Human Biology Muscular & Skeletal System Flashcards
(43 cards)
Functions of the Musculoskeletal System
To work together to support and move the body.
The muscles contract to cause movement
The skeleton facilitates movement by being points of attachment for the muscles
Bones meet at joints allowing the body to take different shapes
The skeleton supports the weight of the body and protects internal organs
Bones produce blood cells
Bones store (and release) minerals and fat
Bone
Bone is a form of connective tissue (it is more extracellular matrix than cells)
That matrix contains large quantities of Calcium, Potassium, Sodium and Phosphorus in a solid state.If our bones were solid, our skeleton would be very heavy and difficult for us to move
So, our bones tend to contain 2 types of bone.
Compact or cortical bone. This bone is dense.
Spongy or cancellous (or trabecular) bone. This bone forms a network, more closely resembling a sponge, with lots of space ‘trapped’ in its structure
Human Skeleton
The human skeleton contains 206 bones.
They are arranged into your axial and appendicular skeleton
Axial skeleton – form the of the head and trunk – the ‘axis’ of the body
Appendicular skeleton – forms the limbs
Axial Skeleton
These bones are largely responsible for protecting vital organs – brain, spinal cord, lungs, heart, liver, kidneys
Essential for the posture of the body
Includes skull, vertebral column, ribs and sternum
Appendicular Skeleton
These bones are largely responsible for position and movement
Include the pectoral girdle with upper limbs, and the pelvic girdle with lower limbs
The ‘girdles’ are how the limbs attach to the axial skeleton
Flat Bones
These bones have two ‘flat’ surfaces made of cortical bone with spongy bone, of relatively even thickness, between them.
They are shield like and are used to protect internal organs. Examples include the sternum, ribs and cranial bones
Long Bones
Long bones have a shaft (diaphysis) like a pipe made of cortical bone with a space in the middle, and ends (epiphyses) of trabecular bone
They provide length and strength, great for limbs! Examples include the femur, humerus, tibia and metacarpals
Long Bone Structure
Diaphysis – Tube of compact bone with a marrow filled cavity. In adults this is yellow marrow (fat storage)
Epiphysis – expanded ends of bone, thin outer cortical bone and inner trabecular bone. In large long bones, the marrow spaces contain red marrow (blood cell production)
Periosteum – a dense, fibrous covering of the bone that extends up to the articular cartilage (not over it)
Short bones
Made predominantly of trabecular bone. They often fit together in a way that limits movement but provide some flexibility and ‘shock absorption’ with stability.Examples are carpal and tarsal bones
Irregular Bones
As suggested by their name, these bones are strange! They are found in the vertebrae and consist of a combination of cortical and trabecular bone.
Examples are found forming the vertebral column which serves a vital role protecting the spinal cord. Many facial bones are also irregular bones.
Sesamoid bones
These bones come in a variety of sizes and shapes. They form in tendons (tissue that attaches muscle to bone).
If those tendons would rub over other bones a lot, these form to protect the tendon. The patella is an example, most others are not given names and are variable between people!
Bone Development
Epiphyseal plates are sites of growth in developing bone
Larger bones tend to be more advanced than smaller bones
Bone is Connective Tissue
Connective tissue occurs when there is a predominance of extracellular matrix
There are three types of cells found in bone: Osteoblasts, Osteoclasts and Osteocytes
Extracellular matrix consists of both organic (40%) and inorganic (60%) components
Organic consists largely of protein (predominantly collagen) and some other protein related molecules
Inorganic material is mostly solid minerals, particularly Ca5(PO4)3OH (hydroxy apatite)
Bone Cells
Osteoblasts – osteoblasts secrete the organic matrix which binds to the minerals that form the bone.
Osteoclasts – are large cells that reabsorb bone matrix. This is necessary for repair of damaged bone, but also for remodelling of growing bones.
Osteocytes – were once osteoblasts that got trapped in their own matrix layer. Once they stop producing matrix and are trapped they sense stress on the bone and can co-ordinate the appropriate remodelling
Bones under stress are encouraged to deposit more matrix to become stronger, by stimulating osteoblast activity.Bone is constantly being turned over and relies on a balance between osteoblast and osteoclast activity
Compact bone
Compact bone is organised into units called osteons consisting of:
Haversian canal – located centrally in the osteon, containing a blood vessel +/- nerve and lymph
Matrix deposited in lamellae – concentric rings of matrix. Between the lamellae, trapped osteocytes live in lacunae. They are able to pass nutrients and signals to nearby cells through canaliculi
Compact Bone
Osteons run parallel to the long axis of the bone. Their strength is maximal in this direction
There are usually some circumferential lamellae lying between the osteons and the periosteum.
There is also usually a small amount of trabecular bone between the marrow cavity and the cortical bone
Spongy Bone
This type of bone is also called trabecular bone… which is easy to remember if you have to remember that the irregular bone patterns are called trabeculae.
Trabeculae are not like osteons with a central canal. They receive their nutrients from the vessels that run in the spaces of the spongy bone.
They are still comprised of lamellae of bony matrix with the same cell patterns as seen in compact bone
Cartilage
Like bone, cartilage is a type of connective tissue. Unlike bone, it is flexible.
Cells of cartilage:
Chondroblasts
Chondrocytes
Just like in bone, the ‘blasts’ are responsible for making and depositing the extracellular matrix and the ‘cytes’ are mature cells that have been trapped in lacunae in their own matrix.
Extracellular matrix:
Fibres – mostly collagen
Chondrin – a protein – carbohydrate complex
It is actually the fibres of the ECM that are used to determine the type of cartilage
Blood Supply
Cartilage does NOT contain blood vessels. The perichondrium – a layer of fibrous connective tissue that surrounds cartilage contains blood vessels.
The cells of cartilage, therefore, rely on diffusion of nutrients and wastes across relatively large distances. In order for this to be viable, they have a very slow metabolism and slow rate of cell division.
As a result, healing of damaged cartilage is a slow process, and in fact the cartilage may never fully heal.
Articular cartilage – forming joint surfaces on the ends of bones, does not even have a perichondrium. This cartilage is very unlikely to fully heal after damage.
Hyaline Cartilage
Hyaline cartilage contains collagen fibres.
They are so fine and so closely packed that a light microscope is not able to even see that there are fibres!
This provides great strength and smooth surfaces to the tissue.
This form of cartilage is found on articular surfaces of bones as well as the rings of the trachea and bronchi. Epiphyseal plates and developing bones are also made from hyaline cartilage.
Elastic Cartilage
Elastic cartilage contains collagen fibres – not quite as tightly packed as in hyaline cartilage, but also contains elastic fibres.
This provides a great ‘springiness’ to the tissue and the capacity to return quickly to its original shape if deformed.
The ears contain elastic cartilage.
Fibrocartilage
Like hyaline cartilage, this type contains collagen fibres. However, they are not packed nearly as tightly as in hyaline cartilage.
As a result, fibrocartilage has some compressibility. This allows it to act as a shock-absorber.
This form of cartilage is found in areas that are frequently weightbearing. The intervertebral discs and menisci of the knee contain fibrocartilage.
Classification of Joints
Joints are classified in two different ways:
Functionally – referring to their range of motion
immobile, slightly movable or freely movable
Structurally – based on the type of connective tissue that binds the bones
Fibrous, cartilaginous or synovial
These are mixed up in the Nelson Textbook! Ignore it
Fibrous joints
These joints are places where bones meet, and are joined together by tough, fibrous tissues (these often become calcified)
Having multiple bones allows for multiple growing locations faster growth in childhood than if it was a single bone.
Examples are sutures of the skull. As these joints start out ‘softer’ in infants, it allows for some movement of the bones, particularly required during the process of being born!
