Add CN nervous system cells

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}

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}