Neuroethology: The study of brain and behavior.

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Reading assignment Konishi and Menzel 2003

• Neuroethology The study of brain and behavior.
• Take home points from this paper
• The field of neuroethology is broad in
• Questions asked addressed.
• Species used.
• Behavioral and neurophysiological methods used.
• What distinguishes Neuroethology from other
  fields in neuroscience is the emphasis on
  behavior.

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• Neurons the biological basis of
• sensory input
• Sensory/memory integration
• Learning and memory
• Higher mental processes
• Production of behavior

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Electrical properties of neurons

• Neurons are able to establish and maintain a
  differential electrical charge across their
  membrane (capacitance)
• That differential charge is capacitance
  Potential energy, or force, that drives ions to
  move volts (V)
• Like pressure in a fire hose.
• Based on distribution of (cations) and
  (anions)
• When the charge moves across the membrane, its
  rate of movement is its current (I)
• Water out of the hose.
• The flow of current is mediated by the overall
  permeability of the membrane (resistance R )
• The hose nozzle
• The rate of flow (conductance g) is inversely
  related to membrane resistance
• Ohms law
• Voltagecurrent x resistance (VIxR) OR
  currentconductance x voltage (IgxV)
• Thus the current across a neurons membrane can be
  described as the amount of electrical pressure
  times the permeability of the membrane

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• The differential charge is established by
• Electrical gradients (the force that drives and
  charges together)
• Concentration gradients (a process by which atoms
  randomly distribute)
• Active ion pumps which use ATP to move (for
  example) 3 Na out for 2 K in

At rest there are 110 Na 201 K
insideoutside
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• Currents flow through channels
• Channels are proteins that can
• Selectively or non selectively allow ions to pass
  in or out of the cell.
• be active
• Ligand gated
• Electrically gated
• or passive (leak channels)

Normally cell membranes intentionally but
passively leak a small amount of current
The resting state of a cell
Neurons typically maintain a resting potential of
-60 to -70mv
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• The action potential an electrical pulse that
  travels the length of the axon
• Follow the links below for interactive animations
  of ion currents that occur during an action
  potential

http//www.psych.ualberta.ca/ITL/ap/ap.swf
http//www.blackwellpublishing.com/matthews/channe
l.html
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• The synapse Where the impulse is passed from one
  cell to another
• Two basic kinds of synapses
• Electrical (gap junctions)
• Very fast
• Excitatory
• Does not require neurotransmiters
• Chemical
• Requires a neruotransmitter of some sort
• Fast (but slower than electrical)
• Can excite or inhibit
• Can modulate the permeability of a post synaptic
  element for an extended period of time

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• Types of synapses
• Axo-dendritic
• Dendro-dendritic
• Dendro-axonic
• Axo-axonic
• Dendro-somatic
• Axo-somatic

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• The synaptic process Key events of a chemical
  synapse
• Action potential reaches the axon terminal where
  the presynaptic element resides.
• Causes the opening of CA channels.
• Ca forces the movement of microtubules onto
  synaptic vesicles pressing them to the
  presynaptic element.
• Vesicles bind to specific sites on the
  presynaptic element and open, spilling their
  contents (a neurotransmitter) into the synaptic
  cleft
• Neurotransmitters (the ligand) bind to receptors
  at specific binding sites on the post synaptic
  cell membrane causing either
• Deformation of the receptor protein which opens a
  ion channel
• Deformation of the receptor protein which
  activates a second messenger (G-protein coupled
  receptors).
• Ultimately both mechanisms can either cause
• depolarization of the post synaptic element
  (EPSP)
• hyperpolarizing of the post synaptic element
  (IPSP)

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Typical excitatory vs inhibitory synaptic events
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Synapses There not that simple
The take home message here is that a synapse is
like a tiny computational compartment!
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G-protein coupled receptors
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The neuromuscular junction synapse from neuron
to muscle
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Synapses change synaptic plasticity

• Plasticity occurs for a number of reasons
• Development aging
• Experience (learning, exhaustion)
• The net result of plastic nervous systems is that
  they can adapt!

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Electrophysiology Direct method(s) for
monitoring neurons

• Intracellular (glass electrode)
• Patch electrode
• Sharp electrode
• Extracellular (wires/metals)
• Hook electrodes
• Beveled wire
• Silicon electrodes

• Examples of Indirect methods
• FMRI
• CT
• Optical immaging
• Calcium immaging