1. When head flexes in meridian plane, exterior muscles exert force to support the head. There is also compressive force exerted on the first cervical vertebrae at the atlantooccipital joint.

2. Let F is muscle force & R is reaction at the joint. We get a three forces system which is concurrent at joint O. Hence we can apply Lami’s theorem on the force system.

Where α is angle with horizontal of muscle force and β is angle of reaction of joint with horizontal.

Hence muscles must apply 50 N force to support the head and reaction force developed at the joint is 88 N.

Movements Of Neck And Spine

1. Neck: It can rotate in horizontal plane. It can do lateral bending. It can also do flexion and extension in meridian plane.

2. Spine: Spine can do flexion and extension in meridian plane. It can also do lateral bending. It can also have rotational movement in horizontal plane.