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
