What is the primary difference between the axial and appendicular skeleton?

The axial skeleton forms the central axis of the body and includes the skull, vertebral column, and rib cage. Its main roles are protection of vital organs and providing central support. In contrast, the appendicular skeleton consists of the bones of the limbs (arms and legs) and the girdles (pectoral and pelvic) that attach them to the axial skeleton. Its primary function is locomotion and manipulation of objects, allowing for a wide range of movements.

How do ligaments and tendons differ in their function?

Both ligaments and tendons are made of dense regular connective tissue, but they connect different structures. Ligaments connect bones to other bones, primarily providing stability to joints and preventing excessive movement. Tendons, on the other hand, connect muscles to bones. Their role is to transmit the force generated by muscle contraction to the bones, thereby facilitating movement across a joint. Think of ligaments as joint stabilizers and tendons as muscle-to-bone connectors for movement.

What are the main functions of the skeletal system beyond just support and movement?

While support and movement are primary, the skeletal system has several other critical functions. It acts as a protective shield for delicate internal organs, such as the brain (by the skull) and heart/lungs (by the rib cage). Bones also serve as a vital reservoir for essential minerals like calcium and phosphorus, playing a key role in mineral homeostasis. Furthermore, the red bone marrow within certain bones is the site of hematopoiesis, the production of all blood cells, and yellow bone marrow stores fat.

Explain the three main types of joints based on their mobility.

Joints are classified into three main types based on the degree of movement they permit. Fibrous joints (synarthroses) are immovable, with bones held together by dense fibrous connective tissue, like the sutures in the skull. Cartilaginous joints (amphiarthroses) allow slight movement, where bones are united by cartilage, such as the intervertebral discs or the pubic symphysis. Synovial joints (diarthroses) are freely movable joints, characterized by a fluid-filled joint cavity, articular cartilage, and a fibrous capsule, enabling a wide range of motions like those in the knee or shoulder.

What is the significance of bone marrow in the skeletal system?

Bone marrow is a crucial component located within the cavities of bones. There are two types: red bone marrow and yellow bone marrow. Red bone marrow is responsible for hematopoiesis, the production of all types of blood cells (red blood cells, white blood cells, and platelets). This makes the skeletal system a vital site for maintaining the body's blood supply and immune function. Yellow bone marrow, predominantly found in the medullary cavity of long bones, primarily serves as a site for fat storage, which can be converted to red marrow in cases of severe blood loss.

Skeletal System

Biology

NEET UG

Version 1Updated 21 Mar 2026

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The skeletal system, a robust internal framework, provides structural support, protection for vital organs, and a crucial lever system for movement in vertebrates. Comprising bones, cartilage, ligaments, and tendons, it serves as a dynamic tissue reservoir for minerals like calcium and phosphorus, and houses the bone marrow responsible for hematopoiesis (blood cell formation). This intricate biolo…

Quick Summary

The skeletal system is the body's internal framework, composed of bones, cartilage, ligaments, and tendons. It's broadly divided into the axial skeleton (skull, vertebral column, rib cage) for protection and central support, and the appendicular skeleton (limbs and girdles) for movement.

Bones provide structural support, protect vital organs, and act as levers for muscle action. They also store essential minerals like calcium and phosphorus, and house bone marrow for blood cell production (hematopoiesis).

Cartilage provides flexibility and cushioning in joints. Ligaments connect bones to bones, stabilizing joints, while tendons connect muscles to bones, facilitating movement. Joints, classified as fibrous (immovable), cartilaginous (slightly movable), or synovial (freely movable), dictate the range of motion.

Understanding the number and names of bones, types of joints, and common disorders like osteoporosis and arthritis is key for NEET.

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Key Concepts

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Total Bones (Adult): — 206

Axial Skeleton: — 80 bones (Skull 29, Vertebral Column 26, Rib Cage 25)

Appendicular Skeleton: — 126 bones (Pectoral Girdle 4, Upper Limbs 60, Pelvic Girdle 2, Lower Limbs 60)

Bone Cells: — Osteoblasts (build), Osteoclasts (resorb), Osteocytes (maintain)

Joint Types: — Fibrous (immovable, e.g., sutures), Cartilaginous (slightly movable, e.g., intervertebral discs), Synovial (freely movable, e.g., knee, shoulder)

Ligaments: — Bone to Bone

Tendons: — Muscle to Bone

Functions: — Support, Protection, Movement, Mineral Storage (