Medsci-Musculoskeletal system

Fibres

-1/3 of dry weight. -made up of collagen fibres (type I and V). -resists tension (stretching/pulling)

Ground substance

-2/3 of dry weight. -hydroxyapatite resists compression (squeezing/crushing)

Bone trabeculae

-Cannot be too thick (max 0.4mm) due to blood vessels need to supply osteocyte with blood (nutrients)

Osteoporosis is a disease where bone resorption occurs at a faster rate than bone deposition. Due to its high surface area spongy bone exhibits a greater loss of mass and density. Name the region of a lond bone that is most likely affected, and the cell that would have high activity level in a patient with this disease

Epiphysis /osteoclast

The organisation of a long bone

Epiphysis, Metaphysis, Diaphysis, (metaphsis, epiphysis)

Skeletal muscle tissue

is striated and under voluntary control

The primary role of the protein Destine in skeletal muscle is to attach

Z-lines between myofibrils

perforating (sharpey's fiber)

collagen fibres make up periosteum

Spongy bone

house red bone marrow

A bone with large amounts of osteoid is

more flexible

Meaning of cells (osteo=bone)

oestogenic=cell reserve osteoblast=bone formation osteocyte=bone maintenance osteoclast=bone destruction

periosteum

outer layer of the bone -outer fibre-cellular sheath surrounding the bone

Trabeculae are found in

spongy bone

The influx of water into unloaded cartilage is caused by:

the high concentration of soluble ions in the cartilage matrix

Endosteum -which covers all inner layers

thin, inner fibre-cellular layer lining medullary cavity

Fat storage is what type of bone marrow

yellow

A tendon

-Attaches a muscle to a bone -is very good at resisting tension. -Contains parallel bundles of collagen fibres -Is a n extension of the fused endomysium, perimysium and epimysium of a muscle.

The function of muscle is to

-Help communicate -Generate heat that helps maintain body temperatures -Pull on bones, thereby moving the body -move materials through the body

Respect to spongy bone

-It has higher turnover than the other type of lamellar bone -Nutrients and oxygen diffuse in towards the centre of its structural unit -it supports the outer shell or cortex of a bone -In long bone, it is found primarily in the epiphysis

True facts about muscle

-Muscle pull on bones, they do no push bones -The muscle's attachment to the bone which moves the least is the origin of that muscle -The muscle's attachment to the bone which moves the most is the insertion of the muscle -The main movement the at occurs when the muscle contracts is the action of the muscle

Tissues found in bones

-Nervous tissue -Adipose tissue -Bone -Dense connective tissue

Interstitial growth

-Occurs in softer tissues that can deform. -This process involves the cells dividing, secreting more extracellular matrix and growing the tissue from within. Because bone is designed to resist deformity it can only grow by adding new bone onto an existing surface (apposition growth).

Lamellar bone

-Oxygen diffusion occurs in the opposite direction to unit formation for all types of lamellar bone -Osetocytes are typically no more than 0.2mm from a blood supply -the outer layers of an osteon are older than the central layers -"cutting cones" are required to form secondary osteoblasts but not primary osteons

Associated with compact bone

-Perforating and central canals -Osteocytes -Canaliculi -Concentric lamellae

The skeleton does the following

-Supports soft tissue -Enclose and protect the brain and spinal cord -Provides attachment points for tendons of skeletal muscles -Store minerals, especially calcium and phosphorous.

Articular capsule of synovial joints

-Vili or folds of synovial membrane are often found projecting into the joint space -there are variable numbers of adipocytes in the subintima -the fibrous layer is well innervated -thicker parts of the fibrous layer are often called intrinsic ligaments

terms associated with osteoclasts

-monocyte progenitor cell -clear zone -syncytium -apoptosis

Function of connective tissue found in skeletal muscle

-to help protect myocytes from becoming overstretched -to permit the passage of blood vessels and nerves to the muscle cells. -to act the mould or template in which muscle is constructed and repaired -to help distribute the force generated by myocyte contraction to the tendon

What is the double meaning of bone

1. Bone the organ (cause it is made up of different types of tissues). 2. Bone the tissue (one of the tissues found in the bones of the skeleton).

Extracellular matrix is made up of (two things)

1. Fibres (oganic) and 2. Ground substance (inorganic)

Bone reabsorption

1. Monocyte precursor cells leave BV and start to fuse on bone surface 2. osteoclasts form and start dissolving bone 3. osteoclast eventually die (apoptosis) resorption stops 4. Blood vessels grow into new space

Types of bone

1. mature (woven) 2. immature (collagen randomly waved ranged fibres-woven. not strong due to randomly arranged fibres and is present in the womb)

how much water is in bone

20-25%

Joint definition and classification

A joint or articulation is any point at which two (or more) bones interconnect. This union will be a compromise between the need to provide support and the need to remain mobile. By looking at the different tissues and the shape of the articulating surfaces (the joint's structure) the function of the joint can often be determined.

Hyrdoxyappetite in between collagen fibres

Acts like glue

Precursor, location and function of osteogenic cell

Also known as osteoprogenitor cells. Location: Surface of bone in the periosteum and endosteum. Also found inside the canals of compact bone. Function:Normally dormant but can divide and supply developing bone with bone-forming cells. Precursor: Unspecialised stem cells (mesenchyme = embryonic CT).

articular cartilage

Articular cartilage is a specialised type of hyaline cartilage (a type of connective tissue). The primary function of articular cartilage is to protect the ends of bones that come together to form a joint. This connective tissue forms a thin layer, typically 1-7mm thick, which is attached to the bone. Articular cartilage can absorb shock, support heavy loads and provide a smooth, near frictionless surface when combined with synovial fluid (CoF= 0.002-0.005). As long as its highly specialised tissue structure remains intact it can fulfil its function for most of your life. The degradation of this tissue leads to the disease arthritis.

Bone growth

As child's bone grows into an adults bone, it must go through appositional growth and reabsorption. As the the bone grows outwards the inner bone is absorbed.

Mature or lamellar bone

As osteoblasts repost new bone onto a surface (appositional growth), they do so in layers or sheets (lamellae). The collagen fibres are typically put down in the same direction within a layer, but can alternate up to 90 degrees out of phase between the layers. This enables bone to withstand forces from different directions, making it significantly stronger. There are two forms of lamellar bone, spongy and compact bone

Atrophy

Atrophy means a decrease in the size of the myocytes. Muscular atrophy occurs when muscles are not used or stimulated by motor neurons. For example when a limb is immobilized in a cast for a period of time or if a muscle is paralysed. Muscle atrophy also occurs as part of the complex pathology in diseases such as heart failure, diabetes, cancer and AIDS. The normal loss of muscle mass starts at the age of 20 years. The rate of loss is accelerated after the age of 50. By the time we reach 80 years approximately 40% of our muscle mass will be lost. Muscle is replaced by fat and connective tissue. Some of that loss is due to individual bre shrinkage ie atrophy; some is due to bre loss ie hypoplasia. If atrophy is not permitted to proceed too far, it can normally be reversed.

The skeletal is made up of the

Axial and appendicular sections

Collagen fibres at the myotendinous junction

Blend wiht the collagen fibres in the endomysium

Appositional growth

Bone grows outwards. 1. Osteogenic cells divide forming osteoblasts which deposits osteoid 2. some osteoblasts become trapped in lacunae eventually becoming osteocytes 3. when growth stops osteoblasts can convert back into osteogenic cells or die. osteoid is fully calcified

Haemopoiesis and fat storage are both types of

Bone marrow

In a particular zone of articular cartilage, chrondocytes have the following characteristics: They are round in shape and occur by themselves between collagen fibres which run perpendicular to the surface. Which zone of articular cartilage are the chrondocytes most likely to be in?

Calcified cartilage

The musculoskeletal system

Can disappear with discontinuous use

Which blood vessels are found within canals, located inside the shaft of a long bone?

Diaphyseal arteries and veins

The outermost extension of connective tissue that surrounds a muscle is the

Epimysium

Bone = specialised connective tissue (1/4 primary tissue)

Fairly low cell count but is made up of cells. Extracellular matrix around the cells. lots of water, fibre, ground substance.

Diarthosis

Freely moveable joint, low stability, high movement, appendicular skeleton 80% of appendicular skeleton

Deep fascia

Groups muscles with similar functions together

An adult has more muscle than a child. How did that increase in muscle mass occur?

Hypertrophy

Synarthosis

Immovable joint, high stability, low movement, axial skeleton

Hypertrophy -

Increase in muscle size is due to increases in the size of bres (hypertrophy) rather than any increase in fibre numbers (hyperplasia). The myocytes themselves will increase in diameter with more myo brils packed into each muscle cell.Typically, the effect will be an increase in overall muscle size and strength but the same number of cells will still contribute to the contraction. Various factors can stimulate skeletal muscle hypertrophy including repetitive contraction of muscles to near maximal tension (heavy resistance training) and the use of anabolic steroids. Anabolic steroids are variants of the male sex hormone testosterone, which have been synthesised by pharmaceutical companies. These steroids increase protein synthesis through their interactions with speci c target tissues that include skeletal muscle and bone. Anabolic steroids don't just target muscle and bone tissue, they can also effect other tissues which can have side effects such as; acne, hair loss, excess hair gain in the wrong places, liver failure, shrivelled testes, infertility, increased susceptibility to coronary artery disease and extreme mood swings 'roid rage'.

Diaphysis

Is the middle section of the bone. in the centre of the bone contains medullary cavity(bone marrow). Surrounding that is the endosteum

Compact bone

Is the outer shell cylinder, they are light (low in material) and strong. thinner than diaphysis

Cartilage

Its hyaline form is the most abundant and reduces friction at joints

Spongy bone

Made up of rods and beams. the inside bit of the epiphysis bit of the bone

Appendicular skeletons is for

Movement and fat storage. Contains 126 bones (some paired)

Muscle stability

Muscle plays a very important role in stabilising joints and maintaining posture. Muscle is especially important in stabilising those joints that have a wide range of movement. In these joints, stability (normally provided by the ligaments and/or the articular capsule) has been replaced with active contraction of the surrounding muscles.

Muscle communication

Muscles are used for facial expression, body language, writing and speech.

Precursor, location and function of osteoblast cells

Precursor is osteogenic cells. Location: Usually in a layer under the peri or endosteum. Whenever new bone is being formed. Function: Synthesis, deposition and mineralisation of osteoid

osteoclast

Precursor= fusion of monocyte (white blood cells) progenitor cells. (up to 20 cells fused together -fusion of many cells=syncytium). Location= at sites where bone resorption is occurring. Function= secretes acid and enzyme to dissolve the mineral and organic components of bone. Image= ruffled borders, theres a space around the cell and there is a nuclei.

osteoblast

Precursor= osteogenic cell. Located usually in a layer, under the peri or endpsteum and wherever new bone is being formed. Function= synthesis, deposition and mineralisation of osteoid.

Osteogenic cell (also known as osteoprogenitor cells)

Precursor=unspecialised stem cells (mesenchyme = embryonic CT). Located on the surface of bone in the periosteum and endosteum. Also found inside canals compact bone. Function= normally dormant but can divide and supply developing bone with bone-forming cells.

Appositional growth forming a primary osteon

Primary osteons are formed around an existing blood vessel on the surface of bone (normally in the periosteum). This occurs when the bone is growing and new bone tissue is being deposited onto an existing surface

Haemopoiesis

Red bone marrow, red tissue makes red blood cells.

Transfer force of the muscle to its tendons

Sarcomere myofibril myofibre endomysium perimysium epimysium

Satellite cells (Myoblasts)

Satellite cells lie beside muscle fibres outside the sarcolemma but within the same basement membrane. Because myocytes are large multinucleated cells, created when many myoblasts fused together (= Syncytium), they are unable to divide by mitosis. Satellite cells are the only cells in muscle that can divide and fuse with other satellite cells and myocytes to repair any damage that may have occurred. While the number of muscle bres is more or less set at the time of birth, satellite cells do have a limited ability to replace muscle bres that die from old age or injury.

muscle-Heat production

Skeletal muscle can produce as much as 85% of our body heat. This heat is used to maintain the body at 37oC for normal function.

amphiarthosis

Slightly movable joint, medium stability and movement

Muscle- Control of body openings and passages

Some ring-like muscles (sphincters) help control the admission of light (eyelids and pupils) and food and drink (muscles around the mouth) that enter our bodies. The elimination of waste is also controlled by the urethral and anal sphincters (smooth and skeletal muscle). (Normally the passage of food and liquid through the gut is also controlled by smooth muscle. )

Functions of the skeletal system

Support, protection, movement, haemopoiesis, fat storage, calcium and phosphorus reserve.

Axial skeleton is for

Support/protection and haemopoiesis. 80 bones (some paired)

Synovial fluid

Synovial uid is a clear or slightly yellowish uid that is an ultra ltrate of blood plasma that leaks out of the vessels in the synovial membrane (subintima). Other components, not found in the blood ltrate, are secreted by the synoviocytes. One such component is Hyaluronic acid. Free cells are also found in low concentrations within synovial uid. These cells tend to be monocytes, lymphocytes, macrophages and synoviocytes. The function of synovial uid includes joint lubrication, shock absorption, chondrocyte metabolism and overall joint maintenance.

Z-lines

The Z-lines of adjacent sarcomeres within a myocyte are held together by a number of structural proteins. One such protein is called Desmin. - These proteins help align sarcomeres between the myo brils. The result is that sarcomeres shorten together and pull in unison. It is believed this is why skeletal muscle bres (myocytes) have a uniform striated appearance under the microscope. - At the surface of a myocyte the Z-lines of the outermost myo brils are attached to the sarcolemma, and to the surrounding basement membrane and endomysium. A group of proteins (called a 'protein complex') are responsible for this.

Function of the Skeletal Muscle Connective Tissue

The connective tissue layers of muscle (epi, peri and endomysium) are continuous and blend with each other at the appropriate level. These brous layers have four major functions. 1. To provide the organisation and scaffolding upon which the muscle is constructed. 2. To provide a medium for blood vessels and nerves to gain access to the myocytes. 3. To prevent excessive stretching and therefore damage to the myocytes. 4. To distribute the forces generated by muscle bre contraction. Background knowledge: - Sequential sarcomeres in a myo bril share a Z-line. - When all the sarcomeres in a myo bril are stimulated to contract, all the Z-lines are pulled closer together by the laments that make up the A and I bands (sliding lament theory). Therefore the whole myo bril will shorten. If myofibrils acted independently, damage to just one sarcomere in the chain could render the entire myo bril useless. However this is not the case. Myocytes that are cut in 'vivo' can still exert a pulling force on the muscle tendons.

Bone histology

The connective tissue matrix of bone is about 50-60% crystallised mineral salts.

Deep Fascia and Muscle Compartments

The deep structures of the body are usually covered in a wrapping of dense connective tissue (regular and irregular) called deep fascia. The deep fascia underlies skin and the subcutaneous tissue (also known as superficial fascia). Muscles that are supplied by the same nerves (innervation) or have a similar action can sometimes be found grouped together in a regions called a compartment. The outer sleeve and walls of the compartments are made up of deep fascia. The walls or septa are often referred to as investing fascia (eg. intermuscular septa, interosseous membranes). Where investing fascia comes into contact with bone it fuses with the periosteum. In most areas the outer layer of a muscle (epimysium) can move and glide under the deep fascia. In other areas the deep fascia is part of the muscle tendon and can act as an attachment point for the muscle.

Osteocyte

The precursor is osteoblast. Location= trapped within lacunae inside bone. Osteocytes can communicate with neighbouring cells through their long cellular processes and canaliculi. Function= bone tissue maintenance.

Joint cavity

The term joint cavity is misleading as it implies a large space within the joint. In reality the joint cavity is the small area between the articulating surfaces, while the peripheral margins of the joint cavity are lled by the collapsing and in-folding of the synovial membrane (villi). This potential space is lled with a fluid called synovial uid. The amount of synovial uid inside a healthy joint cavity rarely exceeds 1ml, even in large human joints such as the knee.

Muscle movement

This is the most obvious function of muscle. Movement is not confined to the movement of the bones in the skeletal system. Other examples of movement include; moving gut contents & lymph transportation (smooth muscle) and circulating blood (cardiac muscle).

Simple synovial joints

Unlike the other types of joints found in the human body, synovial joints are not restricted by the properties of a specific tissue or tissues which hold the ends of the bones tightly together. Apart from the articular capsule, the ends of the articulating bones in a synovial joint are mostly free. This permits a wide range of motion but can also introduce instability. All synovial joints have 4 common features. We will look at each in greater detail.

Example of synarthrosis

a suture in the skull

Compact bone is

arranged in units called ostend (haversian systems).

medullary cavity

bone marrow (adult-yellow bone marrow)

Bone lining (osteogenic) cells can differentiate into another cell type found associated with bone. Once these cells have differentiated into their new cell type they can then

deposit and mineralise osteoid

Joints that allow a wide range of motion

diarthorsis

Which event must occur first in appositional growth of bone

differentiation of periosteal cells into osteoblasts

long bones grow in length by a different process called

endochondral ossification

The membrane that lines the medullary cavity of a long bone?

endosteum

Bone is made up of

extracellular matrix and cells

Ratio of appositional growth and bone reabsorption

in children there is more appositional growth

The tissue bone is too rigid to grow by a process called

interstitial growth

Muscular Dystrophy

is a disease where the protein Dystrophin is not transcribed correctly, or is missing. This results in myocytes that have a weaker sarcolemma that can tear easily, eventually causing the death of the cell.

The alignment of osteons in compact bone?

is along line of physical stress on a long bone

Dystrophin

is an example of a protein that helps form this bridge between the myocyte and surrounding connective tissue. It is also thought to contribute to the strengthening of the sarcolemma while transmitting contractile forces generated by the sarcomeres to the surrounding endomysium.

The breakdown of bone matrix

is called bone resorption

Joints by function

synarthroses are most likely to be used for growth

Osteoid (not cell0, (organic competent of new bone)

the organic extracellular matrix (mainly collagen) of bone, synthesised by osteoblasts prior to mineral deposition. Collagen accounts for 70% of osteoid with the remainder consisting of proteoglycans and other proteins. This precursor mates is eventually infiltrated with bone salts (hydroxyapatite) and this process is called calcification. This makes the bone strong but also dense, thus nutritive fluids cannot diffuse freely through it. secretes a lot of collagen.