MSK week 1 Flashcards
Three types of muscles and their description
Skeletal- voluntary- striated- somatic nervous system
Cardiac-involuntary-striated- autonomic nervous system
Smooth- involuntary- non-striated-autonomic nervous system
What makes up a motor unit?
One alpha neurone and all the muscle fibres (cells) it supplies.
What determines whether it is a fine movement or a powerful movement?
Fine movements will have fewer muscle fibres to each alpha neurone than a powerful movement will have.
What are the differences between skeletal and cardiac muscle?
Skeletal muscle- neurogenic initiation of contraction
- neuromuscular junctions are present
- no gap junctions
- Calcium entry is entirely from the sarcoplasmic reticulum
Cardiac
- myogenic initiation of contraction
- no neuromuscular junctions
- Gap junctions present
- Calcium from ECF and sarcoplasmic reticulum.
What do muscles consist of? (break it down into the cells etc)
Muscle- muscle fibres- myofibril (specialised intracellular structure) - sarcomeres (functional unit)
What is contained within a sarcomere?
The myosin and actin filaments that cross over to produce contraction. They are called collectively cytoskeletal elements.
Describe the process of an action potential causing muscle contraction.
Action potential arrives at the synapse and acetyl choline is transported across it. The action potential is then initiated in the muscle fibre and it travels along it and down the T tubule. This causes calcium release from the lateral sacs of the sarcoplasmic reticulum.
The calcium then binds to troponin meaning tropomyosin moves out of the way and an actin and myosin cross bridge can form (process powered by ATP)
How is contraction ended?
The action potential stops firing therefore calcium is reabsorbed by the sarcoplasmic reticulum. This means tropomyosin moves back into its blocking position and contraction ceases.
What are myofibrils?
Each muscle cell contains several of these. It is the contractable intracellular unit.
What is a sarcomere?
The functional unit of the muscles
Where are sarcomeres found?
Between two Z lines.
What is the M line?
The line down the middle of the A band and H zone.
What is the H zone?
Space where only thick filaments are.
What is the I band?
Space where only thin filaments are.
What is the A band?
The area of overlapping thick and thin filaments.
Gradation of skeletal muscle tension depends on two factors?
Number of muscle fibres contracting (more motor units=stronger contraction)
Tension developed by each contracting muscle fibre (influenced by length of muscle fibre and thickness of muscle fibre)
What is motor unit recruitment?
Recruiting more motor units to increase the strength of a contraction.
Describe tetanus
A muscle twitch lasts longer than the action potential for it. Therefore if you summate action potentials you can cause the muscle twitch to become stronger. Tetanus is a muscle fibre that is being constantly stimulated without time to relax to produce maximal muscle contraction.
When can maximal tetanus occur?
When a muscle is at its optimal length before contracting.
Two types of skeletal muscle contractions
Isotonic contraction- e.g. moving objects and body movements. Length of muscle fibre changes but muscle tension stays the same.
Isometric contraction e.g. supporting objects in a fixed position. Length of fibre stays the same but muscle tension changes.
What are the differences between skeletal muscles?
Enzymatic pathways for ATP synthesis
Resistance to fatigue- some have many mitochondria, some have few.
The activity of myosin ATPase- determines the speed at which energy is made available for cross bridging.
Describe the metabolic pathways that supply ATP in a muscle fibre
Transfer of a high energy phosphate from creatine phosphate to ADP. Immediate source of ATP.
Oxidative phosphorylation (main source when oxygen is present)
Glycolysis (main source when oxygen is not present)
Three types of skeletal muscle fibres
Slow oxidative (type 1) fibres Fast oxidative (type 2a) fibres Fast glycolytic (type 2b) fibres
Describe slow oxidative fibres
Used for prolonged relatively low intensity aerobic activities e.g. walking, maintaining posture.
Describe fast oxidative fibres
Used for moderate exercise. They are an intermediate between the other two. Examples are jogging.
Describe fast glycolytic fibres
Used for intense, short term exercise in anaerobic conditions e.g. jumping
What is a reflex action?
A stereotyped response to a specific stimulus. It is the simplest form of co-ordinated movement
What is a stretch reflex?
Negative feedback that resists passive change in muscle length to obtain optimal resting length.
What is the sensory receptor involved in a stretch reflex?
Muscle spindle
Describe the stretch reflex
By stretching the muscle you stretch the spindle cell, this increases firing of afferent neurons. These synapse within the spinal cord with the alpha motor neurones (efferent limb) that innervate the stretched muscle. This results in muscle contraction.
Describe muscle spindles
Collection of specialised muscle fibres known as intrafusal fibres. Located within the belly of the muscle and run parallel to ordinary fibres.
What is special at muscle spindles nerve supply?
They have their own nerve supply of gamma neurones that adjust the level of tension in the muscle spindles to maintain their sensitivity.
Three types of joints
Fibrous, cartilaginous and synovial.
Describe fibrous joints
Bones united by fibrous tissue
Hard, not-moveable joints e.g. in the skull.
Describe cartilaginous joints
Bones united by cartilage.
Allow limited movement. e.g. chostochondrol joints, intervertebral discs.
Describe synovial joints
Bones separated by a cavity containing synovial fluid and united by a fibrous capsule.
What is the purpose of a synovial membrane
It has the vascular supply, it contains synovial cells (which secrete synovial fluid)
What are the articular surfaces of synovial joints covered in?
Hyaline cartilage.
What is the function of articular cartilage?
Low friction lubricating surface. Helps to prevent wear and tear to joints.
Distributes contact pressure to subchondral bone.
Describe the extracellular matrix of cartilage
Contains water (70%), collagen (20%)and proteoglycans (10%) Synthesised, organised, degraded and maintained by chondrocytes. Articular cartilage is avascular and it receives its nutrients and oxygen from synovial fluid.
In normal joints, rate of ECM …… does not exceed
Degradation does not exceed rate at which it’s replaced.
What happens to cartilage with age?
Water content decreases. Composition of proteoglycans changes. Type 2 collagen decreases.
How is water distributed within the cartilage?
Unevenly- 80% is near the articular surface.
What is the function of water within the cartilage?
Helps to maintain the resiliency of the tissue and contribute to the nutrition and lubrication.
Where is the highest concentration of proteoglycans in cartilage?
highest in middle and deep zones of the cartilage.
What is the role of proteoglycans in cartilage?
Compressive properties and load bearing.
What is the role of collagen in cartilage?
Maintains cartilage architecture and provides tensile strength and stiffness.
Catabolic and anabolic factors of cartilage matrix turnover
Catabolic- stimulate proteolytic enzymes and inhibit proteoglycan synthesis. TNF alpha and IL-1.
Anabolic- stimulate proteoglycan synthesis and counter the effects of IL-1. TNF beta and insulin-like growth facor-1.
What is released by chondrocytes to have a negative impact on extracellular matrix components
Metallo-proteinase enzymes e.g. collagenase
Markers of cartilage degradation
Increased levels of serum and synovial keratin sulphate. (level increases with age and with OA)
Type II Collagen in synovial fluid (indicate cartilage breakdown)
What are the functions of synovial fluid?
Lubricate joint- facilitates movement
Minimises wear and tear
Supplies chondrocytes with O2 and removes CO2.
General characteristics of synovial fluid
Continuously replenished and absorbed by the synovial membrane. Highly viscous (mainly due to presence of hyaluronic acid) Viscosity varies with joint movement.
How are constituents of synovial fluid derived?
Uric acid- dialysis of blood plasma.
Does synovial fluid contain cells?
Normally very few mononuclear leukocytes.
What changes in synovial fluid can occur?
Changes in viscosity and elacicity during movement.
Rapid movement- not viscous, highly elastic
Slow movement- viscous, not very elastic.
Describe synovial fluid in inflammatory conditions
Viscosity would be low
May be straw to yellow coloured.
Will be translucent
Contains 2000-75000 white cells.
Describe synovial fluid in sepsis
Viscosity would be variable as would colour. However it would be opaque and often have greater than 100,000 white cells.
Describe normal synovial fluid
Viscosity is high. Colour of synovial fluid is colourless and transparent. Very few white cells (<200)
Describe the nuclei of skeletal muscle cells
Multinucleated and are near the edge of the fibre.
Describe the mitochondria distribution, force and stamina of each type of muscle fibre
Slow oxidative fibres- lots of mitochondria. Resistant to fatigue and produce relatively little force.
Fast oxidative fibres- relatively fast contracting and reasonably resistant to fatigue.
Fast glycolytic fibres- very few mitochondria, fatigue quickly and produce great force.
What are muscle fibres grouped into?
Fasicles.
What is the connective tissue that surrounds several fascicles called?
Epimysium
What is the connective tissue that surrounds a single fascicle called?
Perimysium
What is the connective tissue that surrounds a single muscle fibre called?
Endomysium