6B - Nervous Coordination Flashcards
How is resting potential is created and maintained in a neurone’s membrane?
- sodium-potassium pumps move sodium ions out of neurone, membrane isn’t permeable to sodium, so they can’t diffuse back in
- pumps also move potassium ions in to neurone, membrane is permeable to K ions, so they diffuse back out through K ion channels
- makes outside of cell positively charged compared to inside
What happens when a stimulus is detected in neurone cell membranes?
- cell membrane excited
- sodium ion channels open
- membrane is more permeable to sodium, so sodium diffuse into neurone down gradient
- inside of neurone is less negative
What happens during depolarisation?
- if potential difference reaches threshold, more sodium ion channels open
- more sodium ions diffuse rapidly into neurone
What happens during repolarisation?
- sodium ion channels close and potassium ion channels open
membrane is more permeable to potassium so ions diffuse out of neurone down gradient - membrane starts going back to resting gradient
What happens during hyperpolarisation?
- potassium ion channels are slow to close, too many K ions diffuse out of neurone
- potential difference becomes more negative than resting potential
What is meant by the refractory period?
- ion channels are recovering and they can’t be made to open (sodium channels close during repolarisation and potassium channels close during hyperpolarisation)
What is meant by the ‘all or nothing’ nature?
- once threshold is reached, an action potential will always fire with same change in voltage
- if threshold isn’t reached, action potential won’t fire
- a bigger stimulus won’t cause a bigger action potential, makes them more frequent instead
What is meant by saltatory conduction?
- in a myelinated neurone, depolarisation only happens at nodes of Ranvier
- neurone’s cytoplasm conducts enough charge to depolarise the next node
impulse ‘jumps’ from node to node
How does an impulse travel along a non-myelinated neurone?
- impulse travels as a wave along the whole length of axon membrane
- slower than saltatory conduction
How does axon diameter affect speed of conduction of action potentials?
- action potentials are quicker along axons with bigger diameters, less resistance to flow of ions
- less resistance = depolarisation reaches other parts of neurone quicker
How does temperature affected speed of conduction of action potentials?
- temperature increase = conduction increases
- ions diffuse faster
What is the structure of myosin filaments?
- have hinged globular heads, move back and forth
- has binding sites for actin and ATP
What is the structure of actin filaments?
- binding sites for myosin heads
- contains tropomyosin, helps myofilaments move past each other
What happens when tropomyosin blocks the actin-myosin binding site?
- myofilaments can’t slide past each other because myosin heads can’t bind to actin
What happens when an action potential stimulates a muscle cell in muscle contraction?
- depolarises the sarcolemma
- depolarisation spreads to sarcoplasmic reticulum
- SR releases stored stored calcium ions into sarcoplasm
- causes reticulum to release stored calcium ions into sarcoplasm
What happens when calcium ions bind to the protein attached to tropomyosin?
- causes protein to change shape
- pulls tropomyosin out of actin myosin binding site
- active site is exposed, myosin head binds
What is the bond formed when a myosin head binds to an actin filament?
- actin-myosin cross bridge
What enzyme is activated by calcium ions?
- ATP hydrolase
What does ATP hydrolase do?
- hydrolyses ATP into ADP and Pi to provide energy needed for muscle contraction
What does the energy released from ATP cause the myosin head to do?
- causes it to bend
- pulls actin filament along in a rowing-type action
What does another ATP molecule provide energy to break and what happens as a result?
- actin-myosin cross bridge
- myosin head detaches from actin filament after its moved
What happens after myosin head detaches from actin filament?
- myosin head reattaches to different binding site further along actin filament
- new cross bridge is formed and cycle is repeated
How do the cross bridges cause the muscle to contract?
- many cross bridges form and break very rapidly, pulling actin filament along
- shortens the sarcomere, causing muscle contraction
What happens when the muscle stops being stimulated?
- calcium ions leave binding sites and are moved by active transport back to sarcoplasmic reticulum
What does this cause tropomyosin molecules to do?
- move back , so they block actin-myosin binding sites again
What happens to the actin filaments when no myosin heads are attached to them?
- slide back into their relaxed position, lengthens sarcomere
In which 3 ways are ATP and phosphocreatine continually generated?
- aerobic respiration
- anaerobic respiration
- ATP-phosphocreatine (PCr) system
How is ATP generated through aerobic respiration?
- via oxidative phosphorylation in mitochondria
What type of exercise is aerobic respiration good for?
- long periods of low-intensity exercise
How is ATP generated through anaerobic respiration?
- rapidly by glycolysis
- makes pyruvate, converted to lactate by lactate fermentation
- lactate can build up in muscles and cause muscle fatigue
What type of exercise is anaerobic respiration good for?
- short periods of hard exercise e.g sprints
How does the PCr system generate ATP?
- By phosphorylating ADP, adding phosphate group taken from PCr
- generates ATP very quickly
What type of exercise is PCr system good for?
- short bursts of vigorous exercise e.g tennis serve
What do you use slow twitch and fast twitch muscles fibres for?
- slow twitch - posture (lots in the back)
- fast twitch - fast movement (lots in eyes and legs)
What are slow twitch and fast switch muscle fibres good for in terms of exercise?
- slow twitch - endurance activities
- fast twitch - short bursts of speed and power
How fast do slow twitch and fast twitch muscle fibres get tired?
- slow twitch - long time
- fast twitch - very quickly
How fast and how is energy released from slow twitch and fast twitch fibres?
- slow twitch - slowly through aerobic respiration, lots of mitochondria and blood vessels supply muscles w/O2
- fast twitch - quickly through anaerobic respiration using glycogen, few mitochondria or blood vessels
What colour are slow twitch and fast twitch muscle fibres?
- slow twitch - reddish, rich in myoglobin
- fast twitch - whitish, don’t have much myoglobin
