muscle structure and contraction Flashcards
Motor Neurone Structure [2]
- Each motor neurone has several ‘end plates’.
- This allows coordinated contraction along the muscle, and also control of the amount of force
Small force = fewer stimulated
Larger force = more stimulated
Neuromuscular Junction Structure [3]
- Where a motor neurone meets a muscle
- The function of the synapse is the same as a cholinergic synapse
- Instead of receptors on a post-synaptic neurone, they are on the membrane of the muscle and this is depolarised
Similarities between cholinergic synapses and the neuromuscular junction [4]
- Acetylcholine is the neurotransmitter
- Acetylcholinesterase breaks this down
- Acetylcholine attaches to receptors, which cause sodium ion channels to open
- Both have sodium-potassium pumps in the membrane
Differences between cholinergic synapses and the neuromuscular junction [5]
CHOLINERGIC SYNAPSE
- Excitatory or inhibitory
- Neurone to neurone
- Sensory, intermediate and motor can be involved
- Stimulates a new action potential
- Receptors on the post-synaptic neurone membrane
NEUROMUSCULAR JUNCTION
- Only excitatory
- Neurone to muscle
- Only motor neurones
- No new action potential
- Receptors on the muscle fibre membrane
Muscle Structure [5]
Skeletal (striated) muscle is made up of specialised cells called muscle fibres. Each fibre contains:
- several nuclei
- many mitochondria
- an extensive sarcoplasmic reticulum (specialised endoplasmic reticulum, Ca2+ store)
- contractile elements called myofibrils (organelles with highly organised cytoskeleton, sliding filaments)
Each myofibril consists of a chain of repeating units called sarcomeres with a characteristic pattern of lines, zones and bands.
Role of Bones in Human Movement
Act as levers
Role of Ligaments in Human Movement
Attach to the skeleton across joints, stabilizing them
Role of Muscles in Human Movement
Provide the force by contracting to move the bones
Role of Tendons in Human Movement
Attach muscle to bone
Role of Nerves in Human Movement
Coordination of muscle contraction
Muscles & The Skeleton [4]
- Skeletal muscles cause the skeleton to move at joints
- They are attached to skeleton by tendons
- Tendons transmit muscle force to the bone
- Tendons are made of collagen fibres and are
very strong and stiff
Antagonistic Muscle Action [5]
- Muscles are either contracted or relaxed
- When contracted the muscle exerts a pulling force, causing it to shorten
- Since muscles can only pull (not push), they work in pairs called antagonistic muscles
- The muscle that bends the joint is called the flexor muscle
- The muscle that straightens the joint is called the extensor muscle
3 Types of Muscle
Cardiac Muscle
Smooth Muscle
- Involuntary and controlled by autonomic nervous system
Skeletal Muscle (striped/striated)
- Voluntary and controlled by somatic nervous system
Muscle Structure
- A single muscle contains approx 1000 muscle fibres
- These fibres run the whole length of the muscle
- Muscle fibres are joined together at the tendons
What makes up muscles? [5]
Muscle
Muscle Fibre Bundle
Muscle Firbre
Myofibrils
Myofilaments
What is Sarcoplasm?
Muscle cytoplasm
Myofibrils and Sarcomeres [3]
- Each myofibril is made up of many sarcomeres.
- The sarcomere is mainly composed of two proteins, actin and myosin
- The arrangement of actin and myosin give the striped appearance of the myofibril
Myosin
Many of these myosin molecules stick together to form a thick filament
Actin [3]
- The thin filament consists of a protein called actin
- The thin filament also has another protein, tropomyosin wrapped around it
- Tropomyosin can move, exposing myosin binding sites
What is The Sliding Filament Theory? [4]
- When the muscle contracts the sarcomeres become shorter
- The actin and myosin do not change in length
- Instead they slide past each other (overlap)
- Actin filaments are pulled past the myosin
filaments
Neuromuscular Junction [3]
- Action potentials arrive at motor end plates, which release the transmitter acetylcholine.
- Acetylcholine binds to receptors on the muscle fibre membrane, causing depolarisation.
- Depolarisation spreads through the transverse tubules to the sarcoplasmic reticulum, which releases Ca2+ ions.
Sliding Filament Theory [7]
- Ca2+ ions causes tropomyosin to move away from actin binding sites, exposing them.
- The myosin head can now attach to the actin filament, forming actinomyosin cross-bridges (The myosin head has an
ADP and Pi attached to it). - The myosin head moves, pulling the thin actin filament along. (This movement causes the ADP and Pi to be released).
- The actinomyosin cross-bridge is broken as a new ATP attaches to the myosin head.
- The myosin head ‘re-sets’ using energy from the hydrolysis of ATP.
- The ATPase that does this is located in the myosin heads and is activated by Ca2+ ions.
- If the calcium ion concentration drops, tropomyosin moves back and covers the myosin binding sites.
Repetition of the cycle [3]
- One ATP molecule is split by each actinomyosin bridge in each cycle. This takes only a few milliseconds
- During a contraction 1000’s of actinomyosin bridge in each sarcomere go through this cycle
- However the bridges are all out of synch, so there are always many cross bridges attached at any one time to maintain force
Muscle fibres and ATP production [3]
- Muscle cells need to be able to access to large supply of ATP when intense exercise begins
- ATP has to be resynthesized during exercise
They have 3 ways of producing ATP: - From creatine phosphate or phosphocreatine (first 10s of exercise)
- Anaerobic respiration
- Aerobic respiration
Creatine Phosphate [5]
- As ADP levels increase, creatine kinase converts creatine phosphate into creatine
- The energy released converts ADP back into ATP
- This action is known as substrate level phosphorylation
- Muscle cells are able to store much more CP compared to ATP
- ONLY muscle cells use CP for ATP
2 types of muscle fibre [2]
- Fast & Slow Twitch Fibres
- Most animals have both present, although the proportions may vary significantly
Slow-twitch fibres
- Contract more slowly and less powerfully
- Work for longer periods of time
How are slow-twitch fibres adapted for aerobic respiration? [3]
- Large store of myoglobin, an oxygen-storage molecule
- Good blood supply
- Many mitochondria
(used for long distance running)
Fast-twitch fibres
- Contract rapidly and more powerfully
- Work for shorter periods of time
How are fast-twitch fibres adapted for anaerobic respiration?
- High concentration of enzymes for anaerobic respiration
- Phosphocreatine store
- High concentration of glycogen
(used during sprinting, weight lifting)
