Welcome to synapses, neurons and brains!

This module's purpose is to acquaint you with "The materialistic mind – your brain’s ingredients". You will become intimately acquainted with the beauty and variety of neurons – the elementary building block/microchips of the brain. We will highlight a big controversy between two great anatomists (Ramon y Cajal and Camillo Golgi) who both received the Nobel Prize in 1906. They asked whether the neuron is a separate “independent” unit (like other cells in other tissues) or whether it is part of a continuum? We will next discuss the neuron as an input-output device and highlight a key property of the nervous system, namely that neurons connect to each other via a wonderful devise called “synapse”.

In this module we will discuss the "Electrifying brain – passive electrical signals". We will show that neurons are electrical device and learn what enables neurons to become “electrifying”. Here we will describe only the passive (vs. active) electrical properties of neurons. We will show that, at the quiescent state, the difference in electric potential across the cell’s membrane is always negative inside the cell (“the “resting potential”); we next show that the membrane behaves like an electrical (resistance-capacitance) RC circuit and highlight the notion of “membrane time constant” and, consequently, the ability of neurons to summate (in time) successive (synaptic) inputs (“electrical memory”) – a fundamental mechanism utilized by the brain. We will also show that when the synapse is activated, it generates an analog electrical signal (“the post-synaptic potential”, PSP) in the receiving (“post-synaptic”) cell. Most interestingly, there are two types of synapses in the brain – “excitatory” and “inhibitory” – we will discuss how these two opposing signals interact in the receiving ``neuron. This module is more technical than the more descriptive first two lessons; we encourage those of you who are not familiar with basic electricity (resistance, capacitance, Ohms law and Kirchoff’s law) to read about these in the sources links for this week’s lecture.

In this module we are covering "Electrifying brains – active electrical spikes". In the previous module we learned that: 1-neurons are electrical devices, 2 - that the membrane behaves as an RC circuit, 3 - that synapses operate by opening a new cross-membrane conductance attached with a battery. In the present module we will proceed to deal with the active electrical aspects of neurons. Synaptic inputs are the elementary (input) sources to neurons and, typically, many (excitatory) of them are required to summate (“temporal summation”) to generate a highly (“all or none”) output signal – the notorious spike (or “action potential”). In our current understanding, sensory, motor, emotional, etc., information is represented by a particular set of neurons that “fire” these spikes. So no movies or music in your brain only spikes representing (coding for) these movies and music. We will focus on the membrane mechanisms underlying the generation of the spike and in particular on the model of Hodgkin & Huxley for the spike which is probably the most fundamental and beautiful model in neuroscience. Hodgkin & Huxley received the Nobel Prize in 1963.