Page 25 - Handbook of Electronic Assistive Technology

12 HANDBOOK OF ELECTRONIC ASSISTIVE TECHNOLOGY

FIGURE 1-7 Basic motor system� Courtesy of Fig. 2-4 The control of movement. The blood supply to the brain. Barnes, L.,
Fairhurst, C., 2011. Hemiplegia Handbook for Parent and Professionals. Mackeith Press. Hemiplegia Handbook

about the world around us are also relayed back from our peripheries, back to the spinal
cord and upward using all our different senses such as pain, position, temperature and
gross sensation. This occurs using peripheral nerves – simple wiring to and from the CNS
going in (the senses), or out (the motor unit). Simple chemical transmitters are used to
pass information across small gaps (or synapses) between the various elements of these
systems (e.g., from central corticospinal pathway to peripheral motor nerve to muscle). In
turn, all muscles work in opposing pairs at each joint: a larger agonist muscle (e.g., biceps
at the elbow) and a smaller antagonist muscle (e.g., triceps at the elbow).
The complexity of the CNS requires a robust support system as we saw during devel-
opment and embryology. In an adult, the brain needs about a fifth of the blood supply,
oxygen and energy requirements of the whole body. This is pretty greedy as it’s so com-
paratively small.
As we saw during our review of embryological development, blood flows up in a pair
of frontal internal carotid arteries and a pair of back vertebral arteries. In the mature
system these form a loop at the base of the brain (Fig. 1-8) and send off a series of arter-
ies (including anterior, middle and posterior cerebral arteries, but a large number of
smaller vessels).
Blockage can be caused by structural damage, clot or fluid embolus, and occurs most
commonly in the middle cerebral artery. This feeds and oxygenates the basal ganglia and
motor areas of the cortex.