Part 2: We Need to Talk About the Gamma Motor System

30 years ago this year Job’s Body was published. This 8-part essay is a tribute to Deane Juhan’s unparalleled narrative of the body.

The Enigma of Changing Habits — You Have to Get Somatic (Part 2 of 8. See part 1)

Included in this essay is an interdisciplinary synthesis between aspects of Deane Juhan’s “Job’s Body” and Eckhart Tolle’s “The Power of Now.” Infusing physiology with presence reveals an unexpected answer to the compelling question, “Why is it so hard to change a habit?”


TThe alpha aspect of our “alpha-gamma” muscular-nervous system gets most of the attention. The alpha system is the part of the nervous system through which we have conscious control of our muscles via the cerebral cortex.

“The principal *is* elegantly simple.”

The study of the gamma aspect of the alpha-gamma muscular-nervous system is the study of how we default to habituated patterns. The gamma system holds clues for why suddenly moving in a way we’re not used to — or the anticipation of a new movement — feels so wrong. The gamma system governs our reflexes and has tremendous power over both our physical form and our sense of self — power we unconsciously hand over in exchange for not having to attend to how we are moving as we go about the busy-ness of living (Juhan p.223).

It is through this system that an action which initially arose as a choice, then, repeatedly performed, became a habit; what was at first an original and spontaneous response (“x”), eventually fell from awareness, lost the quality of choice, and we came to know the “feeling” of doing “x” as “me” (Juhan pp. 232, 263). The gamma system is a mirror reflecting back: unless we maintain presence, the default position is the accumulation of previously established, conditioned muscular responses.

“It is these relatively fixed pathways and responses which control the range of behavior and style of movement that are so characteristic of each species; a cat and a small dog have pretty much the same…structure, yet each moves this structure about in ways which clearly identify it as canine or feline. These distinctly different styles of moving similar physical frames [in the human] are the result of different patterns of integrating sensory information and of organizing motor commands, primarily in the spinal cord and in the older, “reptilian” portion of the brain — that is, the centers of gamma motor control” (Juhan p. 216).

A Reflex Arc

The gamma motor system runs through the brainstem and produces responses similar to the genetically inherited spinal reflex arcs. Spinal reflex arcs allow for instantaneous movement because the motor control occurs through the spine without the additional time of travelling to and being processed by the brain. The spinal reflex arcs work with two mechanisms — the muscle spindles and the Golgi tendon organs — “to resist any sudden, unexpected change in muscle length,” and thereby “maintain a sense of ‘normalcy’ throughout every phase of the active use of my muscles” (Juhan p. 213, italics mine).

The significance for trying to change a habit is that until new muscle lengths are set, the previously established individual muscular settings of both resting tone and our familiar movements will always be adhered to, even as we try to do something new.

Resetting the muscle lengths of our familiar, habitual movement patterns requires awareness, assessment of the current movement patterns, new options for movement, and a good deal of deliberate practice. These steps can be followed through any modality that combines both physical awareness and psychology.

Muscle Spindles and Golgi Tendon Organs

A muscle spindle is a bundle of specialized muscle fibers surrounded by skeletal muscle cells. Wrapped around the spindle is a sensory ending called the anulospiral receptor. The anulospiral receptor senses only the movement of the muscle itself, rather than any other surrounding activity, as it registers the length and speed of the muscle’s changing lengths (Juhan pp. 192–195). Through the spindles, “movement and sensation are joined directly together in a firm embrace” (p. 193). By forming a reflex arc with the spinal cord, the spindles make “the most direct linkage we have between local sensory events and local motor response” (p. 194). (Here begins the formation of an essential physiological principle in the recovery from sensory-motor amnesia.)

The Golgi tendon organs comprise an unconscious yet adaptable tension-feedback system that controls the degree of stretch in a muscle. The Golgis measure the degree of tension — the net amount of work force — that results from the changing length of the muscles. The Golgis are located in the connective tissue tendons of muscles, the tissue that connects the contractible belly of a muscle to a bone. By registering the tension load, the Golgis set the threshold value for our muscles’ required tension (the “base tonus” which varies from person to person).

Is the Body the Self?

A therapeutic task of somatic psychotherapy is to gain access to what we are doing muscularly and energetically which otherwise, to some degree, is under our radar. By studying the ways we move and inhibit movement, we are studying the beliefs by which we keep ourselves over-bounded or under-bounded. Much wisdom is to be gained through developing this dialogue with our physicality.

Patterns of Somatic Distress from “Emotional Anatomy” by Stanley Keleman

However, the body may not always be synonymous with the self; who are we when the body breaks down? Are we the flesh that gets ill, injured, old, and ultimately, dies? The physical body registers, manifests and remembers so much of what we think and do, and while we are each responsible for our own body, there is so much that is ultimately out of our hands. I perceive our scars are maps of where we’ve been, but that they are not the territory. The effect of life’s wear and tear on our mortal flesh is ultimately not the be-all and end-all of who we are most essentially. Paradoxically, though, we often do find ourselves as a result of the breakdowns.


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Next in Part 3: Reclaiming Locus of Control / Why We Don’t Already Include the Spindles and the Golgis In the Changing of a Habit / The Patterns We Live By: Osteoblasts and Osteoclasts