Biology

Movement, Cycles and Rhythms

Actions for Movement, Cycles and Rhythms'

The control of movement is often divided into mechanisms of reflexes and of voluntary movement.

What is a reflex? It is a stereotyped, automatic movement evoked by a specific stimulus. It is uniform across members of a species. Some examples in humans are the patellar or kneejerk reflex, the salivary reflex, the orienting reflex, and the pupillary reflex.

In reviewing the reflex arc, pay special attention to proprioception, the distinction between alpha and gamma motor neurons, muscle spindles, the stretch reflex, and primary motor cortex. (Prof. Suzuki also discusses the basal ganglia and the cerebellum, but in another lecture that I have not assigned. They are covered in the embedded book chapter by Kalat, entitled "Movement".)

Further, let's think about the cycles in our behavior. They are ancient and varied. We certainly inherited them from species that evolved earlier than we did.

We harbor a number of rhythms. Generally we have cellular cycles that augment the day-night rhythm to regulate our behavioral cycles. There are possibly very long cycles that govern our evolution. Men and women both run on cycles, though with differences. But do our cycles still make biological sense?

Questions (answer one)

• Can you point to any movements that do not involve reflexes--or some reflexes that do not involve movement?

• Sleep is tied to recovery of normal function and memory formation. Why does it make sense, then, to stop for sleep just because the sun sets? Why not sleep just whenever we have a backlog of memories to form or we're under stress or sick? Does the wide variation in our daily experience require such an extreme regularity of sleep regulation? Since we don't learn or exercise the same amount each day, why do we nevertheless sleep the same amount? A number of possible answers are given in the first 10 minutes of this fascinating podcast, but offer your own insights as well.

• Furthermore, women show more pronounced cycles in sex hormones than men do, including menstrual cycles and a rather imprecise biological clock with a different origin. Is this an evolutionary leftover, no longer necessary or helpful for humans? Would you want the equivalent of a birth control pill for all of our cycles.