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Neurons and AP
Neurons and Action Potentials
| Question | Answer |
|---|---|
| What are the three types of Neuron? | Sensory (Pick up stimuli from receptor cells/Sense organs), Inter/Relay Neurons (present in the CNS to transfer the impulse from a Sensory to a Motor), Motor Neurons (Transmit impulses from Relay nuerons to effector cells such as Muscles). |
| Give the Major physiological components of a Neuron (Mammals): | Dendrites (carry impulses to Cell Body), Cell Body (with nucleus), Axon, Schwaan Cells (Myelin Sheath), Axon Terminal (Synapses), Nodes of Ranviar. |
| Neuron Cell Body: | This collects all the action potentials from surrounding dendrites and if the combined effect is great enough, the action potential will be propagated along the axon. |
| What are the stages of an action potential (Starting with the resting state of the neuron). | Resting Potential (Polarised), Depolarisation, Repolarisation, Hyperpolarisation and back to resting. |
| How is a neuron membrane kept polarised: | Na/K pump constantly uses ATP to actively move Na+ ions out of the cell and K+ into the cell (in a ratio of 3:2, respectively), along with facilitated diffusion of K+ ions out of the cell again, this keeps the inside of the cell relatively negative. |
| Resting Potential: | This is the potential difference between the outside and the inside of a neuron at rest, it is typically -70mV and is maintained by the action of more Na+ ions than K+ ions outside and inside. |
| Describe what happens during Depolarisation: | A stimuli causes enough sodium channels to open and the Na+ ions diffuse along their concentration and electrochemical gradients into the cell, the inside is now more positive than the outside. 40mV is now the Potential differences. |
| What happens during Repolarisation. | At 40mV, Sodium channels close and K+ channels open, allowing for K to diffuse along their concentration and electrochemical gradients. This begins to restore the resting potential with Na+ inside and K+ outside. |
| Hyperpolarisation: | The K+ channels are slow to close and much more K+ ions than required diffuse out of the cell, this causes an 'Overshoot' and the potential difference drops below the normal resting potential. |
| How is the Resting Potential restored after hyperpolarisation: | The K+ channels and Na+ channels are both closed and the Na/K pump begins to move Na+ outside and K+ inside once again, restoring the -70mV resting potential. |
| What are the two refractory periods: | Absolute refractory period and Relative Refractory period. |
| Absolute refractory period: | This is directly after the Na+ channels are opened and it is completely impossible for another action potential to be propagated, as the Na+ channels are already open and the majority of Na+ ions are inside the cell. |
| Relative Refractory Period: | This is after the hyperpolarisation and the Na/K pump is functioning, as more and more Na+ ions are pumped out, it is possible for the Na Channels to open again, although the threshold is high, it reduces over time as more Na move out. |
| What are two factors that determine the speed of conduction along a neuron: | Diameter of a Neuron and the Presence of a Myelin Sheath (Schwaan Cells). |
| How does the presence of a Myelin Sheath increase the speed of conduction: | By Saltatory conduction. An action potential jumps between the small exposed areas on a neuron, called Nodes of Ranviar. This means that the potential will only occur here and jump, rather than moving along the entire length. |
| What important functions does the refractory period serve: | It can determine the how intensily the organism will feel a stimulus, i.e. an extreme stimuli will be able to cause APs more frequently by overcoming the relative refractory period. Also, it prevents backwards conduction. |
| What is the All or Nothing Principle: | This is the theory that all action potentials are of the same strength (40mV), and that a certain threshold has to be bypassed before an action potential will occur (passed -55mV). This is because enough Na Channels have to be open before an AP can occur. |
| What determines how intense a stimuli is felt: | The frequency of AP along the neuron. |
| What is Summation: | This is when multiple APs or Neurotransmitters from more than one presynaptic membrane have their effects added together to cause an action potential along the Axon / Postsynaptic Dendrite. |
| What is the name given to the junction between an Axon and a Dendrite: | A Synapse. |
| Name the major sections of a synapse: | Presynaptic membrane, postsynaptic membrane, synaptic cleft, Vesicles (with NT), Receptors, Sodium Channels. |
| Describe the events at the Presynaptic membrane (Axon Terminal) as an action potential arrives at a Synapse. | Depolarisation occurs and Ca2+ channels open, Ca2+ ions diffuse in, then bind to vesicles containing Neurotransmitters, activating them, they bind to PreSyn Membrane release Neurotransmitters by Exocytosis into Synaptic Cleft. |
| Describe the events at the postsynaptic Knob after Neurotransmitters are released into the Synaptic Cleft. | The neurotransmitters bind with receptor proteins on the postsynaptic membrane, causing ion channels to open (Na+ etc), this causes Na+ to diffuse in, if enough ions diffuse in an action potential will be generated. |
| Describe what happens to neurotransmitters in the synaptic cleft: | They bind with receptors and are then hydrolysed by enzymes, broken down and diffuse back into the presynaptic membrane to be remade into Neurotransmitters. |
| Summation (Neurochemical context): | This is when multiple synapses from Axons meet at one Synaptic cleft to one single PostSynaptic neuron and they are all releasing neurotransmitters to cause the postsynaptic neuron to fire an action potential. |
| Accommodation: | This is when there have been so many action potentials along a presynaptic neuron that there are no more neurotransmitters left to transmit. This protects the effectors from overstimulation (such as muscle tetanus) |
| Facilitation: | This is when an action potential is generated on the postsynaptic membrane by the build up of channels opening from many neurotransmitters being released from many action potentials from one presynaptic neuron. |
| Give a benefit of chemical transmission: | It can help to filter out low level stimuli, as while all action potentials are the same and require the same depolarisation to occur, different synapses require different levels of neurotransmitter to open enough Na+ channels. |
| Give another benefit of chemical transmission: | Integration of signals, some are inhibitory and some are excitatory, the addition and overall effect will only be either inhibition or excitation. |
Created by:
mjwilson1988
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