neck, head
頚 centers on the neck and, by extension, the head as the body part connected by the neck.
頚 is a simplified variant of 頸. The traditional form 頸 combines 巠 (likely phonetic) with 頁 (head) to express the neck. The modern simplified left side 圣 is a shorthand replacement.
The right side 頁 means head or page, and the left side 圣 looks like a simplified neck shape. Picture a head (頁) attached to a neck (圣) to remember 頚 as neck.
For ケイ, imagine a neck so stiff it looks like the letter K: K -> ケイ, and the head (頁) sits stiffly on top.
cervical vertebrae
cervical spinal cord; cervical cord
carotid endarterectomy; CEA
decapitation
inseparable friend; sworn friend
cervical neuro-muscular syndrome
cervical plexus
jugular vein
neckbones
caroticotympanic arteries