Tissues/Biomechanics Flashcards
What does the neural tube develop into?
brain and spinal cord (CNS)
what do neural crest cells develop into?
dorsal root ganglia cells (sensory)
what do somites develop into?
most of the skeleton:
skeletal muscle of the neck, trunk & limbs
tendons & ligaments
dermis on the back & limbs
What are somites of the dermis, skeletal muscle and skelton called?
dermis = dermatome
skeletal muscle = myotome
skeleton = sclerotome
What is a dermatome
area of skin innervated by the sensory neurons from a single spinal segment/ nerve (dorsal root)
What is a myotome
collection of muscle fibres innervated by the motor neurons from a single spinal segment/ nerve (ventral root)
What will damage to a spinal nerve cause?
sensory loss in the dermatome and weakness in a muscle whose majority of muscle fibres recieve innervation from motor neurons exiting through that spinal nerve
Define a tissue
Group of similar cells and their extracellular products organised to perform a common function
Define an organ
an organ must include 2 or more types of tissues, that work together to perform a specific function
Define an organ system
An organ system involves multiple organs that work together to coordinate activities for the organism
Is skeletal muscle an organ?
An organ must include 2 or more types of tissues, that
work together to perform a specific function.
Each muscle consists of skeletal muscle tissue,
connective tissue (e.g. tendon), is innervated by
nervous tissue, and has a rich supply of blood
(includes epithelial tissue).
A “skeletal muscle” therefore is an organ
Is bone, like a cervical vertebrae an organ?
Bones are organs; although they consists primarily of osseous (connective) tissue, bones have a vast supply of nervous tissue, fibrous tissue lining their cavaties, and muscle and epithelial tissue in their blood vessels
What is the function of connective tissue?
Protect other tissues, binds together tissues, storage of fats and minerals, support organs structurally and functionally
What are the four tissue types?
Epithelial
Muscle
Nervous
Connective
What type of cells do connective tissues consist of?
Mesenchymal cells
What are elastic fibres?
allows tissues to= stretch and return to shape. They are interwoven with collagen, appear wavy and are smaller
What are collagen fibres?
strong and stretch- resistant
the most abundant in the body
high tensile strength
long unbranching & flexible
What are the three types of connective tissue?
Connective tissue proper
supporting connective tissue
fluid connective tissue
What are the types of connective tissue proper?
Loose eg. adipose tissue
Dense - Regular, Irregular and Elastic
What are the two types of supporting connective tissue
Cartilage and bone
What are the three types of cartilage
Hyaline - most common and covers articular ends
Fibrous - resists compression eg. pubic symphysis
Elastic - web like mesh, highly flexible
What are the two types of bone?
Compact - forms the hard outside of the bone
Cancellous (spongey) - within the interior of the bone
Describe the role of osteoprogenitor cells in bone
They are located in the periosteum and endosteum and differentiate into osteoblasts and osteocytes. Osteoblasts secrete collagen and osteoid whilst osteocytes maintain the ECM. Whilst white blood cells differentiate into osteoclasts, which reabsorb bone
What are the two type of fluid connective tissue?
Blood and lymph
What is the name of the space that surround chondrocytes in cartilage?
Lacuna
What is the function of epithelial tissues?
Covers body surfaces, lines cavities, forms glands, the internal and external lining of many organs and body tubes
What is the form/ cellularity of epithelial tissue?
densely packed minimal ECM free apical surface basal surface is attached to underlying connective tissue via a basement membrane avascular richly innervated high regeneration capacity
What is the function of muscle tissue?
Responsible for movement and support of body parts, movment of materials within the body and temperature regulation
What are the three muscle tissue types?
Skeletal, Smooth and Cardiac
What does a muscle cell contain?
Many nuclei
Myofibrils
Myofilaments
What are myofilaments
protein filaments within the cell
thin (actin) and thick (myosin) filaments
aligned in contractile units (sacromeres) that function to provide mechanical work
What are myofilaments
protein filaments within the cell
thin (actin) and thick (myosin) filaments
aligned in contractile units (sacromeres) that function to provide mechanical work
What are the properties of a muscle organ?
Contractility: ability to shorten and thicken, and develop tension
Excitability: ability to respond to appropriate stimuli
Extensibility: ability to be stretched without damage
Elasticity: ability to store some energy, and recoil to the resting length
What is the function of neural tissue?
Receives, transmits and integrates information to control body activities
What are the two types of neural cells?
Neurons and glial cells
What is a motor unit
1 motorneuron, its motor axon and all of the muscle fibres it innervates
What is the difference between stress and strain?
Stress is force over area and thus has units, whilst strain is the extension over the original length and has no units (expressed as a percentage)
What are the different types of forces that can be applied?
Compression
Bending
Torsion
Shear
Describe the load-deformation curve for bone
The elastic region where the Pa rises lineally until the yield point. At the yield point the Pa is no longer rising lineally, until it reaches the plastic region where permanent damage occurs. It then reaches its ultimate load and the Pa drops off dramatically until ultimate deformation or failure occurs
Define elasticity and viscoelasticity
Elasticity - the ability of a solid to recover its shape when the deforming forces are removed
Viscoelasticity - materials for which the relationship between stress and strain depends on time
Define creep and stress relaxation
Creep - if the stress is held constant the strain increases with time
Relaxation - if strain is held constant, stress decreases with time
What is hooke’s law?
deformation is proportional to the applied stress up to a certain point. this point is called the elastic limit. beyond this point additional stresses will cause permanent deformation
How do bones adapt to applied bending?
resorption and formation occurs in an ellipsoidal formation which increases the cross-sectional moment of intertia, making the bone more resistant to bending
How do bones respond to being loaded in torsion?
Failure is more likely to occur in areas with a thinner outershell. As a result the cross-sectional area will increase by reformation and thus better resist torsion
How does repetitive loading affect bone?
In most materials, repeated loading of a specimen at stresses lower than failure stress, can cause fracture. This is caused by failure fatigue
How does the growth in length of bones occur?
It occurs through endochondral ossification at the epiphyseal plates which is a temporary disc of hyaline cartilage
What are the zones of endochondral ossification?
Zone of resting cartilage Zone of proliferation Zone of maturation Zone of provisional calcification Zone of regression Zone of ossification Zone of resorption
How does load bearing exercise affect tendons?
They become stiffer
What is an apophysis?
a natural swelling, projection or outgrowth of an organ or part such as the process of a vertebra
What type of tendon injury is more common in children vs adults?
Children - avulsion
Adults - mid-substance failure
What is rheumatoid arthritis?
inflamation of the synovial membrane that lines the inside of the joint capsule and produces the synovial fluid
what is osteoarthitis?
degeneration of the articular cartilage
How does periosteal and epiphyseal growth differ?
periosteal growth is appositonal and increases in width. This is slow and continues throughout life to increase bone diameter
Epipshyseal growth is longitudinal and increases width. This growth usually occurs around the end of a bone diaphysis and ends when epiphyseal fusion occurs.
What are some features of post-natal development and maturation of the skeleton?
separate ossification centres grow and fuse to adult form
sex charactistics on bones develop
teeth and paranasal sinuses give shape and size to face
neck elongates, increasing mobility of the head
upper limb more developed at birth
thorax changes shape - circular vs oval cross-section
ribs change from horizontal to oblique
secondary curves develop on vertebral column
cubitus valgus increases
genu varum, then genu valgum are normal phases
cortical drift
How does articular cartilage respond to exercise?
It does not increase in mass in response to exercise, however it may atrophy with a lack of exercise or loading
How does articular cartilage respond to damage?
Articular cartilage is avascular, so it does not repair well especially when a rapid supply of nutrients is needed to recover
How does aging affect the vertebral column?
ossification of ligaments
osteoporosis
= loss of height and increased curvature
What is the function of tendons?
transmit force from muscle to bone
absorb, store and release energy
power amplification
protect muscle from damage
How do energy storage tendons differ from regular tendons?
Eg. achilles and patellar tendon
increased elasticity and fatigue resistance
contributes significantly to total body work
What is energy buffering and amplification in tendons?
Buffer - during jump landing or walking down a hill, the tendon lengthens to prevent eccentric muscle damage
Amplifier - during stance, achilles tendon slowly stores and quickly releases energy during push-off to propel to the next step
How do we determine tendon stiffness?
From tendon strain (ultrasound) and angle joint torque (strain gauge)
How do mechanical properties of a tendon affect muscle output?
A more compliant tendon requires a higher level of muscle contraction before force is generated around a joint
There is a delay between the activation of a muscle and its production of force - the electro-mechanical delay
A more compliant tendon = greater electro-mechanical delay, less force transmitted for given change in length
What are the effects of age on muscle?
reduction in muscle mass (sarcopenia)
reduction in number and size of muscle fibres (atrophy)
neuromuscular changes - reduction in capacity to detect infor and activate muscles - motor units remodel
can be partially offset by resistance exercise
What are the effects of exercise on tendons?
can induce tendon hypertrophy and increase tendon stiffness
type and intensity of exercise can impact the effects
time-course varies > de-training
What are the mechanics of ligament injury?
ligaments fail when tensile loads exceed capacity
often awkward positions of landing
joint dislocation is often associated with ligament damage
abnormal motion between bony articulation predisposes to articular damage
what are the grades of ligament injury
Grade 1 - damage to some collagen fibres
Grade 2 - more extensive number of fibres damaged
Grade 3 - complete rupture
How do ligaments heal?
Tri-phasic response
inflamation, proliferation and remodelling
how do the mechanical properties of ligaments change during healing?
decreased stiffness
decreased load at failure
altered site of failure
the entire ligament is weakened
What are the 5 mechanical mechanisms of tendon injury?
- excessive force
- repeated overload
- normal forces applied to a weakened tendon
- stress-shielding
- forces applied in an alternative direction
define:
perimysium
epimysium
endomysium
perimysium - groups muscle fibres into a fascicle
epimysium - fibrous tissue that surrounds skeletal muscle
endomysium - surround each muscle fibre
What influences individual muscle force (N)?
muscle architecture, muscle length muscle fibre length, pennation angle, PSCA specific tension - fibre type number/discharge rate of motorunits type of contraction passive force
What is PCSA
Physiological cros-sectional area
Muscle volume over fibre length
What is the muscle length-tension relationship?
Fibre length changes with contraction and joint angle. This impacts the muscle’s ability to produce force as fillaments can be too close or too far apart to generate force efficiently. Optimal length-tension relationship will produce the most force
What is specific tension?
the maximum force exerted by the fibres per unit of PSCA
higher in type II muscle fibres
What is Henneman’s size principle?
small motor units are recruited first. With greater excitatory input the number of motor units increase and the size of the recruited motor units increases.
Assumption: motor units within the same pool receive the same drive
Increased drive = more motor units and bigger motor units
How does the type of contraction affect force?
an eccentrically contracting muscle can produce more force at the same muscle length than a concentrically contracting muscle
eccentric contractions have a higher torque for the same motor drive
What is the force-velocity relationship?
As filaments slide past each other faster, fewer cross-bridges are able to attach and generate force.
As the relative filament velocity decreases, more cross bridges have time to attach and generate force
What is Hill’s Mechanical model?
Muscle tendon units are made up of:
contractile component - muscle fibres, actin and myosin cross-bridges
Series elastic component - intracellular titin, tendon
Parallel elastic component - connective tissue, epimysium and perimysium, endomysium and passive cross bridge connections
Total muscle force = ACTIVE + PASSIVE TENSION
For the same amount of neural drive which will produce the most force
A - A muscle that is shortening quickly
B - a muscle that is lengthening
C- a muscle that is maintaining its length
D - a muscle that is shortening slowly
B - a muscle that is lengthening (eccentric contaction)
What is muscle tone?
refers to muscle mechanical properties and the muscle’s response to stimuli
‘a slight constant tension of healthy muscles’
What is hypertonia?
High muscle tone
associated with pain and increased collagen content in the connective tissue matrix
causes long term contracture > muscle shortening > reduced joint range of motion > bone deformities
causes reduced muscle volume
What is hypotonia?
low muscle tone
very little or no dystrophin is produce, thus little muscle force can be produced
muscle weakness, fatigue, wasting and muscle shortening occurs
What is sarcopenia?
loss of lean body mass and muscle weakness associated with advancing age
Over 35 yrs old = 1-2% per year
over 60yrs old = 3% per year
What changes occur to muscle tissue during ageing?
- satelite cells reduce their ability to repair injured muscle through loss of numbers and function
- muscle fibres decreases in number and size
- fibre types move from predominately slow-twitch
- myofillament reduce their maximal force, elasticity and myosin content
- mitochondria numbers are reduced and lose enzyme content
- adipose tissue increases both intra-muscularly and inter-muscularly
- excitation-contraction coupling is disrupted and deficits in calcium release occur
