Unit 7: Run for Your Life Flashcards
What is the skeletal muscle?
It is the type of muscle you use to move like the biceps and triceps to move the lower arm. They are attached to bones by tendons. They contract and relax to move bones at a joint.
What are ligaments?
Attach bones to other bones, to hold them together.
What is an example of the muscles and tendon working in the lower arm?
When your biceps contract your triceps relax. This pulls the bone so your arm bends (flexes) at the elbow. A muscle that bends a joint when it contracts is called a flexor.
But when your triceps contracts your bicep relaxes. This pulls bone so your arm extends (straightens) at the elbow. A muscle that straightens a joint when it contracts is called an extensor.
What is it called when muscles work together to move a bone?
Antagonistic pairs
What is the skeletal muscle made up of?
It is made up of large bundles of long cells, called muscle fibres.
What is the cell membrane called on the muscle fibres called and the structure of the muscle fibres?
Sarcolemma. Bits of this are folded inwards across the muscle fibres and stick into the sarcoplasm (muscle cells cytoplasm). These folds are called transverse (T) tubules and they help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre.
What are the internal membranes?
Called sarcoplasmic reticulum runs through the sarcoplasm. The sarcoplasmic reticulum stores and releases calcium ions that are needed for muscle contraction.
Why do muscle cells have lots of mitochondria?
To provide ATP that is needed for muscle contraction.
Muscle cells contain many nuclei, what is this called?
Multinucleate
What are myofibrils?
Long, cylindrical organelles. They are made up of proteins and are highly specialised for contraction.
What are the thick myofilaments called?
Made up of protein called myosin.
What are the thin myofilaments called?
Made up of a protein called actin.
What do the dark bands show you under a microscope of a myofibril?
Dark bands contain the think myosin filaments and some overlapping thin actin filaments are called A-bands
What do the light bands show under a microscope
Light bands contain thin actin filament only- these are called I-bands
What are myofibrils made up of?
Made up of many short units called sarcomeres. The ends of the sarcomeres are marked with a Z-line and are joined together here at the Z-line lengthways. In the middle of each sarcomere is an M-line in the middle of the myosin filament. Around the M-line is the H-zone. The H-zone only contains myosin filaments.
What is the sliding filament theory?
1) Myosin and actin filaments slide over one another to make sarcomere contract- the myofilaments themselves don’t contract and the myosin and the actin molecules stay the same length.
2) The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract.
3) Sarcomeres return to their original length as the muscle relaxes.
How does muscle contraction occur (stage 1)?
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. Actin filaments have a binding site for myosin heads, called actin-myosin binding sites. Two other proteins called tropomyosin and troponin are found between actin filaments. These proteins are attached to each other and help the myofilaments move past each other.
How does muscle contraction occur (stage 2)?
In a resting (unstimulated) 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 myosin-actin binding site on the actin filaments
How does action potential trigger an influx of calcium ions?
Action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolemma. Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum, which causes the release of calcium ions to be released into the sarcoplasm. Calcium ions bind to troponin, causing it to change shape. This pulls the attached tropomyosin out of the action-myosin binding site on the actin filament. Exposes the binding site, which allows the myosin head to bind. The bond is formed when a myosin head binds to an actin filament called the actin-myosin cross-bridge.
How is ATP provided?
Calcium ions activate ATPase and break down ATP, to provide the energy needed for muscle contraction. The energy released from ATP moves the myosin head, which pulls the actin filament along in a rowing action.
How is the cross bridge broken?
ATP provides energy to break down the actin-myosin cross-bridge so the myosin head detaches from the actin filament after it’s moved. The myosin head reattaches to a different binding site further along the actin filament. A new actin-myosin cross-bridge is formed and the cycle repeats as it attaches, moves, detaches, and reattaches. Many cross-bridges are formed and break very rapidly, pulling the actin filament along - which shortens the sarcomere, causing muscle contraction. The cycle continues as long as calcium ions are present and bound to troponin.
What happens when the excitation stops and the calcium ions leave the troponin molecules?
When the muscle stops being stimulated, calcium ions leave their binding sites on the troponin and are moved by active transport back into the sarcoplasmic reticulum (ATP needed). The troponin muscles return to their original shape, pulling the attached tropomyosin molecules back with them. This means the tropomyosin blocks the actin-myosin binding sites again. Muscles aren’t contracted because no myosin heads are attached to actin filaments (no actin-myosin cross bridge). Actin filaments slide back to their relaxed position, which lengthens the sarcomere.
What are the properties of slow-twitch muscle fibres?
Muscle fibres contract slowly. Muscles you use for posture, e.g. those in the back, have a high proportion of them. Good for endurance activities, e.g. maintaining posture, and long-distance running. Can work for a long time without getting tired. Energy is released slowly through aerobic respiration. Lots of mitochondria and blood vessels supply the muscles with oxygen. Reddish in colour because they are rich in myoglobin- a red-coloured protein that stores oxygen.
What are the properties of fast-twitch muscle fibres?
Muscle fibres contract very quickly. Muscles you use for fast movement, e.g. those in the eyes and legs, have a high proportion of them. Good for short bursts of speed and power, e.g. eye movement and sprinting. Get tired easily and very quickly. The energy is released quickly through anaerobic respiration using glycogen (stored glucose). There are few mitochondria or blood vessels. Whitish in colour because they don’t have much myoglobin (so they can’t store much oxygen).