Mr p bio 8 muscles Flashcards
what are the 3 types of muscle?
- smooth- contracts without conscious control, in organs
- cardiac - contracts without conscious control, in heart
- skeletal muscle- used to move
what is the role of skeletal muscles?
-attached to bone by tendons
-ligaments attach bone to other bones
-pairs of skeletal muscles contract and relax and move the bones at a joint
-bones are incompressable so act as levers
what are antagonistic pairs?
muscles that work together to move a bone
the contracting muscle= agonist and the relaxing muscle= antagonists
what is the structure of skeletal muscles?
-large bundle of long cells called muscle fibres
-cell membrane of muscle fibres= sarcolemma
-bits of sarcolemma fold inwards across the muscle fibre and stick into sarcoplasm
-folds are called transverse tubules
what do transverse tubules do?
help spread the depolarisation through the sarcoplasm so they reach all parts of the muscle fibre
what is the structure of the sarcoplasm?
a network of internal membranes runs through the sarcoplasm called sarcoplasmic reticulum.
Sarcoplasmic reticulum stores and releases Ca2+ needed for muscle contraction
many mitochondria for ATP for contraction
multinucleate and have lots of myofibrils containing proteins specialised for contraction
what do myofibrils consist of?
bundles of thick and thin myofilaments that move past each other to make muscles contract
thick= myosin protein
thin= actin protein
what do A-bands look like under a microscope?
dark bands contain thick myosin filaments and some overlapping thin actin filaments
what do I-bands look like under a microscope?
light bands that only contain thin actin filaments
what is the structure of myofibrils?
-made of short units called sarcomeres
-ends of each sarcomere marked with z lines
-middle of sarcomere is an M line
- around m line is a h-zone- only myosin present
how is myosin’s structure adapted for muscle contraction?
have globular heads that are hinged so can move back anf forth and each has a binding site for ATP
how is actins structure adapted for muscle contraction?
have binding sites for myosin heads, called actin myosin binding sites
another protein called tropomyosin is found between actin filaments
what is happening, in terms of actin and myosin, when muscles are at rest?
- at rest, the myosin- actin binding site is blocked by tropomyosin so the myofilaments cant slide past each other as the myosin heads cant bind to the actin filaments
describe how Ca2+ enters the sarcoplasm during the process of muscle contraction
- AP from the motor neurone stimulates a muscle cell, depolarises the sarcolemma
- depolarisation spreads down the T-tubules to the sarcoplasmic reticulum
- SR releases stored Ca2+ into the sarcoplasm
- influx of Ca2+ into the sarcoplasm triggers muscle contraction
describe how an actinmysoin cross bridge is formed after influx of Ca2+ during muscle contraction
- Ca2+ bind to troponin attached to tropomyosin, causing protein to change shape
6.pulls to tropomyosin out of the actin myosin binding site on the actin filament
7.exposing the binding site, allowing myosin head to bind - bond formed when myosin head binds to actin filament called actinmyosin cross bridge
describe how a power stroke occurs during muscle contraction
Ca2+ also activates the enzyme ATP hydrolase, which hydrolyses ATP, to provide energy needed, energy released from ATP causes the myosin head to bend which pulls the actin filament along in a stroke action called a power stroke
how is the Actin myosin cross bridge broken?
-Another ATP molecule provides energy the break the actinomyosin cross bridge.
-The myosin head detaches from the actin filament after it has moved.
-ATP is used to recock the myosin head (put it back to the start position), and reattaches to a different binding site further along the actin filament.
-A new actin-myosin cross bridge is formed and the cycle is repeated
how do the filaments return back to their rest states following contraction?
-When muscle stops being stimulated, Ca2+ leave their binding sites and are moved by active transport back into the SR (also requires ATP).
-This causes tropomyosin to move and block the actin-myosin binding sites again.
-During this state the actin filaments can slide back to their relaxed position – lengthening the sarcomere.
what do fast and slow twitch muscle fibres allow?
-Fast muscle fibres allow rapid movement but for short periods of time
-Slow twitch muscles allow us to maintain activity for long periods of time without fatigue.
what are the differences between fast and slow muscle fibres? (8)
fast:
-short contraction
-fewer capillaries
-mainly anaerobic
-fewer, smaller mitochondria
-large store of calcium ions in sarcoplasmic reticulum
-lots of glycogen
-faster rate of ATP hydrolysis in myosin heads
-fatigues rapidly (lactate formation)
(short opposite)
what is the ATP- phosphocreatine system?
- ATP formed by phosphorylating ADP
- done by adding phosphate group taken from PCr
3.PCr stored in cells and the ATP-PCr system generated ATP quickly - Pcr runs out after a few seconds- used for short bursts of vigorous exercise
- PCr system is anaerobic + alactic
what is photocreatine used for?
muscle fibres only store enough ATP for contraction for up to 3-4 secs so muscles store chemical called phosphocreatine which can donate a phosphate to restore ATP
