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OCR Biology A - Neuronal Communication

Anatomy and Physiology22 CardsCreated about 1 month ago

This deck covers key concepts in neuronal communication, including action potentials, synaptic transmission, and factors affecting nerve impulse conduction.

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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. grad...
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 move...
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 ...
More intense the stimulus …
The more frequently the neurons fire
Synaptic cleft
Gap between pre-synaptic and post-synaptic Neuron
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OCR Biology A - Neuronal Communication
TermDefinition
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