Bone and Biomechanics Flashcards
Human Tissue Act 2008
Bodies come from bequests (gifts)
Consent is required from the donor and the immediate family members
Body parts are plastinated
Most body parts held for 18 months (or often longer) and will then be cremated.
4 basic Tissue types
- Epithelial - covers exposed surfaces eg skin
- Connective - fills internal space eg blood
- Muscle - contracts to produce movement
- Nervous - conducts electrical impulses to send messages
Epithelial Tissue
Physical layer of protection due to thick, dense layer.
Controls permeability.
Made up of :
Epithelia (covering)
Glands - exocrine and endocrine.
Connective Tissue
Allows the transport of fluids and dissolved materials.
Can store energy
Defend body
Includes:
- Connective tissue proper (lose and dense) = Collagen fibre (strong rope) and Elastic fibre (stretches)
- Fluid connective tissue = blood, lymph
- Supportive connective tissue = (cartilage, bone)
Muscle Tissue
- Skeletal muscle = attached to skeleton, allows movement
- Cardiac muscle = in heart
- Smooth muscle = in organs
Nervous Tissue
Instructs body parts what to do
Receives and transfers messages
Made up of neurons and glia
Homeostasis
The maintenance of an internal stable environment.
Requires regulatory mechanisms to make sure the controlled variable stays at a set point (normal range).
Feedback - Variable moves too far from the set point so body attempts to ‘return to normal’
Feedforward - Body alters a variable to minimise the effect of an anticipated event.
Anatomical Position
Upright facing forwards, Feet together, Arms by side with palms facing forwards Right = person's right ie our left Left = person's left ie our right Always refer to this position when describing the location of a body part
Terms used to describe location of body part
Superior = Above Inferior = Below
Anterior = Infront Posterior = Behind
Medial = close to midline Lateral = further from midline
Proximal = Close to main body
Distal = Distanced from main body
(Only used to describe limbs)
Deep = Closer to middle / further from surface Superficial = Closer to surface
Division of the body - Planes
Sagittal Plane - Divides the body into left and right pieces
Midsagittal or median plane = divides right down your exact midline = mirror image.
Coronal - Divides the body into front and back sections
Transverse - Divides the body into top and bottom sections
Angular Movements
- Flexion = decreases angle, bring fleshy parts closer together
- Extension = increases angle
Feet: - Dorsiflexion = toes brought up
- Plantar flexion = toes pointed towards the ground
- Abduction = Movement at joint moves limbs away from the body
- Adduction = Movement at the joint moves limbs towards midline
- Circumduction = Combination of flexion, extension, adduction and abduction.
Rotation Movements
Rotation = rotating around the long axis of a joint. Lateral = external Medial = internal
Specialised movements:
Pronation = Palm faces posterior
Supination = Palm faces anterior (bones are parallel)
Inversion = Sole of foot faces towards midline Eversion = Sole of foot faces away from midline
Movements in Planes
Sagittal = Flexion, Extension, Plantarflexion, Dorsiflexion Coronal = Abduction, Adduction, Inversion and Eversion Transverse = Rotation, Pronation, Supernation
Functions of the skeleton
- Hard tissue used for support!!
- Allows movement
- Protects organs
- Provides storage for minerals
- Contains red marrow which produces red blood cells
Types of Bones
- Compact bone = strong, good at transmitting force in 1 direction
- Cancellous bone (spongy) = shock absorbing, channels forces (common in ends of bones)
Bone classes
- Long bone = longer than they are wide
Lever for movement
Thicker / compact - Short bone = Similar length and width
Mostly cancellous
Shock absorbing
eg carpals, tarsals - Flat bone = used for muscle attachment or large
surface area to protect organs eg skull - Irregular bone = often have holes
don’t just usually have cancellous bone
Divisions of the skeleton
Axial Skeleton = bones of the core eg skull, vertebral
Used for protection
Appendicular Skeleton = Bones of the limbs
Important for movement
Axial Bones
Skull
- Cranium (vault) = top part - Used for protection and muscle attachment
- Facial Bones (jaw, chin etc) - Protects sensory organs
- Join at sutures
Vertebral Column = Main function is to keep the trunk upright. Also Support (organs and head) Divisions : Cervical (7), Thoracic (12), Lumbar (5), Sacral, Coccyx.
Rib Cage
- Ribs and Sternum
Appendicular Bones
Limbs:
Top region of arm = Arm
Bottom region of arm = Forearm
Top region of leg = Thigh
Bottom region of leg = Leg
Structure = single long proximal bone (humerus, femur)
Two distal long bones (radius, ulna, tibia, fibula)
Hands = Phalanges (14), Metacarpals (5), Carpals (8)
Feet = Phalanges (14), Metatarsals (5), Tarsals (8)
Humans are bipedalism = require stability + movement in lower limbs. Have a stable ankle joint.
However in upper limbs:
Humerus shorter/ lighter than femur as needed for movement rather than stability.
Hands are adapted for manipulation and precision.
Girdles
- Pectoral Girdle (shoulder) = clavicle (stabilising)
and scapula (attaches upper limb to axial skeleton, muscle attachment and mobile)
- Pelvic Girdle = hip bones and sacrum (attaches lower limb to axial skeleton)
Female pelvic cavity more circular and open to aid childbirth.
Bone Tissue Extracellular components
A hard connective tissue which helps to maintain shape.
2 extracellular components:
1. Organic (33% bone matrix)
Largely made up of collagen (protein) fibres which are a little stretchy so allow some flexibility and resist tension.
- Inorganic (67% bone matrix)
Largely made up of mineral salts such as hydroxyapatite and other calcium minerals. This makes bone hard and resistant to compression.
Bone tissue Cellular components
- Osteogenic cells
= Stem cells that produce osteoblasts
2.Osteoblasts (Makes)
= Produce new bone matrix
- Osteocytes (Maintains)
= Mature bone cells which recycle proteins and minerals. Also communicate with osteoblasts and osteoclasts to determine how much bone needs to be made and destroyed. - Osteoclasts (Breaks)
= Remove bone matrix
Compact Bone
Osteon structure:
Circumferential lamellae contain osteons
Osteon is a longitudinal unit within compact bone.
It provides a pathway for blood vessels/ nerves.
Central canal is a tunnel containing the blood vessels and nerves.
Interstital / concentric lamellae are a series of cylinders around the central canal.
Amongst these are lucunae which is where osteocytes sit.
Canaliculi are channels that run from central canal through lamellae and out to osteocytes so they are able to receive nutrients.
Cancellous Bone
Composed of trabeculae (criss cross bones).
Marrow fills the cavities between these bones.
Trabeculae do not need a central canal because they’re thin so have canaliculi coming from the surface.
Osteocytes sit within lucanae in between lamellae / on surface.
Trabeculae bones are orientated in a certain way (criss crossed) because it allows them to collect and absorb force from different directions and then direct it in a single direction.
Bone remodelling
Bones grow in width and length.
They are able to grow in width because osteoblasts located on the surface of bone secrets bone matrix to the bone surface. Osteoclasts will also remove bone from the interior to increase space in the centre and prevent the bone from becoming too dense.
Bone Homeostatsis
Bone is constantly being formed and destroyed. If the body needs minerals, bone is broken down to mobilise these. Remodelling also allows bone to respond to stresses / traumas. To maintain homeostasis, we have certain nutritional and exercise requirements.
Imbalance between osteoblastic and osteoclastic activity
When osteoclastic > osteoblastic activity we get a condition called osteopenia. Usually fine unless we get clinically significant version called osteoporosis.
This is when bone thinning makes the bones more prone to fractures.
Women are more at risk due to loss of estrogen post-menopause. Other lifestyle factors can put you more at risk eg lack of exercise (exercise stimulates cell formation as it tells your body you will be using it), nutritional factors etc
Bone Growth - Endochondral ossification
At 6 weeks after fertilisation, bones begin as a cartilage model. Overtime this transforms into bone through endochondral ossification:
As the cartilage enlarges, the centres start calcifying. Blood vessels begin to come to the surface of the cartilage, bringing osteoblasts with them which, forming bone on the surface. Blood vessels will go into the cartilage centre bringing osteoblasts with them to form a calcified matrix. As osteoblastic and osteoclastic behaviour proceeds, the diaphysis of the bone will form (longer shafts). These are the primary ossification centres. Epiphysis (ends of bone) are the secondary ossification centres as they develop second.
The epiphysis will remain separated from the diaphysis by an epiphyseal plate allowing the diaphysis to lengthen. When growth is finished (around puberty) they will fuse together.
Joints (articulation)
= Where 2 bones meet
Involves bone shape and soft tissues which determine if there is free or controlled movement.
Less Bony congruence (bone surfaces that join) = More soft tissue required.
Soft tissues
No inorganic component.
Cartilage =
1. Hyaline (in every type of joint)
2. Fibrocartilage (in some joint)
(In general collagen fibres in a ground substance with chondrocytes (osteocytes for cartilage) located in lacuna and no blood vessels meaning nutrients need to diffuse through matrix).
Hyaline
Very thin barely visible collagen fibres
High water conc helps to resist compression
Functions -
Moulds to surfaces of bones where they join
Provides smooth frictionless movement.
However over time they will degrade with age
Fibrocartilage
Collagen fibres are thicker and all aligned in 1 direction with stresses.
Can resist tension and compression coming from different directions.
Functions:
Generally located at articulations which experience both compression and tension.
Deepening + supporting the articulation
Act as a buffer / shock absorber to distribute force over a wider area.
Ligaments and Tendons
Composed of DFCT - dense fibrous connective tissue, collagen, elastin, fibroblasts.
= Very slow healing due to limited blood supply
Ligaments
Connect bone to bone
Function:
Restricts movement due to minimal elastin and more collagen.
Tendons
Connect muscle to bone
Function:
Facilities and controls movement (more elastin = greater stretch)
Tissues vs Structures
Tissues = basic unit of cells and other stuff grouped together in a specific structure to perform a specific function. Structures = something made up of tissue
Types of Joints
- Fibrous
Tissue = DFCT, Structure = ligament
Limits movement and provides stability = cranial sutures - Cartilaginous
Tissue = Fibrocartilage, connected entirely by cartilage
Small amount of movement but also provides stability =
intervertebral discs - Synovial
Most joints
Synovial Joints
Free moving and give very little stability.
Composed of a complex association of tissues and structures.
Joint capsule wraps around the joint with the space inside called the joint cavity lined by the synovial membrane which secretes synovial fluid. Ligaments wrap around to connect the bone to bone.
Hyaline (articular) cartilage is a very thing layer which covers where the bone meets bone.
Fibrocartilaginous pads / structures = cushioning and shock absorber, disperse weight ie meniscus in knee.
Ligaments at synovial joints
Capsular ligaments - Hold bones together
MCL (medial collateral ligament) - connects femur to tibia = restricts abduction
LCL - connects femur to fibula = restricts adduction
Intracapsular ligaments - Restricts movement between bones
ACL (anterior cruciate ligament) - attaches from anterior of tibia to posterior of femur = restricts posterior displacement of femur
PLC - attaches from posterior of tibia to anterior of femur = restricts anterior displacement of femur
Synovial Joint Movements
Can be either
- Uniaxial (movement about 1 axis)
- Biaxial (2 axes)
- Multiaxial (many axes)
Synovial Joint Shapes
-Plane
Multiaxial, sliding and gliding, flat articular surfaces
eg intercarpal
-Hinge
Uniaxial, flexion and extension
-Pivot
Uniaxial, rotation
eg radioulnar
-Condylar
Biaxial, flexion and extension as well as rotation when
fixed.
eg knee
-Ellipsoid
Biaxial, every type of movement other than rotation
eg wrist
-Saddle
Biaxial +, every type of movement other than rotation but
also has opposition (obligatory rotation)
eg thumb
-Ball and socket
Multiaxial, every type of movement
Osmosis
The diffusion of water molecules across a semi-permeable membrane down a concentration gradient.
Osmotic pressures are used to help maintain cell shape.
Water
Males have slightly higher water % (60%) due to higher muscle mass % compared to females (50% water) which have a higher fat %.
Intake water, absorbed through the digestive tract and is a byproduct of some metabolic processes. Water is lost through sweat, respiration, urine (majority) and faeces.
Water Movement
Isotonic = ICF and ECF concentrations are balanced Hypertonic = High solute (low water) concentration in the ECF, thus water will move out of the cell causing it to become flaccid. (if this continues may lead to dehydration as water concentration has still decreased in both ECF and ICF). Hypotonic = Low solute, high water concentration in ECF, thus water moves into the cell causing it to become turgid
Ionic Balance - Membrane Potential
Cellular membrane potential is whats excitable in a cell.
Excitable tissues = muscle and nerve.
The distribution of Na+ and K+ ions across a membrane determine the membrane potential.
ECF = High Na+, Low K+
ICF = High K+, Low Na+
Resting membrane potential = -70mV
To maintain this ions can pass through the membrane passively using ion channels / pores (or use an active method).
Na+ and K+ gradients
Chemical gradient
- Na = into cell
- K = out of cell
Electrical gradient
- Na and K = into cell (-70mV = ECF more negative)
Electrochemical gradient
- Na = into cell
- K = out of
Changes in Membrane potential
Depolarisation = The membrane potential becomes less negative (more positive) as chemical stimulus opens the sodium ion channels.
Repolarisation = MP goes back down to -70mV, stimulus is removed and excess sodium ions are transported out of the cytosol.
Hyperpolaristion = MP becomes more negative as chemical stimulus has opened K channels.
Muscle Types
Smooth - no voluntary control, usually lines hollow organs
Cardiac - in heart, no voluntary control
Skeletal - Attached to bone, under voluntary control
Skeletal Muscle
Main function - generate tension / force (in 1 direction by shortening).
Other functions:
-Support / protect soft internal organs
-Voluntary control over major openings
-Utalises energy and converts it into heat to maintain core body temperature
-Provides a major store for energy and protein
Whole Muscle Structure
Muscle is composed of a bundle of fascicles.
Fascicles are composed of a bundle of muscle fibres.
Muscle fibres are made up of myofibrils.
Repeating unit of myofibrils are sarcomeres.
Sarcomeres are made up of myofilaments.
Skeletal Muscle Structure
An individual skeletal muscle fibre = 1 single muscle cell (contains many nuclei).
Skeletal muscle is richly supplied with blood vessels and nerve fibres, allowing sufficient supply of glucose and oxygen to satisfy demand.
Connective tissue surrounds skeletal muscle and connects bone to muscle.
Individual Fibre structure
Individual fibres are surrounded by a surface membrane called sarcolemma. Transverse tubules (T Tubules) penetrate into the fibre so they can conduct electrical signals down into the core of the muscle fibre. Sarcoplasmic reticulum is a membranous, tubular network which wraps around the the myofibrils and will store and release Ca2+ when an AP is conducted along the T Tubule. The terminal cisternae form a triad with T Tubules.
Sarcomere Structure
Composed of thick filaments (myosin) and thin filaments (actin) which interlace.
Actin - Made up globule (G-actin) which assemble to form filamentous protein strands (F-actin). 2 F-actin strands twist and terminate 1 end of the z line.
Myosin - A molecule made up a long thin tail and a globular head which has the ability to flex. Pairs of myosin molecules assemble with their tails pointing towards the M line to form the filament.
Muscle Contraction
Muscle contractions triggered by electrical events in the brain travel down the spinal cord to motor neurons. The AP is then conducted out of the CNA along motor axons to the muscle fibres. Where the axon meets the muscle fibre = Neuromuscular junction. Each muscle fibre receives contact from 1 motor neuron. Motor neurons and the fibres it controls = motor units.
Arrival of an AP at the NMJ initiates synaptic transmission generating AP in postsynaptic fibres. This triggers excitation-contraction coupling.
Excitation-Contraction Coupling
- AP reaches NMJ triggering AP in muscle fibre
- AP spreads along the muscle fibre sarcolemma surface and then penetrates down into T tubule.
- This initiates depolarisation which is detected by the voltage sensor. The voltage sensor initiates direct coupling with the ryanadine receptor (RyR) (Ca2+ release channels) causing it to activate and release Ca2+ from the sarcoplasmic reticulum into the sarcoplasm.
- Ca2+ in the sarcoplasm binds with the contractile apparatus. Cross bridge cycling then takes place where myosin binds actin the filaments slide, generating force.
- SERCA will then use ATP to pump Ca2+ back from the sarcoplasm into the sarcoplasmic reticulum.
- Relaxation can occur as there will be no Ca2+ binding with the contractile apparatus.
Cross Bridge Cycling
- ATP binds with myosin head causing the dissociation of myosin from actin.
- ATP hydrolysis causes a shape change so the myosin head is ‘cocked’. ADP and inorganic Phosphate has been formed which remain bound.
- Myosin is now in line with a new binding site on the actin filament.
- Myosin binds actin forming a cross bridge
- The power stroke will then occur when the myosin heads flex. This generates forces pulling the thin filament towards the centre of the sarcomere.
- Another ATP molecule will then bind with theb myosin head and the cycle will repeat as long as we have Ca2+ available.
Muscle Tension
Tension depends on:
- The rate at which we deliver the electrical event of AP.
- The number of fibres which we use to generate force.
Frequency Stimulation
Single AP = brief contraction causing a twitch.
Muscle fibre re-stimulated before it has completely relaxed causes a summation.
Many AP = sustained period of contraction generates a contraction called tetanus.
Amount of force delivered
When a muscle is activated, the amount of force delivered depends on:
- Number of cross bridges formed
- Number of muscle fibres activated
- Amount of force produced by each fibre
(The amount of force is generally matched to the situation requiring the force).
Each muscle fibre has an optimal length where it will be strongest.
Too stretched = very little overlap between myosin and actin filaments making it difficult to slide and generate tension.
Too slack = Unable to get a good cross bridge due to too much overlap between the filaments.
Recruitment
The number of fibres activated is regulated by the how many neurons are active at 1 time. Small number of active neurons tends to produce low force. The process of activating more motor units to make more force is called recruitment.
Muscle Form
Muscle form determines function. This depends on:
- Length
Fibres can shorten up to 50% of their resting length, impacting the range of movement. Large range of movement requires long fibres.
- Number of muscle fibres
The amount of tension generated is proportional to CSA - cross sectional area.
High CSA = more fibres = more tension = more force
- Arrangement of muscle fibres
Parallel = fibres are arranged vertically between tendons allowing greater shortening = greater range of movement.
Pennate = fibres arranged oblique to tendons. This allows a greater CSA = more force and then stronger muscle. However results in reduced shortening (can only shorten to half the amount of shortest fibres) = reduced range of movement.
Anatomical Levers
Bone = lever
Joint = Pivot / fulcrum
Muscle contraction = pull / applied force
Load = External / internal weight
Muscle Action
Concentric: Muscle is active, change in joint position, shortening of muscle.
Eccentric: Muscle is active, change on joint position, lengthening of muscle.
Isometric: Muscle is active, no change in joint position or muscle length.
Muscle Roles
Agonist: Prime Mover, acts concentrically
Antagonist: Oppose against, acts eccentrically
Stabilisers: Muscle is active and holding a joint still. Action is isometric
Neutralisers: Muscle eliminates an unwanted movement caused by another muscle.
Concentric Actions
Anterior muscle during flexion
Posterior muscle during extension
(opposite for knee)
Lateral muscle during abduction
Medial muscle during adduction
Biceps Brachii
Attaches anteriorly to humerus, elbow and shoulder
= shoulder and elbow flexion
Also runs down and attaches to radius
= can cause supination at radius / ulna joint
Triceps Brachii
Attaches posteriorly to shoulder and elbow
= Shoulder and elbow extension
Also runs down and attaches to ulna
Deltoid
Attached to clavicle, scapula and humerus.
Sits laterally to shoulder joint = shoulder abduction
Also has fibres anteriorly and posteriorly to joint = shoulder flexion and extension
Iliopsoas (hip)
Runs from vertebrae and attaches to the femur.
Sits anteriorly to the hip joint = hip flexion
Gluteus Maximus
Attaches to hip bone, sacrum, coccyx and femur.
Sits posteriorly to hip bone = Hip extension
Quadriceps femoris
Made up of 4 muscles 1. Rectus femoris (superficial) Attaches anteriorly to hip = Hip flexion 2. Vastus Lateralis 3. Vastus Intermedias 4. Vastus Medialis
All 4 attach to patella and tibia anteriorly via patella ligament = Knee extension
Hamstrings
Made up of 3 muscles
- Biceps femoris
- Semi-membranous
- Semi-teninosus
All 3 cross the hip and knee posteriorly = hip extension and knee flexion.
Also help rotate knee slightly when fixed.
Tibialis Anterior
Crosses ankle anteriorly = dorisflexion.
Tendon also attaches to medial side of foot = foot inversion.
Triceps surae
Made up of 2 muscles
1. Gastrocnemius
Attaches to femur and crosses posteriorly to knee joint = knee flexion
2. Soleus
Joins with gastrocnemius forming a thick tendon which crosses posteriorly to ankle = plantaflexion
Quadrupedal Standing
Standing on all 4 limbs.
In this position limbs are active at many joints = high energy demand.
Bipedal Standing
Standing on 2 limbs means there is relatively small area of contact with the ground via plantar surface of the feet. This is more energy efficient.
Line of gravity runs down through our body which allows some joints to lock. This helps maintain a stable, upright stance with minimal muscular effort. Bone joints and muscles are needed to help maintain balance as our feet are insufficient size to provide only balance solution.
Line of gravity
Hip: Line of gravity is posterior to the hip joint so it is pushed into extension where the ligaments are tight. Anterior Capsular ligaments of the hip are taut (tight) whilst posterior ligaments are lax (lose) so joint is locked.
Knee: Line of gravity is anterior to the knee so it is pushed into extension where the ligaments are tight.
Ankle: Line of gravity falls anteriorly to ankle joint, causing it to fall into dorsiflexion.
Plantarflexors stabilise this position and thus energy will be consumed as this joint is not locked.
Bipedal walking
Basic pattern = gait cycle Stance phase (60%) = feet on the ground Swing phase (40%) = one foot off the ground These phases are separated by a double stance phase Heel strike = heel hits the ground Toe off = toes pushing off to repel forwards We will focus on 6 key stages of the cycle (for each need to think about which muscles are acting concentrically and eccentrically).
Early Stance
Hip - In flexion and moving to extension
Knee - In extension (locked for stability)
Ankle - In dorsiflexion and moving into plantarflexion
Mid Stance
Hip - Still in flexion and moving to extension
Knee - Moving into slight flexion
Ankle - Still in dorsiflexion moving into plantarflexion
Late Stance
Hip - In extension
Knee - In extension but moving into flexion
Ankle - In full plantarflexion
Early Swing
Hip - In extension but moving into flexion
Knee - In flexion
Ankle - In dorsiflexion (allow clearance of foot during swing)
Mid Swing
Hip - In flexion
Knee - In flexion
Ankle - In dorsiflexion
Late Swing
Hip - In flexion
Knee - In flexion but moving into extension
Ankle - In dorsiflexion
