Question

What muscle causes goose bumps? Which vertebrae don't have a body?

Answer 1

Arrector pili muscle.
Atlas (C1) vertebra.

Explanation:

The goose bumps or piloerection is caused by the contraction of arrector pili muscle. This is a tiny muscle in the skin. It is attached to hair follicle. It contracts in response to cold, fear etc (sympathetic activity).

Fig 1 : The diagram of cross section of skin showing arrector pili muscle :

The first cervical (C1) vertebra also known as atlas has no "body".

Fig 2 : Atlas

Fig 3 : For comparison, here is a diagram of a cervical vertebra other than atlas, which has a "body" :