Muscles Flashcards
What are the types of muscle and where are they found
Cardiac–in heart
Smooth - in walls of blood vessels and gut
Skeletal- attached to bone moving body
Describe the structure of a muscle
Whole muscle Bundles of muscle fibres Muscle fibre Myofibril Sarcomere Actin and myosin
How are cells arranged in a muscle
Cells fused together in a long line
Myofibril run through the middle of the cells
Share cytoplasm (sarcoplasm) cell membrane (sarcollema) and endoplasmic reticulum (sarcoplasm reticulum) and nuclei
What is the advantage of the cell arangemnet in a muscle
Junctions would be a point of weakness so makes muscle stronger
Parralell Myofibril make them stronger
What is the function of the sarcoplasm reticulum
Store Ca2?+ for release for muscle contraction
What two proteins make up Myofibril
Actin and myosin
How is actin arranged
Actin molecules are soluble proteins arranged in a helix shape
Tropomysin follows shape of actin
Troponin attaches to Tropomysin
How is actin arranged
Actin molecules are soluble proteins arranged in a helix shape
Tropomysin follows shape of actin
Troponin attaches to Tropomysin
What is Tropomysin
Blocks actin mysoin binding sites
What is Troponin
Ca2+ binding site on Tropomysin
Describe the structure of myosin
Made of many parallel fibres of myosin made of insoluble tail and soluble head that stick out
Name the sections on a Sarcomere
Z line- middle of I band
I band - only actin
A band- actin and mysoin overlap
H zone- only myosin
What is a neuromuscular junction
Where a motor neurone meets a muscle fibre
Describe and explain the distribution of neuromuscular junctions across the muscle fibre
Regular intervals
Rapid and Simultaneous contraction
What is a motor unit
All muscle fibres supplied by one motor neurone acts a one unit
What is the advantage of having motor units
Allows control of force exerted (more units stimulted= more force)
How is the sarcollema de polarised
Ap reaches the neuromuscular junction
Ca2+ voltage channels open allowing ca2+ to diffuse in.
Cause vesicles containing neurotransmitter to diffuse towards and fuse with postsynatic membrane, exocytosis
Acetylcholine diffuses across Synaptic left binding to Na+ receptors on sarcolemma.
Channels open Na+ Diffuse in = de polarisation
Why is it important for acetyl choline to be broken down
To prevent over stimulation
What are the similarities if a neuromuscular junction with a cholinergic synapse
Use acetyl choline through diffusion
Bind to na receptors causing them to open
Enzymes used to breakdown acetylcholine
Na/k pump used to repolarised
What are the differences between neuromuscular junctions and cholinergic Synapses
Neuromuscular:
Only exhibitory not inhibitory
Only motor neurone not any other type
End of AP pathway
What are the two types of muscle fibres
Slow and fast twitch
Describe slow twitch fibres
Weak contractions over a long period of time
How are slow twitch fibres adapted and for what
Adapted for endurance and aerobic Respiration
Low glycogen storage
Large myoglobin supply (oxygen store)
Good blood supply
Many mitochondria
What are fast twitch fibres
Contract very rapid, powerfully for short amount of time
How and what are fast twitch fibres adapted for
Anaerobic Respiration, intense exercise
Large glycogen storage (high rate resp because anaerobic = not efficient)
Large phosphocreatin supply
Thicker and more numerous myosin filaments
Large conc of enzymes involved in anaerobic Respiration
By what mechanism do muscled contract
Sliding filament theory
What is the evidence for the sliding filament theory
A band stays same length (so filaments don’t shorten)
I band and H zone decrease causing overlap of filaments
How are muscles stimulated
Ap reaches neuromuscular junctions causing voltage gated Ca2+ channels to open so ions diffuse in
Vesicles with acetylcholine diffuse and fuse with presynaptic membrane. Exocytosis
Acetylcholine diffuses across the syntactic cleft
Binds to Na+ channels on sarcolemma opening them. Ions diffuse in de polarising membrane.
How do muscles contract (starting from de polarisation of sarcollema)
Ap travels down t tubules to sarcoplasm reticulum
Ca2+ channels open and ions are released from sarcoplasmic reticulum into cytoplasm.
Ca2+ binds to Troponin causing Tropomyosin to change shape revealing binding sites for myosin on actin
Actin myosin Cross Bridge forms
ADP and pi released = power stroke= slide actin filament
ATP attaches and is hydrolysed= myosin head detaches and is recocked to original position
What is the function of the sarcoplasmic reticulum in muscle contraction
Actively transports calcium ions fro cytoplasm for release via diffusion for muscle contraction.
What is the function of calcium ions in muscle contraction
Bind to Troponin changing shape of Tropomyosin allowing actin myosin Cross Bridges to form
Activates ATP Hydrolyse for recock
How are muscles relaxed
No ap= calcium ion channels close and ions actively transported back in
Less ions = Tropomyosin changes to original shape = blocks binding sites
No actin myosin Cross Bridges so no sliding of filaments
Antagonistic muscle pulls filaments apart
How are muscles relaxed
No ap= calcium ion channels close and ions actively transported back in
Less ions = Tropomyosin changes to original shape = blocks binding sites
No actin myosin Cross Bridges so no sliding of filaments
Antagonistic muscle pulls filaments apart
What role does ATP play in muscle stimulation
Allows recock of myosin head
Allows ca2+ to be actively Transported into to sarcoplasmic reticulum again for muscle relaxation
Used to repolarise sarcollema
