synapse

• a synapse is a function between two neurones
• voluntary action: starts in the brain and maybe the result of external events
• a voluntary action, unlike reflex reactions, it does not happen automatically, meaning you can decide whether you want to carry out the action or not
• brain send motor impulses to the spinal cords -> these make the synapse with motor fibres, which enter spinal nerves and make connections to the set of muscles needed to produce an effective action
• one of the main functions of the brain to coordinate these actions; so that they happen in the right sequence
• all reflexes are involuntarily done and are involuntary actions
• at a synapse, a branch at the end of one fibre in close contact with the cell body or dendrite of another neurone
• an impulse from the fingertips needed to pass through atleast three neurones before reaching the brain
• the regions where neurones next are also called synapse
• when an impulse arrives at the synapse, vesicles in the cytoplasm release a tiny amount of neurotransmitter substance
• it rapidly diffuses across the gap called the synaptic cleft
• this binds with neurotransmitter receptor molecules in the membrane of the neurone on the other side of the synapse
• this then sets of an impulse in the neurone
• sometimes several impulses have to arrive at the synapse before enough transmitter substance can be released
• this causes an impulse to be fired off in the next neurone
• synapse summary:

  1. vesicles release neurotransmitter substance into the synaptic cleft
  2. the neurotransmitters travel through the gap via diffusion
  3. the neurotransmitter substance bind with receptor molecules on the dendrite
  4. a nerve impulse is triggered in this neurone
• synapse control the direction of the impulse because neurotransmitter substances are only synthesized on one side (axon terminal)
• synapse ensure that the impulse travel in on direction only
• the receptor molecules at synapse are also present only on the side of the dendrite
• they slow down the speed of nerve impulses slightly, this takes time for the chemical to diffuse across the synaptic cleft
• drugs:

  • produce effect by interacting with the receptor molecules; in the synapse of the brain
  • heroin, stimulates receptor molecules in the synapse in the brain, triggering the release of dopamine (neurotransmitter); giving ecstacy