Gravity Sense Part 1

Overview of the Gravity Sense

Please notice that in the above Oliver Developmental Model, the gravity sense (in red) is the foundation of all the sensory-motor feedback system.

Most people don't think a lot about gravity. However, our developmental systems are designed to take gravity extremely seriously. Postural instability is one of human’s biggest liabilities. Our cells, organs, and body systems are all affected by gravity. The definition of gravity is the force of attraction of everything on earth toward the center of the earth. Why is this sense so important?

To emphasize the importance of the gravity sense, one most understand that this sense starts to develop in the very earliest part of embryonic development. Why is the sense of gravity prioritized in human development? Every movement in our body is predicated on adjusting and reacting to gravity.

One of our greatest needs of survival is the ability to stay upright and control our movements in gravity. Our eyes must work with our inner ear so that we do not get seasick or dizzy moving our heads in everyday activities.

Our ears are attached to our gravity sense through the audio-vestibular nerve (CN 8) to help us understand how space and distance are to be measured. We also understand that those who have trouble with gravity have a hard time feeling safe. They may be safe, but they do not feel safe.

The organs of the inner ear are the semi-circular canals. As you saw in the video clip, gravity is sensed when the head or body move out of alignment slightly. The liquid in the inner ear hits the hair cell at the base, informing the brain of the direction and acceleration of the movement.

The canals are designed to read three unique axes of movement in space: yaw, roll, and pitch. The acceleration upward, like in an elevator or trampoline, is also read by a different mechanism: a saccule at the base of the complete canal structure.

For any person working in sensory-motor development (SMD), knowing and using these axes can be helpful and important for improved function of the gravity sense. I like to break down the understanding of the axes of the gravity sense into practical ways of thinking.

I use shorthand labels to identify the level and adjustment of checks and activities.

Gravity Axes

Yaw : Turning the body or head to the side, as in a log roll or turning to look behind you.         

Roll: Body or head leaning to one side, as in I’m a Little Teapot or dropping ear to shoulder.

Pitch: Body or head going forward or back, as touching toes or looking up to the sky.

Gravity Levels

High Level = Standing posture which is a high gravity challenge

Medium Level= Sitting Posture which is a medium gravity challenge

Low Level= prone or supine which are a low gravity challenge, with prone being the lowest gravity challenge

Postures that Trigger Gravity Sense

The gravity sense can be affected by either head and neck movements or full body movements. Abbreviations for different postures:

H/N= Moving only neck and head

F/B= Full body

Lastly, the gravity sense may affect or be affected by what I call the gates of the body:

the shoulders
the hips
the knees
the ankles
the feet

Challenges or assists to the gravity sense:

Vision
Hearing
Body Space Sense
Tone
Pain
Trauma

Assignment: Watch the video at the top again. Observe what you are seeing in the gates of the body list above. Draw a stick figure. highlight or circle the gates of the body being affected by the gravity challenge.

Review Questions

1.   Why is the gravity sense prioritized in human development?

2.   What happens when people are gravity insecure? Name 5 possible reactions.

3.   What are the three axes (the names of spatial movement) in gravity?

4.   What are the three levels of gravity? Why are these good to remember?

5.   Why is it so important to be very gentle when activating the gravity sense?