Muscle Contraction and Homeostasis Flashcards
What is the microscopic structure of a skeletal muscle?
- Actin is thinner than myosin
- I band = actin and myosin do not overlap
- A band = actin and myosin overlap
- H zone = only myosin
- The distance between Z lines is called the sarcomere
What are slow twitch muscle fibres?
- Contract more slowly and less powerfully over a longer period
- Found in calf muscle which contracts to maintain upright position
- Aerobic respiration to prevent build up of lactic acid
- Large store of myoglobin to provide oxygen
- Supply of glycogen to provide metabolic energy
- Large supply of blood vessels
- Lots of mitochondria to produce ATP
What are fast twitch muscle fibres?
- Contract rapidly and powerfully for a short period
- Intense exercise like weight lifting
- Biceps
- Thicker myosin filaments
- High concentration of enzymes involved in anaerobic respiration
- Store of phosphocreatine which creates ATP in anaerobic conditions
What happens at a neuromuscular junction?
- There are lots of junctions so transmission is quick, rather than slow with just one junction
- Synaptic vesicles fuse with presynaptic membrane and release acetylcholine which diffuses to the post synaptic membrane, opening sodium ion channels so Na+ enter
- AC broken down so muscle is not overstimulated
What happens during muscle contraction?
- Tropomyosin prevents myosin head from attaching to binding site on actin
- Ca2+ released from ER cause Tropomyosin to pull away from binding sites
- Myosin head attaches
- Head of myosin changes angle, moving actin filament along it and releasing ADP
- ATP fixes to myosin head causing it to detach from myosin
- ATP is hydrolysed to ADP by ATPass providing energy for myosin head to return to its original position
- Head of myosin reattached to binding site further along actin filament and he cycle continues
What is homeostasis?
The maintenance of a constant internal environment in organisms
What is the desired level called?
The set point
How do ectotherms control body temperature?
- Expose themselves to the sun
- Take shelter
- Gain warmth from ground
- Generate metabolic heat
- Colour variations
How do endotherms control body temperature?
- Vasoconstriction/dilation
- Shivering
- Sweating
- Raising and lowering of hair
- Behavioural mechanisms
How is body temperature controlled?
- There is a change in normal blood temperature
- Detected by receptors in the skin which send impulses to the hypothalamus
- Either the heat gain centre or heat loss centre is activated
- Impulses are sent to stimulate action
- Core temperature is unaffected because blood temperature gives a prior warning
- Core temperature is measured in the blood passing through the hypothalamus
What are the common characteristics of hormones?
- Produced by hands
- Secreted into blood
- Carried in blood plasma to the target cells which have receptors complimentary to the hormone
- Effective in small quantities and have widespread and long lasting effects
How do hormones function?
- Using the second messenger model
- The hormone adrenaline approaches receptor site and fuses t it, activating an enzyme inside the membrane
- The enzyme converts ATP into cyclic AMP which acts as a second messenger than activates other enzymes that turn glycogen to glucose
What is the difference between alpha cells and beta cells?
- Alpha cells are larger and produce glucagon
* Beta cells are smaller and produce insulin
What is the structure of a muscle?
Whole muscle > bundle of muscle fibres, surrounded by nerves and capillaries > single muscle fibre containing nucleus > single myofibril with sarcomere > actin and myosin
Where does blood glucose come from?
- Diet (breakdown of carbohydrates)
- Breakdown of glycogen (glycogenolysis) in liver and muscle cells
- Gluconeogenesis (production of glucose from other sources other than carbohydrates
