Muscle Contraction Flashcards
Explain how muscles work together to lower your arm
- when your tricep contracts your bicep relaxes
- the tricep pulls on the tendon attached to the ulna which applies a downwards force
- so the fore arm lowers
- muscles work antagonistically
Compare and contrast the action of synapses and neuromuscular junctions
- the neurotransmitter in a neuromuscular junction is always acetylcholine, in synapse can be noradrenaline, acetylcholine or another transmitter
- neuromuscular junction causes muscle contraction but a synapse causes an action potential in post-synaptic cell
- they are both activated by action potentials
- in both neurotransmitter diffuses across cleft
- in both enzymes break down the neurotransmitter
- different receptors on post-synaptic membrane, in neuromuscular junction receptors are nicotinic cholinergic receptors but in synapse can have various receptors depending on neurotransmitter
Explain how movement involves muscles, tendons, ligaments and joints
- skeletal muscles are attached to bones by tendons
- ligaments attach bones to other bones at a joint to prevent dislocation and hold bones in places
- the elbow is an example of a synovial joint
- synovial fluid lubricates the joint
- the synovial membrane produces synovial fluid
- cartilage pads where bones meet to reduce friction as bones move
Describe the structure and function of skeletal muscle (voluntary muscle)
- cross-striations (striated)
- cells are elongated (cylindrical) and are multinucleate (multiple nuclei)
- attached to bones and tendons
- contract quickly but also fatigue quickly
- controlled by somatic nervous system
Describe the structure and function of smooth muscle (involuntary muscle)
- unstriated
- spindle shaped cells all with a single nucleus (mononucleated)
- found in the walls of blood vessels (arteries and veins), digestive system (gut, stomach) and airways (bronchi and bronchioles)
- muscle fibres contract slowly and don’t fatigue
- controlled by the autonomic nervous system
Describe the structure and function of cardiac muscle
- cardiac muscle is myogenic but the rate of contraction is controlled by the autonomic nervous system
- found in the heart
- made of muscle fibres connected by intercalated disks
- muscle fibres are branched to allow nerve impulses to spread quickly through whole muscle
- each muscle fibre has a single nucleus (mononucleated)
- semi-striated
- muscle fibres contract rhythmically and don’t fatigue
What is skeletal muscle made up of?
- skeletal muscle is made up of large bundles of long cells called muscle fibres
- the muscle fibres are surrounded by connective tissue containing blood vessels and nerves
- the cell membrane of the muscle fibres is called sarcolemma
- bits of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm, these folds are called transverse (T) tubules - they help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
- a network of internal membranes called the sarcoplasmic membrane runs through the sarcoplasm - it stores and released calcium ions that are needed for muscle contraction
- muscle fibres have lots of mitochondria to provide ATP for muscle contraction
- muscle fibres have lots of long, cylindrical organelles called myofibrils which are made up of proteins and are highly specialised for contraction
Describe the structure of myofibrils
- myofibrils contain bundles of thick and thin myofilaments that move past each other to make muscles contract
- thick myofilaments are made up of the protein myosin
- thin myofilaments are made up of the protein actin
- myofibrils are made up of short units called sarcomeres
- A band - thick myosin filaments and some overlapping thin actin filaments
- I bands - thin actin filaments only
- Z line - the end of each sarcomere
- M line - the middle of each sarcomere, also the middle of the thick myosin filaments
- H zone - around the M - line, only contains thick myosin filaments
Describe the sliding filament theory
- thick myosin filaments and thin actin filaments slide over each other to make the sarcomeres contract
- the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
- during contraction the A band stays the same, the I band shortens, the H zone shortens and the sarcomere shortens
Describe the structure of myosin filaments
- myosin filaments have globular heads that are hinged so they can move back and forth
- each myosin head has a binding site for actin and a binding site for ATP
Describe the structure of actin filaments
- actin filaments have binding sites for myosin heads called actin-myosin binding sites
- two other proteins called tropomyosin and troponin are also found between actin filaments and help myofilaments move past each other due to troponin having binding sites for calcium
What happens when the muscle is in its resting state?
- in a resting muscle the actin-myosin binding site is blocked by tropomyosin which is held in place by troponin
- so myofilaments can’t slide past each other because the myosin heads can’t bind to the actin-myosin binding site on the actin filaments
Explain how muscles work together to raise your arm
- when your bicep contracts your tricep relaxes
- tendons attached to the radius pull on the radius which applies an upwards force
- this causes the fore arm to raise
- muscles that work together to move a bone are called antagonistic pairs
Describe the process of muscle contraction
• when an action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolemma, depolarisation spreads down the T-tubules to the sarcoplasmic reticulum
- this caused the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm
• calcium ions bind to troponin, causing it to change shape
- this pulls the attached tropomyosin out of the way of the actin-myosin binding site on the actin filament
- this exposes the binding site which allows the myosin head to bind, the bond formed when a myosin head binds to an actin filament is called an actin-myosin cross bridge
• calcium ions also activate the enzyme ATPase which breaks down ATP into ADP + Pi, this provides the energy needed for muscle contraction
• the energy released from ATP moves the myosin head which pulls the actin filament along in a kind of rowing action
• ATP also provides the energy to break the actin-myosin cross bridge, so the myosin head detaches from the actin filament after its moved
• the myosin head then reattaches to a different binding site further along the actin filament, so a new actin-myosin cross bridge is formed and the cycle is repeated
• many cross bridges form and break very rapidly, pulling the actin filament along which shortens the sarcomere, causing the muscle to contract
• the cycle will continue as long as calcium ions are present and bound to troponin
What happens when the muscle stops being stimulated?
• when the muscle stops being stimulated, calcium ions leave their binding sites on the troponin molecules and are moved by active transport back into the sarcoplasmic reticulum
• the troponin molecules return back to their original shape, pulling the attached tropomyosin molecules with them
- this means the tropomyosin molecules block the actin-myosin binding sites again
• muscles aren’t contracted because no myosin heads are attached to actin filaments so the actin filaments slide back to their relaxed position which lengthens the sarcomere
