Cavitation is an effect where a bullet passing through soft tissue, as demonstrated in the video below:
It isn't just the bullet that causes damage when it passes through a body. Cavitation can have an equally devastating effect on the tissue and, in particular nerves. When the bullet passes through JFK's neck, there is the damage caused by the bullet and damage caused by cavitation. The bullet passes through an area called the Brachial Plexus, an area dense in nerves coming out of the spinal column. In the diagram below the red dot represents the approximate position the bullet enters his upper back/lower neck:
Comments from Dr. Robert Artwohl explaining why we saw the arms stiffening upward.
“JFK’s reaction to the neck wound was, for all intents and purposes,
instantaneous to the hit at Z-223/224. As the bullet passed through his neck, the
pressure cavity caused an immediate and wide spread stimulation of all the nerves in the immediate vicinity, that is of the brachial plexus, the large group of nerves that emerge from C5-T1.
These are the nerves that supply motor function to the arms.”"Comments from neurologist Dr. Strully in a letter sent by Dr. Strully to Dr. Robert Artwohl, dated April 9, 1994 as to an even greater possible extent of the muscle contractions:
"Before all else, it is necessary to remember that this assassination reveals a sequence of neural responses initiated in the neck by the
shock wave and cavitation induced by the bullet in its traverse of the neck. This
traumatized all structures in a 6 inch radius in all directions from the path of passage through the neck. This spread of forces occurred in a
fraction of a second, traumatizing all neural structures in the immediate vicinity within a fraction of a second as determined by the speed of the missile according to ballistic studies.
As a result, contraction of the muscles innervated by nerves closest to the bullet's path took place first; -- right deltoid, left deltoid, right biceps followed by the left biceps and sequential contraction of all muscles in the forearms, hands, chest, abdominal walls and paraspinal muscle groups, with muscles in the lower extremities, farthest from the shock wave, responding last. All neural structures in the neck were stimulated at the same moment…” [posted by Brian Roselle]
The effect of cavitation causes an "instantaneous" contraction of all the arm muscles. This is clearly seen in the Z-film as JFK's elbows fly up to their highest point and the top half of his body appears to momentarily stiffen. It is a radical, extreme and instantaneous reflex reaction caused by the wholesale damage of nerves in the Brachial Plexus.
How quickly is "instantaneous" for a reflex reaction:
"While human reaction times tend to require hundreds of milliseconds, "One of the fastest [neural feedback] loops is from arm sensors to spinal cord and back out to arm muscles: it takes 110 milliseconds for feedback corrections to be made to an arm movement." (William H. Calvin, "The unitary hypothesis: A common neural circuitry for novel manipulations, language, plan-ahead, and throwing?" in Tools, Language, and Cognition in Human Evolution, edited by Kathleen R. Gibson and Tim Ingold. Cambridge University Press, pp. 230-250, [1993].)
So there could already be a reaction of a subject's arms in as early as 110 milliseconds, the equivalent of two Zapruder frames. But, of course, with JFK and Gov. Connally shot between 223 and 224, we should not be able to discern a significant reaction before frame 226. While only a few milliseconds later, this would still be too late.
However, an experiment cited by conspiracist Milicent Cranor demonstrates that even less time may be required.
Cranor summarizes a study published in the British journal, Brain (Brown P, Rothwell JC, Thompson PD, Britton TC, Day BL, and Marsden CD. New observations on the normal auditory startle reflex in man. Brain 1991; 114:1891-1902):
Auditory Stimulus Response Times in Milliseconds (m/s)
The following figures come from a study by Brown et al, published in the British journal, Brain. The authors tested the latency period (time it takes to respond) of the auditory startle reflex in 12 healthy volunteers ranging in age from 18 to 80 years. While relaxing in a chair, the subjects were randomly treated about every 20 minutes to a tone burst of 124 decibels, the equivalent BANG! of a car backfire 20 feet away. The average latency period of the relevant muscle groups in milliseconds:
Neck: 58 m/s (range 40-136 m/s)
Paraspinal muscles: 60 m/s (range: 48-120 m/s)
Forearm Flexors: 82 m/s (range: 60-200 m/s)
Forearm Extensors: 73 m/s (range 62-173 m/s)
Thumb: 99 m/s (range 75-179 m/s)
Back of Hand: 99 m/s (range 72-176 m/s)
The authors concluded:
"The most generalized startle response to the standard sound stimulus employed consisted of eye closure, grimacing, neck flexion, trunk flexion, slight abduction of the arms, flexion of the elbows and pronation of the forearms. There was considerable variation in the degree to which this response was expressed, and in some subjects only eye closure and flexion of the neck was apparent."
[See Cranor, "Neurology and Jiggle Analysis"]
The experiment demonstrated that, in response to an auditory stimulus, quantifiable physical reactions can be observed occurring most quickly in muscles the shortest distance from the brain: in the neck as quickly as 40 milliseconds (less than one Zapruder frame), in the paraspinal muscles as quickly as 48 milliseconds (less than one Zapruder frame), in the forearm flexors as quickly as 60 milliseconds (slightly more than one Zapruder frame), in the forearm extensors as quickly as 62 milliseconds (slightly more than one Zapruder frame), in the thumb as quickly as 75 milliseconds, and in the back of the hand as quickly as 72 milliseconds.
