3 FINAL ascending tracts: 11 05 PNS & Reflexes - PHYL 301

What are tracts?

Different spinal cord tracts are how Sensory and motor neurons travel

Ascending tract

Sensory (delivers information to brain)

• Carries information from receptors → CNS (sensation)

• Major pathways

  • Posterior (dorsal) column

  • Spinothalamic tract

  • Spinocerebellar tract

Descending tract

Motor (delivers information to periphery)

What do all tracts involve?

Spinal cord and brain

Posterior (Dorsal) Columns

• Transmits fine touch, two-point discrimination, vibration, proprioception, & pressure

  • PC: Fine T(w)o Vib(ration) Prop(ioception) Pressure

• Cuneate Fasciculus (fasciculus cuneatus):

  • “cuneate” = wedge-shaped

  • Transmits information from T6 and superior areas → cerebrum

• Gracile Fasciculus (fasciculus gracilis)

  • gracile = slender

  • Relays sensory info from T6 and inferior areas → cerebrum

Posterior Column: First

Posterior Column: Second-order neuron

• Spinal cord or brainstem → thalamus

• Neurons decussate (cross over) in medulla oblongata of brainstem

• Form medial lemniscu

Posterior Column: Third-order neuron

Thalamus → somatosensory cortex in cerebral cortex

What is somatotopy?

organized mapping of body parts in the brain

• Primary somatosensory cortex: different areas receive signals from different parts of the body

  • Located in postcentral gyrus in parietal lobe of brain

Sensory homunculus

maps where sensory signals from different body parts go in the brain

What do larger areas mean in somatotopy?

More neurons dedicated to that part

• ex. Hands are very senstiive, large area with many neurons dedicated to it

Spinothalamic Tracts

• Spinal cord→thalamus

• Lateral spinothalamic tracts: relay temperature & pain

• Anterior spinothalamic tracts: relay crude touch & pressure

Stop let’s take a pause and stop the crude pranks

Spinothalamic Tract Neurons: First-order neurons

sensory neurons w/ dorsal root ganglion cell bodies → spinal cord

Spinothalamic Tract Neurons: Second-order neurons

Spinal cord dorsal horns → thalamus

Spinothalamic Tract Neurons: Third-order neurons

thalamus → somatosensory cortex

Spinocerebellar Tracts

• Spinal cord→ cerebellum

• Both tracts involved in (unconscious) proprioception

• Posterior (dorsal) spinocerebellar tract

• Anterior (ventral) spinocerebellar tract

Spinocerebellar Tract Neurons: First & Second Order

• Less Stops

• First-order neurons:

  • proprioceptor nerve endings of neurons w/

  • dorsal root ganglion cell bodies → spinal cord

• Second-order neurons:

  • spinal cord dorsal horns → cerebellum

• Both tracts involved in (unconscious) proprioception

• Spinocerebellar proprioception is ipsilatera