human skeleton anatomy
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Human Skeleton Anatomy: Bones, Joints, Ligaments & Tendons

If you’re interested about learning the basic anatomy of our skeletal system and connective tissue, you’re in the right place. The goal is to distinguish and define bones from ligaments & tendons and understand how joints work. All types of bones and joints are categorized, so all four categories have main definitions, structure, types, and characteristics.

Bones

Definition

Bone is supportive tissue, a rigid organ made up of mainly collagen and calcium. Constantly growing, regenerating, and living organ that supports the body. More bones are connected into a bigger frame we know of as Skeleton, which is our main support system that gives our bodies shape, and strength and protects the soft tissues.

Bones Function

The main functions of the bones are:

  • To provide structural support for the whole body
  • To protect internal organs and soft tissues
  • To facilitate and assist movement patterns
  • To store minerals and lipids
  • To produce red and white blood cells and platelets

Bone Structure

Bone is a very complex organ with different specialized cells and unique functions, here we will cover the basics of bone structure.

The Bone is composed of two main parts:

  • Compact or cortical bone which is the outer layer that is harder, more rigid and dense and
  • Trabecular, Spongy or Cancelous bone that is the inner layer, which is less dense,

The bone has a more rigid, dense, and strong part but also a more flexible and adaptable one. The Bone matrix is composed mainly of elastic collagen (ossein) and gel-like Ground substance. The combination of different minerals that bind to it, is what makes the bone strong and rigid.

If you’re into anatomy, make sure you do not miss out on:

  • Cortical Bone
  • Trabecular Bone

The Cortical bone is the strong, white, and rigid part. The inner layer is the cortical bone is known as the endosteum and the outer layer is the periosteum. Cortical bone stores calcium, provides support and facilitates movement. It is made up of columns known as osteons that have a central Haversian canal (with blood vessels that nourish the bone) surrounded by lamellae of the matrix (comprised of inorganic salts and organic material) where the osteoblast (bone-forming cells) and osteoclast (bone-resorbing cells) are located.

The Trabecular bone is the internal tissue found at the end of long bones. A metabolically active tissue where red bone marrow is located, with the main function of producing blood cells. It is more vascular and lighter tissue in comparison to compact bone

Bone Cells:

  • Osteoblasts – bone formation cells
  • Osteoclasts – bone resorption cells
  • Osteocytes – regulator cells

Types of Bones

  • Flat Bones mainly function to protect internal organs such as the brain, heart, or stomach (skull, ribs, sternum)
  • Short Bones are cuboidal bones found in the feet and hands, supporting and stabilizing joints (carpals)
  • Long Bones are long bones, usually on the extremities or fingers that facilitate and assist movement and support our stature (tibia, femur, humerus)
  • Irregular Bones have different shapes, mainly functioning to provide organ and posture support (vertebrae, sacrum)
  • Sesamoid Bones are those bones embedded in the tendons that protect them and assist joint movement (patella)
  • Sutural bones are small and irregularly shaped bones in various sizes, locations, and shapes (between skull)

Bones in the Human Body

Here is a list of the main bones in the Human Body, excluding the smaller ones.
And oh, don’t forget the numbers are for both sides.

Skull (22)

Cranial (8)
Facial (14)
Ears (6)

Chest (26)

Hyoid bone (1)
Sternum (1-3)
Ribs (24)

Spine (26)

Cervical vertebrae (7)
Thoracic vertebrae (12)
Lumbar vertebrae (5)
Sacrum vertebrae (5)
Coccyx vertebrae (1-4)

Arms & Shoulders (64)

Humerus (2)
Scapula (2)
Clavicles (2)
Ulna (2)
Radius (2)
Hand (54)
-Carpals (16)
-Metacarpals (10)
-Phalanges (28)

Pelvis (6)

Pelvis
Ilium
Ischium
Pubis
Sacrum
coccyx

Legs (60)

Femur (2)
Patella (2)
Tibia (2)
Fibula (2)
Foot (52)
-Tarsals (14)
-Metatarsals (10)
-Phalanges (28)

Bones, Tendons, Ligaments - Anatomy, Structure, Function

Ligaments

Definition

A ligament is a type of connective tissue that connects bone to bone, mainly providing support and limiting excessive mobility and movement. It is adaptable, flexible, and provides passive support.

Ligament Function

The most important functions of ligaments are:

  • Holding the bones together
  • Limiting excessive mobility, twists, and movements
  • Providing passive support and injury prevention
  • Preventing bone separation
  • Stabilizing joints

Ligament Structure

The ligament has a hierarchical structure.
Starting from the whole ligament, this splits into smaller parts called fascicles. These fascicles are made up of more basic fibrils and fibroblasts (cells that produce collagen and build ECM). Then each fibril is made up of Sub-fibril, smaller units, who consist of many microfibrils.

The ligament is composed of fibrous collagenous fibers and fibrocytes with gel-like ground substances.

Types of Ligaments

Color-wise, there are:

  • White Ligaments: Fibrous, Harder, Non-elastic, and more rigid types of ligaments. Their main function is to provide passive support.
  • Yellow Ligaments: a more flexible type of ligament, made up of more elastic fibers.

Judging by their location there are:

  • Capsular ligaments, are located in a joint with a capsule and head like shoulders and hips, which have extra-capsular and intra-capsular supportive ligaments that function to protect and stabilize a joint.
  • Cruciate ligaments are paired ligaments that cross each other, a great example would be the knee, having Anterior and Posterior Cruciate ligaments

There are also Articular (Natural, human) and artificial ligaments (artificially made).

Ligaments Characteristics

Ligaments are flexible and adaptable, which means they can change their elasticity. Overly stretching of the ligaments might make them more flexible than necessary which can bring unhealthy and unstable hypermobility, which happens when a joint can move over the stable and normal range of motion.

Ligaments have collagen fibrils which are smaller in volume in comparison to tendons, plus ligaments have a higher percentage of proteoglycan matrix than tendons.

Because the ligaments have a more complex structure, their behavior is harder to be analyzed during load transmission.

Ligaments are viscoelastic. This means that they change shape if stretched, or under tension but they return to their original length.

  • Self-regeneration is slightly limited in ligaments since they aren’t as blood nourished in comparison to bones, however, periodontal ligaments stem cells are involved in the regeneration of periodontist ligaments. A tear in your ligament won’t heal by itself and grow back exactly the same, but it might be for scar tissue that is less elastic and functional.

Example of Ligaments in the Knee
There are many ligaments in the body (around 900) so here is an example of the ligaments present in one of the main and most complex joints in the body, the knee.

  • ACL Anterior cruciate ligament
  • PCL Posterior cruciate ligament
  • MCL Medial collateral ligament
  • LCL Lateral collateral ligament

Tendons

Definition

Tendon is a type of connective tissue that connects bone to muscle. It is a white, tough, dense, and fibrous band that can withstand tension and transmit force.

Tendon Function

  • To attach bones to muscles or other structure
  • To attach muscles to bones or other structure
  • To store elastic energy
  • To transmit mechanical forces
  • To provide passive support
  • To support and connect the musculoskeletal system

Tendon Structure

The main component of tendons is collagen fibers. The outer layer of a tendon is the fascia, while the fascicles are bound through the endothelium.
The tendon consists of smaller fiber that has fascicles that contain collagen fiber made up of smaller fibers known as collagen fibril, inside of which is tropocollagen.

The specialized ECM-creating cells found in tendons are tenocytes, found in the collagen fibers of a tendon.

Collagen type I is dominant with around 60-80%, while collagen type III is usually under 10% present. Tendons also have elastin, proteoglycans, and minerals.

Tendons: Injury & Repair

Tendon injuries occur most commonly in the areas of the biggest joints like the shoulders, hips, and knees. Aside from acute tendon injury, humans also suffer tendinitis, which is an inflamed or irritated tendon that can cause pain. This can be caused by the previous injury but also by a repetitive strain, irregular posture, or overuse.

Connective tissue regeneration is significantly slower in comparison to bones, however, it has been shown that tendons do repair themselves over time. Some of the MMP enzymes and matrix components that they produce can help in their regeneration, which usually takes some time.

When it comes to acute injury of a joint, the RICE method is practiced and helpful unless the medical specialists choose a different treatment, which depends on the injury. RICE protocol includes rest, ice, compression, and elevation.

Other methods to reduce inflammation & pain and recover faster may apply: ice packs, rest, drink more water, increase intake of vitamin C, collagen, Boswellia, fish oil and antioxidants, slow mobility movements, massage therapy, and physiotherapy exercises.

Tendon Characteristics

Viscoelastic tissue – which means it can change its shape under tension, and return back. While starched and under tension at the same time, tendons can save up elastic energy which can be released later on for more efficient movement. This phenomenon is famous in the Achilles tendon in runners and jumpers, where the use of this elastic energy has a high impact on the performance of the jump.

Examples of Tendons in the Body

Here are some examples of tendons present in the human body:

  • Ocular Tendon
  • Trapezium tendon
  • Supraspinatus tendon
  • Triceps tendon
  • Gluteus Maximus tendon
  • Quadriceps tendon
  • Hamstring tendon
  • Gastrocnemius tendons
conclusion

Anatomy can be a large and complex subject, however, distinguishing between bones, ligaments, and tendons is crucial. As a quick recap, bone is the rigid tissue that supports our body. Tendon is the white and tough connective tissue that connects bone to muscle, while ligaments connect bone to bone and provide passive support.

Frequently Asked Questions

How can I strengthen or regenerate my tendons?

Methods like consistent, proper weightlifting was shown to help, along with taking the needed nutrients, such as vitamin A, omega 3s, Manganese, and vitamin D. Note that tendons and ligaments don’t respond to exercise as muscles, but the strength gain may be due to increased need of regeneration, along with which thickening adaptation may happen to lift objects that weigh more.

What is the most commonly injured ligament?

ACL or Anterior cruciate ligament is the most commonly injured ligament in the human body.

How many tendons are in the human body?

There are approximately 4,000 ligaments in a human body.

What is the main function of ligaments?

To provide support, prevent an excessive range of motions, and attach bone to bone.

How many ligaments are in the human body?

There are approximately 900 ligaments in a human body.

How to prevent ligament injury?

Don’t overstretch your ligaments to access hypermobile positions and work your muscle stabilizers of a specific joint.

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