Describe the structure of a muscle fibre and explain the structural and physiological differences of fast and slow twitch muscle fibres

Transcription

1 Describe the structure of a muscle fibre and explain the structural and physiological differences of fast and slow twitch muscle fibres Muscles are made of myofibrils lying parallel to each other Each myofibril is made up of sarcomeres Cytoplasm of the myofibrils is called sarcoplasm Actin and myosin make up a large part of the sarcomere SLOW TWITCH MUSCLE FIBRES Known as oxidative/red muscles fibres due to rich blood supply and high levels of myoglobin The contract relatively slowly and can stay in tetanus (when the muscles contract and remain as short as possible) for a very long time. Required for steady action over a period of time used to maintain body posture Lots of mitochondria Rich blood supply So, they can continue to respire aerobically without needing to respire anaerobically Rely on glucose as a fuel supplied by the blood vessels so they can continue to produce ATP for as long as the oxygen is available FAST TWITCH MUSCLE FIBRES Known as glycolytic/ white muscles fibres due to lack of blood vessels and rich gltcogen stores Contract rapidly making them suitable for rapid bursts of activity Thy often function anaerobically causing them to fatigue quickly Relatively few blood vessels low numbers of myoglobin Low mitochondria Contain rich glycogen stores which can be converted to glucose for aerobic respiration Also has creatine phosphate which can be used to form ATP from ADP Genes and training affect the development of the twitch muscle fibres. Explain the contraction of skeletal muscle in terms of the sliding filament theory, including the role of actin and myosin, troponin, tropomyosin, calcium ions, ATP and ATPase The sliding filament theory explains the pattern seen when the muscle contracts Z-Line end of sarcomeres I bands- actin only

2 A band - myosin filament and overlapping regions H Zone- Myosin filaments only M line- Middle of the myosin filaments Dark A bands stay the same length but the light ones get shorter ACTIN: One of the contractile proteins. Two chains of Actin monomers, Actin's shape provides myosin binding sites at regular intervals, also has a tropomyosin chain wrapped around it which covers the myosin binding sites and troponin MYOSIN: Contractile protein to bring about contraction, two long polypeptide chains twisted together ending in two large globular heads, has ADP and phosphate bound to it and the head also has enzyme ATPase TROPONIN: protein associated with tropomyosin attached regularly along the chain CALCIUM IONS: released from the sarcoplasmic reticulum in response to a stimulus THE PROCESS 1) Calcium ions bind to troponin molecules changing their shape 2) They pull on the tropomyosin chain pulling them away from the myosin binding sites exposing them ready for action 3) Myosin globular heads bind forming acto-myosin bridge 4) ADP and phosphate are released changing the shape of the myosin causing the head to move forward and the actin filaments move along it causing the sarcomere to shorten 5) Free ATP binds the myosin changing its shape again and breaking the bridge 6) ATPase is activated which needs calcium ions to work 7) ATP is hydrolysed to provide energy for the myosin to return to its original position 8) Calcium ions remain in the sarcoplasm with continued stimulation, if not, they are pumped back into the sarcoplasmic reticulum using ATP. Recall the way in which muscles, tendons, the skeleton and ligaments interact to enable movement, including antagonistic pairs, extensors and flexors MUSCLES: largely made up of protein, work in antagonistic pairs to do work TENDONS: muscle to bone. They are strong and hard. White fibrous tissue and collagen fibres. Secure attachment and shock absorber.

3 LIGAMENT: hold bones together in the correct alignment. Elastic to allow joint movement SKELETON: made up of bone. bones embedded in a collagen matrix and calcium salts. dense but strong under compression- reduce weight moved around CARTILAGE: Hard but flexible. Made up of chrondocytes in a collagen matrix. HYALINE: end of bones Keeping the bones lined up I essential for the working of a joint. Ends of the bone are shaped to move smoothly over each other If a joint consisted of bone and bone, they would wear each other away To prevent this, the bones are lined with rubbery cartilage to allow joints to be articulated smoothly Most mobile joints also produce synovial fluid which fills the joint cavity ensuring friction free movement MUSCLE MOVEMENT Bones of the lower arm are attached to biceps and triceps of the upper arm by tendons When biceps contract the triceps relax This pulls the bones so the arm bends BICEPS: FLEXORS When triceps contract and biceps relax the arm straightens TRICEPS: EXTENSORS Muscles work in pairs because they can only pull when they contract- they are antagonistic pairs Describe how to investigate respiration practically The volume of oxygen taken up or the volume of carbon dioxide given out gives the rate of respiration A repirometer measures the amount of oxygen taken in Each tube contains potassium hydroxide solution which absorbs the carbon dioxide given off Control tube is set up to ensure that the results are only due to the woodlice respiring- mass can also affect rate of respiration The syringe is used to set the manometer fluid at a known level The apparatus is left for about 20 minutes During this time, there will be a decrease in the amount of air in the test tube This will decrease the pressure causing the red liquid in the manometer to move towards the test tube The distance moved by the liquid is measured

4 Value can be used to calculate oxygen uptake per minute Variables are controlled e.g. temperature Experiment is repeated to increase reliability Understand that cardiac muscle is myogenic and describe the normal electrical activity of the heart and how the use of ECG can aid the diagnosis of CVD and other heart conditions Myogenic: The heart can set up its own wave of depolarisation without external stimulation Sinoatrial node sets up a wave of depolarisation. This passes through the walls of the atria causing atrial systole. The depolarisation is held at the atriventricular node as the atria empty blood into the ventricles. The depolarisation passes to the Bundle of His which penetrates through the Purkyne tissue to the apex of the heart. The atriventicular valves close to prevent back flow of blood. This causes ventricular systole from the base- up. The semi lunar valves are forced open and blood flows out of the arteries. The pressure change during diastole causes the semi lunar valves to close. ECG ECG is used to investigate the rhythms of the heart by producing a record of the electrical activity of the heart Depolarisation causes tiny electrical changes on the surface of the skin Electrodes attached to the skin measure these changes Some heat conditions only show up when the person is exercising arrhythmias, atrial fibrillation, tachycardia Explain how genes can be switched on and off by DNA transcription factors including hormones Anabolic steroids steroid hormones closely related to the male sex hormone testosterone Natural testosterone can pass through the cell surface membrane The hormone binds to receptor molecules in the cell Carried into the nucleus where they modify gene expression Hormone receptor complex acts as a transcription factor It binds to the DNA switching particular genes linked to protein synthesis on This changes the mrna produced which affects the numbers and types of proteins/enzymes produced Bigger, stronger muscles result synthetic testosterone gives hormones with a longer life in the body Can have severe side effects: infertility, impotence, high blood pressure and heart attacks

5 Erythropoietin Peptide hormone binds to receptor molecule in cell surface membrane They activate a second messenger in the cell cytoplasm Triggers protein kinase cascade Final product enters nucleus and acts as a transcription factor Modifies mrna made affects numbers and types of enzymes made to make more red blood cells Erythropoietin is a naturally occurring hormone so it is very hard to isolate Excess of red blood cells thickens the blood and can lead to strokes and heart attacks More red blood cells means that oxygen is carried to respiring muscles more efficiently Erythropoietin can be used to treat anaemia Explain how variations in ventilation and cardiac output enable rapid delivery of oxygen to tissues and the removal of carbon dioxide from them, including how heart rate and ventilation are controlled and the roles of cardiovascular control centre and the ventilation centre During exercise, more oxygen is needed in the rapidly respiring tissue CO2 and lactic acid also need to be removed When exercise stops, the body needs to return to normal The heart uses a negative feedback system To increase the amount of oxygen, the heart increases the heart rate (number of beats per minute) The heart also increases the cardiac volume (The volume of blood pumped at each heart beat) Heart rate x cardiac volume = cardiac output How is the heart rate controlled? The cardiovascular centre in the medulla oblongata controls the heart rate Chemical and stretch receptors in the lining of the blood vessels and chambers of the heart send impulses to the cardiovascular centre Nervous control of the heart is autonomic and is divided in to sympathetic and parasympathetic nervous system Impulses travelling down the sympathetic nerves are excitatory by increasing the frequency of impulses from the sinoatrial node and impulses travelling down the parasympathetic nerves are inhibitory RESPONDING TO EXERCISE: When exercise starts, the blood vessels dilate in response to the hormone adrenaline which is released with exercise and this reduces the impulses sent from the baroreceptors and they almost stop

6 responding. When they do not stimulate the cardiovascular centre, it automatically sends impulses down the sympathetic nervous system to increase the heart rate and increase the blood pressure again. 1) As the atria fill with blood at the beginning of the cardiac cycle, chemical and stretch receptors in the blood vessels and the chambers of the heart send impulses to the cardiovascular control centre 2) During exercise, the walls of the heart are stretched more than usual by the big blood muscle blocks squeezing the blood so the cardiovascular centre gets sent more impulses than usual as the receptors are stretched more than usual 3) Impulses sent down the sympathetic nerves to the SAN increasing the heart rate 4) Increased stretching of the heart also means that the heart muscle contracts harder so more blood is expelled at each stroke RETURNING TO NORMAL 1) Baroreceptors in the sinuses of carotid arteries in the neck are important as exercise ends 2) As blood pressure in the arteries increases, the baroreceptors sends impulses to the cardiovascular centre 3) This sends impulses down the parasympathetic nerve to slow down the heart rate and cause vasodilation to lower the blood pressure LUNGS Tidal volume: the volume of air that enters and leaves the lungs at each natural resting breath Breathing rate: how many breaths are taken in a minute VENTILATION RATE: TIDAL VOLUME X BREATHING RATE Ventilation needs to supply oxygen to tissue and remove CO2 Controlled by the respiratory/ inspiration centre in the medulla oblongata The expiratory centre controls FORCED exhalation 1) During inhalation: The respiratory centre sends impulses down the sympathetic nerves causing the diaphragm and intercostal muscles to contract. 2) As the lungs inflate, this increases their volume. This means that the pressure is lowered in the lungs 3) Air enters the lungs due to the pressure difference between the lungs and the air outside 4) As the lungs inflate, the stretch receptors in the wall of the bronchi send impulses to the inspiratory centre

7 5) This inhibits their action so they stop stimulating the breathing muscles causing exhalation During exercise, the volume of carbon dioxide in the blood increases- this decreases the ph in the blood. The chemoreceptors in the medulla, carotid arteries and the aorta detect ph changes and send impulses to the intercostal muscles and the diaphragm. This increases TIDAL VOLUME and BREATHING RATE. This also speeds up gaseous exchange SPIROMETERS Spirometer has an oxygen filled chamber with a movable lid Person breathes through a tube connected to the lid When the person breathes in, the lid moves down and when they breathe out, the lid moves up Movements are recorded by a pen attached to the chamber The pen writes on a rotating drum creating a spirometer trace The soda lime in the tube the person breathes in from absorbs the carbon dioxide so it does not affect the tidal volume or breathing rate (ventilation rate) The volume of air in the chamber decreases over time as oxygen is breathed in for respiration carbon dioxide absorbed by soda lime. Spirometers can be used to investigate the effect of exercise on breathing rate: The person is connected to spirometer at rest and the reading is taken for a minute; the person then exercise; reading continued for a minute after this Discuss the role of the hypothalamus and the mechanisms of thermoregulation Homeostasis: maintenance of a steady internal state in the body regardless of external conditions Feedback systems help to maintain a constant internal temperature LOW CRITICAL TEMPERATURE: temperature at which thermoregulatory measures work to conserve heat and metabolic reaction rates increase to produce extra heat LOW LETHAL TEMPERATURE: temperature at which the chemical reactions of the body can no longer work to meet the demands If the temperature gets too high, the enzymes denature and this stops metabolic reactions HIGH CRITICAL TEMPERATRURE: temperature at which thermoregulatory measures work to get rid of excess heat The metabolic rate of reaction continues to go up with temperature Receptors in the brain detect changes to the blood temperature Receptors in the skin detect changes in the external environment A rise in blood temperature results in the heat loss centre being activated

8 This results in vasodilation- the increase in blood flow close to the skin Sweating increases Erector pilli muscles lie flat Shivering stops A decrease in blood temperature results in the activation of the heat gain centre Impulses sent to effectors to decrease blood flow close to the skin (vasoconstriction) Erector pili muscles contract so hairs stand straight to trap a layer of insulating air Involuntary muscle contractions to bring about shivering VASODILATION: Sphincter muscles relax and the atriovenous shunt closes so more bloo d flows through the superficial capillaries and less blood flows through the deeper shunt vessels. This means that moe blood is flowing closer to the skin's surface increasing the gradient between the skin and environment temperature. So more blood is lost by radiation and conduction VASOCONSTRICTION: Sphincter muscles contract so less blood flows through the superficial capillaries and more blood flows in the deeper shunt vessels. This means more blood flows away from the skin's surface decreasing the temperature gradient between the environment and the skin. This means less blood is lost by radiation and conduction