21.6 Locomotion Flashcards
What are central pattern generators?
Neural circuits that produce rhythmic outputs in the absence of rhythmic inputs
Where are the central pattern generator neurons for walking found?
In the spinal cord (lower thoracic and lumbar regions)
What is the role of the midbrain for locomotion?
Initiates and modulates spinal neural circuitry
- control start, speed and stop of locomotion
Which tract is involved in locomotion?
(Medial) Reticulospinal tract
How does the medial reticulospinal tract control locomotion?
Controls axial and extensor motor neurons - e.g. extends legs to maintain posture
What system is in place for feedback regulation of locomotion?
Proprioceptive feedback from muscle afferents
Explain how the following diagram may explain central pattern generation for walking
- Walking is initiated when a steady input excites two (+) interneurons that each connect to the flexor and extensor motor neurons
- Interneurons generate bursts of alternating outputs as they each inhibit each other via another set of (-) interneurons
- Flexion on one side is at same time as extension on the other side
What is the characteristic gait seen in Parkinson’s? Why is this seen?
Freezing and festination (small, shuffling steps)
Due to destruction of dopaminergic neurons from basal ganglia to the mesencephalic locomotor region in the midbrain
What is hemiplegia?
Paralysis on one side - often from stroke
What gait characteristic is seen in hemiplegia?
Limping
How can syphilis (tabes dorsalis form) affect gait?
Tabes dorsalis is a form of neurosyphilis - where bacteria damages spinal cord and peripheral nervous tissue –> loss of proprioception
So there is an abnormal gait due to loss of feedback
How can peripheral neuropathy affect walking?
(Like syphilis) - lack of proprioception, resulting in an abnormal gait
May take wide, swinging steps to avoid tripping over own foot
How does the crossed-extensor reflex underlie locomotion?
This is where when one limb extends, the other limb flexes.
