The Skeletal System
The skeleton has 206 bones, these bones support your body and allow you to move. The skeleton also provides protection to vulnerable organs like the Brain, Heart and Lungs. The bones in the skeleton also manufacture blood cells and store useful minerals.
Functions of the Skeleton
- Support - the skeleton provides support for the soft tissues of the body, enabling us to stand upright.
- Movement - the skeleton provides anchorage for muscles so they can pull effectively. The bones also act as levers for pulling.
- Protection - the skeleton protects vital organs. The rib cage protects the heart and lungs, while the brain is protected by the skull.
- Storage - bones are made of calcium phosphate. They can act as store of these two important minerals.
- Production of Blood Cells - hematopoiesis, occurs in the red marrow found within the cavities of long bones.
- Energy storage. Stored in adipose cells of the yellow marrow, Fat, serves as an energy reservoir.
There are two types of bone tissue: compact and spongy. As the names suggest, the two types differ in density.
Compact Bone- Compact bone is dense, hard, and makes up the exterior portion of all bones. This gives the bone it's protection
Spongy Bone - Spongy bone is inside the compact bone and is very porous (full of tiny holes). Spongy bone occurs in most bones.
Types of Bone
- Long Bones: Long bones are made primarily of compact bone, except at the ends (epiphysis) which has only a thin layer of compact bone covering a great deal of spongy bone. Examples of long bones include the humerus and femur.
- Short Bones: These are bones shaped like the carpals and tarsals, and contain mostly spongy bone.
- Flat Bones: Examples of flat bones are those of the skull. Contain spongy bone in between surrounding layers of compact bone.
- Irregular Bones: Examples are the vertebrae.
- Sesamoid Bones: An example is the patella. Sesamoid bones are enclosed in tendons
Divisions of the Skeleton
The human skeleton is divided into two parts. These are -
- Axial Skeleton
- Appendicular Skeleton
Axial Skeleton - The 80 bones of the axial skeleton form the vertical axis of the body. They include the bones of the head, vertebral column, ribs and breastbone or sternum.
- Parietal (2)
- Temporal (2)
- Frontal (1)
- Occipital (1)
- Ethmoid (1)
- Sphenoid (1)
- Maxilla (2)
- Zygomatic (2)
- Mandible (1)
- Nasal (2)
- Platine (2)
- Inferior nasal concha (2)
- Lacrimal (2)
- Vomer (1)
- Malleus (2)
- Incus (2)
- Stapes (2)
- Cervical vertebrae (7)
- Thoracic vertebrae (12)
- Lumbar vertebrae (5)
- Sacrum (5) Fused together
- Coccyx (4) Fused together
- Sternum (1)
- Ribs (24)
Appendicular Skeleton - The appendicular skeleton consists of 126 bones and includes the free appendages and their attachments to the axial skeleton.
- Clavicle (2)
- Scapula (2)
- Humerus (2)
- Radius (2)
- Ulna (2)
- Carpals (16)
- Metacarpals (10)
- Phalanges (28)
- Coxal, innominate, or hip bones (2)
- Femur (2)
- Tibia (2)
- Fibula (2)
- Patella (2)
- Tarsals (14)
- Metatarsals (10)
- Phalanges (28)
Types of joint
A joint - where two bones come together. In terms of the amount of movement they allow, there are three types of joints: immovable (Skull and Pelvis), slightly movable (Inter Vertebral) and freely movable (Hip, Knee and Elbow).
- Plane - Carpals
- Hinge - Humerus and Ulna
- Pivot - Head of Radius and Ulna
- Condyloid - Metacarpals
- Saddle - Thumb
- Ball and Socket - Humerus and Scapula
The majority of articulations between bones are synovial joints. All synovial joints are freely moveable joints.
They are characterized by the presence of a closed space or cavity between the bones: the joint cavity (= synovial cavity).
The articulating surfaces of the bones are covered by a thin layer of very smooth hyaline cartilage (articular cartilage) and lubricated by a special fluid, the synovial fluid secreted by the synovial membrane which lines the cavity. This fluid is composed of mucopolysaccharides, is highly viscous and slippery and reduces friction.
Ligaments and Tendons
A ligament is a tough band of white, fibrous, slightly elastic tissue. This is an essential part of the skeletal joints; binding the bone ends together to prevent dislocation and excessive movement that might cause breakage. Ligaments also support many internal organs; including the uterus, the bladder, the liver, and the diaphragm and helps in shaping and supporting the breasts.
A tendon is a tough yet flexible band of fibrous tissue. The tendon is the structure in your body that connects the muscle to the bones. The skeletal muscles in your body are responsible for moving your bones, thus enabling you to walk, jump, lift, and move in many ways. When a muscle contracts, it pulls on a bone to cause this movement. The structure that transmits the force of the muscle contraction to the bone is called a tendon.
Muscle is a contractile form of tissue. It is one of the four major tissue types, the other three being epithelium, connective tissue and nervous tissue. Muscle contraction is used to move parts of the body, as well as to move substances within the body.
The muscular system consist of three different types of muscle tissues : skeletal, cardiac, smooth.
There are two types of muscle control in the system and they are the involuntary muscles, and the voluntary muscles. Examples of voluntary muscles are in our arms and legs where we control their movement. The heart, or the cardiac muscle, is an example of involuntary muscle.
Skeletal muscle is a type of striated muscle, attached to the skeleton. Skeletal muscles are used to facilitate movement, by applying force to bones and joints; via contraction.
Cardiac muscle is a type of striated muscle found within the heart. Its function is to "pump" blood through the circulatory system by contracting. Unlike skeletal muscles and smooth muscles, which contract in response to nerve stimulation, cardiac muscle is myogenic, meaning that it stimulates its own contraction. A single cardiac muscle cell, if left without input, will contract rhythmically at a steady rate; if two cardiac muscle cells are in contact, whichever one contracts first will stimulate the other to contract, and so on.
Smooth muscle is a type of non-striated muscle, found within the "walls" of hollow organs; such as blood vessels, bladder and gastrointestinal tracts, Smooth muscle is used to move matter within the body, via contraction; it generally operates "involuntarily", without nerve stimulation.
Muscle has four major functional characteristics:
- Contractibility - The ability to contract or make shorter.
- Excitability - the ability to respond to stimulation and regulation by nervous impulses and hormones.
- Extensibility - The ability to be stretched or extended from the normal resting length
- Elasticity - The ability to return to the original shape following extension or contraction.
Further reading on the Skeletal System and Muscles