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NEURONAL COMMUNICATION
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- 1RESTING POTENTIAL DEFINITIONWhen a neurone is not transmitting an impulse. Outside more positively charged than inside. It is said to be POLARISED -70mV
- 2CREATION OF A RESTING POTENTIAL3 sodium ions pumped OUT, 2 potassium ions pumped IN. More sodium outside so they diffuse back in & potassium ions diffuse out. BUT, most sodium ion channels are closed, preventing movement of sodium ions. SO, more positively charged ions outside.
- 3ACTION POTENTIAL DEFINITIONThe change in the potential difference across the neurone membrane of the axon when stimulated- making it DEPOLARISED +40mV
- 4PROCESSES OF AN ACTION POTENTIALEnergy of stimulus causes some sodium VGICs to open, sodium ions diffuse IN. Inside less negative, so more sodium VGICs open (positive feedback). When potential difference reaches +40mV, sodium VGICs close and potassiums open. Potassium ions diffuse OUT, reducing the charge.
- 5PROCESS OF AN ACTION POTENTIAL .2The inside of the axon is now more negative than the outside. Initially, lots of potassium diffuse out, inside becomes more negative than resting state (hyperpolarisation). Potassium channels close and pump helps return to resting state (repolarisation)
- 6PROPAGATION OF ACTION POTENTIALSAn action potential causes sodium channels to open causing Na ions to diffuse IN. The concentration of Na increases causing them to diffuse sideways down concentration gradient (local current) This increases voltage causing sodium VGICs to open so action potential moves down neurone
- 7SALTATORY CONDUCTIONIn myelinated axons, depolarisation can only occur at nodes of Ranvier where no myelin is present. SO, longer localised circuits arise between nodes so action potential jumps from one node to another.
- 8FACTORS AFFECTING SPEED OF TRANSMISSIONAxon diameter- bigger the axon, faster the impulse as there is less resistance to flow of ions in the cytoplasm
Temperature- higher temperature, faster the impulse up to a certain point - 9THE ALL OR NOTHING PRINCIPLEA certain level of stimulus, the threshold value, always triggers a response. If threshold is reached, same size action potential will always be triggered. Intensity can be determined by frequency of action potentials
- 10TYPES OF NEUROTRANSMITTERExciatory- result in the depolarisation of the postsynaptic neurone
Inhibitory- result in hyperpolarisation of postsynaptic neurone. Prevents an action potential from being triggered - 11TRANSMISSION ACROSS SYNAPSESAction potential reaches end of presynaptic neurone. Depolarisation causes calcium ion channels to open so Ca diffuses in. Vesicles containing neurotransmitters fuse with presynaptic membrane, and neurotransmitters are released by exocytosis. They diffuse across the synaptic cleft and bind with receptor molecule, causing sodium ion channels to open, sodium ions to diffuse in and an action potential to be propagated
- 12ROLE OF SYNAPSESEnsure impulses are unidirectional- receptors only present on postsynaptic membrane.
Allow an impulse from one neurone to be transmitted to multiple neurones or visa versa - 13SUMMATIONSpatial- when a number of presynaptic neurones connect to one postsynaptic neurone - build up of neurotransmitter
Temporal- when a single presynaptic neurone releases neurotransmitters as a result of an action potential several times over a short period
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- A level Biology Fichas sobre NEURONAL COMMUNICATION, creado por liv harvey el 10/06/2017.
- Creado por
- liv harvey · jun 2017
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- 11 jun 2017
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