# The Cervical Spine Model¶

The cervical spine model is the neck of the human model. It is always present when the human model is used.

The cervical spine model contains 7 vertebrae with 3 DoF spherical joints from T1 to C2, a 1 DoF joint between C2 and skull and 136 muscle fascicles. The center of rotations is based on Amevo et al. 1991.

The cervical spine model is part of the Trunk model, and the segments, joints and kinematics are therefore included by default.

The segments of the cervical spine model are always present, but the muscles are not enabled by default. Some of the neck muscles are defined by the shoulder model, so the muscles of the cervical spine model can only be enbled when both arms with muscles are present.

## Example Configuration¶

Enabling muscles from the cervical spine model, requires that the arms also enabled.

#define BM_ARM_RIGHT ON
#define BM_ARM_LEFT ON
#define BM_ARM_MUSCLE_BOTH ON
#define BM_TRUNK_CERVICAL_MUSCLES ON