2.3 2007PSY

• Synaptic transmission

  The relaying of information across the synapse by means of chemical neurotransmitters.
• Postsynaptic Potential


  Alterations in the membrane potential of a postsynaptic neuron, produced by liberation of neurotransmitter at the synapse
• Effects postsynaptic potentials can have on the neuron

  -Hyperpolarization

  -Depolerization
• How do neurotransmitters cause PSPs

  Neurotransmitters attach themselves to a binding site (eg. like a lock and key)
• Ligand


  A molecule that binds specifically to a binding site of another molecule.
• Places synapes can occur

  -Smooth surface of a dendrite

  -Dendritic spine

  -Between two terminal buttons
• What happens in the synaptic vesicles with an action potential

  They fuse with the membrane and break open, spilling their contents into the synapse
• Postsynaptic receptor


  A special protein molecule in the postsynaptic membrane of a synapse that contains a binding site for a neurotransmitter
• Binding site


  The location on the postsynaptic receptor that the neurotransmitter (or another ligand, like a drug) binds to
• After binding, postsynaptic receptor open

  Neurotransmitter dependent ion channels (as opposed to voltage dependent ion channels).
• voltage dependant ion channel


  An ion channel that opens or closes according to the value of the membrane potential
• Neurotransmitter dependent ion channel


  An ion channel that opens when a molecule of a neurotransmitter binds with a postsynaptic receptor
• Two types of Neurotransmitter dependent ion channel


  -Ionotropic

  -Metabotropic
• Ionotropic receptors (Direct)


  -When a neurotransmitter attaches to the binding site the ion channel opens

  -Changes are faster and last shorter
• Metabotropic Receptor (indirect)


  -When a neurotransmitter attaches to the binding site it activates a G protein, which activates an enzyme to produce a second messenger, opening an ion channel elsewhere in the membrane of the cell

  -Changes are slower and last longer
• G protein


  -Activated when neurotrasmitter binds to a metabotropic receptor

  -Activates an enzyme to simulate the production of a second messenger
• Second messenger can


  -Open and close ion channels

  -Turn on and off genes, thus terminating or initiating the production of proteins
• The nature of the PSP is determined by

  the characteristics of the postsynaptic receptors (i.e. the type of neurotransmitter dependent ion channels that are opened)
• Four types of neurotransmitter-dependent ion channels

  Sodium (Na+)

  Potassium (K+)

  Chloride (Cl-)

  Calcium (Ca2+)
• When k+ channels open

  Exits the cell, hyperpolarizing, and producing Inhibitory Postsynaptic Potentials (IPSP)
• When the NA+ ion channels open

  Enters the cell, depolarizing, producing Excitatory Postsynaptic Potentials (EPSP)
• When the Cl- ion channels open


  If opens at rest, nothing happens. The influx in the cell causes hyperpolerization
• When the Ca2+ ion channels open


  Has two effects, influx activates enzymes and creates EPSPs
• Two mechanisms end PSPs

  -Reuptake

  -Enzymatic Deactivation
• Reuptake


  A neurotransmitter's reabsorption by the presynaptic neuron
• Enzymatic deactivation

  The destruction of a neurotransmitter by an enzyme after its release - for example, the destruction of acetylcholine by acetylcholinesterase
• Neural Integration


  Process by which the inhibitory and excitatory potentials summate and control the firing rate of a neuron
• Function of autoreceptors

  -Involved in synthesis (the creation and release) of neurotransmitters

  -When a neurotransmitter binds to it and stops the synthesis of neurotransmitters
• Axoaxonic Synapses


  -Synapses between the axons of two neurons

  -it affects the probability of neurotransmitter release in the response to any action potential passing through the axon of the postsynaptic neuron

  
• Neuromodulators


  -A naturally secreted substance that acts like a neurotransmitter

  -They are not restricted to the synaptic cleft. Instead, they can diffuse through the extracellular fluid.

  -most are peptides

  -modulate the activity of neurons in particular parts of the brain
• Peptides


  Chains of amino acids (building blocks of proteins).
• Hormones


  -Chemical substances released by endocrine glands or other cells located in organs such as the stomach, brain, and kidneys.

  -Cells that release these release them into the extracellular fluid.
• target cells

  cells that have receptors for a particular hormone
• order for neuronal communication


  >neurotransmitter release

  >receptor binding

  >ion channels open or close

  >ions move in and out of the cell

  >postsynaptic cell potential changes

  >neural integration occurs to determine if there is an action potential