The pontine reticular formation and the lateral vestibular nucleus both excite extensors in order to maintain posture.
The pontine is normally modulated by central projections. If the spinal cord is cut above the pontine reticular formation, this inhibition is lost and the extensors are stimulated even more. This results in deceribate rigidity.
Cutting the dorsal root with get rid of the deceribate rigidity because is disconnects the Ia afferents. This shows that deceribate rigidity is caused by hypersensitivity of the muscle spindle and is therefore considered gamma rigidity.
The lateral vestibular nucleus is normally modulated by the cerebellum. If you cut the spinal cord above the lateral vestibular nucleus, it will increase excitation of extensors and restore the deceribate rigidity. This is considered alpha rigidity.
Deceribate animals can show the walking reflex if their weight is supported.
They also have tonic neck and tonic labyrinth reflexes. |