Muscle Contractions Flashcards
What is the sacolemma
Membrane
What is the myofibril
Block of protein, some thick some thin
What is the sarcomere
Single unit of muscle
The distance between adjacent Z-lines
What is the sarcoplasmic reticulum
Sack filled with calcium
Form of adaptation of the muscles
What 2 proteins are involved
Actin (thick)
Myosin (thin)
Why do myofibrils appear striped
Altering light coloured and dark coloured bands
A band = dark
(I band = light)
Why do A bands appear darker
Actin and myosin filaments overlap in this region
What is the H zone
Part of A band which is exclusively myosin
Why is the Z-line
Centre of each I band
What happens when the muscle contracts
Sacromeres shorten so pattern of dark and light bands change
What proteins are in actin’s structure
Actin
Tropomyosin
Troponin
What is a neuromuscular junction
Where motor neurone meets skeletal muscle fibre
Why are there many neuromuscular junctions spread through the muscle
Means can be quick muscle contractions as they simultaneously, making it powerful
This is essential for survival
What is the role of tropomyosin
Covers up myosin binding sites then shifts out of place to expose them and allow myosin to bind
Describe the cycle of muscle contraction
Calcium arrives, bonds to Troponin Causes Tropomyosin to pull away Myosin binding sites exposed Myosin binds to actin Myosin head pivots, causes actin to move ATP attaches, causing head to detach ATP hydrolysis provides energy for head to reposition Cycle continues as long as calcium present
What happens when nerve meets neuromuscular junction
Synaptic vesicles fuse with membrane and release acetylcholine
This diffuses into membrane changing permeability
Causes sodium ions to enter
Sodium ions depolarise membrane
Enzyme breaks acetylcholine which diffuses back
What happens after sodium ions enter muscle membrane
Action potential travels down T-tubules
Tubules contract with sarcoplasmic reticulum
Causes calcium ion channels to open
(Then muscle contraction cycle occurs)
What happens when muscle relaxes
Nervous stimulation stops
Calcium ions actively transported back to sarcoplasmic reticulum
Using energy from ATP hydrolysis
Tropomyosin blocks actin filament
Myosin heads no longer able to bind to actin filament
Contraction stops
What is the role of calcium
Stimulates ATPase in myosin heads
Binds calcium sites
How is ATP required in muscle contractions
Detaches myosin head
Transport calcium back into sarcoplasmic reticulum
Why do dead bodies muscles stay contracted
When dead no ATP
So myosin head can’t detach
What are the 2 types of muscle fibre
Slow-twitch
Fast-twitch
What are slow-twitch fibre
Contract slowly as less powerful contraction over long period of time
(Adapted for endurance work)
Also adapted for aerobic respiration to avoid build up of lactic acid (this would affect their efficiency)
What are the 4 main characteristics of muscle tissue
Excitable
Contractile
Elastic
Extensible
What are fast-twitch muscle fibres
Contract rapidly
Produce powerful contractions over a short period of time
Adapted for intense exercise
What are the adaptations of slow-twitch fibres
Large store of myoglobin (stores oxygen)
Supply of glycogen (source of metabolic energy)
Many bloody vessels (to deliver oxygen and glucose)
Many mitochondria (produce ATP)
What are the adaptations of fast-twitch fibres
Many thick myosin filaments
Many enzymes involved in anaerobic respiration
Store of phophocreatine (supply energy for muscle contraction as can rapidly generate ATP from ADP in anaerobic respiration)
