Exploring Neuroethology: Understanding Brain and Behavior through Electrophysiology

1. 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.

2. Neurons: the biological basis of • sensory input • Sensory/memory integration • Learning and memory • “Higher mental processes” • Production of behavior

3. 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: • 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”

4. 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 1:10 Na+ & 20:1 K+ inside:outside

5. 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

6. 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

7. 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

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

9. 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)

10. Typical excitatory vs inhibitory synaptic events

11. Synapses: There not that simple The take home message here is that a synapse is like a tiny computational compartment!

12. G-protein coupled receptors

13. The neuromuscular junction: synapse from neuron to muscle

14. 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!

15. 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