**Question:** Articular disc of TMJ is made up of:

A. Hyaline cartilage
B. Synovial cartilage
C. Cancellous bone
D. Fibrous tissue

**Core Concept:** The TMJ (Temporomandibular Joint) is a synovial joint located at the articulation of the mandibular condyle with the temporal bone. The articular disc, also known as the disc-articular disc or disk, is a fibrocartilaginous structure that separates the condyle from the glenoid fossa of the temporal bone.

**Why the Correct Answer is Right:** The articular disc in the TMJ is made up of **synovial cartilage** due to its low friction properties, which are essential for smooth jaw movement. Synovial cartilage has a smooth, gel-like matrix composed of proteoglycans, type II collagen, and water, which reduces friction between the condyle and fossa during jaw movement.

**Why Each Wrong Option is Incorrect:**

A. **Hyaline cartilage** is incorrect because it has a dense, compact matrix composed of type II collagen, which is not suitable for reducing friction in a synovial joint.

B. **Cancellous bone** is incorrect as it is a type of bone tissue characterized by a porous trabecular structure, which doesn't serve the purpose of the articular disc in TMJ.

C. **Cancellous bone** is incorrect for the same reason as option B.

D. **Fibrous tissue** is incorrect because it lacks the necessary low-friction properties required for the articular disc in the TMJ. Fibrous tissue consists of interwoven collagen fibers that provide strength and support but lacks the gel-like matrix of synovial cartilage, which is essential for reducing friction in a synovial joint.

**Clinical Pearl:** The correct composition of the TMJ articular disc ensures smooth movement of the mandibular condyle within the glenoid fossa, enabling efficient jaw movement and reducing wear and tear on the joint components. Understanding the anatomy and composition of the articular disc is crucial for diagnosing and treating disorders related to the TMJ.