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Introduction to Computational Neuroscience Lecture 2: Structure and function of the NS lunes, 5 de septiembre de 16 Lesson Title 1 Introduction 2 Structure and Function of the NS 3 Windows to the Brain 4 Data analysis 5 Single neuron models 6 Network models 7 Artificial neural networks 8 Artificial intelligence 9 Learning and memory 10 Perception 11 Attention & decision making 12 Brain-Computer interface 13 Neuroscience and society 14 Future and outlook 15 Projects presentations 16 Projects presentations lunes, 5 de septiembre de 16 Basics Analyses Models Cognitive Applications Physiology Anatomy Function Structure Clinical Computational Information processing Cognitive Behavioral Cellular, Molecular, Developmental, Evolutionary,... lunes, 5 de septiembre de 16 “One of the difficulties in understanding the brain is that it is like nothing so much as a lump of porridge” R.L. Gregory Eye and the Brain: the psychology of seeing, New York, 1966, McGraw-Hill lunes, 5 de septiembre de 16 “What I cannot create, I don’t understand” R. Feynman lunes, 5 de septiembre de 16 Where mental faculties sit? vs. Hippocrates Ancient Egypt Plato Aristotle lunes, 5 de septiembre de 16 Galen What are the building blocks? 1906 Nobel Prize in Medicine or Physiology lunes, 5 de septiembre de 16 Learning objectives • Cell types (neurons and glial cells) • Methods of communication (synapses) • Organization of the NS (the basic plan) lunes, 5 de septiembre de 16 Introduction to the NS Gross anatomy of the CNS Neuronal signaling lunes, 5 de septiembre de 16 Most animals have a nervous system that allows responses to stimuli lunes, 5 de septiembre de 16 Evolution of the NS lunes, 5 de septiembre de 16 Evolution of the NS lunes, 5 de septiembre de 16 Evolution of the NS lunes, 5 de septiembre de 16 Division of the vertebrate NS 2 The nervous system has central and peripheral parts: The Human Brain CNS PNS Central Nervous System (CNS) * Brain * Spinal cord Peripheral Nervous System (PNS) Nerves outside the brain and spinal cord * Cranial nerves * Spinal nerves lunes, 5 de septiembre de 16 Figure 1–1 Central and peripheral nervous systems. The Division of the vertebrate NS lunes, 5 de septiembre de 16 Division of the CNS CHAPTER 1 Cerebral hemisphere Diencephalon The brain itself has multiple subdivisions: Brainstem Introduction to the Nervou Cerebellum Spinal cord Cerebrum Diencephalon Cerebellum Brainstem Brain stem Cerebellum A lunes, 5 de septiembre de 16 B C Division of the PNS Sensory division Picks up sensory information and delivers it to the CNS Motor division Carries information to muscles and glands * Divisions of the Motor division * Somatic carries information to skeletal muscle * Autonomous carries information to smooth muscle, cardiac muscle, and glands lunes, 5 de septiembre de 16 Function of the NS CNS and PNS must work in harmony to carry 3 main functions lunes, 5 de septiembre de 16 Function of the NS CNS and PNS must work in harmony to carry 3 main functions 1 Receive sensory input Monitor changes occurring inside and outside the body (changes = stimuli) * Sensory receptors gather information * Information is carried to the CNS lunes, 5 de septiembre de 16 Function of the NS CNS and PNS must work in harmony to carry 3 main functions 2 Perform integration To process and interpret sensory input and decide if action is needed Sensory information is used to create * Sensations * Memory * Thoughts * Decisions lunes, 5 de septiembre de 16 Function of the NS CNS and PNS must work in harmony to carry 3 main functions 3 Generate motor output A response to integrated stimuli is given * Decisions are acted upon * Impulses are carried to effectors (muscles or glands) lunes, 5 de septiembre de 16 Cellular elements 2 cell categories in the nervous system: Neurons (information processing, signaling elements, 100 billion) Glial cells (supporting roles, 10 x neurons) lunes, 5 de septiembre de 16 Neurons: compartments Brainstem Cerebellum Spinal cord Diencephalon Brainstem Neurons have specialized zones for collecting, integrating, conducting, and transmitting information. Cerebellum A B C Figure 1–2 Three-dimensional reconstruction of the entire CNS, seen from the left side (A), from directly in front (C), and from halfway in between (B). The eyes are included with the reconstruction because, as described in Chapter 2, the retina develops as an outgrowth from the neural tube. Soma supports metabolic and synthetic needs Dendrite Dendrites receive information from other neurons via synapses Axon conducts information away from cell body lunes, 5 de septiembre de 16 Synapse Axon Figure 1–3 Schematic view of a typical neuron, indicating synaptic inputs to its dendrites (although other sites are possible) and information flow down its axon, reaching synaptic endings on other neurons. Information flow is unidirectional due to molecular specializations of various parts o neurons, as described in Chapters 7 and 8. The pink segments covering the axon represent the myelin sheath that coats many axons (see Figs. 1-24 and 1-30), and the gap in the axon represents a missing extent that might be as long as a meter in the longest axons. Neurons: synaptic contacts 22 Figure 1–20 Potential sites of synaptic contacts. Most synapses consist of an axon terminal contacting a dendrite and are therefore called axodendritic (AD) synapses. However, all other possible combinations occur at least occasionally, giving rise to two-part names indicating the presynaptic and postsynaptic elements. These include axosomatic (AS) synapses, dendrodendritic (DD) synapses, and axoaxonic synapses with the postsynaptic element being another axon terminal (AA1) or the initial segment of an axon (AA2). (Based on an illustration in Pannese E: Neurocytology: fine structure of neurons, nerve processes, and neuroglial cells, New York, 1994, Thieme Medical Publishers.) 21 Chemical (neurotransmitters) AA2 DD AA1 AD AS CHAPTER 1 Electrical AD Introduction to the Nervous System Synapse: axonal end abupts on other neuron (dendrites). A few thousand per cell 2 to 20 nm space (Cajal vs Golgi) 1 µm long where the axon is separated from extracellular space only by fingerlike projections from Schwann cells. The myelin between two nodes is an internode and is formed by a single Schwann cell (Fig. 1-24); adjacent internodes form the projections that cover the node The Human Brain Electrical A Figure 1–21 Synapses densely distributed over the surface of CNS neu campal neuron developing in tissue culture. The cell body (not seen in directed against MAP2, a microtubule-associated protein restricted to the originating from other neurons not visible in this field form a dense netw directed against synaptotagmin, an integral membrane protein of synap axon terminal is superimposed on part of the dendrite, appears yellow.) B of a rat), stained for MAP2 as in A, showing neuronal cell bodies and den the cell bodies and dendrites, were stained with a fluorescent antibody d terminals (red fluorescence). A third dye (DAPI) was used to stain the nucle and Pietro De Camilli, Yale University School of Medicine. B, from the cover p nf D * * At * m Computational advantages Table 1–2 lunes, 5 de septiembre de 16 Components of the Peripheral Nervous S Cell or Cell Part Type Neuronal cell bodies Sensory neurons Neurons: diversity CHAPTER 1 Neurons come in a variety of sizes and shapes, but all are variations of the same theme Introduction to the Nervous System C 5 (Actual size) B A Cell bodies range from 5 to 100 micras in diameter Most axons around 1 mm but some 1 m D F G E lunes, 5 de septiembre de 16 Figure 1–4 Examples of multipolar (A to E), bipolar (F), and unipolar (G) neurons, all drawn to about the same scale to demonstrate the range of neuronal sizes and shapes. All were stained by the Golgi method (see Fig. 1-14A); dendrites are indicated by green arrows, axons by blue arrows. A, Purkinje cell from the cerebellar cortex. B, Granule cell from the cerebellar cortex. C, Projection neuron from the inferior olivary nucleus. D, Spinal cord Neurons: functional types Sensory neurons take nerve impulses from sensory receptors to CNS Sensory receptors may be the end of a sensory neuron itself (a pain or touch receptor), or may be a specialized cell that forms a synapse with a sensory neuron lunes, 5 de septiembre de 16 Neurons: functional Interneurons occur entirely within the CNS Convey nerve impulses between various parts of the CNS lunes, 5 de septiembre de 16 Neurons: functional Motor neurons carry nerve impulses from CNS to muscles or glands Have many dendrites and a single axon Cause muscle to contract or glands to secrete lunes, 5 de septiembre de 16 Neurons: segregation CHAPTER 1 Introduction to the Nervous System 9 Neuronal Cell Bodies Synthesize Macromolecules Neuronal cell bodies and axons are largely segregated within the CNS The neuronal cell body is the site of synthesis of nearly all the neuron’s enzymes, structural proteins, membrane components, and organelles, as well as some of its chemical messengers. Its structure (Fig. 1-9) reflects this function. The nucleus is large and pale-staining, with most of its chromatin dispersed and available for transcription; it contains one or more prominent nucleoli, which are actively involved in the transcription of ribosomal RNA. The cytoplasm contains abundant rough endoplasmic reticulum and free ribosomes for protein synthesis, together with stacks of Golgi cisternae for further processing and packaging of synthesized proteins. Many mitochondria are also present to meet the energy requirements of continuous, very active protein synthesis. Ribosomes, whether studding the surface of the rough endoplasmic reticulum or free in the cytoplasm between the cisternae, are stained intensely by basic dyes, appearing by light microscopy as clumps called Nissl bodies or Nissl substance (Fig. 1-10). Nissl bodies are particularly prominent in large neurons, a consequence of the large total volume of cytoplasm contained in their processes, Grey matter: cell bodies and dendrites (pinkish due to blood supply) Figure 1–7 Horizontal slice of a whole human brain, approximately 6 mm thick, stained by a method that differentiates between gray and white matter. Pretreatment with phenol makes the white matter resistant to the blue copper sulfate stain, so white matter appears white and gray matter appears bright blue. (Prepared by Pamela Eller, University of Colorado Health Sciences Center.) White matter: axons (myelin) DRG From sensory receptors AG To viscera To skeletal muscle lunes, 5 Figure 1–8 Division ofde the 16 CNS into gray matter and white matter, as typified by the thoracic spinal cord in cross section. Gray matter contains de septiembre Glial cells (PNS) Schwann cell nucleus c Glia = glue in Greek Unrolled internode Ol c c Schwann cells: * Form myelin sheath in the PNS * Speed up axonal transmission nf AxM Axon A Myelin Schwann cell: nucleus cytoplasm Axon Ol B Ol Satellite cells: * Support clusters of neuron bodies (ganglia) lunes, 5 de septiembre de 16 AxM m nf Figure 1–28 CNS myelin sheaths, here in a transverse section of a rat’s optic nerve. Each axon contains microtubules (m) and neurofilaments (nf) F s m w f t a b n ( S Glial cells (CNS) Microglia Oligodendrocytes * Dispose of debris * Respond to injury * Form myelin sheaths Astrocytes Ependymal * Mop up excess ions * Connect neurons to blood vessels (Bloodbrain barrier) * Scar tissue * Line ventricles * Secrete CSF lunes, 5 de septiembre de 16 Neurons vs. Glial cells Glial cells (astrocytes) could be involved in processing The vast majority of neurons do not divide. Why? Glial cells divide Most brain tumors are gliomas lunes, 5 de septiembre de 16 Introduction to the Nervous System Gross anatomy of the CNS Neuronal signaling lunes, 5 de septiembre de 16 Figure 3–3 A, Average brain weights of human males and females at different ages. Notice how the brain grows rapidly after birth, doubling in the first year of life, before reaching its full size at about age 11 years. At all ages, male brains have a greater average weight than female brains. However, as indicated in B, adult female brains actually account for a greater percentage of body weight than do adult male brains. Brain growth is substantial in utero, and we are born with brains that are very large relative to body size. After the brain growth spurt of the first 1 to 3 years of life, body growth takes over, and the brain weight–body weight ratio declines progressively until about age 17. (Plotted from data in Dekaban AS, Sadowsky D: Ann Neurol 4:345, 1978.) Gross anatomy Opossum Rabbit Kangaroo CHAPTER 3 Humans have large brains relative to other animals (1.1 to 1.7 kg) 1.2 0.9 0.6 0.3 0 .5 1 2 Chimpanzee Lion Elephant Gross5 Anatomy and General Organization of the Central Nervous cm Male 0.0 Cat Brain (kg)/Body (kg) Brain weight (kg) A Human Figure 3–4 Brains of a series of representative mammals, all reproduced at the same scale. Brain size is partly related to body size (e.g., cat versus lion, human versus elephant) and partly related to mental abilities (e.g., lion versus human). Not all parts of the brain change size in proportion to one another. For example, the olfactory bulbs of opossums and coyotes (blue arrows) are relatively large, those of monkeys and chimpanzees (green arrows) are proportionally much smaller, and those of humans are barely discernible at this magnification. (From www.brainmuseum.org, courtesy Dr. Wally Welker; supported by NSF grant 0131028.) Female 1.5 Rhesus monkey Coyote 3 4.5 6.5 8.5 11 14 17 20 26 35 45 53 Age (years) More complex interconnections and selective expansions of cerebral cortex involved in higher functions B 0.15 0.12 Fem 0.09 Mal 0.06 0.03 0.00 0 .5 1 2 3 4.5 6.5 8.5 11 14 17 20 Age (years) Figure 3–3 A, Average brain weights of human males and females at different ages. Notice how the brain grows rapidly after b Figure 3–5 The relative sizes of brainat of about a rhinoceros first year of life, before reaching its fullthesize ageand11 years. At all ages, male brains have a greater average weight than fem alleged brain of the author. as indicated in B, adult female brainsthe actually account for a greater percentage of body weight than do adult male brains. Brain g Although the rhino’s body weight about 30 times greater, its brain in utero, and we are born with brainsisthat are very large relative to body size. After the brain growth spurt of the first 1 to 3 years weight is likely to be only half as takes over, and the brain weight–bodygreat. weight progressively until about age 17. (Plotted from data in Dekaban AS, Sado (Rhino, ratio courtesydeclines Albrecht Dürer. Author, courtesy Mr. and 4:345, 1978.) Mrs. Nolte. Suggested by an illustration in Cobb S: Arch Neurol 12:555, 1965.) Opossum 400 gr at birth 1400 gr adult (due to increase in myelin and new connections) 50-80k neurons die every day Coyote Rabbit Rhesus monkey Human Cat Kangaroo Lion 5 cm Chimpanzee Elephant Figure 3–4 Brains of a series of representative mammals, all reproduced at the same scale. Brain size is partly related to body lion, human versus elephant) and partly related to mental abilities (e.g., lion versus human). Not all parts of the brain change size i another. For example, the olfactory bulbs of opossums and coyotes (blue arrows) are relatively large, those of monkeys and chimpa are proportionally much smaller, and those of humans are barely discernible at this magnification. (From www.brainmuseum.or Welker; supported by NSF grant 0131028.) lunes, 5 de septiembre de 16 Frontal lobe (9) Gross anatomy (motor cortex) Parietal lobe (10) (somatosensory cortex) 14 15 16 Overview of the subdivisions of the CNS Cerebral cortex 7 Occipital lobe (11) (visual cortex) 8 Temporal lobe (12) 6 (auditory cortex) Limbic lobe (13) (drives, emotions, memory) Caudate nucleus (14) Basal ganglia 7 5 Cerebral hemisphere Lenticular nucleus (movement control; related structures in brainstem) (putamen [15] and globus pallidus [16]) Hippocampus (5), amygdala (6) (limbic structures; drives, emotions, memory) Cerebrum Thalamus (7) (relay to cortex) Diencephalon Brain Cerebellum (1) (coordination) Midbrain (2) Brainstem Central nervous system Hypothalamus (8) (control of autonomics) Pons (3) Medulla (4) 9 10 13 7 8 11 2 3 12 Spinal cord lunes, 5 de septiembre de 16 1 4 1 Figure 3–25 Overview of the subdivisions of the CNS. The major structures listed here, as well as many related structures, are the subjects of subse- Gross anatomy Cerebral hemispheres are folded and convoluted * Gyri: bumps * Sulci: grooves Corpus callosum is a huge bundle of axons connecting the two hemispheres (severed in split-brain patients) Ventricles filled with cerebro-spinal fluid that bath the brain and provide protection and chemical environment of neurons lunes, 5 de septiembre de 16 Gross anatomy Cerebral cortex: outermost 6 layered structure of the neural tissue of human and other mammals (2-4 mm). Key role in high cognitive functions (memory, attention, language, ...) lunes, 5 de septiembre de 16 Gross anatomy CNS contains systematic distorted maps lunes, 5 de septiembre de 16 Introduction to the Nervous System Gross anatomy of the CNS Neuronal signaling lunes, 5 de septiembre de 16 Neuronal signaling Within the neuron (conduction) To achieve long distance (several cm), rapid communication (150 m/s), neurons have evolved special abilities for sending electrical signals (Action potentials) Between neurons (transmission) Communication between neurons is achieved at synapses by the process of neurotransmission lunes, 5 de septiembre de 16 Electrical properties Lipid bilayer at the cell surface acts as a capacitor (able to store charges) Neurons spend a lot of energy to keep different concentration of ions inside and outside (resting membrane potential -70 mV) lunes, 5 de septiembre de 16 Electrical properties Neuron membranes are filled with pores that enable the selective pass of ions (ion channels) Ion channels open and close as a function of the membrane potential (voltage-gated channels) Diffusion: when channels open ions tend to move to less crowded places lunes, 5 de septiembre de 16 Conduction: Action http://www.youtube.com/watch?v=7EyhsOewnH4 lunes, 5 de septiembre de 16 Conduction: Action potential An action potential is conducted whenever an input of threshold intensity or above is applied to the initial part of an axon (each action potential has the same strength) lunes, 5 de septiembre de 16 Conduction: Action potential Saltatory conduction: action potential jumps between nodes but needs to be regenerated Speed up of transmission * unmyelinated 5 m/s * myelinated 150 m/s (toe - spine in < 7 ms) lunes, 5 de septiembre de 16 quickly to the original resting potential. B, Injection of little more than half action potentials. At the termination of the current pulse the membrane stay potentials continue at a slower rate. C, Replacing the Cl− in the solution bath it to behave like a myotonic fiber. (From Adrian RH, Bryant SH: J Physiol 240: Conduction: Action potential Figure 7–19 A puff York, 1851, Rudolph G Puffer fish (fugu) contains a potent poison that blocks Na+ channels resulting in failure to generate action potentials lunes, 5 de septiembre de 16 Neuronal signaling Within the neuron (conduction) To achieve long distance (several cm), rapid communication (150 m/s), neurons have evolved special abilities for sending electrical signals (Action potentials) Between neurons (transmission) Communication between neurons is achieved at synapses by the process of neurotransmission lunes, 5 de septiembre de 16 Synaptic transmission Electrical synapses: gap junctions between cells that allow ions to flow from one neuron to another (also in cardiac cells) Chemical synapses: most neurons communicate by means of neurotransmitters at chemical synapses. The receiving neuron THE POST responds with a graded potential that may or may not initiate7.2an action potential Reserve vesicles RRVP Transmitter Recycling Action potential Release machinery Postsynaptic receptors PSC [Ca 2+] lunes, 5 de septiembre de 16 which, on release, may activate a corresponding pool of postsynaptic receptors (Walmsley et al., 1998). The RRVP is replenished from a large reserve Fig che exa con con repl poo pote thro cha vesi the rele Synaptic transmission 1 Action potential arrives to the axon terminal (pre-synaptic neuron) stimulates the release of packets of neurotransmitters into the synaptic cleft 2 Neurotransmitters diffuse across the synaptic cleft 3 Neurotransmitters bind to receptors at the post-synaptic neuron causing ion channels to open lunes, 5 de septiembre de 16 Synaptic transmission http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/ 0072437316/120107/anim0015.swf::Chemical%20Synapse lunes, 5 de septiembre de 16 Synaptic transmission EPSP IPSP Depending on which receptor is activated at the post-synaptic neuron the electrical response can be excitatory or inhibitory lunes, 5 de septiembre de 16 Synaptic transmission Neural integration refers to the conduction and addition of all PSP produced by various excitatory and inhibitory synapses. It determines if an action potential is generated. Two types: 1 Temporal summation lunes, 5 de septiembre de 16 Synaptic transmission Neural integration refers to the conduction and addition of all PSP produced by various excitatory and inhibitory synapses. It determines if an action potential is generated. Two types: 2 Spatial summation lunes, 5 de septiembre de 16 Synaptic transmission Synaptic strength can be enhanced or depressed by changing neurotransmitter release or the density of receptors (synaptic plasticity) Drugs, diseases, and toxins interfere with synaptic neurotransmission (alcohol, nicotine, marihuana, antidepressants, botox,...) too much botox... lunes, 5 de septiembre de 16 Summary • • NS evolved to provide a fast and coordinated response to stimuli. • Neurons have specialized compartments to receive (dendrites), integrate (soma), conduct (axon), and transmit (synapses) impulses. • NS is divided in CNS (brain and spinal cord) and PSN (cranial and spinal nerves), with further subdivisions involved in specialized processing. 2 types of cells: neurons (information processing) and glial cells (supporting role). lunes, 5 de septiembre de 16 To know more http://cnx.org/content/m47519/latest/? collection=col11569/latest Chapters 1 and 3 The human brain: an introduction of its functional anatomy, John Nolte, Mosby, 2002 lunes, 5 de septiembre de 16 Lesson Title 1 Introduction 2 Structure and Function of the NS 3 Windows to the Brain 4 Data analysis 5 Single neuron models 6 Network models 7 Artificial neural networks 8 Artificial intelligence 9 Learning and memory 10 Perception 11 Attention & decision making 12 Brain-Computer interface 13 Neuroscience and society 14 Future and outlook 15 Projects presentations 16 Projects presentations lunes, 5 de septiembre de 16 Basics Analyses Models Cognitive Applications