Biology - Musculoskeletal system

  • Two main parts are epiphysis and diaphysis

  • Epiphysis:

    • The larger section at the end of the bone is the epiphysis (epiphyses when plural)
    • Contains spongy bone and red marrow, which contains the stem cells for blood cells, filling the spaces in the spongy bone. 
    • Epiphysis meets diaphysis in the metaphysis, a narrow area containing the epiphyseal plate or growth plate. 
    • The epiphyseal plate contains hyaline cartilage in a growing bone. However, once growth stops, it is replaced by osseous tissue, and the epiphyseal plate becomes the epiphyseal line.

  • Diaphysis:

    • Tubular shaft that runs between the proximal and distal end of the bone.
    • Walls consist of hard/compact bone
    • The hollow section is the medullary cavity. 

  • Medullary Cavity:

    • Filled with yellow bone marrow, which stores fat to be used as a energy source when needed 
    • Contains a fragile membranous lining known as the endosteum, where bone growth, repair, and remodeling occur.

  • The outer lining of bone::

    • Covered in a tough fibrous membrane known as the periosteum, which contains blood vessels, nerves, and lymphatic vessels that nourish the bone
    • Tendons and ligaments are attached to the bones at the periosteum. 
    • Purpose of the periosteum is to cover and protect the outer surface of the bone
    • Periosteum covers entire surface of the bone except where epiphysis meets the other bones to form joints. Here epiphysis is covered with articular cartilage, a thin layer of cartilage reducing friction and acting as a shock absorber. 

  • Nutrient Foramen is a small, smoothed-walled hole that allows blood vessels present on the outer surface of the bone to go through and reach the bone marrow

  • Nutrient artery carries blood to the bone marrow, allowing efficient flow of nutrients and oxygen and removing waste products, such as carbon dioxide and acid. 

  • Hard bone/compact bone:

    • On the wall/outer layer of bones
    • Made of osteons (cylindrical shapes containing nerves), viens, arteries
    • Has bone marrow cavity
    • Bone marrow stores fat
    • Forms diaphysis of bone

  • Spongy bone/cancellous bone:

    • Inside bones
    • Light, spongy, soft with honeycomb network of branches
    • Found in and maes up epiphysis
    • Made up of trabeculae
    • Bone marrow produces red and white blood cells

  • Bones are strong as they contain the protein, collagen which provides strength, and the mineral calcium phosphate

  • Collagen forms a forms a soft network and calcium phosphate hardens and strengthens it, allowing bones to be flexible and durable 

  • Bones are lightweight as spongy bone has fluid, bone marrow cells and some fat cells which fill parts within its branches. Lightweight quality is from honeycomb structure of spongy bones 

  • Cartilage:

    • Form of dense and flexible connective tissue
    • Avascular (lacking blood vessel)
    • Aneural (lack nerve supply)
    • Flexible
    • Resistant to compression
    • Main cell type is chondrocytes
    • Consists of collagen and elastic fibers
    • Fibers allow cartilage to be able to be drawn and stretched and provide a smooth surface for movement of bones at the joint
    • Glucose proteins (proteoglycans) in cartilage allows for the trapping of water
    • As cartilage is avascular, it utilizes diffusion to obtain nutrients so healing of cartilage to be extremely slow

  • 3 forms of cartilage: hyaline, fibrous, elastic

  • Hyaline cartilage

    • Smooth surface, allowing tissue to slide/glide easily and provides flexibility and support
    • Most widespread and common cartilage 
    • Resembles glass
    • Has matrix containing closely packed collagen fibers, making it tough but still slightly flexible. 
    • Contains ground substance
    • Consists of a bluish-white, shiny ground elastic material, whose matrix contains chondroitin sulphate, with many fine collagen fibrils and chondrocytes. 
    • In embryonic stage, bone starts as hyaline cartilage but later ossifies. 
    • Hyaline cartilage is in the connection between ribs and sternum, the nasal cartilage and articular cartilage

  • Fibrous cartilage

    • Has many collagen fibers 
    • Toughest form of cartilage
    • Has no perichondrium 
    • Has a matrix containing dense bundles of collagen fibers embedded with chondrocytes, making it tough and durable and perfect to provide support and rigidity
    • Fibrous cartilage is in the intervertebral discs , the menisci, the callus, between the pubic symphysis and at the junction where tendons insert into the bone

  • Elastic cartilage

    • Flexible 
    • Contains elastin tissue 
    • Has tensile strength of collagen fibers and resistance to compression
    • Provides support
    • Surrounded by perichondrium 
    • Chondrocytes are located between a network of threadlike elastic fibers, making it flexible and resilient due to the abundance of elastic fibers 
    • Elastic cartilage is in the internal support of the external ear, auricle of the outer ear and in the epiglottis

  • Cartilage vs. bone:

    • Cartilage is avascular; bone isn’t
    • Bone has more organized microarchitecture
    • Matrix is firm and flexible in cartilage but tough and inflexible in bones
    • Bone cells lie in lacunae singley while cartilage cells can lie singly or in small groups
    • Bone has bone marrow center; cartilage doesn’t

  • Ligament:

    • A ligament is tough and fibrous connective tissue that connects bone to bone, holding structure together and keeping it stable at the joints while allowing flexibility
    • Ligaments often connected to moveable bones (e.g. knee)
    • Have strong collagen fibres

  • Skeleton:

    • Axial skeleton is bones along the axis of the body including the skull, vertebral column and rib cage
    • Appendicular skeleton is appendages (things that are added or attached) such as upper and lower limbs , pelvic girdle and shoulder girdle
    • Skull provides protection and structure to the brain, eyes, muscular attachments to the face and nerves and vessels that are somewhat connected to the brain or face. The base of the skull allows for nerve connections through foramina (holes)

  • Ribs:

    • Main structure of the thoracic cage 
    • 12 pairs of ribs, numbered from top to bottom
    • First rib connected to the collarbone or clavicle by the costoclavicular joint
    • First 7 are considered true ribs which are joined to the sternum (breastbone) by the sternocostal joints
    • Ribs 8-10 connect to the sternum indirectly, by first joining to the 7th rib
    • The last 2 ribs don’t articulate any (floating)
    • Protect the thoracic cavity (the area behind the ribs where there is hollow empty-like space)
    • Flexible movement to allow for sufficient breathing (contracting and expanding along with the diaphragm)
    • Assists with the creation of red blood cells when young
    • Allows room for muscle attachment

  • Vertebrae

    • 33 individual interlocking bones forming the spinal column
    • Each one has 3 components: vertebral body, vertebral arch and transverse processes
    • Vertebral body is weight bearing
    • Vertebral arch protects spinal cord
    • Transverse processes is for ligament attachment
    • 7 cervicals - back of neck
    • 12 thoracic - little movement, firmly attached to ribs and sternum
    • 5 lumbar - lower back, weight bearing
    • 5 fused of the sacral region - connects spine to hip bone
    • 4 fused in the coccyx - balance when sitting, helps with pelvic floor

  • Discs in body

    • Plates of cartilage that bind the disc to the vertebral body that are along the spine
    • Shock absorbant
    • Prevents the vertebrates from grinding and eroding
    • Load distributor
    • Allows movement
    • Hold the spine together for stability
    • When someone ‘blows a disc’, it means it is out of place and can cause pain down the sciatic nerve (down the leg and into the foot), numbness and limits movement as discs control movement
    • They typically blow in the lower back
    • Compresses spinal nerve
    • Portion of the disc nucleus pushes through crack in the annulus (ring shape outer part of the disc)

  • Movements

    • Flexion = bending
    • Extension - straightening
    • Abduction - moving away from center of body
    • Adduction - coming closer to center of body
    • Protrusion - forward
    • Retrusion - backward
    • Elevation- superiorly to the reference axis
    • Depression- inferiorly to the reference axis
    • Lateral rotation - rotation going out from center of body
    • Medial rotation- rotation coming towards the center of body
    • Pronation- medial rotation of the radius, resulting in the palm of the hand facing posteriorly (if in anatomical position) or inferiorly (if elbow is flexed)
    • Supination- lateral rotation of the radius, resulting in the palm facing out from the body
    • Mnemonic - 'Supinate to the Sun and Pronate to the Plants' (Supinate: palm towards the Sun, Pronate: palm towards the Plants)
    • Circumduction - combination of: flexion, abduction, extension, adduction
    • Deviation - ulnar and radial abduction of the wrist
    • Opposition - bringing the thumb in contact to a finger
    • Reposition - separating the thumb from the digits
    • Inversion- plantar side toward the medial plane
    • Eversion- plantar side away from the medial plane

  • Muscle:

    • Three types of muscle: smooth, skeletal, cardiac
    • Smooth muscle - lines the walls of inner organs. When smooth muscles contract, they help organs carry out their functions. Contractions are involuntary and performed subconsciously.  Found in the walls of hollow organs: intestines, stomach, trachea, uterus (for women), urinary bladder
    • Skeletal muscle - attached to bones by tendons and the most common muscle. Contractions are voluntary and used for almost everything, such as blinking or running.
    • Cardiac muscle - found in the walls of the heart. When this muscle contracts, it pumps blood and the heart beats. Contractions are involuntary. 

  • Slow oxidative fibres - supports long endurance activities, maintains resistance to fatigue, aerobic respiration reliant and low power muscle contractions

  • Fast oxidative fibers  - contracts muscle quickly, generates more power, calve muscles do more work in acceleration, fatigues quickly

  • Why do muscles need tendons:

    • Tendons help to attach skeletal muscles to the skeleton. 
    • Tendons are tough connective tissues that are wedged between the muscle and the bone, connecting them.

  • Muscles and joints:

    • Muscles are connected to the ends of bones which meet at a joint
    • When the muscles contract, they pull on the bones, making them move
    • Muscles can only contract, so to extend or lengthen bones, pairs of muscles have to work opposite each other, so at least two muscles are needed at every joint to allow smooth and easy movement.