Skeletal Muscle 1 Flashcards
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Sarcotubukar system made up of
Sarcoplasmic reticulum and transverse tubules
Thin filaments are found in the muscle in the form of
G actin which are polymerased to form a strand called f actin, which are interwoven over one another to form helix
What are regulatory proteins of muscles
Tropomyosin and Troponin
Tropomyosin?
Rod like protein which covers the site for myosin attachment on the F actin molecule. Forms part of thin filamentd
Troponin
It’s a globular protein complex. Forms part of thin filaments. Troponin C, binds to Ca2+. Troponin I is inhibitory in function. Troponin T is Attached to tropomyosin
What is Titin?
Protein that holds myosin filament to center of I band
What does thick filament consist of
S symmetrical halves that are mirror imagined of each other.
Had 6 peptide chains. 2 identical heavy chains
4 light chains
What are the 2 binding sites of myosin molecule
Binding site for Actin
ATP ase site
Nebulum?
Runs in the middle of thin filament
What are the anchoring proteins?
Alpha actin
Titin
Nebulin
Dystrophin
When there is contraction, what essentially happens in the contractile proteind
Calcium enters sarcolemma, binds with troponin. Interacts with tropomyosin and displace it from active site of actin for myosin binding. Calcium therefore very important for activation of thin filament
When is thick filament activated
When ATP binds to it and is hydrolyzed to ADP. Myosin head in high energy state will bind to actin.
What is the rate determining step of muscle contractions
Availability of calcium in sarcoplasm
What is the motor end plate
Part of sarcolemma which interacts with the motor neurone
Which enzyme breaks down Ach
Acetylcholine esterase
Neuromuscular junction is made up of
Motor end plate, motor neurone and synaptic cleft
Which receptor in t tubule is activated by action potential
Dihydropyridine receptors
Which gates are opened as a result of activation of dhp receptors
Voltage gated foot proteins/ ryanodine channel/ Ca release channel. Channels present in cisterns of the sarcoplasmic reticulum
Muscle relaxation is initiated by
Ach broken down by AchE. After which sarcoplasmic reticulum recaptures Ca2+
Drugs that block the release of Ach?
Botulinum toxin, lack of Ca, excess of Mg
B prevents release of ach by blocking fusion of ach containing vesicles with pre synaptic membrane and prevents exocytosis. Has therapeutic use to relieve pain and pathological contraction
Lack of calcium also leads to blocking of exocytosis of the secretory vesicles
Drugs that block transmission at neuromuscular junction?
Curaruform drugs, eg, D tubocurarine
Prevent passage of impulses from nerve ending into muscle
Done by competing with Ach for the receptor sites on post synaptic membrane
Drug prevents ach from activating receptors decreasing permeability of membrane and inability to initiate action potential
Used to control convulsions or during surgery when complete muscle relaxation is required
Drugs that stimulate muscle fibre by Ach like action
Methacholine, carbachol, nicotine
Drugs that stimulate neuromuscular junction by inactivation achE
Neostigmine, physostigmine, diisopropyl fluorophosphate
Fluorophosphate used as powerful military nerve gas poison
Myasthenia gravis ?
Antibodies in bodies destroy receptors and ach cannot act upon them to cause an action potential
Alpha actinic function :
Cross link actin filaments at area of z line
Titin function
Largest known protein in the body. Connects the z line to the m line in the sarcomere and forms the sec of the muscle
Nebulin function
Nebulin is an actin-bindingproteinwhich can bind upto 200 actin molecules. Nebulin length is proportional to the length of the thinfilament. It may function as a regulator of thinfilamentlength during sarcomere assembly.
Function of dystrophin
Dystrophin is aproteinfound in muscle cells. It is one of a group ofproteinsthat work together to strengthen muscle fibers and protect them from injury asmusclescontract and relax.
Motor end plate potential?
Membrane potential formed in the form of graded potential after ach binds to receptors
Ach is broken down into
Acetyl coA and choline
