1 / 16

Communication via Synapses

Communication via Synapses Synapses are a fundamental part of neural pathways as they regulate decision-making in terms of exciting or inhibiting the post-synaptic neurons. Review: Action potentials (AP) reach terminal bud of the pre-synaptic neuron.

cassia
Download Presentation

Communication via Synapses

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Communication via Synapses • Synapses are a fundamental part of neural pathways as they regulate decision-making in terms of exciting or inhibiting the post-synaptic neurons. • Review: • Action potentials (AP) reach terminal bud of the pre-synaptic neuron. • Neurotransmitters (NT), chemical messengers, diffuse across the synapse to bind with receptors on the post-synaptic membrane. • Neurotransmitters are: • Excitatory, which means they excite the post-synaptic neuron (contributing to depolarisation and propagation of the AP. • OR: • Inhibitory, hyperpolarising the post-synaptic neuron and preventing AP.

  2. Neurotransmitters can be excitatory or inhibitory • Neurotransmitters (NT) are proteins • diffuse across the synaptic cleft • bind with a receptor on the post-synaptic neuron. • Whether or not the post-synaptic neuron propagates the action potential depends on: • Which NT diffuses across • Which receptors they bind to • Which ions flow in/out of the post-synaptic neuron • Whether or not depolarisation reaches threshold • Excitatory NTs cause depolarisation • e.g. ACh, dopamine • NT binds, Na+ channels open, Na+ rushes in • Membrane potential depolarises, AP propagated • Inhibitory NTs cause hyperpolarisation • e.g. GABA, dopamine (on different pathways) • NT binds to receptor • K+ channels open, K+ rushes out • OR Cl- channels open, Cl- rushes in • Membrane potential become more negative • Action potential is prevented from propagating 0mv depolarisation threshold resting -70mv hyperpolarisation time

  3. http://www.youtube.com/watch?v=-pfG6yHAQ5U This is a useful example of an inhibitory neurotransmitter.

  4. Decision-making in the Central Nervous System (CNS) The axons of many pre-synaptic neurons feed into the dendrites of one post-synaptic neurons via synapses. The ‘decision’ whether or not to propagate the action potential along the axon of the post-synaptic neuron takes place in a region of the cell body called the axon hillock. This is achieved through summation of the incoming impulses. If the total impulse reaches threshold, the post-synaptic neuron depolarisesand the action potential is propagated. If the sum does not reach threshold, the AP is not propagated. There are two main methods of summation: temporal and spatial. action potential axon synapse axon hillock

  5. Decision-making in the Central Nervous System (CNS) • Temporal summation • Action potentials arrive in rapid succession • Depolarisation in the axon hillock is summative • If it reaches threshold before repolarisation, the AP is propagated. • Spatial summation • Action potentials arrive simultaneously from multiple sources • Some neurotransmitters are excitatory (increasing depolarisation) • Other NTs are inhibitory (hyperpolarising). • Summation in the axon hillock is summative. • If it reaches threshold the AP is propagated.

  6. How do psychoactive drugs affect the brain? • Before thinking about how drugs affect the synapses, be sure you understand how they work and are reset. • Some NTs have a normal excitatory function • Other NTs have a normal inhibitory function • In general, psychoactive drugs can: • Increase or decrease the release of NTs (e.g. THC – cannabis) • Breakdown re-uptake proteins which are responsible for returned used components of NTs to the pre-synaptic neuron (ready to use again) • Block re-uptake proteins (e.g.cocaine) • Mimic or block NTs, binding to the receptors on post-synaptic membranes • Inhibit production of new NTs

  7. Excitatory drugs increase post-synaptic transmission • Examples: • Nicotine, amphetamines, cocaine • What is the effect of cocaine? • Normal: • Dopamine acts as excitatory NT • Dopamine is re-uptaken by pumps on the pre-synaptic membrane. • With Cocaine: • Cocaine blocks re-uptake pumps • Dopamine remains in synaptic cleft • More dopamine continues to be released • Summative increase in post-synaptic transmission • Effects on mood: • Dopamine is involved in reward pathways, enhancing feelings of pleasure • Longer-lasting feelings as dopamine is not re-uptaken • Effects on behaviour: • feelings of euphoria • increased energy and alertness • highly addictive • association with depression as body reduces production of own dopamine over time

  8. Inhibitory drugs decrease post-synaptic transmission • Examples: • Alcohol, benzodiazapines, THC • What is the effect of tetrahydrocannibol (THC)? • Normal: • Dopamine release is moderated (inhibited) by GABA • With THC: • THC mimics cannabinoids and inhibits GABA release by binding to cannabinoid receptors • GABA cannot inhibit dopamine release • More dopamine is released • Effects on mood: • Dopamine is involved in reward pathways, enhancing feelings of pleasure • Not as extreme release of dopamine as with cocaine, but still higher than normal • Effects on behaviour: • intoxication • hunger • memory impairment • potential dependency

  9. http://www.youtube.com/watch?v=bCChf2WHNE4

More Related