatteral
Decussats in medulla (decussation of pyramids)
Tracts
Corticospinal: direct control of movements below the head
Lateral = limb muscles
Anterior = axial muscles
Corticobulbar: direct control of movements in head and neck

18. Corticospinal Tracts
Axons of upper motor neurons descend to pyramids of medulla oblongata
75-85% decussate and descend in the lateral corticospinal tracts. Supply all levels of body
Remaining fibers descend decussate near level of synapse with lower neurons. Supply neck; upper limbs

19. direct control of movements below the head
Direct Pathways
Contralatteral
Decussates in medulla (decussating of pyramids)
Corticospinal Tracts
direct control of movements below the head
Lateral column tracts = limb muscles
Anterior column tracts= axial muscles