Study Question Sixteen

• Q16. A dog with the completely cut T1 section of the spinal cord was placed on a treadmill in a supported doggy harness, and when it was started the dog could actually move its legs in a normal doggy walk. However, the dog could NOT control its movements (start/stop), the treadmill had to start and end the movements. Explain why the dog was still alive, and how this experiment worked.
• Spinal Cord Function

  • The spinal cord is responsible for relaying signals between the brain and the body, but it also contains neural circuits known as central pattern generators (CPGs), which can produce rhythmic patterns of movement independently of the brain. These circuits are particularly important for locomotion.
• Location of Injury

  • The T1 segment of the spinal cord primarily affects the upper thoracic and forelimb motor control. While this injury interrupts signals to and from the brain, it does not eliminate the capacity for lower motor neurons and spinal circuits below the injury (e.g., in the lumbar region) to function.
• Central Pattern Generators (CPG's)

  • CPGs are networks of neurons in the spinal cord that can generate rhythmic motor patterns, such as walking. These circuits can coordinate the movements of the legs without requiring input from the brain. When the treadmill is activated, the mechanical motion helps stimulate these CPGs, allowing the dog's legs to move in a walking pattern.
• Proprioception and Sensory Feedback:

  • Even though the T1 injury disrupts the transmission of sensory information to the brain, the spinal cord can still process some local reflexes. Sensory receptors in the muscles and joints can provide feedback to the spinal circuits that help modulate the movement, contributing to a more coordinated motion.
• Lack of Voluntary Control:

  • The dog cannot start or stop the movement because the brain (particularly the areas involved in voluntary motor control) is no longer able to communicate with the lower motor neurons. The movements are entirely reliant on the activity of the CPGs, which are rhythmically activated by the treadmill's movement.