Muscular skeletal Flashcards
What is the structural classification of muscle?
Smooth
Skeletal
Cardiac
What is the functional classification of muscle?
Slow contracting
Fast contracting
Describe slow contracting muscle
Metabolically economical Weak contraction Don't tire Can contract for a long time Take a long time to contract Half the diameter of fast contracting
Describe fast contracting muscle
Metabolically expensive (use lots of ATP)
Strong contraction
Tire quickly
Contract in less than 10 seconds
What is the biochemical classification of muscle?
Red (lots of mitochondria)
White (not much mitochondria)
What does smooth muscle look like?
- Uninucleate
- Unbranches fibres
- Unstriated
- Oval shaped
What does cardiac muscle look like?
- Branched
- Slightly striated
- Has intercalated discs
- Has purkinje fibres (contain glycogen)
What are the 6 functions of skeletal muscle?
1) Movement
2) Maintain posture and body position
3) Communication
4) Control of openings and passageways
5) Maintainance of tempetature
6) Support soft tissues and shield visceral organs
What are the 5 characteristics of skeletal muscle?
1) Elasticity (returns to resting length after being stretched)
2) Extensibility (capable of being stretched)
3) Contractibility (shortens when stimulated)
4) Conductivity (local electrical change triggers a wave of excitation down the muscle fibre)
5) Excitability (contract when there is a nerve input
What is the epimysium of skeletal muscle?
- Connective tissue which surrounds the whole muscle (surrounds all fasicles, blood vessels and nerves)
- Continuous with tendons, allowing connection to the bone
What is the perimysium of skeletal muscle?
Connective tissue which surround each fasicle
What are fasicles in skeletal muscle?
Bundles of muscle fibres
What are myocytes
Muscle fibres which are the same as muscle ‘cells’
Multinucleate
Where are the myonuclei located in skeletal muscle?
At the periphery
What is the endomysium of skeletal muscle?
- Connective tissue which surrounds each INDIVIDUAL myocyte (muscle cell/muscle fibre)
- Overlays the sarcolemma
What is the sarcolemma?
Cell membrane of myocytes
What is the sarcoplasmic reticulum?
- Endoplasmic reticulum of myocytes
- In the sarcoplasm, surrounding the myofibrils
What is the sarcoplasm?
- The cytoplasm of the myocyte
- Contains plenty of glycogen
- Surrounds myofibrils and sarcoplasmic reticulum
What are myofibrils?
- Made of many functional repeat units (sarcomeres)
- Many myofibrils make up a myocyte
What are T-tubules?
- Invaginations of the sarcolemma
- Allow depolarisation to travel to the myofibril
- Allows fast muscle contraction all at the same time
Where are myocytes derived from?
Myoblasts
Describe the method of skeletal muscle contraction
long so write down
1) Acetylcholine released from presynaptic motor neuron and binds to a nAChR on the muscular end plate
2) Depolarisation of the sarcolemma, which spreads down the t-tubules the the sarcoplasmic reticulum
3) Na+ influx stimulates the opening of Ca2+ channels in the sarcoplasmic reticulum
4) Ca2+ into the sarcoplasm
5) Ca2+ binds to troponin C causing troponin I to release its hold on actin
6) Confirmational change in troponin, tropomyosin can move, exposing the actin-myosin binding site on actin
7) Myosin head (bound to ADP and Pi) binds to actin forming a ‘cross-bridge’
8) Pi released, strong cross bridge formed. THEN, there is a confimational change as myosin returns to its relaxed position - power stroke (pulls actin along with it)
9) Myosin head detaches when ATP binds
10) Myosin head is an ATPase, breaks down ATP into ADP and Pi, which provides the energy to cause the myosin head to return to the ‘cocked’ postion
What is the z-line?
Where actin is anchored
What is the H-zone?
Un-overlapped myosin
What is the M-line?
- The bare zone
- In the middle of the H zone
What do accessory proteins do?
Maintain the integrity of the sarcomere structure
Where is titin found and what does it do?
- Anchored to the Z line
- Attached to myosin
- Acts as a ‘spring’ to prevent over contraction
Where is nebulin found and what does it do?
- Wraps around the actin filaments
- Made of repeating units which contain binding sites for actin
- Dictates the length of the actin filaments
Where are cap Z and alpha-actin found and what do they do?
- Make up the Z- line
- Cap actin at the + end to prevent polymerisation
- Anchor actin the the Z line
Where is tropomodulin found and what does it do?
- Caps actin at the - end (near the M-line0
- Prevent de-polymerisation
What is the function of tropomyosin?
Dimer which regulates the binding of myosin head to actin
What are the 3 types of troponin and what do they do?
T = bind a single molecule of tropomyosin C = bind to Ca2+ I = bind to actin and inhibits contraction
What toxin inhibits the K+ channel?
Dendrotoxin from the mamba snake
What toxin prevents Ach release?
Botulinum (BOTOX)
What toxin inhibits the AchR?
Curare
What toxin inhibits the Ca2+ channel?
w-conotoxin
What toxin inhibits the Na+ channel?
Tetrodotoxin
What toxin causes food poisoning and how?
- BOTOX (botulinum)
- Endoproteinase (cleaves SNARE proteins)
- Leads to muscle weakness, paralysis and death
What are the symptoms of BOTOX poisoning?
- Dry mouth, double vision
- Diarrhoea and vomiting
- Paralysis of the limbs and respiratory muscles
What are the clinical uses of botulinum toxin?
1) Treatment of stabismus (cross-eyed)
- Inject into extraoccular muscles
2) Treatment of biepharospasm (uncontrolled eyelid movement)
What is the structure of myosin?
- Coiled-coil
- 2 heavy chains and 4 light chains
- Globular domain at the end of the heavy chain
How does myosin assemble?
Spontaneously into filaments
What is the structure of actin?
- Double alpha-helix of F-actin made of many monomers of G-actin
What happens during aerobic exercise?
1) Stimulation of slow fibres
2) Conversion of fast glycolytic (IIb) fibres to fast oxidative fibres (IIa)
3) Increase in fatigue resistance
4) No change in muscle strength
What happens during anaerobic exercise?
1) Stimulation of fast fibres
2) Enlargement of myofibril size by addition of new myofilaments (no change to the number of fibres)
3) Increased diameter of muscle fibre
How is ATP formed in anaerobic conditions?
- Creatine ingested from the diet and transported to the muscles via the bloodstream
- In the muscles creatine kinase catalyses the synthesis and breakdown of phosphocreatine (phosophorylated creatine)
- Phosphocreatine at rest
- Broken down into creatine in the first few minuted of intense exercise, releasing ATP
Advantages and disadvantages of anaerobic respiration
Advantage - ATP produced in the absence of O2
Disadvantage - low ATP yeild (2 x ATP) and produces toxic products (lactic acid)
What 3 things cause fatigue of fast twitch fibres?
1) ATP synthesis decrease, due to shortage of glycogen
2) Lactic acid increase
- Lowers pH of sarcoplasm
- Prevent normal functioning
3) Faliure of motor neurons
- Due to decreased availability of Ca2+
- No production of ACh
What is muscle fatigue?
Progressive weakening of muscle contraction leading to no response
