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Skeletal system

The skeletal system

Every skeletal system is unique. No two humans will have the same skeletal system. They will have the same amount of bones, but the way the skeletal system is constructed, the way the bones interact and move is unique. The movement and the construction of the skeletal system determines which yoga poses will go easy and which yoga poses won’t go easy. We can’t compare two people doing yoga (asana), simple by doing poses, without bearing in mind the difference in skeletal system.

The skeletal system consists of bones and cartilage, ligaments and other connective tissue that connects and stabilize the bones.

The skeletal system has five primary functions:

  • Support: the skeletal system supports the whole body
  • Storage: calcium (one to two kilo) is stored in the bones, just as fat and other minerals
  • Creation red blood cells:  red blood cells, white blood cells and other parts of blood are created in the red bone marrow, inside the bone
  • Protection organs are mostly surrounded by bones. For example the ribcage protects the heart and lungs.  Our skull protects the brain
  • Leverage: a lot of bones are functioning as a lever to make movement possible.

The spine

  • The spine consists of 26 bones: 24 vertebras and the sacrum and coccyges.
  • The cervical spine consists of seven vertebrae
  • The thorax spine consists of 12 vertebrae: T1-T12
  • The lumbar spine consists of 5 vertebrae: L1-L5. The fifth lumbar vertebra is connected to the os sacrum
  • Our spine is not straight. If you look from the side you will see four curves: The thoracic and sacral curves are primary curves. The cervical and lumbar curves are secondary curves.
  • If somebody is standing up straight the weight of that person has to be transformed to the sacrum. The curves help to align us and bring our weight down. They also help prevent injuries by giving the spine flexibility.
  • Our thorax is made up by our thoracic vertebras, our ribs and our sternum. The thorax protects the heart and lungs and other internal organs. Our muscles who play a role in breathing are attached at the thorax. We have 12 pairs of ribs. Seven true ribs who are connected to the sternum and five pair of false ribs who are not directly connected to the sternum. Three are connected together and to rib seven. The other two ribs are called floating ribs, because they are not connected to the sternum.

Shoulder girdle and arm

  • Our shoulder girdle consist of our two scapulae and our two clavicles. The clavicles are connected with the sternum. This is the only connection between the shoulder girdle and our axial skeleton. Both scapulae are supported and are held in place by skeletal muscles. They are not connected to our thorax.
  • The position of the clavicle (the outside edge more turned forward or backwards) determines how far the upper arm can be raised backwards, without moving the shoulder girdle. Moving the upper arm upwards and backwards is needed for backbends.
  • Our upper arm has one single bone: the humerus. It runs from the scapula to our elbow, where it forms a connection with the bones of our lower arm: the radius and ulna. The olecranon of the ulna forms our elbow. The distal end of the radius forms our wrist joint.
  • Our hand consists of eight carpal bones, five metacarpal bones (palm of our hand), and five phalanges (fingers).

Pelvic girdle and legs

  • Our pelvis girdle connects with our femora (thighbones). Because our legs and pelvic girdle have to support the weight of our body these bones are stronger and bigger than the bones of our shoulder girdle. The upper edge of our pelvic girdle is the crista iliaca (iliac crest); this is an attachment place for a lot of muscles and ligaments.
  • Our pelvis protects our delicate organs of the abdominopelvic cavity while anchoring the powerful muscles of the hip, thigh, and abdomen. Several bones unite to form the pelvis, including the sacrum, coccyx (tail bone) and the left and right coxal (hip) bones.
  • Women tend to have a smoother and lighter pelvis than men. Their pelvis is wider and lower and the opening of the pelvis is bigger. The pelvis is constructed differently because women have to be able to give birth. A lower and wider pelvis makes it easier to bend forward and to rotate legs outwards (lotus pose).
  • The legs consist of the femur, patella, tibia and fibula. The femur is the longest and heaviest bone of our skeleton. The head of the femur (epiphysis) is connected to the pelvis with muscles and ligaments. On the outside of your hip, you can feel your trochanter major. The distal end of the femur is part of our knee joint.
  • The tibia is the biggest bone of our lower leg. It’s connected with the femur in the knee joint. The thinner fibula is connected with the tibia at the far end (lateral) of our leg. There is no connection between fibula and femur.
  • Our ankle consists of seven tarsal bones, five metatarsal bones (their distal edges form the balls of our feet) and five phalanges (our toes).

Joints

  • A joint is a place where two bones connect. We have different joints in our body. Some can’t move at all, some can move a little and some can move a lot. The bigger the movement, the weaker the joint. The important ones for yoga are:
  • Shoulder joint: this joint has the most flexibility of all joints. It is formed by the union of the humerus, the scapula (shoulder blade), and the clavicle (collarbone). It is made up of two separate joints – the glenohumeral and acromioclavicular joints. These two joints work together to allow the arm both to circumduct in a large circle and to rotate around its axis at the shoulder.
  • The glenohumeral joint is a ball-and-socket joint formed between the articulation of the rounded head of the humerus (the upper arm bone) and the cup-like depression of the scapula, called the glenoid fossa The glenoid fossa forms a very shallow socket, so the muscles, ligaments and cartilage of the shoulder joint reinforce its structure and help to prevent dislocations. To further reinforce the shoulder, the four muscles of the rotator cuff extend from the scapula and surround the head of the humerus to both rotate the arm and prevent dislocation.It’s the joint that gets dislocated easiest. The ligaments are fairly loose giving this joint its flexibility.
  • Elbow joint: there are two joints here: humerus and ulna (strongest of the two) and humerus and radius. The elbow joint is a complex joint formed between the distal end of the humerus in the upper arm and the proximal ends of the ulna and radius in the forearm. The elbow allows for the flexion and extension of the forearm relative to the upper arm, as well as rotation of the forearm and wrist.
  • The rounded distal end of the humerus is divided into two joint processes – the trochlea on the medial side and the capitulum on the lateral side. The pulley-shaped trochlea forms a tight joint with the trochlear notch of the ulna surrounding it. On the lateral side, the concave end of the head of the radius meets the rounded, convex capitulum to complete the elbow joint. The loose union of the capitulum of the humerus and the head of the radius allows the radius to pivot as well as flex and extend. The pivoting of the radius allows for the supination and pronation of the hand at the wrist.
  • Hyper flexibility in the elbow joint is common. It the joint is overstretched – what can happen in downward dog pose – the joint can get damaged. Building muscles in the arm, helps to prevent overstretching the joint.
  • Hip joint; the hip joint is one of the most important joints in the human body. It allows us to walk, run and jump. It bears our body’s weight and the force of the strong muscles of the hip and leg. Yet the hip joint is also one of our most flexible joints and allows a greater range of motion than all other joints in the body except for the shoulder. The hip joint is a ball-and-socket joint formed between the os coxa (hip bone) and the femur. A round, cup-shaped structure on the os coax, known as the acetabulum, forms the socket for the hip joint. The rounded head of the femur forms the ball of the joint. If we bend forward, we are actually bending forward from the hips.
  • Knee joint – brings the weight of the body over from the femur on the tibia. The knee joint is one of the strongest and most important joints in the human body. It allows the lower leg to move relative to the thigh, while supporting the body’s weight. Movements at the knee joint are essential to many everyday activities, including walking, running, sitting and standing.
  • The knee is a joint formed between three bones: the femur, tibia and patella. Two rounded, convex processes (known as condyles) on the distal end of the femur meet two rounded, concave condyles at the proximal end of the tibia The patella lies in front of the femur on the anterior surface of the knee with its smooth joint-forming processes on its posterior surface facing the femur.
  • Two internal ligaments – the anterior and posterior cruciate ligaments – also help to maintain the proper alignment of the knee. The anterior cruciate ligament plays an important role in preventing hyperextension of the knee by limiting the anterior movement of the tibia. Directly behind the ACL is the posterior cruciate ligament which  prevents the posterior movement of the tibia relative to the femur.
  • On both sides of the knee joint are two more ligaments: the lateral collateral ligament and the medial collateral ligament. They prevent the knee from moving to far inwards or outwards When we do poses where the knee is bend at a 90 degree angle we must take care we don’t let the knee ‘fall’ inwards or outwards, otherwise we put too much pressure on these ligaments.
  • Ankle joint: the bones of the ankle and foot form the most distal region of the lower limb in the appendicular skeleton. These bones are responsible for the propulsion, balance, and support of the body’s weight through many diverse activities, such as standing, walking, running, and jumping.
  • The ankle joint is formed by the union of the lower leg bones – the tibia and fibula – and the talus bone (one of a group of bones collectively known as the tarsus, located in the foot). Together, these three bones form a tight joint that permits the plantar flexion and dorsiflexion of the foot.

 

Source: Anatomie en fysiologie - Een inleiding - Frederic H. Martini & Edwin F. Bartholomew & www.innerbody.com
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