1 / 15

SYNAPSES AND DRUGS

Learn about synapses, neurotransmitters, and the effects of drugs on synaptic function. Explore the stages of a cholinergic synapse and the neuromuscular junction. Find out how drugs can mimic or inhibit neurotransmitter action.

earley
Télécharger la présentation

SYNAPSES AND DRUGS

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. SYNAPSES AND DRUGS

  2. What is a synapse? • A synapse is the junction between 2 neurones. • There is a very narrow gap of about 20nm between neurones called the synaptic cleft. • An action potential cannot cross the synaptic cleft, so nerve impulses are carried by chemicals called neurotransmitters.

  3. A Synapse • Pre-synaptic neurone = neurone sending impulse • Post-synaptic neurone = neurone receiving impulse

  4. Neurotransmitter • Neurotransmitter is made by the pre-synaptic neurone and is stored in synaptic vessels at the end of the axon. • The membrane of the post-synaptic neurone has chemical-gated ion channels called neuroreceptors. These have specific binding sites for neurotransmitters.

  5. Acetylcholine is a common transmitter. Synapses that have acetylcholine transmitter are called cholinergic synapses. Some neurones form more than 1 synapse. This is an electron micrograph of synapses between nerve fibres and a neurone cell body. Cholinergic Synapses

  6. What happens at a cholinergic synapse? Stage 1 • An action potential arrives at presynaptic membrane. Voltage gated calcium channels in the presynaptic membrane open, calcium ions enter the presynaptic neurone.

  7. What happens at a cholinergic synapse? Stage 2 • Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft.

  8. What happens at a cholinergic synapse? Stage 3 • Acetylcholine diffuses cross the synaptic cleft and binds to specific neuroreceptor sites in the post synaptic membrane.

  9. What happens at a cholinergic synapse? Stage 4 • Sodium channels open. Sodium ions diffuse into the postsynaptic membrane causing depolarisation, which may initiate an action potential.

  10. What happens at a cholinergic synapse? Stage 5 • Acetylcholinesterase breaks down acetylcholine. The products diffuse back into the presynaptic neurone where acetycholine is resynthesised using ATP from the mitochondria.

  11. Neuromuscular Junctions • Same stages as cholinergic synapses, but in this case the postsynaptic membrane is the muscle fibre membrane, (Sarcolemma). Depolarisation of the sarcolemma leads to contraction of muscle fibre.

  12. Drugs • Drugs which have molecules of similar shape to transmitter substances can affect protein receptors in postsynaptic membranes. • Drugs that stimulate a nervous system are called AGONISTS • Drugs that inhibit a nervous system are called ANTAGONISTS.

  13. DRUG ACTION EFFECT Mimic a neurotransmitter Switch on a synapse Stimulate the release of a neurotransmitter Switch on a synapse Open a neuroreceptor channel Switch on a synapse Block a neuroreceptor channel Switch off a synapse Inhibit the breakdown enzyme Switch on a synapse Inhibit the Na+K+ATPase pump Stop action potentials Block the Na+ or K+ channels Stop action potentials Various effects of drugs on synapses:

  14. Effect of nicotine and atropine

  15. Summary • A synapse is the point where 2 nerve cells meet. Tiny gap = synaptic cleft. • Chemical transmitter released from presynaptic neurone diffuses across synaptic cleft & fits into receptors on postsynaptic membrane. May cause postsynaptic neurone to depolarise & set up action potential. • Neuromuscular junction = motor neurone connects with muscle fibre – similar to a synapse. • Many drugs affect synapses.

More Related