Problem 30 - Anatomy and Physiology of Animals

Question

Which of the following are joined by a symphysis? a. adjacent vertebrae b. the first rib and the sternum c. the end and shaft of a long bone d. the radius and ulna bones

Step-by-Step Solution

Answer

The adjacent vertebrae are joined by a symphysis.

Step 1: Understand What a Symphysis Is

A symphysis is a type of cartilaginous joint where the bones are joined by fibrocartilage. These joints allow for slight movement and are commonly found in the midline of the body.

Step 2: Analyze Each Option

Examine each of the given options to determine if the involved structures form a joint through a symphysis. - Option a (adjacent vertebrae): The intervertebral discs between vertebrae are made of fibrocartilage, a characteristic of symphyses. - Option b (first rib and sternum): This is a synchondrosis, another type of cartilaginous joint, not a symphysis. - Option c (end and shaft of a long bone): These are connected by an epiphyseal plate during growth, not a symphysis. - Option d (radius and ulna bones): These are connected by an interosseous membrane, not a symphysis.

Step 3: Identify the Correct Answer

Based on the analysis, the correct answer is option a, adjacent vertebrae, because they are joined by intervertebral discs made of fibrocartilage, which exemplifies a symphysis.

Key Concepts

Cartilaginous Joint

Cartilaginous joints are a type of joint where the bones are connected mostly by cartilage. They are different from synovial joints, which are highly mobile, because cartilaginous joints tend to offer limited movement. These joints can be found in areas where some flexibility is necessary, but stability is crucial.

There are two main types of cartilaginous joints:

• Symphyses
• Synchondroses

Symphyses involve the presence of fibrocartilage, allowing slight movement. Examples include the joints between the vertebrae in the spine. Synchondroses, on the other hand, use hyaline cartilage. They are typically found in places like the growth plates in children's long bones.

The main purpose of these joints is to allow limited movement while maintaining strength and support in the body structure.

Fibrocartilage

Fibrocartilage is a tough yet flexible type of cartilage. It is found in areas of the body that act as cushions between joints. This specialized tissue contains a rich matrix of collagen fibers, which make it extremely durable and capable of withstanding pressure.

Some characteristics of fibrocartilage include:

• High tensile strength
• Ability to absorb compressive forces
• Presence in areas requiring support and limited movement

This type of cartilage is not as pliable as elastic cartilage, which allows it to maintain form and integrity even under stress. Its unique properties make fibrocartilage perfect for joints like those in the spine, where both support and slight mobility are needed.

Intervertebral Discs

Intervertebral discs are the fibrocartilaginous cushions between each vertebra in the spine. These discs play a critical role in maintaining the flexibility and strength of the vertebral column. They are essential in absorbing shock during activities like jumping and running.

An intervertebral disc is composed of two main parts:

• The anulus fibrosus – the outer ring made of tough fibrocartilage
• The nucleus pulposus – a softer, gel-like center

The anulus fibrosus provides the disc with structure, while the nucleus pulposus acts like a shock absorber. Together, these components allow the spine to twist and bend slightly without damage. These discs are key examples of symphysis joints, as they join adjacent vertebrae and allow for slight movements across the vertebral column.