diff --git a/src/cognition-and-neuroscience/cn.tex b/src/cognition-and-neuroscience/cn.tex index f256556..35c4eee 100644 --- a/src/cognition-and-neuroscience/cn.tex +++ b/src/cognition-and-neuroscience/cn.tex @@ -8,6 +8,8 @@ \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} +\DeclareAcronym{cns}{short=CNS, long=central nervous system} +\DeclareAcronym{pns}{short=PNS, long=peripheral nervous system} \begin{document} diff --git a/src/cognition-and-neuroscience/img/brain_lobes.png b/src/cognition-and-neuroscience/img/brain_lobes.png new file mode 100644 index 0000000..730871a Binary files /dev/null and b/src/cognition-and-neuroscience/img/brain_lobes.png differ diff --git a/src/cognition-and-neuroscience/img/brain_sections.png b/src/cognition-and-neuroscience/img/brain_sections.png new file mode 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a/src/cognition-and-neuroscience/img/neural_system.png b/src/cognition-and-neuroscience/img/neural_system.png new file mode 100644 index 0000000..0977f76 Binary files /dev/null and b/src/cognition-and-neuroscience/img/neural_system.png differ diff --git a/src/cognition-and-neuroscience/sections/_nervous_system.tex b/src/cognition-and-neuroscience/sections/_nervous_system.tex index ae06243..9a73009 100644 --- a/src/cognition-and-neuroscience/sections/_nervous_system.tex +++ b/src/cognition-and-neuroscience/sections/_nervous_system.tex @@ -316,4 +316,458 @@ In a neuron, there are four regions that handle signals: \begin{example} Seizures are caused by misfiring neurons. -\end{example} \ No newline at end of file +\end{example} + + + +\section{Information transfer between two neurons} + + +\subsection{Electrical synapse} + +\begin{minipage}{0.55\textwidth} + \begin{description} + \item[Structure] \marginnote{Electrical synapse} + The neuronal membranes of the presynaptic and postsynaptic neurons are in contact at \textbf{gap junctions} and + the cytoplasm of the two neurons is virtually continuous through connecting \textbf{pores}. + \end{description} +\end{minipage} +\begin{minipage}{0.35\textwidth} + \centering + \includegraphics[width=\linewidth]{./img/electric_synapse.png} +\end{minipage} + +\begin{description} + \item[Functioning] + The two neurons are \textbf{isopotential} (i.e. they have the same membrane potential) and + the ions of the presynaptic neurons are instantaneously transmitted to the postsynaptic neuron. + + \item[Properties] \phantom{} + \begin{itemize} + \item Fast transmission. + \item Allows for synchronous operations involving groups of neurons. + \item The strength of the signal cannot be modulated. + \end{itemize} +\end{description} + + +\subsection{Chemical synapse} + +\begin{description} + \item[Structure] \marginnote{Chemical synapse} + The synaptic cleft separates the presynaptic and postsynaptic neurons. + \begin{description} + \item[Neurotransmitter] + Chemical substance received by the receptors of the postsynaptic neuron. + + The effect of a neurotransmitter is decided by the receiving receptor and not by the cell transmitting it. + + \item[Presynaptic terminals] + Swellings at the end of the axon that contain synaptic vesicles. + + \item[Synaptic vesicles] + Vesicles containing neurotransmitter molecules. + \end{description} + + \item[Functioning] + The release of neurotransmitter molecules is based on the following steps: + \begin{enumerate} + \item An action potential arriving at the terminal of a presynaptic axon causes the calcium ion (Ca$^{2+}$) voltage-gates to open. + \item Ca$^{2+}$ flow into the cell and + cause the synaptic vesicles to bind to the cell membrane to release neurotransmitters into the synaptic cleft. + \item Neurotransmitters cross the synaptic cleft and bind to the receptors of the postsynaptic neuron. + Depending on the neurotransmitter and the receiving receptor, there might be a generation of \ac{epsp} or \ac{ipsp}. + \end{enumerate} + + \begin{center} + \includegraphics[width=0.9\linewidth]{./img/chemical_synapse.png} + \end{center} + + When a receptor recognizes the neurotransmitter, it is released back into the synaptic cleft. + To avoid a constant stimulation of the receptors, neurotransmitters are inactivated: + \begin{itemize} + \item The synaptic terminal can reuptake neurotransmitters through transporter proteins. + \item Neurotransmitters might degenerate or be broken down by special enzymes. + \item Neurotransmitters can be released far away from the site of the receptors. + \end{itemize} + + \item[Properties] \phantom{} + \begin{itemize} + \item Slow transmission. + \item The signal can be modulated. + \item Has specific effects depending on the neurotransmitter and the receptors. + \end{itemize} +\end{description} + + + +\section{Neural circuit} + +\begin{description} + \item[Neural circuit] \marginnote{Neural circuit} + Group of interconnected neurons that process a specific kind of information. + + \begin{remark} + The behavioral function of each neuron is determined by its connections. + \end{remark} + + \item[Types of neurons] \phantom{} + \begin{description} + \item[Sensory neuron] \marginnote{Sensory neuron} + Carry information from the peripheral sensors to the nervous system for both perception and motor coordination. + + \item[Motor neuron] \marginnote{Motor neuron} + Carry information from the nervous system to muscles and glands. + + \item[Interneuron] \marginnote{Interneuron} + Intermediate neurons between sensory and motor neurons. + \end{description} +\end{description} + +\begin{remark} + In vertebrates, a stimulus causes multiple neural pathways to simultaneously encode different information. + This allows for parallel processing to increase both the speed and reliability of the information transfer. +\end{remark} + +\begin{description} + \item[Neural pathways types] \phantom{} + \begin{description} + \item[Divergent pathway] \marginnote{Divergent pathway} + One neuron activates many target cells. + Typically happens at the input stages of the nervous system + to ensure that a single neuron has a wide and diverse influence. + + \item[Convergent pathway] \marginnote{Convergent pathway} + Many neurons activate a single target cell. + Typically happens at the output stages of the nervous system + to ensure that a motor neuron is activated only when a sufficient number of neurons are firing. + \end{description} + + \item[Neuron firing types] \phantom{} + \begin{description} + \item[Excitatory neuron] \marginnote{Excitatory neuron} + Neurons that produce signals that increase the probability of firing of the postsynaptic neurons. + + \item[Inhibitory neuron] \marginnote{Inhibitory neuron} + Neurons that produce signals that decrease the probability of firing of the postsynaptic neurons. + + \begin{description} + \item[Feed-forward inhibition] + Excitatory neurons connected to inhibitory interneurons to block other downstream neurons. + Allows to enhance the active pathway and to block other antagonist actions. + \begin{figure}[H] + \centering + \includegraphics[width=0.4\textwidth]{./img/feedforward_inhibition.png} + \caption{Example of feed-forward inhibition} + \end{figure} + + \item[Feed-back inhibition] + Excitatory neurons connected to inhibitory interneurons that return to the same neurons to inhibit them. + Prevents the overload of neurons or muscles. + \begin{figure}[H] + \centering + \includegraphics[width=0.4\textwidth]{./img/feedback_inhibition.png} + \caption{Example of feed-back inhibition} + \end{figure} + \end{description} + \end{description} +\end{description} + + + +\begin{example}[Knee-jerk reflex] + By tapping the patellar tendon (below the kneecap), the following happens: + \begin{enumerate} + \item The sensory information is conveyed from the muscle to the spinal cord (central nervous system). + \item The nervous system issues motor commands to the muscles which results in the knee jerk. + \item Inhibitory commands are issued to stop antagonist muscles. + \end{enumerate} + + \begin{center} + \includegraphics[width=0.8\textwidth]{./img/knee_jerk.png} + \end{center} +\end{example} + + +\section{Neural system} + +\begin{figure}[H] + \centering + \includegraphics[width=0.3\textwidth]{./img/neural_system.png} + \caption{Composition of the nervous system} +\end{figure} + + +\subsection{\Acl{pns} (\acs{pns})} + +The \acl{pns} is composed of: +\begin{descriptionlist} + \item[Nerves] \marginnote{Nerves} + Groups of axons and glia. + + \item[Ganglia] \marginnote{Ganglia} + Groups of neuron bodies outside the \acl{cns} +\end{descriptionlist} + +The \ac{pns} has the following functions: +\begin{itemize} + \item Delivers sensory information to the \acl{cns}. + \item Carries commands from the \acl{cns} to the muscles. + \item Supplies the \acl{cns} with information regarding both the external and internal environment. +\end{itemize} + +The \ac{pns} has the following divisions: +\begin{descriptionlist} + \item[Somatic nervous system] \marginnote{Somatic nervous system} \phantom{} + \begin{itemize} + \item Sensory neurons that receive information from the skin, muscles, and joints. + \item Converts perceived spatial and physical information into electrical signals for the \acl{cns} to process. + \item Controls the voluntary muscles. + \end{itemize} + + \item[Autonomic nervous system] \marginnote{Autonomic nervous system} \phantom{} + \begin{itemize} + \item Controls internal organs (viscera), the vascular system, and involuntary muscles and glands. + \item Divided into three systems: + \begin{descriptionlist} + \item[Sympathetic system] \marginnote{Sympathetic system} + Operates antagonistically against the parasympathetic system. + Handles the body's response to stress (using norepinephrine). + + Physically, the sympathetic system originates from the spinal cord. + Its ganglia are closer to the spinal cord, + therefore the axons from the \acl{cns} to the ganglia are shorter than the axons from the ganglia to the organs. + + \begin{example} + Stimulates adrenal glands to prepare the body for action (fight or flight), + increases heart rate, + diverts the blood from the digestive tract to the somatic musculature, \dots + \end{example} + + \item[Parasympathetic system] \marginnote{Parasympathetic system} + Operates antagonistically against the sympathetic system. + Acts to preserve the body's resources and restore homeostasis (using acetylcholine). + + Physically, the parasympathetic system originates from the base of the brain and from the sacral spinal cord. + Its ganglia are outside the spinal cord, sometimes inside the affected organs, + therefore the axons from the \acl{cns} to the ganglia are longer than the axons from the ganglia to the organs. + + \begin{example} + Slows heart rate, stimulates digestion, \dots + \end{example} + + \item[Enteric system] \marginnote{Enteric system} + Controls the involuntary muscles of the gut. + \end{descriptionlist} + \end{itemize} +\end{descriptionlist} + + + +\subsection{\Acl{cns} (\acs{cns})} + +\begin{description} + \item[Meninges] \marginnote{Meninges} + Three layers of membrane protecting the brain and the spinal cord. + \begin{descriptionlist} + \item[Dura mater] The outermost and thickest layer. + \item[Arachnoid mater] The middle layer. + \item[Pia mater] The innermost and most delicate layer. It adheres to the brain's surface. + \end{descriptionlist} + + \item[Cerebrospinal fluid] \marginnote{Cerebrospinal fluid} + Fluid that allows the brain to float and prevents it from simply sitting on the skull surface. + It also reduces the shock to the brain and the spinal cord in case of rapid accelerations/decelerations. + + The fluid is located in: + \begin{itemize} + \item The space between the arachnoid mater and the pia mater. + \item The brain ventricles. + \item Cisterns and sulcis. + \item The central canal of the spinal cord. + \end{itemize} + + \item[Blood-brain barrier] \marginnote{Blood-brain barrier} + Barrier between the brain's capillaries and the brain's tissue. + It protects against pathogens and toxins. + + \begin{remark} + The effectiveness of the barrier also prevents drugs to treat mental and neurological disorders from passing through. + \end{remark} + + \item[Spinal cord] \marginnote{Spinal cord} + Acts as a relay for the information coming in and out of the brain. + It is enclosed in the vertebral column. +\end{description} + +\begin{remark} + Most pathways in the \ac{cns} are bilaterally symmetrical: + the sensory and motor activities of one side of the body are handled by the cerebral hemisphere on the opposite side. +\end{remark} + +\begin{description} + \item[Brain] \marginnote{Brain} + + \begin{minipage}{0.6\textwidth} + \begin{description} + \item[Brain stem] \marginnote{Brain stem} + Regulates basic life functions such as blood pressure, respiration, and sleep/wakefulness. + It is divided into three sections: + \begin{itemize} + \item Medulla. + \item Pons. + \item Midbrain. + \end{itemize} + \end{description} + \end{minipage} + \begin{minipage}{0.35\textwidth} + \centering + \includegraphics[width=\linewidth]{./img/brain_sections.png} + \end{minipage} + + \begin{description} + \item[Cerebellum] \marginnote{Cerebellum} + Contains lots of neurons and is responsible for: + \begin{itemize} + \item Maintaining posture. + \item Coordinating head, eye, and arm movement. + \item Regulating motor control (i.e. adjustments to the movement). + \item Learning motor skills. + \end{itemize} + + \item[Diencephalon] \marginnote{Diencephalon} + \phantom{}\\ + \begin{minipage}{0.6\linewidth} + \begin{description} + \item[Thalamus] \marginnote{Thalamus} + Sorts incoming sensory information (except the sense of smell) of the \acl{pns} and + sends them to the sensory regions of the cerebral hemispheres. + \item[Hypothalamus] \marginnote{Hypothalamus} + Regulates the autonomic nervous system and homeostasis through the pituitary gland (which releases hormones). + Handles the motivation system of the brain by favoring behaviors the organism finds rewarding. + \end{description} + \end{minipage} + \begin{minipage}{0.35\linewidth} + \centering + \includegraphics[width=\linewidth]{./img/diencephalon.png} + \end{minipage} + + \item[Telencephalon/Cerebral hemispheres] \marginnote{Telencephalon/Cerebral hemispheres} + Consists of: + \begin{description} + \item[Cerebral cortex] + Made of gray matter (body of neurons). + + \item[White matter] + (axons and glial cells). + + \item[Basal ganglia] \marginnote{Basal ganglia} + Receive inputs from sensory and motor areas and + mostly send them through the thalamus to the frontal lobe. + + They have a crucial role in motor control and reinforcement learning. + This happens through two pathways: + \begin{description} + \item[Direct pathway] When active, it causes the disinhibition of the thalamus and has the consequence of initializing movement. + \item[Indirect pathway] When active, it causes the inhibition of the thalamus and consequently inhibits movement. + \end{description} + To activate the direct pathway and inhibit the indirect pathway, the substantia nigra pars compacta (SNc) releases the neurotransmitter dopamine. + + \begin{example}[Parkinson's disease] + In patients affected by Parkinson's disease, the dopamine-related neurons in the SNc are lost causing + an overactivation of the indirect pathway that inhibits movement. + \end{example} + + \item[Amygdala] \marginnote{Amygdala} + Responsible for recognizing a stimulus and reacting to it. + Involved in attention, perception, value representation, decision-making, learning, memory, \dots + + \item[Hippocampus] \marginnote{Hippocampus} + Responsible for long-term memory and spatial memory. + \end{description} + + \item[Cerebral cortex] \marginnote{Cerebral cortex} + Surface of the brain which covers around 2.2m$^2$ to 2.4m$^2$. + To cover more surface, the cortex has infoldings (sulci and gyri) which also allow to connect neurons with shorter axons. + + There are two symmetrical hemispheres connected through the corpus callosum and four different lobes. + + \begin{figure}[H] + \centering + \begin{subfigure}{0.25\linewidth} + \centering + \includegraphics[width=\linewidth]{./img/brain_surface.png} + \caption{Visualization of sulci and gyri} + \end{subfigure} + \begin{subfigure}{0.35\linewidth} + \centering + \includegraphics[width=\linewidth]{./img/brain_lobes.png} + \caption{Lobes of the brain} + \end{subfigure} + \end{figure} + + \begin{description} + \item[Frontal lobe] \marginnote{Frontal lobe} + \phantom{} + \begin{description} + \item[Motor cortex] \phantom{} + \begin{itemize} + \item Planning and execution of movement. + \item Contains neurons that directly activate somatic movement neurons in the spinal cord. + \end{itemize} + + \item[Prefrontal cortex] \phantom{} + \begin{itemize} + \item Long-term planning. + \item Decision making. + \item Motivation and value. + \end{itemize} + \end{description} + + + \item[Parietal lobe] \marginnote{Parietal lobe} + Receives and integrates information from the outside world, the body, and memory. + + \begin{description} + \item[Somatosensory cortex] + Receives information regarding touch, pain, temperature, and limb position. + \end{description} + + \begin{remark} + Neurons responsible for a specific part of the body are clustered together. + \end{remark} + + + \item[Occipital lobe] \marginnote{Occipital lobe} + \begin{description} + \item[Visual cortex] + Responsible for vision. + Encodes features like luminance, spatial frequency, orientation, motion, \dots + \end{description} + + \begin{remark} + Neurons responsible for processing a specific feature are clustered together. + \end{remark} + + + \item[Temporal lobe] \marginnote{Temporal lobe} + \begin{description} + \item[Auditory cortex] + Responsible for processing sound. + \end{description} + + \begin{remark} + Neurons responsible for processing a specific sound frequency are clustered together. + \end{remark} + + \item[Association cortex] \marginnote{Association cortex} + Portion of the cortex that has neither sensory nor motor responsibility. + Receives and integrates inputs from many cortical areas. + + \begin{description} + \item[Multisensory neuron] + Cell activated by multiple sensory modalities. + \end{description} + \end{description} + \end{description} +\end{description} \ No newline at end of file