Sublime

As the muscle spindle senses a muscle being stretched to its end range, it sends a message to the spinal cord. The CNS reacts with a motor neuron telling the muscle to contract to avoid being overstretched and possibly injured. This is known as the stretch reflex, or myotatic (which means muscle tension) reflex.

Figure 1.20. The lengthening of the myofascia is sensed by the muscle spindle, which signals the spinal cord. The spinal cord responds with an efferent (motor) nerve signal for the muscle to contract.

Sometimes you will exhibit reflexive agency - agency as an automatic response to the situation you’re in. You have a preference, you have the ability to satisfy it, so you do that. What could be more natural?

More than a century after Pavlov’s characterization, our bodily reaction to change is no longer called a reflex. It’s termed the orienting response,

When a muscle is stretched and the stretch reflex is activated, an inhibitory interneuron in the spinal cord sends a message to the opposite muscle group to relax.

The reflex arc creates the contraction of the muscle, which is predominately isometric. Further deceleration of the body’s movement then loads the connective tissue, which eventually reaches a point at which the force required to lengthen it farther has been absorbed by the increasing stiffness of the elastic fiber. Once it reaches the point at

A refractory period (the brief period needed to restore the resting potential) of about 20 seconds occurs with RI; however, RI is thought to be less powerful than PIR.

The spinal cord also coordinates certain reflexes and movement patterns independent of the brain and brain stem.