What muscle causes goose bumps? Which vertebrae don't have a body?
Arrector pili muscle.
Atlas (C1) vertebra.
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" :