Overview
This lecture introduces the main ascending (sensory) and descending (motor) spinal cord pathways, including their functions, anatomical locations, and naming conventions.
Ascending (Sensory) Pathways
- Ascending tracts carry sensory information from the periphery to the brain.
- Dorsal columns transmit fine touch, proprioception (body position), and vibration.
- Fasciculus gracilis (medial, yellow) carries lower limb sensory fibers.
- Fasciculus cuneatus (lateral, green) carries upper limb sensory fibers.
- Arms are lateral to legs; cuneatus is lateral to gracilis in the spinal cord.
- Spinothalamic (anterolateral) tracts relay pain, temperature (lateral), and crude touch (anterior).
- Spino-cerebellar tracts (dorsal and ventral, purple) deliver subconscious muscle and joint information to the cerebellum for posture and movement coordination.
Descending (Motor) Pathways
- Descending tracts carry motor commands from the brain to muscles.
- Responsible for movement, muscle tone, reflexes, and some sensory modulation.
- Pyramidal tracts pass through medullary pyramids and are called corticospinal tracts.
- Lateral corticospinal tract controls skilled voluntary movements, especially limbs.
- Anterior (ventral) corticospinal tract controls axial (central/trunk) muscles.
- Naming tip: tract origin is first part of name; destination is the second part (e.g., corticospinal, spinocerebellar).
Extra-pyramidal Tracts
- Rubrospinal tract (from red nucleus) controls limb flexors.
- Tectospinal tract (from superior colliculus) mediates visual reflex movements of head/neck; mostly in cervical spinal cord.
- Vestibulospinal tract (from vestibular nuclei) has lateral and medial parts and controls posture and balance by affecting extensor muscles.
- Reticulospinal tract (from reticular formation) affects reflexes, muscle tone, and regulates respiratory/circulatory systems.
Key Terms & Definitions
- Ascending tract — pathway carrying sensory info from body to brain.
- Descending tract — pathway carrying motor commands from brain to body.
- Fasciculus gracilis — fibers for lower limb fine touch/proprioception.
- Fasciculus cuneatus — fibers for upper limb fine touch/proprioception.
- Spinothalamic tract — transmits pain, temperature, and crude touch.
- Spinocerebellar tract — conveys unconscious proprioceptive info to cerebellum.
- Corticospinal tract — conveys voluntary motor signals from cortex to spine.
- Extrapyramidal tracts — various motor tracts not passing through medullary pyramids (rubrospinal, vestibulospinal, etc.)
Action Items / Next Steps
- Review previous tutorial parts on neuron sequences and spinal cord anatomy.
- Learn tract names and their origins/destinations for identification on diagrams.
- Be able to match tracts to their primary sensory or motor functions.