Muscle tissue Flashcards
Describe the 3 types of muscle
> Cardiac Muscle - Small cells (single nucleus per cell) - Involuntary contraction - Limited ability to repair > Smooth muscle - found in walls of intestines/organs/blood vessels - involuntary contraction - can repair itself if damaged - single nucleus per cell > Skeletal muscle - Larger cells (up to 30cm) with many nuclei - Voluntary contraction - limited ability to repair
What are the functions of muscle tissue
> Produce movement > Stabilise body position > Regulate organ volumes > Move substances within body > Produce heat
What are the properties of muscle tissue
> Excitability - respond to chemicals from nerve cells
Conductivity - carries electrical signals over membranes to co-ordinate contraction
Contractility - shorten to generate force
Extensibility - stretch without damage
Elasticity - return to original shape
Describe skeletal muscle + how it is formed
> attaches to bone/skin/fascia via tendons/aponeuroses
Striated - light/dark band (actin and myosin fibres)
Voluntary control of contraction and relaxation
Formation:
> fusion of mesodermal cells = myoblasts
> each myoblast has own nucleus - muscle cells have many nuclei
> left over myoblasts become satellite cells = stem cells that divide to repair damage to muscle fibre
what are the functions of SKELETAL muscle?
> Produce skeletal movement
Maintain body position
Support soft tissue e.g abdominal wall/pelvic floor
Guard body openings
Maintain body temp - shivering/contraction for heat
Nutrient store
Proprioception - body knowing where it is in space
Describe the makeup of skeletal muscle
- Muscle
> surrounded by epimysium = irregular fibrous CT
- exterior collagen layer which connects to deep fascia
- allows friction free movement against tissues - Fascicle (bundles of muscle fibres)
> surrounded by perimysium
- more flexible (50% each collagen + elastin)
- Contains blood and nerve supply to fascicles - Muscle Fibre (single cell)
> surrounded by endomysium
- even more elastin for greater elasticity
- capillaries and nerve fibres contacting cells
- satellite cells can repair damage
*EPI/PERI/ENDOMYSIUM = all come together to form tendon/aponeurosis
Innervation and blood supply to muscle cells
Innervation
- many muscle cells are innervated by single nerve = motor neuron (each cell has own terminal branch)
- Motor neuron + cells it innervates = motor unit
Blood supply
- extensive vascular supply
- each cell is in contact with 1 or 2 capillaries
(nerve and capillaries follow same path within endomysium)
Describe the key features of muscle cells
Nuclei/sarcolemma/ t tubules/ sarcoplasmic reticulum
- Multinucleated = arranged around outside of cell
> Sarcolemma - cell membrane
- surrounds sarcoplasm (filled with myofibrils)
- change in transmembrane potential causes contractions
> Transverse (T) Tubules - folds of sarcolemma into cell - carry AP into cell allowing whole cell to contract in co-ordination
- filled with extracellular fluid
> Mitochondria - in rows throughout cell - near proteins that use ATP in contraction
> Sarcoplasmic reticulum - membrane around each myofibril (transmit AP to myofibril)
- has chamber at each end = terminal cisternae that attach to t tubules (2 tc + 1 t tubule = triad)
- terminal cisternae release Ca2+ to trigger contraction
Features of a muscle cell cont. (myofibres/myofilaments/sarcomeres)
> Myofibrils
- threads separated by sarcoplasmic reticulum
- made up of bundles of proteins = myofilaments
Myofilaments
- thick (myosin) and thin (actin) filaments
- contractile proteins of muscle
- overlap - striations - I band=only thin filament
(1 thick = surrounded by 6 thin) - A band= both
- arranged into compartments = Sarcomeres (separated by z discs)
Sarcomeres
- contractile unit of muscles
- t tubules encircle sarcomeres near zone of overlap
* Z disc - attaches thin filament to those of next sarcomere
* Titin - attaches thick filament to z disc & mid line
Describe myosin and actin filaments + role of troponin and tropomyosin
> Contractile proteins
- myosin binds to actin pulling thin filament along during contraction
Myosin (2 golf clubs twisted together)
- heads extend towards thin filaments
- tail binds to other myosin molecules
~ 300 molecules (600 heads) per thick filament
Actin
- thin filaments are made up of actin/troponin/tropomyosin
- binding site is hidden by tropomyosin - in contraction calcium binds to troponin which moves tropomyosin - exposing binding site
- held in place by z discs
Describe the structural proteins of the sarcomere
> Titin
- anchors thick filaments to m line and z disc
- key role in eccentric contraction as can stretch to 4 times its length (z disc to myosin)
Myomesin
- m line: connects to titin and adjacent thick filaments
Nebulin
- inelastic protein which helps align thin filaments
Dystrophin
- links thin filament to sarcolemma
- transmits tension to tendon
Describe the process of contraction via action potential
- Nerve Impulse reaches axon terminal
- Acetylcholine diffuses across synapse
- Sodium channels on sarcolemma open
- Change in potential creates AP over sarcolemma
- T tubules carry AP into cell
- Terminal cisternae release calcium ions
- Calcium binds to troponin - unveiling binding site
- Contraction cycle begins
Describe Cross- bridge formation
- Binding site is revealed
- ATP is hydrolysed to ADP + Pi - priming myosin head
- Myosin head attaches to actin = cross bridge (adp + pi are released)
- power stroke - head pivots to pull thin filament along
- New ATP molecule binds to head - breaks cross bridge
Will repeat as long as ATP and calcium are present
Describe the process of relaxation
- Acetylcholinesterase - breaks down ACh in synapse
- AP ceases
- Calcium ion channels close
- Active ion pumps bring calcium ions back into terminal cisternae
- Contraction ends as troponin and tropomyosin recover binding sites
- Muscle passively returns to original length
Describe the 3 methods of producing ATP
- Creatine Phosphate (supplies maximal contraction for around 15 seconds)
- Method of storing ATP
- Creatine + ATP = creatine phosphate
- easily broken down - Anaerobic respiration (30-40 seconds max activity)
- glucose is broken down to pyruvic acid and ATP when O2 not present
- pyruvic acid becomes lactic acid which diffuses to blood
- too much lactic = temp muscle fatigue - Aerobic activity (anything over 30 seconds)
- pyruvic acid is converted to ATP, water and heat when O2 is present
- fatty/amino acids can also be used
