ABSTRACT
Descending pathways Five important tracts descend from brain to spinal cord; four of these come from closely neighbouring parts of the brain, in the brainstem and medulla. These are the reticular formation, the vestibular nuclei, the red nucleus, and the tectum; the fifth source of descending fibres is the cerebral cortex. :
Reticular formation If you take the brainstem, and remove all its sensory and motor nerve nuclei, all the fibre tracts that have to go through it, and all other well-demarcated structures, a considerable area of terra incognita is left unaccounted
Clinical box 10.1 Motor neuron diseases There exist a number of disease conditions involving the motor neurons, exhibiting a range of clinical and pathological patterns but all characterized by motor neuron degeneration and disabling motor dysfunction. The most common such condition is ‘amyotrophic lateral sclerosis’ (ALS) or Lou Gehrig’s disease, after the famous baseball player who succumbed to the disease. It is an incurable, relentlessly progressive and ultimately fatal degenerative condition. Clinically, the condition is suggested by progressive weakness and examination ndings in keeping with both classical ‘upper’ and ‘lower’ motor neuron lesions, that is: increased tone and hyper-reexia (UMN), alongside fasciculations and muscle wasting (LMN).
