diff --git a/src/cognition-and-neuroscience/cn.tex b/src/cognition-and-neuroscience/cn.tex index 4f8a5f6..f256556 100644 --- a/src/cognition-and-neuroscience/cn.tex +++ b/src/cognition-and-neuroscience/cn.tex @@ -4,9 +4,19 @@ \date{2023 -- 2024} \def\lastupdate{{PLACEHOLDER-LAST-UPDATE}} +\DeclareAcronym{psp}{short=PSP, long=postsynaptic potential, long-plural=s} +\DeclareAcronym{epsp}{short=EPSP, long=excitatory postsynaptic potential, long-plural=s} +\DeclareAcronym{ipsp}{short=IPSP, long=inhibitory postsynaptic potential, long-plural=s} +\DeclareAcronym{ap}{short=AP, long=action potential, long-plural=s} + + \begin{document} \makenotesfront + \printacronyms + \newpage + \input{./sections/_introduction.tex} + \input{./sections/_nervous_system.tex} \end{document} \ No newline at end of file diff --git a/src/cognition-and-neuroscience/img/action_potential.png b/src/cognition-and-neuroscience/img/action_potential.png new file mode 100644 index 0000000..3b4cab1 Binary files /dev/null and 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b/src/cognition-and-neuroscience/sections/_nervous_system.tex new file mode 100644 index 0000000..ae06243 --- /dev/null +++ b/src/cognition-and-neuroscience/sections/_nervous_system.tex @@ -0,0 +1,319 @@ +\chapter{Nervous system anatomy and physiology} + + +\begin{description} + \item[Central nervous system] Brain and spinal cord. + \item[Peripheral nervous system] Nerves that branch off from the brain and the spine. +\end{description} + +\section{Individual cells} + +% A nervous system has two types of cells: +% \begin{descriptionlist} +% \item[Neurons/nerve cells] +% \item[Glia cells/neuroglia] +% \end{descriptionlist} + + +\subsection{Glia cells / Neuroglia} +\marginnote{Glia cells/Neuroglia} +Cells that support neurons. +There are 2 to 10 times more glia cells than neurons.\\ + +\begin{minipage}{0.89\textwidth} + \begin{descriptionlist} + \item[Microglia] \marginnote{Microglia} + Immune system cells located in the central nervous system. + They intervene in response to toxic agents or to clear dead cells. + \begin{itemize} + \item Responsible for antigen presentation (determine the type of external agent). + \item Become phagocytes (cells that ingest harmful agents) during injuries, infections, or degenerative diseases. + \end{itemize} + + \begin{remark} + In patients affected by Alzheimer's disease, microglia may become hyperactive and damage neurons. + \end{remark} + \end{descriptionlist} +\end{minipage} +\begin{minipage}{0.1\textwidth} + \centering + \includegraphics[width=\textwidth]{./img/microglia.png} +\end{minipage}\\[1em] + +\begin{minipage}{0.79\textwidth} + \begin{descriptionlist} + \item[Astrocytes] \marginnote{Astrocytes} + Star-shaped cells located in the central nervous system. + They surround neurons and are in contact with the brain's vasculature. + \begin{itemize} + \item Provide nourishment to neurons. + \item Regulate the concentration of ions and neurotransmitters in the extracellular space. + \item Communicate with the neurons to modulate synaptic signaling. + \item Maintain the blood-brain barrier that separates the tissues of the central nervous system and the blood. + \end{itemize} + \end{descriptionlist} +\end{minipage} +\begin{minipage}{0.2\textwidth} + \centering + \includegraphics[width=\textwidth]{./img/astrocyte.png} +\end{minipage}\\[1em] + +\begin{minipage}{0.79\textwidth} + \begin{descriptionlist} + \item[Oligodendrocytes and Schwann cells] \marginnote{Oligodendrocytes\\Schwann cells} + Oligodendrocytes are located in the central nervous system, while + Schwann cells are located in the peripheral nervous system. + \begin{itemize} + \item Produce thin sheets of myelin that wrap concentrically around the axon of the neurons. + This insulating material allows the rapid conduction of electrical signals along the axon. + \end{itemize} + + \begin{remark} + Myelin is white, giving the name to the white matter. + \end{remark} + + \begin{remark} + In multiple sclerosis, the immune system attacks the oligodendrocytes, + slowing or disrupting messages traveling along the nerves. + \end{remark} + \end{descriptionlist} +\end{minipage} +\begin{minipage}{0.2\textwidth} + \centering + \includegraphics[width=\textwidth]{./img/insulation.png} +\end{minipage} + + + +\subsection{Neurons / Nerve cells} +\marginnote{Neurons/Nerve cells} + +A nervous system has around 100 billion neurons. +There are 100 distinct types of neurons varying in form, location, and interconnectivity. + +Generally, a neuron does the following: +\begin{enumerate} + \item Receives some information. + \item Makes a decision. + \item Passes it to other neurons. +\end{enumerate} + +\begin{description} + \item[Eukaryotic cell] \marginnote{Eukaryotic cell} + A neuron is an eukaryotic cell. Therefore, it has: + \begin{description} + \item[Cell membrane] Membrane that separates the intracellular and extracellular space. + \item[Cytoplasm] Intracellular fluid mainly made of proteins and ions of potassium, sodium, chloride, and calcium. + \item[Extracellular fluid] Fluid in which the neuron sits. Similar composition of the cytoplasm. + \item[Cell body/soma] Metabolic center of the cell. + \end{description} + + \begin{figure}[h] + \centering + \includegraphics[width=0.5\textwidth]{img/neuron_eukaryotic.png} + \caption{Neuron as an eukaryotic cell} + \end{figure} +\end{description} + +\begin{description} + \item[Neuron-specific components] \phantom{} + \begin{description} + \item[Dendrites] \marginnote{Dendrites} + Receives the outputs of other neurons. + A neuron has multiple dendrites with different shapes depending on the type and location of the neuron. + \item[Axon] \marginnote{Axon} + Transmitting zone of the neuron that carries electrical signals from the dendrites to the synapses (from 0.1mm to 2m). + A neuron has a single axon. + \item[Synapses] \marginnote{Synapses} + Represents the output zone of the neuron from where electrical or chemical signals can be transmitted to other cells. + A neuron has multiple synapses. + + \begin{description} + \item[Presynaptic cell] Cell transmitting a signal. + \item[Postsynaptic cell] Cell receiving a signal. + \item[Synaptic cleft] Narrow space separating presynaptic and postsynaptic cells (i.e. the space separating two neurons). + \end{description} + \end{description} +\end{description} + +\begin{figure}[H] + \centering + \includegraphics[width=0.9\textwidth]{img/neuron_specific.png} + \caption{Neuron-specific components} +\end{figure} + +There are three types of synapses: +\begin{descriptionlist} + \item[Axosomatic] \marginnote{Axosomatic} + Synapses that a neuron makes onto the cell body (soma) of another neuron. + \item[Axodendritic] \marginnote{Axodendritic} + Synapses that a neuron makes onto the dendrites of another neuron. + \item[Axoaxonic] \marginnote{Axoaxonic} + Synapses that a neuron makes onto the synapses of another neuron. + In this case, the transmitting neuron can be seen as a signal modulator of the receiving neuron. + \begin{figure}[h] + \begin{subfigure}{.3\textwidth} + \centering + \includegraphics[width=\linewidth]{./img/axosomatic.png} + \caption{Axosomatic} + \end{subfigure} + \begin{subfigure}{.3\textwidth} + \centering + \includegraphics[width=\linewidth]{./img/axodendritic.png} + \caption{Axodendritic} + \end{subfigure} + \begin{subfigure}{.3\textwidth} + \centering + \includegraphics[width=\linewidth]{./img/axoaxonic.png} + \caption{Axoaxonic} + \end{subfigure} + \end{figure} +\end{descriptionlist} + +Neurons are divided into three functional categories: +\begin{descriptionlist} + \item[Sensory neurons] \marginnote{Sensory neurons} + Carry information from the body's peripheral sensors into the nervous system. + Provides both perception and motor coordination. + + \item[Motor neurons] \marginnote{Motor neurons} + Carry commands from the brain or the spinal cord to muscles and glands. + + \item[Interneurons] \marginnote{Interneurons} + Intermediate neurons between sensory and motor neurons. +\end{descriptionlist} + +\begin{description} + \item[Principle of connectional specificity] \marginnote{Principle of connectional specificity} + Neurons do not connect randomly but rather make specific connections at particular contact points. +\end{description} + + + +\section{Information transfer within a neuron} + + +\subsection{Neuron functional regions} + +In a neuron, there are four regions that handle signals: +\begin{descriptionlist} + \item[Input zone] \marginnote{Input zone} + Dendrites collect information from different sources + in the form of \aclp{psp} (\acp{psp}). + + \item[Integration/trigger zone] \marginnote{Integration/trigger zone} + \acp{psp} are summed at the axon hillock and an \ac{ap} is generated if a threshold (-55mV) has been exceeded. + + \item[Conductive zone] \marginnote{Conductive zone} + The \ac{ap} is propagated through the axon. + + \item[Output zone] \marginnote{Output zone} + Synapses transfer information to other cells. + + \begin{description} + \item[Chemical synapses] The frequency of \acp{ap} determines the amount of neurotransmitters released. + \item[Electrical synapses] The \ac{ap} is directly transmitted to the next neurons. + \end{description} + + \begin{figure}[h] + \centering + \includegraphics[width=0.8\textwidth]{./img/neuron_transmission.png} + \caption{Transmitting regions of different types of neurons} + \end{figure} + + \begin{figure}[h] + \centering + \includegraphics[width=0.8\textwidth]{./img/neuron_transmission2.png} + \caption{Signal from the input to the output zones} + \end{figure} +\end{descriptionlist} + + +\subsection{Neuron transmission signals} + +\begin{description} + \item[Resting membrane potential] \marginnote{Resting membrane potential} + In a resting neuron, the voltage inside the cell is more negative ($-70$mV) than the outside. + This allows the creation of an electrical signal when needed. + + \item[\Acl{psp} (\ac{psp})] \marginnote{\Acl{psp} (\ac{psp})} + Small change in the membrane potential that alters the resting voltage of the cell. + + A \ac{psp} can be: + \begin{descriptionlist} + \item[Excitatory \ac{psp} (\acs{epsp})] \marginnote{Excitatory \ac{psp}} + Has a depolarizing role: produces a decrease in the membrane potential (i.e. increases voltage inside the cell), + therefore enhancing the ability to generate an \ac{ap}. + + \item[Inhibitory \ac{psp} (\acs{ipsp})] \marginnote{Inhibitory \ac{psp}} + Has a hyperpolarizing role: produces an increase in the membrane potential (i.e. reduces voltage inside the cell), + therefore reducing the ability to generate an \ac{ap}. + \end{descriptionlist} + + A \ac{psp} has the following properties: + \begin{itemize} + \item The amplitude and duration of the signal are determined by the size of the stimulus that caused it. + Overall, the amplitude is small. + \item The signal is passively conducted through the cytoplasm, therefore it decays with distance and is able to travel 1mm at most. + \item A single \acs{epsp} is not enough to fire a neuron. Multiple \acp{psp} are summed at the axon hillock. + There are two types of summation: + \begin{descriptionlist} + \item[Spatial summation] Sum of the \acp{psp} received at the same time. + \item[Temporal summation] Sum of the \acp{psp} received at different time points. + \end{descriptionlist} + + \begin{remark} + The fact that a single \ac{epsp} is not enough to fire a neuron prevents a response to every single stimulus. + \end{remark} + \end{itemize} + + \item[\Acl{ap} (\ac{ap})] \marginnote{\Acl{ap} (\ac{ap})} + Signal generated when the sum of \acp{epsp} exceeds a fixed threshold of $-55$mV (all-or-none). + + \begin{description} + \item[Saltatory conduction] \marginnote{Saltatory conduction} + Mechanism that allows a fast propagation on long distances of \acp{ap}. + \begin{enumerate} + \item Depolarization causes the sodium ion (Na+) channels located in the nodes of Ranvier of the axon to gradually open. + \item Na+ flows into the neuron and further depolarizes it until the Na+ equilibrium potential is reached. + \item With Na+ equilibrium, Na+ channels close and potassium ion (K+) channels open. + \item K+ flows into the neuron and restores the membrane potential until the K+ equilibrium potential is reached. + \item With K+ equilibrium, K+ channels close and + the membrane potential of the neuron is more negative than the resting potential (hyperpolarization). + It will gradually return to its resting potential. + \begin{remark} + During hyperpolarization, Na+ channels cannot open (refractory period). + This has two implications: + \begin{itemize} + \item It limits the number of times a neuron can fire in a given time. + \item Guarantees a unidirectional electrical current flow + (\textbf{Principle of dynamic polarization}).\marginnote{Principle of dynamic polarization} + \end{itemize} + \end{remark} + \end{enumerate} + + \begin{figure}[H] + \begin{subfigure}{.45\textwidth} + \centering + \includegraphics[width=0.85\textwidth]{./img/saltatory_conduction.png} + \caption{Ion channels along the axon} + \end{subfigure} + \begin{subfigure}{.45\textwidth} + \centering + \includegraphics[width=0.8\textwidth]{./img/action_potential.png} + \caption{Triggering of an action potential} + \end{subfigure} + \end{figure} + \end{description} + + + \begin{remark} + As the signal is constantly regenerated, + \Acp{ap} have similar amplitude and duration in all neurons, regardless of the characteristics of the input \acp{psp}. + Therefore, the only way an \ac{ap} has to carry information is by varying frequency and firing duration, making it a binary signal. + \end{remark} +\end{description} + +\begin{example} + Seizures are caused by misfiring neurons. +\end{example} \ No newline at end of file