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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.
Neurons: the biological basis of
1. sensory input
2. Sensory/memory integration
3. Learning and memory
4. “Higher mental processes”
5. Production of behavior
Electrical properties of neurons
1. Neurons are able to establish and maintain a differential electrical charge
across their membrane: (capacitance)
2. 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)
3. When the charge moves across the membrane, its rate of movement is its
current (I)
• Water out of the hose.
4. The flow of current is mediated by the overall permeability of the membrane
(resistance; R )
• The hose nozzle
5. The rate of flow (conductance; g) is inversely related to membrane resistance
Ohms law:
Voltage=current x resistance (V=IxR) OR current=conductance x voltage (I=gxV)
Thus the current across a neurons membrane can be described as the amount
of “electrical pressure times the permeability of the membrane”
The differential charge is established by:
1. Electrical gradients (the force that drives + and – charges together)
2. Concentration gradients (a process by which atoms randomly distribute)
3. Active ion pumps which use ATP to move (for example) 3 Na+ out for 2 K+ in
At rest there are 1:10 Na+ & 20:1 K+ inside:outside
Currents flow through channels
Channels are proteins that can:
1. Selectively or non selectively allow ions to pass in or out of the cell.
2. be active:
• Ligand gated
• Electrically gated
Normally cell membranes
3. or passive (leak channels)
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
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/channel.html
The synapse: Where the impulse is passed from one cell to another
Two basic kinds of synapses:
1. Electrical (gap junctions)
• Very fast
• Excitatory
• Does not require neurotransmiters
2. 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
Types of synapses
1. Axo-dendritic
2. Dendro-dendritic
3. Dendro-axonic
4. Axo-axonic
5. Dendro-somatic
6. Axo-somatic
The synaptic process: Key events of a chemical synapse
1. Action potential reaches the axon terminal where the presynaptic element
resides.
2. Causes the opening of CA+ channels.
3. Ca+ forces the movement of microtubules onto synaptic vesicles pressing
them to the presynaptic element.
4. Vesicles bind to specific sites on the presynaptic element and open, spilling
their contents (a neurotransmitter) into the synaptic cleft
5. 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)
Typical excitatory vs inhibitory synaptic events
Synapses: There not that simple
The take home message here is
that a synapse is like a tiny
computational compartment!
G-protein coupled receptors
The neuromuscular junction: synapse from neuron to muscle
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!
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