The vertex, also known as the crown of the head, is the uppermost point on the human body on the top of the head. It is the part of the body that comes out first (usually) during childbirth.
There are some interesting properties regarding this anatomic location.
Firstly, if one places a cellphone on top of their head, they cannot feel the vibration when they receive a call or text message. Almost every other part of the body can feel the vibration, but not the vertex. This is because the top of the skull is not covered by any muscles, which have receptors that sense vibrations. Ergo, no vibrations can be felt.
Secondly, when one places their hand on top of their head, they experience a sudden drop in muscle strength. This applies to the whole body and can be seen through basic activities such as lifting weights or even through arm-wrestling. The degree of weakness can be up to 10~15% of the muscle’s normal strength.
The reason for this is slightly more complicated. The nervous system remembers trauma and responds to it, such as childbirth where almost everyone (assuming they were born through vertex presentation, the most common) experiences trauma on the top of the head. For example, as labour is quite an intensive procedure, significant pressure is placed on top of the baby’s head as it tries to push out.
Because of this, when pressure or electric signals are exerted on the vertex, the nervous system responds negatively, remembering the trauma from childbirth, and “weakens” throughout the body. This results in decreased force exertion by muscles. The same effect can be achieved when a cellphone is placed on top of the head, as it emits electric signals.
Lastly, the top of the head is not sealed until a few months after birth. This makes a baby’s skull very malleable, and two fontanels, which are gaps between pieces of the skull, remain open for that time. This is seen as “soft spots” on the head which pulsates as there is no bone beneath it.