Next Lesson - Joints
Core
Bones make up the skeleton, providing a rigid framework that supports the body.
Image: The human skeleton from a posterior (behind) view. The main bones of the human skeleton are labelled
Public Domain Source LadyofHats Mariana Ruiz Villarreal [Public domain]
The adult human skeleton comprises 206 bones, each with individual roles within the body. 5 key roles of bones are:
- Support
- Protection
- Movement
- Mineral and growth factor storage (bones store minerals such as calcium and phosphorus, and also growth factors, which are signalling proteins that stimulate cells to grow)
- Haematopoiesis (generation of blood cells from haematopoietic stem cells, the blood-forming stem cells, in the bone marrow). The cells made include erythrocytes (red blood cells) and lymphoid lineage cells (white blood cells such as lymphocytes)
Bones are classified based on their shapes:
Image: The different classifications of shape of bone, the most important being the long, flat, short, irregular and sesamoid bones
Creative commons source by OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]
- Long (e.g. femur and humerus); longer than they are wide and key for locomotion (moving the body from place to place). Common features include a shaft and articulations (joints with other bones) at both ends.
- Flat; generally used for protection or muscle attachment (e.g. the skull and the thoracic cage, including the sternum and ribs).
- Short; small bones that are roughly as wide as they are long, found in some joints (e.g. the carpal bones in the wrist and the tarsal bones in the ankles).
- Sesamoid; bones which sit within tendons or muscle and are used to transfer force (e.g. the patella).
- Irregular; bones which do not occupy any of the other categories (e.g. the vertebrae).
The key bones of the human body
Later lessons will cover each of these bones in further detail. This section is only a brief overview and introduction.
Image: The 5 vertebral regions of the spine, with the number of vertebrae in each region labelled
Modified Public Domain Image
The spine, known also as the vertebral column, extends from the skull to the coccyx. About a quarter of its length is made of intervertebral discs, with the remainder from the vertebrae and sacrum. In total there are 33 vertebrae including:
- 7 cervical vertebrae
- 12 thoracic vertebrae
- 5 lumbar vertebrae
- 5 sacral vertebrae (they fuse to form the sacrum)
- 4 coccygeal vertebrae (they fuse to form the coccyx)
Each vertebra is named after its spinal region (cervical, thoracic, lumbar, sacral or coccygeal), followed by its number within that region, counting down from the top.
For example, the third lumbar vertebra, counting down from the top of the lumbar region, is L3.
Image: A diagram of the location of an intervertebral disc between the vertebrae.
Creative Commons Image source by OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]
Intervertebral discs are named after the vertebrae above and below them.
For example, the disc between L2 and L3 is the L2/3 intervertebral disc.
The cervical, thoracic and lumbar vertebrae are composed of non-fused individual vertebrae capable of independent movement. Those in the cervical and lumbar spine are relatively mobile. Vertebrae in the thoracic spine, on the other hand, are less mobile because they are joined to the ribs, and most of the ribs are joined to the sternum (breastbone) at the front. The sacrum and coccyx are made up of fused vertebrae.
Check out our article on The Spine for more information.
Image: A diagram showing the 3 parts of the innominate (hip) bone.
Modified Public Domain Image
The hip/innominate bone is an irregular bone that forms the hip joint with the femur (thigh bone). This bone attaches to the sacrum (forming the sacroiliac joint, the joint between the sacrum and the ilium) and to the hip bone on the opposite side at the pubic symphysis (the joint at the front where the two hip bones meet), forming the pelvic girdle (the bony ring that connects the legs to the trunk). It is made up of three fused bones:
- Ilium (the upper, fan-shaped part)
- Ischium (the lower back part)
- Pubis (the front part)
The innominate bone has a number of landmarks including:
- Acetabulum; the socket that forms a joint with the head of the femur (the rounded top of the femur). It lies at the point where the 3 fused bones meet. Acetabulum in Latin translates as vinegar cup reflecting its cup shaped form.
- Anterior superior iliac spine; ASIS; the rounded bony projection at the front end of the iliac crest, which can be felt at the front of the hip.
- Iliac crest; a bony ridge on the superior aspect of the ilium.
- Ischial tuberosity; a large knob of bone on the ischium which the body rests on whilst sitting. Colloquially known as the ‘sitting bones’.
Check out our article on conditions of the hip for more information.
Image: A diagram showing the main bones of the leg and knee.
Public Domain Image by Jecowa at English Wikipedia
The lower limb (excluding the foot and ankle) is made up of four bones; the femur, tibia, fibula, and patella.
The femur has two articulations (joints), one at each end. The head of the femur (its rounded upper end) articulates with the acetabulum in the hip/innominate bone, forming the hip joint. The femoral condyles (the two rounded knuckles of bone at the distal, or lower, end of the femur) articulate with the tibia and patella, forming the knee joint; note, the femur does not articulate with the fibula. The femur is the only bone in the thigh.
The patella is commonly referred to as the kneecap. Its primary function is to improve the leverage of the quadriceps tendon (the tendon of the large muscle at the front of the thigh), which makes knee extension (straightening the knee) more efficient, by increasing the angle at which the tendon acts. The patella also provides protection to the knee joint.
The tibia is also known as the shinbone and is the larger of the two bones in the leg. It articulates with the femur at the knee and the bones of the ankle in the foot.
The fibula is located laterally to the tibia, with which it is connected at the top and bottom. Its upper extremity (top end) lies posterior to the head of the tibia (the top of the tibia), below the knee joint. Its lower extremity (bottom end) forms the lateral part of the ankle-joint.
Check out the bones of the lower limb in more detail here.
Also, check out the muscles of the thigh and muscles of the lower leg and the conditions associated with the thigh, knee and lower leg.
Image: Diagram showing the bones of the foot.
Modified Public Domain Image
The bones of the foot are split into three categories, the:
- Tarsals (7): talus (ankle bone), calcaneus (heel bone), cuneiforms (3, wedge-shaped bones), cuboid (cube-shaped), and navicular (boat-shaped)
- Metatarsals (5, the long bones in the middle of the foot): first, second, third, fourth, and fifth metatarsal bone
- Phalanges (14): arranged as proximal, intermediate and distal phalanges, except in the great toe which has only proximal and distal phalanges.
The tarsal bones can be remembered with the helpful mnemonic:
This (Talus)
Circus (Calcaneus)
Needs (Navicular)
Cooler (Cuneiforms)
Clowns (Cuboid)
Check out our article on the bones of the foot and conditions that can affect the foot for more information.
Bones of the Upper Limb
Bones of the Shoulder
Image: Diagram showing the main bones and bony-landmarks of the shoulder joint.
The shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone).
The articulations (joints) between these bones make up the shoulder joints. The glenohumeral joint (the joint between the glenoid fossa, the shallow socket on the scapula, and the head of the humerus, its rounded upper end) is the major joint of the shoulder. The other joint of note in the shoulder is the acromioclavicular joint between the clavicle and the acromion, the bony tip of the shoulder, which is a feature on the scapula.
Check out our articles on bones of the upper limb, muscles of the shoulder and conditions of the shoulder for more information.
Image: Diagram showing the main bones of the arm.
In everyday language, the arm runs from the shoulder to the wrist and is made up of three bones: the humerus, the radius and the ulna. In strict anatomical terms, the arm is only the part between the shoulder and elbow joints, which contains the humerus, and the forearm is the part between the elbow and wrist joints, which contains the radius and ulna.
The humerus articulates with the scapula at the shoulder joint. At the elbow joint it also articulates with the two bones of the forearm, the ulna and radius. The elbow is mainly a hinge joint (it bends and straightens like a door hinge) between the lower end of the humerus and the upper ends of the radius and ulna. The radius also turns against the ulna at the elbow, which lets the forearm rotate.
Check out our articles on bones of the upper limb, muscles of the upper arm, muscles of the forearm, conditions of the arm and conditions of the elbow.
Image: diagram showing the main bone-groups making up the hand.
Public Domain Image
The bones of the hand are split into three categories, the:
- Carpals (8, the wrist bones): Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate
- Metacarpals (5, the bones of the palm): first, second, third, fourth, and fifth metacarpal bone, starting from the thumb to the little finger
- Phalanges (14): arranged as proximal, intermediate and distal phalanges, except in the thumb which has only proximal and distal phalanges.
A helpful (if rather rude) mnemonic to remember the carpal bones of the hand is:
Some (Scaphoid)
Lovers (Lunate)
Try (Triquetrum)
Positions (Pisiform)
That (Trapezium)
They (Trapezoid)
Cannot (Capitate)
Handle (Hamate)
This mnemonic names the carpal bones in each row from lateral (thumb side) to medial (little finger side), starting with the proximal row (nearest the forearm) and then the distal row (nearest the fingers).
Check out our articles on bones of the hand, conditions of the forearm and wrist and conditions of the hand.
To understand bones, their role and their function, first we must understand their composition, specifically connective tissue, cartilage and the bone forming process. These topics are covered in the related lesson here.
- 17913
