5.2.3 Information flowing toward the action, to muscles moving joints and bones

This analysis will be based on major-body action, i.e. arms, legs, back, and head but not fingers, toes, or jaw & tongue

• We are ignoring grasping, speech, and eating, as well as the involuntary actions such as for the heart and lungs
• Restricting ourselves to the head, back, arms, and legs, the analysis for other animals is likely to be similar
• We are reducing the complexity of the back and neck to simplify the analysis

Most bones are rigid. There are some two bone arrangements that can rotate about the axis.

• We shall simplify the analysis by pretending all motion happens at the joint, i.e. that it is the joint that rotates rather than a pair of bones, etc.

Most joints have three degrees of freedom for movement, but limited angles for each degree of freedom.

Muscles can adjust the degree of tension for pulling one bone toward another, thus rotating joints.

• We shall simplify joints by modelling them as gimbal mounts for bones (but more of that later)
• Each degree of freedom needs a pair of muscles to control the rotation within the given plane. It therefore needs a minimum of 6 muscles for most joints.

There is probably a 32 bits or better precision for controlling the tension for each muscle.

Even with major simplification there are at least 14 joints to control whole-body actions.

• shoulders, elbows, and wrists; hips, knees and ankles; waist and neck; are probably a minimal set
• Each has 3 degrees of freedom
• Since each degree of freedom is controlled by a balancing pair of muscles, there are 14 * 3 * 2 = 84 tension control (action) parameters
• Since each muscle requires at least 32 bits of control, there are 2,688 bits of information required for each moment of control.

A reasonable firing rate for neurons is around 1000 per second (1 msec)

• The firing rate tends to be variable, but we shall simplify the analysis by assuming a constant rate (like process control)
• Therefore we assume that every millisecond, each muscle receives an update on current tension control
• with this minimalist assumption, there are 2,688,000 bits per second required to manage the muscles for action
• Assuming a very short action sequence of 1 minute, we need 161 Megabits
• less that 1/100 of the bit-rate required for continuous vision

In evaluating these numbers, we have to keep in mind that we have tried to be extremely conservative. We also have not included requirements for the heart, the lungs, etc.

We also have not included muscles for actions that are different across the various species such as hand motions, or jaw motions (including speech and swallowing).