Transmission Across a Synapse

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Transmission Across a Synapse

• How a Nerve Impulse Travels

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(No Transcript)
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Transmission Across a Synapse

• Communication between two neurons is carried out
  by neurotransmitters at the synapse.
• Synapse
• the site where chemical signals pass between
  neurons

Stimulus
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Transmission Across a Synapse

• The neuron converts the electrical signal to a
  chemical signal in order to pass the information
  to another neuron. The target neuron then
  converts the message back to an electrical
  impulse to continue the process.

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What happens at the synapse?

• The neuron that sends out information is called
  the presynaptic neuron
• The neuron that receives the information is
  called the postsynaptic neuron.

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Transmission Across a Synapse

• After stimulation
• the electrical signal (action potential -
  depolarization) travels down the axon to the axon
  terminals
• Calcium gates openCa2 flow into neuron
• increased Ca2 in the axon terminal initiates
  fusing of vesicles w/ the presynatic membrane

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Release of Neurotransmitter
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Whats a neurotransmitter?

• molecule that is released from neuron to relay
  information to another neuron
• Many different kinds
• 2 types
• Excitatory causes action potential to happen
• Inhibitory stops action potential from happening
• stored in membranous sacs called vesicles in the
  axon terminal
• Released via exocytosis

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Release of Neurotransmitters

• After the increased of Ca2
• Neurotransmitters are released into the synpatic
  cleft and diffused across the gap to the
  postsynaptic neuron
• A neurotransmitter molecule can bind to a special
  receptor on the postsynaptic membrane
• Receptors are membrane proteins that are able to
  bind a specific chemical substance, such as a
  neurotransmitter.

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Two Outcomes

• Excitation
• Na diffuse into postsynaptic neuron
• trigger an action potential, the communication
  process continues
• Inhibition
• block the changes that cause an action potential

Na
Na
Na
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Breaking down neurotransmitters

• Ca2 are actively transported back to the
  synpatic gap
• After binding to the receptor
• comes off (is released from) the receptor and
  diffuses back into the synaptic space
• degraded by enzymes in the synaptic cleft
• or taken back up into the presynaptic axon
  terminal by active transport through a
  transporter

Same for anyunused neurotransmitters
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Some important neurotransmitters

• Norepinephrine
• In the PNS, it is part of the fight-or-flight
  response.
• In the CNS (brain), regulates normal brain
  processes
• Usually excitatory, some times inhibitory
• Acetylcholine Ach
• In the CNS (spinal cord), controls muscles
• In the CNS (brain), regulates memory.
• Usually excitatory.
• Acetylcholinesterase (AChE)
• Enzyme that breaks down acetylcholine at the
  synaptic cleft so the next nerve impulse can be
  transmitted across the synaptic gap

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• http//science.education.nih.gov/supplements/nih2/
  Addiction/activities/lesson2_neurotransmission.htm
  
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