The joint where the neck joins the head is :

Question

UnlockIAS · Accepted Answer

Correct — A, Pivotal joint. A pivot joint is one in which a peg or cylinder of bone rotates inside a ring, so the movement it permits is rotation about a single axis. That is exactly the arrangement at the top of the neck. The first cervical vertebra, the atlas (C1), is a bony ring that carries the skull; the second, the axis (C2), sends up a peg called the dens or odontoid process, which stands inside that ring and is held against its front arch by the transverse ligament. When you shake your head to say 'no', the atlas — and with it the whole skull — swivels around the peg of the axis. Peg inside a ring, rotation about one axis: a textbook pivot joint, which is why school science calls the head-and-neck junction a pivot joint and why (a) is the marked answer. One honest refinement worth carrying, because a careful student will notice the head also nods. The head-neck junction is really a complex of two joints working together: the atlanto-occipital joint, between the base of the skull and the atlas, is a condyloid (ellipsoid) joint and produces the forward-and-backward nodding of 'yes'; the atlanto-axial joint, between atlas and axis, is the pivot and produces the side-to-side rotation of 'no'. NCERT-level science compresses the pair into the single label 'pivot joint', and that is the answer the key rewards. None of the other three options can even produce rotation of the skull, so the question is safe on its face.

Why the other options are wrong — (b) A saddle joint has two saddle-shaped surfaces, each convex in one direction and concave in the other, seated across one another. It allows movement in two planes plus a limited swivel, but not free axial rotation. The classic human example is the carpometacarpal joint at the base of the thumb, between the first metacarpal and the trapezium of the wrist — the joint that lets the thumb swing across the palm and oppose the fingers, which is one of the anatomical foundations of the human grip. There is no saddle joint at the head-neck junction.  (c) A hinge joint moves in one plane only, like a door on its hinges — bending and straightening, and nothing else. The elbow, the knee, the ankle and the joints of the fingers and toes are hinge joints. A hinge could account for the head nodding forwards and backwards, and that is why the option is placed here, but it cannot produce the left-and-right turning of the head that everyone can perform. Since the question asks what kind of joint the head-neck junction is, and rotation is its defining movement, hinge is wrong.  (d) In a ball-and-socket joint the rounded head of one bone sits in a cup-shaped hollow of another, giving movement in all directions — the widest range of any joint in the body. The two human examples are the shoulder (head of the humerus in the glenoid cavity of the scapula) and the hip (head of the femur in the acetabulum of the pelvis). It is a tempting answer because the head can be moved in many directions, but that freedom comes from the whole chain of seven cervical vertebrae acting together, not from a ball sitting in a socket at the skull base. The skull rests on the atlas through paired condyles, not a ball.

Concept: Joints are the junctions where two or more bones meet, and they are classified by how much and in what way they move. Fixed (immovable) joints, such as the sutures between the flat bones of the skull, allow no movement. Slightly movable (cartilaginous) joints, such as those between successive vertebrae with their intervertebral discs, allow a little give. Freely movable (synovial) joints are subdivided by the shape of the meeting surfaces: ball-and-socket (shoulder, hip), hinge (elbow, knee, ankle, fingers), pivot (atlas on axis at the neck; also the proximal radio-ulnar joint of the forearm), gliding (between the small carpal bones of the wrist and the tarsal bones of the ankle) and saddle (base of the thumb). Naming each type with one human example is the whole examinable content of this topic.

State PCS 2024 Q63 — Science & Technology PYQ with Answer

State PCS 2024 Q63 — Science & Technology PYQ with Answer