Neurons & Neuroanatomy What are the characteristics of neurons important for Cognitive Neuroscience? What is the brain structure important for CogNeuro?

Classes of neurons Unipolar - One process extends from body, which can contain both dendrites and axon terminals Bipolar - One axon and one dendrite process. Multipolar - Many dendrite processes. Pseudounipolar - Bipolar cells where the dendrite and axon processes have merged. We’ll be primarily interested in multipolar cells.

Neural membrane There are specialized structures in the neural membrane that allow various elements to cross in and out of the cell –Ion channels: Proteins that cross the cell wall, creating pores that allow ions (Na +, K +, Cl - ) to pass. –Specific to particular ions; more K + channels –Nongated and gated –Ion pumps: Actively transport ions across the membrane, creating an electric gradient across the membrane (3 Na + out; 2 K + in)

Cellular currents There are two types of electrical currents that can pass through a neuron: Active currents are ones that are caused by explicit chemical activity (opening and closing of ion channels); ex - at the synapse and across the surface of the axon Passive currents are ones that simply pass through the cytoplasm, typically as a response to active currents; ex - within the cell body as a result of synaptic activity; within the axon as a result of action potentials.

Action Potential The signal a neuron generates down its axon is called an action potential. All action potentials are the same magnitude (strength), so they are either on or off. An action potential is only generated if the depolarization of the cell membrane crosses a threshold. We determine how excited a neuron is by its firing rate - how many action potentials per second it generates.

Depolarization of the AP As opposed to the nongated ion channels discussed so far, action potentials are driven by gated channels that open in response to high voltage levels (the threshold). In particular, gated Na + channels are opened by membrane depolarization, which allows Na + into the cell. This causes further depolarization, which opens more channels…..

Repolarization of the AP Depolarization also causes voltage- gated K + channels to open, but slightly after the Na + channels. This drives K + out of the cell, reestablishing the resting potential of the cell; this is called repolarization. Because of the delay, K + flows out after Na + stops flowing in, so there is a brief period of hyperpolarization

Neurotransmitter Neurons communicate by sending chemical messages called neurotransmitters to other neurons. These neurotransmitters travel from axon to either the dendrite or the cell body across the synapse. Where a synapse is depends on what the connection type is –Excitatory: Axon to dendrite –Inhibitory: Axon to cell body