chapt 5

• presynaptic membrane: membrane of terminal button that lies adjacent to postsynaptic membrane and through which neurotransmitter is released.

  • sending the signal
• postsynaptic membrane: cell membrane opposite terminal button in synapse; membrane of cell that receives message.

  • gets and receives the signal
• synaptic cleft: space between presynaptic membrane and the postsynaptic membrane
• chemical synapses: the way that it communicates with each other is using chemicals called neurotransmitters
• eletrical synapses: do not use chemical or neurotransmitters to communicate between neurons, they use electrical signals
• two types of synapses: eletrical and chemical
• eletrical synapses:

  • symmetrical (in their pre and post synapses)
  • bidirectional transfer of information, can be unidirectional (info able to go in any direction forwards and backwards)
  • the pre and post cell membranes are close apposiiton to each other separated only by regions of cytoplasmic continuity, called gap junctions
  • ions can flow through the gap junctions, allowing fast transfer of info. Firing one neuron after the other.
• electrical synapses: synchronization of the electrical activity of large populations of neurons.

  • important in functions that requires instantaneous responses, such as reflexes and pacemakers.

  a network of cells using electrical synapses means that a lot of them can fire at a rapid succession, allowing for synchronisation leading to instantaneous reflexes.
• chemical synapses:

  • asymmetric morphology in the pre and postsynaptic (pre and postsynaptic is not the same size/shape)
  • enlarged extracellular space (bigger gap in the synaptic cleft)
  • presynaptic ending is axon terminal, post synaptic is dendrites
• chemical synapses:

  • unidirectional (one sending info, another receiving info. No going both ways)
  • postsynaptic neuron may be sustained (long lasting), reflecting a long-lasting changes in the target (receiving cell)

  most common type of synapses in the vertebrate nervous system.
• pros of chemical synapses having a wider synaptic cleft is that it is long-lasting and allows more possibility of action (excitation and inhibition firing) .

  • leading to more signals and more (sensitivity to) neurotransmitters
• neurotransmitters have to be stored in vesicles in order to be released
• neurotransmitters do not enter the cell, it goes through the receptors
• different receptors for different ions.

  neurotransmitters comes in and binds to the binding site -> the gate will open up -> the ions will flow in.

  • what kind of ions flow in would determine what kind of action it would have (ex: cl- flow in or ca+ flow in - excitatory)
• principles of neurotransmitters:

  • precursor transport -> synthesis -> storage -> release -> exocytosis -> activation -> termination
• quanta release: each vesicle contains one quanta of neurotransmitters (5000 molecules)

  • quanta is the amount of neurotransmitters
• specific channels only let in specific ions

  example: sodium channel only let in sodium ions
• few types of termination of neurons detaching from the receptors:"

  1. diffusion
  2. enzymatic degradation
  3. reuptake
  4. autoreceptors
• EPSP more likely to fire
• IPSP less likely to fire
• Excitatory postsynaptic potential (EPSP):

  • opening transmitter-gated ions channels (Na) in postsynaptic membrane
  • driving na+ into the cell
  • postsynaptic membrane will become depolarized (EPSP)
• Inhibitory postsynaptic potential (IPSP):

  • opens cl- and sometimes k+ channels
  • more cl- enters, k+ outer the cell, producing a hyperpolarization in the post-synaptic membrane
• EPSP: nearer to threshold

  IPSP: further from threshold
• EPSP and IPSP common:

  • no threshold
  • no refractory period (means can keep firing)
  • can summate (means added together)
• 2 ways to summate (add up):

  • spatial summation
  • temporal summation
• spatial summation: adding together of EPSP generated simultaneously at many different synapses on a dendrite

  • this means if they are happening around the same space, it can be added up together
• temporal summation: adding together of EPSPs generated at the same synapse if they occur in rapid succession

  • based on time, means its one after another - consecutive successive EPSP
• EPSP and IPSP can happen at the same time.

  • net stimulation: EPSP + IPSP = no net effect because + and - = nothing
• fast mode: ion channel receptors (ionotropic receptors)

  • lets ion in and out, faster acting
• modulatory mode: g-protein coupled receptors (metabotropic receptors)

  • does not have a gate, it is slower acting

  g-protein tells the cell to put in more receptors in the membrane
• 2 types of learning (classical conditioning)

  1. habituation
  2. sensitization
• neurons that fire together wire together means that neurons are firing together at the same time at the same strength, they tend to form a stronger connection together
• hibituation means that:

  • repeated exposure to the stimulus reduces the response
  • like getting used to it and not have much reaction anymore
• sensitization means that:

  • it will have the same size of response over and over again
  • this is because you do not present the stimulus as much as habitual, not too frequently
  • so the response will still be the same, because you did not do it so frequently