Biomechanics unit 2 - biomech of skeletal muscle tissue deck 1 Flashcards
Define what a tissue is
This is a group of similar cells that perform a common function
What are the 4 principle tissue types
- Epithelial tissue
- Connective tissue
- Muscle tissue
- Nervous tissue.
Think - ‘‘money never comes easy’’
The skeletal tissues that we will be concentrating on in this block are all types of what tissue ?
Connective tissue
What is the most abundant and widely distributed type of tissue in the body?
Connective tissue
What are the overall functions of connective tissues ?
To protect and support the body and its organs, connect and hold them together (hence its name), and to transport substances throughout the body.
What are the 4 main types of connective tissue ?
- Bone tissue
- Articular cartilage
- Tendon
- Ligament.
Think - ‘‘BLT + A’’
Appreciate these points about the remarkable ability of the different connective tissues to withstand repeated loadings over many years:
- Bone tissue must withstand these loads and almost continuously support the body’s weight. At joints, articular cartilage transfer these loads between the bones, cushion the bones against high peak loads and are important in the lubrication of joints. Tendons carry the large forces produced by muscles to bones and ligaments prevent joints being wrenched apart by these large forces
Define what bone tissue is
It is a specialised type of connective tissue
Bone is one of the hardest tissues in the human body, name the only 2 tissues harder than bone in the body
Dentine and enamel in teeth
What are bones formed from
Bone tissue
List the functions of bones
- They support the structures of the body
- Protect delicate structures such as the heart and lungs
- Act as lever arms for movement.
The different bone types are categorised based on their structures and specliased function; list the 4 main bone types
- Long bones
- Short bones
- Flat bones
- Irregular bones
Think - ‘‘its so long and fat’’
e.g. the skull bones are flat to contain and protect the brain whilst the limb bones are long to act as lever arms for movement.
Go over the areas of a bone - think ‘‘MED’’
What 3 things is bone tissue composed of ?
- Bone cells called osteocytes
- A non-cellular component
- An inorganic component
What is the non-cellular component of bone tissue composed of?
Very strong collagen fibres embedded in a jelly-like matrix called ground substance.
What % of the non-cellular component and the dry weight of bone is made up by collagen fibres ?
- 95% of the non-cellular component is collagen fibres
- 25-30% of the dry weight of bones is collagen fibres
Collagen fibres are flexible, but what force do they resist?
Stretching
What is the inorganic component of bone tissue mainly comprised of ?
Calcium and phosphate minerals
How are the calcium and phosphate minerals deposited in bone tissue ?
In the form of calcium phosphate crystals which are deposited within the matrix (ground substance)
What percentage of the dry weight of bone does the inorganic component of bone tissue make up?
65-70%
What gives gives bone its characteristic hardness and rigidity?
The high content of this inorganic component
Bones general consist of what two types of bone tissues ?
- Compact bone
- Cancellous bone
State the other name of compact bone also what part of a bone is usually comprised of compact bone
- The other name for compact bone is cortical bone
- Compact bone forms the outer layer of bones
Comment on the density of compact bone
It has a dense structure
What part of a bone is usually made up of cancellous bone and state the other name for cancellous bone
- Cancellous bone forms the inner part of short, flat and irregular bones. In long bones it lines the inner surfaces and makes up the greater part of the metaphyses and epiphyses.
- The other name for it is spongy bone
Describe the appearance of the overall structure of cancellous bone
It has a mesh like structure
What do the spaces between the mesh in cancellous bone contain ?
Red bone marrow
The relative quantities of compact and cancellous bone vary between bones and even within an individual bone according to what ? and give an example of this
According to the functional requirements of the bone
e.g. In the femur. The head and greater trochanter are covered only in a very thin layer of compact bone yet the shaft has a much thicker layer of compact bone
How do the cells in cancellous bone tend to align themselves?
In the directions that will best support the load on the bone
What is the basic structural unit in compact bone and describe how they are arranged
Basic structural unit is the haversian system. These are arranged longitudinally in columns
Describe the structure of how bone tissue is arranged in a haversian system
The bone tissue is arranged in layers called lamellae forming concentric cylinders around a central canal (haversian canal) (refer to pic)
What is contained within a haversian canal ?
Blood vessels and nerve fibres
What is located between the lamellae and what do they contain?
There are small cavities, called lacunae, that contain osteocytes
How are osteocytes linked to the haversian canals and lacunae, and what is carried across these links ?
- Each osteocyte is linked to the Haversian canal and other lacunae by minute channels, called canaliculi
- Along the canaliculi nutrients are carried from the blood vessels.
What fibres interconnect the lamellae of the haversian system ?
Collagen fibres
What is each haversian system surrounded by ?
A cement-like ground substance
What is the weakest part of the bones microstructure and why?
The cement-like ground substance surrounding a haversian system, because it does not contain collagen fibres
What is the basic structural unit in cancellous bone?
The trabecula
Describe the arrangement of trabecula
They are arranged in a latticework of branching sheets and columns (fig. A in the pic)
Describe the structure of trabecula and describe how it is similar yet different to the structure of haverian systems in compact bone
- Trabeculae are similar in structure to haversian systems consisting of layers of lamellae with lacunae containing osteocytes connected by canaliculi.
- The main difference is that trabeculae do not contain haversian canals
Why are haversian canals not needed in cancellous bone?
As blood vessels pass though the marrow filled spaces between the latticework of trabeculae, supplying nutrients to the osteocytes through the canaliculi.
How can the behaviour of a material such as compact bone be described to some extent?
Using its mechanical properties
What do the mechanical properties of a material describe ?
The way the material reacts when it is loaded
What are the 2 ways in which a material can be loaded axially?
It can be loaded in tension or in compression
Define what is meant by loading a material in tension
In tension the load is acting to stretch the material like in a rop
Define what is meant by loading a material in compression
In compression the load is acting to compress the material like in the supporting column of a building.
Give 2 examples of compressie and tensile loadings that occur in the bones
The radius and ulna are both put under a tensile load when an object is lifted as shown in (Fig A) and the vertebrae are under a compressive load due to the upper body weight as shown in (Fig B)
To help describe the behaviour of a material under tensile and compressive loads what 2 parameters are used?
- Stress
- Strain
Define what stress is
The force per cross-sectional area
It is a measure of the concentration of the load being supported by a material.
State the equation for calculating stress
Stress = Force / Area
(this is basically the same as pressure)
What are the SI units for Stress?
Newtons per metre squared (N m-2)
Describe what would happen to the stress on a material for the following situations:
- If the magnitude of the load increases (force) e.g. if the load on a supporting column is doubled then the stress will what?
- If the area over which a load is distributed is increased e.g. if the area of a supporting column is doubled then the stress will what?
- The stress will also double - it is proportional to the load (force)
- The stress will half - it is inversely proportional to the area
Define what strain is
The change in length divided by the original length
It is a measure of the amount of deformation a material has undergone.
State the equation for calculating strain
Strain = change in length / original length
. It is the ratio of the change in length of the material to the original length of the material. Thus, the larger the deformation the larger the strain. For example, if the length of a rubber band is doubled, the change in length of the rubber band is equal to its original length and therefore the strain is equal to one.
What are the units for strain ?
It has no units since it is a ratio
