T7 Flashcards
What are skeletal muscles?
It is a type of muscle you can move.
They’re attached to bones by tendons.
Skeletal contract and relax to move bones at a joint.
What is the structure of a skeletal muscle?
It is made up of large bundles of cells called muscle fibres.
The membrane of the muscle fibre is called the sarcolemma.
Bits of the sarcolemma fold onwards across the muscle fibre and stick into the sarcoplasm (muscle cells cytoplasm). The folds are called transverse tubules.
What do the transverse tubules help do?
They help spread electrical impulses throughout the sarcoplasm.
What is the sarcoplasmic reticulum and what’s it’s function?
It is a network of internal membranes.
It’s function is to store and release calcium ions that are needed for muscle contraction.
What are the properties of muscle fibres?
They have a lot of mitochondria to provide ATP.
They are multinucleate so they contain many nuclei.
Muscle fibres have many long cylindrical organelles called microfibrils which are made up of proteins and are highly specialised for muscle contraction.
Explain the structure of microfibrils.
Made up of many short units called sarcomeres.
They contain bundles of thick and thin myofilaments that move past each other to make muscles contract.
Thick myofilaments - protein called myosin.
Thin myofilaments - protein called actin.
What is the structure of a sarcomere?
A-Bands - Dark bands containing myosin and some overlapping actin filaments.
I-Bands - Light bands containing actin filaments only.
Ends of sarcomere is the Z-Line.
Middle of sarcomere is the M-Line.
Around the M-Line is the H-Zone which only contains myosin filaments.
Explain the sliding filament theory.
Myosin and actin filaments slide over one another making the sarcomere contract.
A-Bands stay the same length.
I-Bands get shorter.
H-Zone gets shorter.
Explain the structure of myosin filaments.
They have hinged globular heads so they can move back and forth.
Each myosin head has a binding site for actin for actin and a binding site for ATP.
Explain the structures of actin filaments.
They have binding sites for myosin heads called actin myosin binding-sites.
Between the actin filaments are tropomyosin and troponin which help the myofilaments move past each other.
What blocks the binding site in a resting muscle?
The actin-myosin binding site is blocked by tropomyosin held in place by troponin.
Myosin globular head can’t bind so they can’t slide past each other.
Explain the 3 stages of how a muscle contraction is triggered by an action potential.
1) The action potential triggers an influx of calcium ions.
- action potential depolarises the sarcolemma causing the sarcoplasmic reticulum to release calcium ions which binds to the troponin. This releases tropomyosin revealing the actin-myosin binding site. When the myosin head binds to the actin filament, the bond is called an actin-myosin bridge.
2) ATP provides energy need to move the myosin head.
- Calcium ions also trigger the enzyme ATPase which breaks down ATP into ADP+Pi to provide energy for muscle contraction. The myosin head moves, pulling the actin filaments.
3) …. and break the cross bridge.
- ATP also provides energy to break the actin-myosin cross bridge after the filament has moved where it reattached and repeats the process.
What happens to the calcium ions after muscle contraction?
1) Calcium ions leave their binding site on troponin and are moved by active transport back into the sarcoplasmic reticulum.
2) Troponin molecules return to their original shape pulling the attached tropomyosin molecules to block the actin-myosin binding site.
3) Actin filaments return to their original relaxed position; lengthening the sarcomere.
What are the properties of slow twitch muscle fibres?
- Contract slowly
- Good for endurance (long distance running)
- Work for longer time without getting tired.
- Energy released slowly from aerobic respiration.
- Reddish colour as they are rich in myogoblin.
What are the properties of fast twitch muscle fibres?
- Contract quickly.
- Good for short bursts of speed and power.
- Get tired very quickly.
- Energy’s released from aerobic respiration.
- Whitish colour as they don’t have many myogoblin.
What is aerobic respiration?
It’s the process in which large amounts of energy is released by splitting glucose into CO2, water and energy.
Glucose + oxygen ~> CO2 + H2O + ATP.
The energy released is used to phosphorylate ADP to ATP.
What are the 4 stages of aerobic respiration?
1) Glycolysis.
2) The Link Reaction.
3) Krebs Cycle.
4) Oxidative Phosphorylation.
Explain Glycolysis.
- Splitting of 1 molecule of glucose into 2 molecules of pyruvate.
- Occurs in the cytoplasm.
- Doesn’t require oxygen.
1) Glucose is phosphorylated by adding 2 phosphates from 2 ATP = 2 triose phosphate and 2 ADP.
2) Triose phosphate is oxidised (loses hydrogen) forming 2 pyruvates.
NAD collects hydrogen ions forming 2 reduced NAD.
4 ATP produced so there’s a net gain of 2 ATP.
Explain The Link Reaction.
Pyruvate ~> CO2
NAD ~> acetate
Acetate ~> acetyl coenzyme A
- Occurs in the mitochondrial matrix.
- Occurs twice for every glucose molecule.
1) Pyruvate is decarboxylated (1 carbon removed) so CO2 is removed.
2) NAD is reduced collecting hydrogen from pyruvate which forms acetate.
3) Acetate is combined with coenzyme A to form acetyl coenzyme A.
No ATP produced.
Explain the Krebs Cycle.
- It involves a series of oxidisation-reduction reactions.
- Occurs for every pyruvate molecule.
1) Acetyl CoA combines with oxaloacetate to from citrate.
2) Citrate is converted into a 5C molecule. - Decarboxylation occurs (CO2 removed).
- Dehydrogenation occurs (Hydrogen removed)
- Hydrogen is used to produce Reduced NAD.
3) 5C molecule is then converted into a 4C molecule.
- Decarboxylation and Hydrogenation occur producing Reduced FAD and 2 Reduced NAD.
- ATP produced.
- Substate level phosphorylation occurs.
Explain Oxidative Phosphorylation.
- It is where energy is carried by electrons from reduced coenzymes (reduced NAD and reduced FAD) is used to make ATP.
1) Reduced NAD and Reduced FAD is oxidised to NAD and FAD.
2) Electrons move down electron transport chain losing energy at each carrier. - Electron carriers use energy to pump protons from the mitochondrial matrix into the inter-membrane space.
- Higher concentration of protons in the inter-membrane space than the mitochondrial matrix which creates a electrochemical gradient.
3) Protons move down the electrochemical gradient back to the mitochondrial matrix via ATP synthase.
4) Chemiosmosis - Movement if H+ ions across the membrane generates ATP. - Oxygen is the final electron acceptor.
How can some metabolic poisons target electron carriers in Oxidative Phosphorylation?
It prevents them from passing on electrons by stoping chemiosmosis.
Reduced NAD and Reduced FAD are no longer oxidised so NAD and FAD aren’t generated which stops the Krebs Cycle.
What is anaerobic respiration?
- It doesn’t require oxygen.
1) Glucose is converted to Pyruvate via Glycolysis.
2) Reduced NAD (from glycolysis) transfers hydrogen to Pyruvate to form lactate and NAD.
3) NAD can be then reused in glycolysis. - Production of lactate acid regenerates NAD thus glycolysis is continuous irrelevant of minimal oxygen.
- This means, that small amounts of ATP can still be produced.
What 2 ways can lactic acid be broken down?
1) Cells convert lactic acid back to Pyruvate (which re-enters aerobic respiration at the Krebs Cycle).
2) Liver cells can convert lactic acid back into glucose which means they can be repaired or stored.
The cardiac heart is myogenic. Explain what the term Myogenic means.
It means the heart can contract and relax without receiving signals from neurones.
The electrical activity in the heart creates the patterns of contractions which coordinates the regular heartbeat.
How does electrical activity travel through the heart?
1) Process initiates at the SAN (in the wall of the right atrium).
2) SAN sends out regular waves of electrical activity to the atrial walls.
3) Atria contract at the same time.
- Non conducting collagen tissue prevents waves being passed onto the ventricles so they don’t contact at the same time.
4) SAN ~> AVN which passes the electrical activity to the Bundle of His.
- Slight delay before the AVN reacts which insures that ventricles contract after atria have emptied so blood flows in one direction.
5) Bundle of His (group of muscle fibres) conduct electrical activity to Purkyne fibres (in the ventricle walls)
6) Purkyne fibres carry the waves of electrical activity into the muscular walls of the ventricles causing them to contract simultaneously.
What does an Electrocardiograph record?
It is a machine that records the electrical activity of the heart using electrodes.
When the heart contracts ~> heart muscle depolarises; losing electrical charge.
When the heart relaxes ~> heart muscle repolarises; gains electrical charge.
What is Tachycardia?
When the heart beat is too fast - showing the heart isn’t pumping blood efficiently.
What is Bradycardia?
When the heart beat is too slow.
