Early lectures Flashcards
What are some causes of osteoporosis?
Lifestyle factors: lack of exercise (exercise stimulates the bone cells to make new bone), nutritional factors (good sources of calcium), peak bone mass (bone as a bank) (teenage years + early twenties = building bone mass. Reach this peak in early twenties)
- Old age
What is the genral cartilage composition?
Collagen fibres in a ground substance (resists tension)
Chondrocytes live in lacuna
Nutrients diffuse through matrix by joint loading (normal movement of the joints) (not vascular - does not have blood vessels, when it degrades its gone)
Hyaline (articular) cartilage composition?
Collagen fibres are barely visible
High water content in the matrix
Function is to resist compression
Provides a smooth frictionless surface
Fibrocartilage composition?
Collagen fibres bundles throughout the matrix
Orientation of fibres aligns stresses to resist tension and compression
What are the functions of hyaline cartilage?
- To provide frictionless movement of bones in synovial joints (moveable joints)
Moulds to surfaces of the bone where they articulate and where they move over each other. Tells you about the range of movement
Degrades with age (loses water content, flaking away from bone so degrading)
Trauma (fractures which set up infections and damage articular cartilage. Bone then rubs on bone)
What are some functions of Fibrocartilage?
E.g. meniscus (a structure formed of fibrocartilaginous tissue) they are concave discs of fibrocartilage.
Function = deepens articulation at knee joint. Can adapt to its shape stresses on joint during movement to accommodate it, can resist tension and compression like this.
Distributes forces over a wider area (protecting the articular cartilage underneath). If there is not meniscus, the forces will come over a smaller area and the articular cartilage is more vulnerable to trauma and then developing arthritis
What is bony congruence?
the sum of the bone surfaces that form an articulation. Less BC = more soft tissue support. E.g. knee joint is an area of low bony congruence, hip is a joint of high bony congruence (head goes into deep socket). Where there is low bony congruence, more soft tissue support is needed to deepen the articulation and hold the joint together.
What is the general compisiton of Ligaments and tendons?
formed by dense fibrous connective tissue (DFCT). Has a lot of collagen in it, formed by fibroblasts (cytes). Function is resisting tension only. Some vascularity but minimal compared with bone (can heal, but will heal very slowly)
What are some examples of fibrous joints?
cranial sutures, distal tibiofibular joint (fibula and tibula connection, holding the two leg regions bone together distally.
What are some examples of cartilaginous joints?
intervertebral disc; symphysis.
What are features of synovial joints?
- Complex association of tissues and structures. High congruence = stable (ability to create movement and to stay together)
Facilitation of free movement AND control of movement
Bone ends determine the range of motion at a joint
What is the structure of a synovial joint?
- Bone ends
- Hyaline cartilage (wraps around bone where they may rub)
- Joint capsule of DFCT (can be thickened to form ligaments)
- Joint cavity has synovial membrane which secretes synovial fluid (Fluid filled pockets = there for cushioning and support)
- Ligaments
What are capsular ligaments?
Capsular ligament (joint capsule) - Holds bones together - Tight and thick where more support is required and less movement is required - Loose where movement is allowed Potential space or cavity E.g. collateral (on the side of) ligaments of the knee (Medial restricts abduction Lateral restricts adduction)
What are intracapsular ligaments?
- Restricts movements between bones (contained within the capsule itself, internal to the joint)
E.g. cruciate ligaments
Arise from the tibia and insert into the femur
Anterior cruciate restricts posterior displacement of the femur (skiing, femur will try to slide forward. Femur pops of front of tibia)
Posterior cruciate restricts anterior displacement of femur
What is a key difference between Fibrous and cartilaginous vs synovial
Direct connections between the bone ends vs no direct connect, absolute space. Capsule that surrounds the joint and fluid filled space.
What is the movement at the joint determined by?
The structure of the joint, including:
- Bone end shape
- Ligament location and length
- Body surface contact
Plane joints
Multiaxial
‘Sliding and gliding’
Flat articular surfaces.
Reserved for blocky and short bones E.g. intercarpal and intertarsal joints.
And acception: joint between clavicle and sternum
Hinge joint
Uniaxial
Movements are flexion and extension
E.g. ankle, elbow (humerus with ulna), interphalangeal joints.
Pivot joint
Uniaxial
Movement is rotation
E.g. radioulnar joint.
Between first two cervical vertebrae (C1-C2)
Condylar joint
Biaxial, flexion and extension, rotation (when flexed)
E.g. knee, temporomandibular (TMJ, connects the mandible)
Ellipsoid joint
Biaxial - NO ROTATION, every other movement
E.g. wrist joint
Saddle joint
Biaxial + - circumduction, abduction, adduction, flexion, extension, rotation is obligatory (opposable thumbs, creating some rotation)
E.g. base of thumb joint (carpometacarpal)
Ball and socket joint
Multiaxial - all planes (movements)
E.g. shoulder and hip
Comparision of the shoulder and hip joints?
Shoulder joint - clavicle and scapula holds humorous, lots of joints make this up, made for manipulation of external environments.
Hip joint - only one joint (between hip bone and femur). More ligaments holding things together, for stability.
What is smooth muscle?
Smooth mainly line hollow organs e.g. gut and blood vessels and are not under voluntary control
What is cardiac muscle?
Cardiac muscle is located only in the heart, it generates force to pump blood around the body and is not under voluntary control
What is skeletal muscle?
Skeletal muscle applies force to the bones to control posture and body movements. Allows environment manipulation. It is under voluntary control.
What is the skeletal muscles primary job?
- The primary job is to develop force. (Not shortening, but resisting a lengthening). This force is mainly used to move and to resist the movement of joints
- Muscles develop force in only one direction, that is they can “pull” developing force by shortening. They cannot “push” to develop the force by lengthening. (Not generated by muscle getting longer, but by muscle getting shorter)
- Voluntary control allows us to control our posture and regulate our movements.
What are some secondary jobs of skeletal muscle?
- Provides support and protection for soft internal organs e.g. organs behind abdominal wall
- Provides voluntary control over major openings that allow passage of substances into or out of the body. E.g. mouth, arse
- Converts energy to heat which is used to maintain core temp e.g. homeostasis
- Provides storage for energy and proteins
What is the structure of a skeletal muscle?
Muscle fibres are gathered into bundles called fascicles. These are gathered into bundles called muscles. Each of these are encheathed in connective tissue.
- Around the outside of the muscle is a collection of connective tissue called the epimysium
- Perimysium around the edge of the fascicle. Individual muscle fibres wraped up in this.
- Individual fibers within fasicale have own connective tissue around them called endomysium
- Nerve cell and capillary associated with each muscle fibre. In the individual muscle fibre the myofibrils are the protein that make the force.
How are individual muscle fibres made?
Myoblasts fuse together to form a large multinucleated cell enclosed by a single common membrane.
- -> Hundreds to thousands of nuclei
- -> The specific arrangement of proteins in the cytoplasm give muscle the ability to develop physical force in response to electrical signals from the brain
What are Myofibres made of?
Myofibers are each a collection of bundles of myofibrils. Microfibrils are bundles of contractile proteins running the length of the fibre made up of myofilaments.
What are myofilaments made of?
Myofilaments are made up of highly organised repeated arrays of proteins that give skeletal muscle its characteristic striated (striped) appearance
- Two of the main proteins in the myofilaments are actin (thin filaments) and myosin (thick filaments)
How are myofilaments arranged?
- The thick and thin myofilaments are arranged in a regular hexagonal array when seen in cross section (each thick filament is surrounded by 6 thin filaments)
- The myofilaments are also arranged in a regular pattern along the length of the muscle fibre in repeated units (called sarcomeres)
What are transverse tubules and what do they do?
Transverse tubules (T-tubules) are tubular extensions (invaginations) of the surface membrane that run from the cell surface deep into the fibres in a regular array
There job is to conduct electrical signals deep into the core of the fibre.
What is the sarcoplasmic reticulum and what is its job?
Sarcoplasmic reticulum is an extensive membranous tubular network associated precisely with the T tubules at regular intervals
The job of the SR is to take up and store calcium, then to release Ca into the cytoplasm on receipt of an action potential conducted along the associated T-tubules.
What is a triad?
The terminal chambers (terminal cristae) of each SR structure associate with the T tubules to form a membrane triplet called a triad
What are the thin filaments composed of?
Actin is a globular protein (G-actin). The globules assemble to form filamentous protein strands (F-actin)
- Each thin filament is twisted strand of 2 rows of F actin termination at one end at the Z-line
What does tropomyosin and troponin do?
- Associated with each thin filament is a pair of strands of tropomyosin that attaches to the actin at regular sites via the binding at regular intervals of the globular protein, troponin
- Troponin binds tropomyosin and actin, and has an additional important role in regulating the interaction between actin and myosin during the working cycle.
What are the thick filaments composed of?
- Primarily myosin
- Has a long thin tail and a golbular head
- The thick filament is formed from arrays of pairs of myosin molecules arranged with the tails pointing towards the M-line and forming a complex double headed structure.
- The head of the various myosin pairs form a spiral, each facing one of the 6 surrounding thin filaments (recall the hexagonal array of thick and thin filaments of the myofibril)
- The globular head of myosin has an ATP binding site and has ATPase activity (it can hydrolyse ATP to ADP+Pi, releasing energy in the process)
What is the sliding filament theory?
These contractile proteins develop force by triggered molecular interaction that allows association of the myosin head with the nearby thin actin filament followed by the flexing of the myosin head to allow it to “walk” along the thin filament
- In this process the interlaced thick and thin filaments slide past each other
- The ends of the sarcomere are therefore drawn closer together (Z-lines are drawn closer to central M-line)
What is a neuromuscular junction?
The myelinated axon of a motor neuron terminates at a single point on the muscle fibre (a specialised synapse)
What is a motor unit
A motor neuron and all the muscle fibres its controls
Small vs large motor units
Very big motor units (ie hundreds of fibres) develop a lot of force, but do not provide much control over small increments in force (eg big muscles of leg)
Small motor units (less than 20 fibres) do not each develop much force, but provide for fine control over force because activation of each unit in turn adds only a small amount to the total muscle force (eg small muscle of the hand)
What is recruitment?
The number of motor units activated at any one time, which varies with the amount fo force needed
What 3 things determine muscle function?
- Length of muscle fibres
- Number of muscle fibres
- Arrangement of muscle fibres
What is the organic component of bone’s ECM?
It makes up 33% of the matrix, formed of collagen
These collagen fibres are embedded in ground substance called proteoglycans
Function = resists tension
We have forces from all directions on our bones, collagen gives bones resilience.
Removed collagen makes bones brittle/ break easily
What is the inorganic component of the bone’s ECM?
67% of the matrix, formed by hydroxypaptite
Gives the bones its hardness
Resists compression
Without hydroxyapatite the bones are too flexible
What is the compisition of bone at the gross level?
Forms all of the outer surfaces of bone, and tube of thicker bone in shaft (need more strength there)
- Foramina/ holes (Where the blood vessels penetrate from the outside and go inside to feed and maintain the osteocytes)
Define osteon
longitudinal (lengthwise) circular unit within compact bone (function= maintaining the osteocytes by providing nutrients - brought in by blood)
Define Lamelle
Lamelle = tubes of ECM with collagen fibres aligned to resist forces. Wherever forces are coming from, the bone can resist them. Lamellae form a series of cylinders down the shaft - forming the osteon.
Define central canal
Contains blood vessels and nerves. Helps with signaling between cells
Define Canaliculi
Channels for osteocytes through the ECM
What is bone turn over?
- Maintains normal mature compact bone
Blood vessels bringing in osteoblasts after the osteoclasts have destroyed the ECM and they produce ECM and the osteocytes are trapped in this ECM and then they communicate by way of the lacunae/ canaliculi. This is a ongoing process. Turns into the osteon network.
What is the compisition of cancellous bone?
Trabeculae (struts of lamella bone) each of the components of the cancellous bone is called a trabeculae made of lamella. Organisation of these trabecule isn’t random - organised inside the bones depending on the force (arranged in such a way to diffuse the forces going on in that area). Zone of weakness (less trabeculae)
Marrow fills the cavities, specifically red marrow that produces red blood cells.
Osteocytes housed in lacunae on surfaces of trabeculae (don’t need osteon arrangement). Blood vessels go in a feed these directly.
What are the cellular componants of bone?
Osteoblasts, Osteocytes, Osteoclasts
