Understanding Spinal Tracts and Their Functions

Spinal Tracts Overview

Understanding how information passes back and forth between the brain and spinal cord is essential for grasping the functionality of the nervous system.

Ascending Tracts (Sensory Information)

• Location: White matter, consist of axons of sensory neurons transporting information to the brain.
• Function: Carry sensory signals.

1) Dorsal Column

• Purpose: Transmits visceral pain (e.g., stomach ache) and proprioception (the body's ability to sense its location, movements, and actions).
• Decussation: Occurs in the medulla oblongata.
  • Gracile Fasciculus: Carries information from the midthorax and legs.
  • Cuneate Fasciculus: Handles signals from T6 and above (superior).

2) Spinothalamic Tract

• Location: Situated in the lateral column of the spinal cord.

• Sensory Information: Transmits sensations related to pain, temperature (heat and cold), pressure, tickle, itch, and touch.

• Decussation: Occurs at the level of entry in the spinal cord.

• Pathway to the Brain: Both the dorsal column and spinothalamic tracts convey signals to the thalamus (2nd order neuron), which then relay to the somesthetic cortex (the part of the brain that receives sensory information).

Descending Tracts (Motor Information)

• Function: Carry motor signals from the brainstem and spinal cord, originating typically from the cerebrum.
• Pathway Components: Two neurons in the pathway:
  • Upper Motor Neuron: Soma located in the cerebrum or brainstem; its axon terminates by synapsing with a lower motor neuron in the brainstem or spinal cord.
  • Lower Motor Neuron: Innervates muscles directly.

Example: Corticospinal Tracts

• Function: Transmits motor signals from the cerebral cortex (specifically the motor cortex or pre-central gyrus in the contralateral brain).
• Decussation: Occurs in the medulla oblongata, forming the lateral corticospinal tracts in the spinal cord.

Spinal Cord Injuries

• Concept: Understanding which functions may be lost depending on the location of a spinal injury is crucial.
• Reference: See "Testing Your Comprehension" question 2 on page 510 for practical applications of this knowledge.

Conditions to Know

• Poliomyelitis: A viral disease that can affect motor neurons, leading to muscle weakness and paralysis.
• ALS (Amyotrophic Lateral Sclerosis): A progressive neurodegenerative disease that affects motor neurons, causing muscle weakness, disability, and eventually death.