The skeletal system provides a structural framework and supports the body. It is made up of 206 bones in an adult human. It comprises of bones, cartilage, ligaments and tendons that connect to bones and bones to muscles. The human skeletal system provides definite shape to the body and protection to internal organs. At the time of birth, infants have more bones (~300 bones), which due to fusion in some of the bones, form larger bones and 206 bones remain in a human adult.
Functions of bones
- Bones provide shape to the body.
- Bones act as a protection to internal organs like brain, heart, lungs etc..
- Provides support to the body and anchors muscles.
- Bones serve as storage space for minerals like calcium and phosphate
- Bones helps in facilitating body movements.
- Bones serve as the birthplace for red blood cells.
Human skeletal has two major divisions:
- Axial skeleton
- Appendicular skeleton
The axial skeleton is made up of 80 bones and it constitutes the middle axis. It includes the following regions:
- Auditory ossicles
- Vertebral column
The human skull consists of cranium and facial bones. The function of the cranium is to protect the brain. It is formed of 8 plate-shaped bones joined together at meeting points called sutures. Along with cranium, the remaining 14 bones form the facial bones. Mandible is the only movable bone in the human skull.
It is a U-shaped bone located in the anterior neck. It is an intermediary between the skull and post cranial skeleton. The hyoid bone aids tongue movement and swallowing. It has no articulation with other bones.
Auditory ossicles namely malleus, incus, stapes are three bones in the middle ear that are the smallest bones in the human body. The functions of ossicles are to transmit sound from the air to the cochlea.
Ribs are the long curved bones which constitute the rib cage. The ribs consist of 24 bones in 12 pairs which form the protective cage of the thorax. The ribs protect the thoracic internal organs. They articulate posteriorly with the vertebral column and terminates anteriorly as cartilage.
Sternum or the breastbone is a long bone placed at the central part of the chest. The sternum and ribs make up the rib cage. The sternum is attached to the first seven ribs and also to the Clavicle or collarbone.
The vertebral column is a set of approximately 33 bones called vertebrae which are separated by intervertebral discs. The vertebral column is divided into 5 categories. They are Cervical, Thoracic, Lumbar, Sacrum, Coccyx.
Functions of the Vertebral column
- The vertebral column protects the spinal cord.
- Provides stiffening to the body.
- Provides structural support by balancing the bodyweight
- Provides attachment to pectoral and pelvic girdles and other muscles.
The cervical is the most delicate and the thinnest bones of the vertebral column. The cervical vertebrae are formed of 7 vertebrae. The seven cervical vertebrae are arranged along the length of the neck. They are named according to its position from the skull to the chest. The superior C1 or first cervical vertebrae to C7 or the seventh cervical vertebrae constitute the cervical vertebrae. The C1 vertebrae are named as Atlas whose function is to hold up the skull. Also, C2 is named as Axis since it serves as the axis for the skull and atlas to rotate while turning head from one side to another.
It is placed at the mid-back of the human body. The main function is to hold the rib cage and to protect the heart and lungs. The twelve thoracic vertebrae are named T1 to T12. Thoracic vertebrae are the unique one other than the remaining vertebrae as it supports the ribs.
These are the largest in the vertebral column and comprises of 5 vertebrae bones between the rib cage and pelvis. The lumbar vertebrae are named from L1 to L5. L1 is closest to the thoracic vertebrae whereas L5 is adjacent to the pelvis. The lumbar vertebrae functions as the load-bearing structure.
The sacral vertebrae consist of 5 vertebrae bones which fuse together to form Sacrum. The sacrum is a long wedge-shaped vertebra at the inferior end of the spine. It is a very strong bone which supports the weight of the upper body as it spread across the pelvis into the legs.
The coccyx vertebrae are formed by the fusion of three to five rudimentary bones to form a small triangular bone at the bottom of the vertebral column. The coccyx vertebrae are also referred to as the tail bone. The coccyx serves as an attachment site for ligaments, tendons and muscles. The coccyx may be fractured when a person falls abruptly.
The appendicular skeleton is the part of the human skeletal system that supports the appendages. It consists of 186 bones including the bones of the limbs as well as supporting the pelvic and pectoral girdles.
The appendicular skeleton is divided into 6 regions.
- Shoulder girdle
- Arms and forearms
- Thighs and legs
- Feet and ankles
The shoulder girdle or the pectoral girdle is a set of 4 bones which connects to the arm on each side. The pectoral girdle is part of the appendicular skeleton which are for the upper limbs. In human beings, the pectoral girdle consists of the scapula and the clavicle.
Arms and Forearms
The arm and forearm are constituted of 6 bones. The large bones of the arm include:
- Humerus – Humerus runs from the shoulder socket and joins the radius and ulna at the elbow.
- Radius – Radius is a forearm which runs from the elbow to the thumb side of the wrist.
- Ulna – Ulna, a forearm which runs from the elbow to the ‘pinky’ side of the elbow.
The hands consist of 54 bones which provide support and flexibility to the soft tissues. The bones of hands are categorised into three:
- Carpals – Carpals are a set of 8 irregularly shaped bones located in the wrist area.
- Metacarpals – Metacarpals are bones which are related to each digit, there are 5 metacarpal bones.
- Phalanges – Phalanges are the bones of the fingers. There are 3 phalanges in each finger, except, for the thumb which has two phalanges only.
The pelvic girdle is located in the lower part of the trunk. It a ring-like bony structure. The pelvic girdle consists of two bones sacrum and the coccyx. The pelvic girdle is formed of paired hip bones each made up of ilium, ischium and pubis.
Functions of Pelvic Girdle
- It transfers the weight of the body from the axial skeleton to the appendicular components, especially during the movement.
- Provides attachment from a number of muscles and ligaments enabling movement.
The majority of women have a gynaecoid pelvis and males have an android pelvis. The differences in the structure creates a great pelvic outlet enabling the process of childbirth.
Thighs and Legs
The bones of the legs and thighs are part of the appendicular skeletal system which supports the muscles of the lower limbs. These muscles help in walking, running, standing and jumping. These bones should be strong enough in order to support the body’s weight.
- The Femur or thigh bone is the largest and heaviest bone in the human body. At the proximal end of Femur, there is a rounded prominence which is called as the Head of the Femur.
- The Tibia and Fibula are the two long bones in the lower leg. They are two separate bones but are closely linked at the knee and the ankle.
- The top of Tibia connects to the knee joint and bottom connects to the ankle joint. Although Tibia carries all the body weight, it needs the support of Fibula.
Feet and Ankles
The foot is a firm platform which supports the weight of the body. It is formed of many bones such as the tarsals, metatarsals and phalanges.
- Tarsals: A set of 8 irregular bones situated proximally in the foot in the ankle area.
- Metatarsals: A set of 5 bones each one for a digit. These bones connect tarsals with the phalanges.
- Phalanges: Each toe has 3 phalanges namely the proximal, intermediate and distal.
Tendons joint bones to skeletal muscles. They are made up of connective tissues.
Ligaments join two bones together. They are also a type of connective tissue.
Cartilage provides protection of bones at the joints from wear and tear. They are firm yet softer and flexible than bones.
It forms a structural framework of many parts of the body, e.g. ear, nose, ribs, bronchial tubes, etc.
Diseases Related To Skeletal System
- Osteoporosis: Osteoporosis is a bone-related disease in which the bone density is reduced and increasing the risk of bone fracture.
- Paget’s Disease: It is a chronic bone disease which causes the affected bones to large and misshapen.
- Arthritis: It is the inflammation caused to the joints causing difficulty and pain in movements and limiting the same.
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