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.

Reading assignment: Konishi and Menzel 2003

Neurons: the biological basis of 1. sensory input2. Sensory/memory integration3. Learning and memory4. “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 channelsChannels 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

3. 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

http://www.psych.ualberta.ca/~ITL/ap/ap.swf

http://www.blackwellpublishing.com/matthews/channel.html

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

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 synapses1. Axo-dendritic2. Dendro-dendritic 3. Dendro-axonic4. Axo-axonic5. Dendro-somatic6. Axo-somatic

The synaptic process: Key events of a chemical synapse1. 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 cleft5. 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