Muscles Structue and Function Flashcards
Types of muscle
Smooth
Spindle, non straited, uni nucleated, involuntary, internal organs
Cardiac
Straighted, branched, uni nucleated, intercollated discs, involuntary,heart wall
Skeletal
Straited, tubular, multinucleated, voluntary, attatched to skelton 40/50 body weight
Skeletal muscle
Made of muscle fibres
Each muscle fibre is a syncytial (fused embryonic cells) myoblasts fuse and form muscle cell
Muscle fibres are multinucleated cylindrical and parallel to one another
Function skeletal muscle
Produce and control movement
Connective tissue of skeletal muscle
Contractile and non contractile elements
Protects muscle fibres but need to be extendable and elastic
Connective tissue surrounds muscle,fibres and whole muscle:
> epimysium very dense surrounds whole muscle
> Extends beyond muscle as a tendon and connect to bone tendon blends with fibres if perimysuim
bundles of fibres are called fascicles and are surrounded by perimysium
> fascia supports muscle - surrounds it
> forms pathways for nerves blood vessles and lymphatics- good blood supply for continuous muscle contraction
> Endomysium surrounds individual muscle fibres- thin and inner part is called the basal lamena
Sarcomella
specialised cell membrane which surrounds striated muscle fiber cells.
Sarcoplasm
Muscle fibres cytoplasm
Contains mitochondria glycogen myoglobin
Gel like substance
T tubules
Extension of sarcolema
Invagination a of the sarcolemma
Transmit the action potential from the cell membrane to the myofibrils to stimulate muscle to contract
Sarcoplasmic recticulum
Extends through sarcoplasm
Network of fluid fillied membrane enclosed tubules which surrounds myofibrils
Storages and regulation of calcium released on demand
Myofibrils + myofiliments
Myofibrils= within muscle fibres bundles of fibres
Run in a parallel fashion
Composed x2 myofilaments actin and myosin
Sarcomere
Region between 2 z lines
Contractile unit of myofibrils
Repeated units of over lapping myofilaments
Lattice arrangement
Z line
Dense protein material these supporting proteins run transversely across myofibrils and anchor thin actin filament
Attatched to sacrolema to provide stability
A band
Darker middle composed of actin and myosin over lap near end rejoins
Extends whole length of myosin
I band
Lighter less dense area contains rest of action no myosin
Z lines passes through the centre of each I band
Straition
Alternating A bands and I bands cause striation appearance
H zone
Only thick myosin
M line
Support proteins that hold the myosin filaments together at the H zone is called the M line
Myosin
Two identical twisted polypeptide chains each molecule has to globular head is attached to a flexible neck and a tail
The individual myosin molecules form a thick filament
Heads contain ATP binding sites and enzymes
Actin
Individual actin join to form and actin filament that is twisted into a double helix
Each actin molecule has the myosin binding site where a myosin head can attach
Contains two other protein molecules – tropomyosin and a troponin complex
Regulatory proteins
Help switch muscle contraction processes off and on
- Tropomyosin- component of thin filament when skeletal muscle is relaxed it covers the myosin binding site in actin molecules preventing binding
- Troponin- component of thin filament when Ca+ ions bind to troponin it changes shape this moves tropomyosin away from binding site and muscle contraction begins as myosin binds to actin
Calcium Concentration
An increase in calcium concentration in the sarcoplasm starts muscle contraction
A decrease stops it
Sliding filament theory
- An action potential stimulates the muscle fibre as it travels through its extensive system of T tubules arriving at the neuromuscular junction
- The action potential causes acetylcholine to be released attaching to receptors and then calcium ion channels in the sarcoplasmic reticulin to open
- This causes the calcium ions stored in the sarcoplasmic reticulum to diffuse into the sarcoplasm down a concentration gradient
- C.A.+ ions bind to troponin
- Myosin head contains ATP binding site that acts as ATPase which hydrolises ATP to ADP and energy released is stored in myosin head
- Troponin causes the ancillary protein tropomyosin that normally covers the binding sites on the acting filaments to be moved enabling the energised myosin bulbous head to link with the actin binding site forming cross bridges releasing phosphate
- Once attached the myosin heads change their angle from 90° to 45° as it changes position it pulls the thin filament past the thick filament towards the centre of the sarcomere generating tension = powerstoke requires ATP and after this ADP is released
- At the end of the powerstroke the cross bridge remains firmly attached to the actin until it finds another molecule of ATP as ATP binds to the ATP binding site on the myosin head the myosin head detaches from Actin
Relaxation of muscle
- When action potentials stop the release of ACH stops and acetylchlolinesterase breaks down ACH already in the synaptic cleft
- This ends and the generation of muscle action potentials
- Calcium channels in the sarcoplasmic reticulin close
- Calcium is rapidly transported from the sarcoplasm to sarcoplasmic reticulum
- Levels of calcium fall the tropomyosin slides back over the myosin binding sites on Actin
- Thin filament slip back into relax positions
Muscle tone
Small unit of muscle involuntary contracting to maintain muscle tone results in sustained contraction of muscle fibres What are units are constantly active and inactive Controlled by motor neurons in the brain
Energy for contraction
Sources
X
Explosive very short lived contractions use?
ATP and creatine phosphate
High-intensity exercise
Glycolysis as an energy source it’s stored glycogen from muscle and liver anaerobic cellular respiration
Insurance e.g. longer than 60 seconds
Aerobic cellular respiration
Fascicle
Bundle of skeletal muscle surrounded by perimysium
Fascia
Bundle of connective tissue primarily collagen
