Back to AI Flashcard MakerBiology /LGS A-Level OCR Biology - Unit 5 - Neuronal Communication Part 3
LGS A-Level OCR Biology - Unit 5 - Neuronal Communication Part 3
This flashcard deck covers key concepts from Unit 5 of the OCR Biology A-Level syllabus, focusing on neuronal communication, including action potentials, synapses, and factors affecting nerve transmission.
Threshold potential
The critical level to which a membrane potential must be depolarised to initiate an action potential
-50 mV
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Key Terms
Term
Definition
Threshold potential
The critical level to which a membrane potential must be depolarised to initiate an action potential
-50 mV
Describe and explain how a resting potential is maintained
Na/K ion pump - 3 Na ions out and 2 K into axon; VG Na+ channels are closed to stop Na diffusing in; Some K ion channels are leaky. Effect of conc. gr...
Describe what is happening at the cell membrane during an action potential
Resting membrane potential; Detection of stimuli - causes VG Na^+ to open. Begins to get depolarised; +ve feedback - More VG Na^+ channels open and mo...
Saltory conduction
Propagation of action potential along myelinated axons from one node to another; Done by creating longer local currents; Uninsulated nodes are the onl...
More intense the stimulus …
The more frequently the neurons fire
Synaptic cleft
Gap between pre-synaptic and post-synaptic Neuron
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| Term | Definition |
|---|---|
Threshold potential | The critical level to which a membrane potential must be depolarised to initiate an action potential
-50 mV |
Describe and explain how a resting potential is maintained | Na/K ion pump - 3 Na ions out and 2 K into axon; VG Na+ channels are closed to stop Na diffusing in; Some K ion channels are leaky. Effect of conc. gradient is greater than the electrochemical gradient so diffuse out into extracellular fluid; Cell cytoplasm contain large organic anions (proteins); Results in polarised cell membrane (+ve out/ -ve in) |
Describe what is happening at the cell membrane during an action potential | Resting membrane potential; Detection of stimuli - causes VG Na^+ to open. Begins to get depolarised; +ve feedback - More VG Na^+ channels open and moves in; When potential reaches +40mV VG Na^+ close and VG K^+ open - eflux of K+ causes repolarisation; K+ diffuse back out of the cell; Too -ve, hyperpolarisation; Resting membrane restored by Na/K pump |
Saltory conduction | Propagation of action potential along myelinated axons from one node to another; Done by creating longer local currents; Uninsulated nodes are the only place ions are exchanged across axon membrane |
More intense the stimulus … | The more frequently the neurons fire |
Synaptic cleft | Gap between pre-synaptic and post-synaptic Neuron |
Adaptations of post synaptic neuron | Contains specialised proteins in its membrane that act as acetylcholine receptor sites
They form Na^+ channels, which open in response to acetylcholine (generates action potential) |
Transmission across the synapse | Action potential arrives at presynaptic neuron and calcium ions open, so Ca^+ diffuse into knob; Vesicles move towards membrane and fuse to release acetylcholine into the cleft (exocytosis); Diffuse across cleft and bind to receptors; Na^+ channels on post open and diffuses into post neurone; Membrane is depolarised;
Acetylcholinesterase breaks down acetylcholine; Na^+ channels close and the choline is recycled back into the presynaptic knob |
Role of synapses in the nervous system | Ensures that action potentials travel in one direction; only receptor on post; Filters out low intensity stimulus; many vesicles must be released to cause a post synaptic action potential; Continuous, unimportant stimulus can be ignored; vesicles run out (fatigue) —> acclimatisation; Summation - amplify many low level stimulus |
Are relay neurons myelinated | No |
Which neuron has dendrons | Sensory - one long one |
Do motor neurons end at synaptic knobs as well | No, motor end plate |
Why are mitochondria needed for transmission of impulses across the cleft | Mitochondria in the pre-synaptic bulb is needed for: Energy to move vesicles; Exocytosis; Na+/K+ pump to maintain resting potential; Vesicle formation; Active transport of Ca2+ |
Propagation of action potentials | Once membrane is depolarised Na+ inside membrane attracted to -ve charge ahead and conc gradient causes it to diffuse further into axon, triggering depolarisaton |
Why is saltatory conduction more efficient | Repolarisation requires ATP and less repolarisation is necessary |
Factors affecting speed of conduction | Axon diameter | Temperature |
How does axon diameter affect speed of conduction | Bigger the axon diameter faster the transmission | Less resistance to flow in cytoplasm |
How does temperature affect speed of conduction | Higher the temp, faster the transmission | Ions diffuse faster at higher temp but only up to 40 degrees as proteins get denatured |
Inhibitory synapses | Release transmitters that lead to hyperpolarisation of the postsynaptic membrane so there's no ap |
What is acetylcholine hydrolysed into | Choline and ethanoic acid |
Spatial summation | Several presynaptic neurones connectto postsynaptic neurones | Each releases a transmitter so the conc increases in the synapse |
Temporal summation | Single presynaptic neurone releases transmitter due to several ap in a short time |