Introduction to Neuroscience Presentation 2025 PDF

Introduction to Neuroscience Anatomical-Functional Organization of Nervous System William Carey University College of Osteopathic Medicine Foundations of Medical Neuroscience OMS 6140 Gabor Legradi, MD Professor of...

Introduction to Neuroscience Anatomical-Functional Organization of Nervous System William Carey University College of Osteopathic Medicine Foundations of Medical Neuroscience OMS 6140 Gabor Legradi, MD Professor of Biomedical Sciences Our study of Neuroscience this semester aims to: ❖ Examine structure and function of nervous system from a preclinical point of view. ❖ Define the nervous system as the composite of many subsystems. ❖ Subsystems are hierarchically organized and form functions from simple to highly complex.  Our method of study Supplemental videos for laboratory and lecture WCUCOM Neuroscience (youtube.com) Module 1 Laboratory 1 Overview of structure and function of nervous (Brain external anatomy, meninges) system + Neuronal communication Laboratory 2 (Brainstem) spinal cord and Brainstem regional studies Module 2 Regional study of Neuronanatomy cont., sensory and motor systems Cerebral cortex and cross-disciplinary study of Module 3 integrative systems. Laboratory 3: Telencephalon Arterial supply of the brain and clinically Laboratory 4: Blood supply oriented topics  Not required but recommended Required textbooks if you have trouble starting out in Neuroscience Atlas Neuroanatomy Essential Neuroscience Through Clinical Nolte's The Human Brain 4th Edition Cases in Photographs and 3rd Edition Diagrams 5th Edition Recommended alternative atlas We will continue using the Blumenfeld textbook in OMS2.  Objectives: ▪ Apply principles of systems biology to the study of the nervous system. ▪ Define the most important emergent properties of the central nervous system. ▪ Sketch the basic organization of CNS and PNS. ▪ Interpret block diagrams of the nervous system. ▪ Identify important facts about the brain and its organizational features. ▪ Discuss the nervous system at cellular and systems levels. ▪ Use specific neuroscientific and neuroanatomic terminology to enable discussion of function. Reading material: Siegel and Sapru: Essential Neuroscience, 4th edition, pp.3-20. Blumenfeld, Neuroanatomy Through Clinical Cases: Chapter 2  Blumenfeld, Hal. Neuroanatomy Through Clinical Cases: ▪ “The nervous system “…Accordingly, structures is perhaps the most of the nervous system beautiful, elegant, and can be described on complex system in the multiple levels: body. in terms of macroscopic ▪ Its interconnected brain divisions; networks perform connecting pathways processing that is and cell groupings; simultaneously local individual brain cells; and distributed, and, ultimately, serial and parallel, receptors, hierarchical and neurotransmitters, and global.” other signaling molecules.” CLINICAL ASSESSING MOTORIUM SENSORIUM HIGHER ORDER APPROACHES THREE EXPRESSION PROCESSING OF AND TO THE MAJOR AND CONTROL STIMULI FROM INTEGRATIVE NERVOUS ASPECTS: OF MOVEMENT THE E.G., THOUGHTS, SYSTEM ARE ENVIRONMENT EMOTIONS, FUNCTIONAL IN COGNITIVE NATURE MECHANISMS, INTERPRETATION OF STIMULI IN A SOCIAL CONTEXT Functions of the nervous system can be described as the amalgamation of reflexes, innate patterns of behaviors and learned responses, often leading to adaptation to environment. Components of the nervous system CNS: brain and spinal cord. located inside the dural sac. PNS: Nerves: cranial and spinal. Ganglia: sensory and autonomic (motor). Enteric nervous system. Origin of the Nervous System Human central nervous system (CNS) From a subset of cells in ectoderm. Neural tube later forms the brain (swellings at cranial end) and a caudal continuation in spinal cord. Fluid filled cavities in developing neural tube form the ventricular system. Separate form the neural tube, the peripheral nervous systems is formed from migrating cells of neural crest.  Neuroanatomical localization: Anatomic directions are not dependent on body position, but they are determined by the central axis of the body. Dorsal Ventral Rostral: toward “nose” Caudal: toward “tail” Central core and anatomic directions in CNS. Orientation where the central nervous system lines up with the long axis of the body. E. g. in reptile. FIGURE 2.3: Orientation of the Central Nervous System in Reptiles Blumenfeld, Hal. Neuroanatomy Through Clinical Cases, Two critical terms to know about orientation of CNS Rostral: toward “nose” Caudal: toward “tail” Because of the sharp, about 80-degree inclination between the long axis of the forebrain and brainstem, the meaning of rostral and caudal is modified, Long axis of forebrain depending on localization. ▪ Above the midbrain: Anterior = rostral Long axis of Posterior =caudal brainstem Superior = dorsal Inferior =ventral ▪ Below the midbrain: FIGURE 2.4: Orientation of the Anterior = ventral Central Nervous System in Humans Blumenfeld, Hal. Posterior =dorsal Neuroanatomy Through Clinical Cases, 3rd Edition. Superior = rostral Inferior =caudal  Horizontal section Coronal section Horizontal Coronal (frontal) Sagittal planes. These planes are Horizontal slices of human forebrain, regularly used in replicating the view from axial sections our didactic study in medical imaging (youtube.com) in Gross Human forebrain coronal levels. Anatomical or Identification of septum, preoptic area, histological images hypothalamus, basal nuclei. (youtube.com) as well as in Mid-sagittal section medical imaging. Medial view of the brain, focusing on cerebral cortex. (youtube.com)  Coronal sectioning plane Horizontal sectioning Cross section of plane spinal cord Same as axial in Obtained by medical imaging sectioning at the axial plane Clinical imaging of head and brain The human brain: ▪ 2% of body mass ▪ 20% of body oxygen ▪ 14% of total blood flow ▪ 25% of total body glucose ▪ Uses a functional recruitment of capillaries; ▪ Its internal blood flood is mainly determined by autoregulation ▪ Brain (CNS) shielded from abnormal variations of ionic composition; ▪ And systemic sources of potentially toxic substances. ▪ Concepts: blood-brain barrier. Blood-cerebrospinal fluid barrier. Cellular composition of the nervous system Neurons – developmental, anatomical, functional/computational units of C. S. von Bartheld the nervous system. 80-100 billion J Chem Neuroanat. 2018 neurons in human CNS. November ; 93: 2–15. Interact by synaptic contacts. Soma* = cell body; processes: dendrites* and axons* Potentially 10,000 synaptic contacts per neuron. Neuroglia or glia – like neurons glial cells are also derived from Typical mammalian neurons and neuroepithelial cells but are synaptic interactions. considered support cells. 40-50 billion Most mammalian neurons are Other - blood vessels (endothelial multipolar (several dendrites, cells) about 25% of non-neuronal usually one axon that will branch cells in the brain extensively close to its termination) Movement of materials or information away Myelinated axon from soma (cell body), toward axon terminal is called anterograde. Oligodendrocyte, forming myelin sheath in CNS Movement of materials or information toward the soma is called retrograde. Organization of a typical (chemical) synapse A typical mammalian central synapse  Organization of CNS Gray matter – high concentration of nerve cell bodies. White matter – general term for bundles of axons (tracts) in CNS congregations of Myelinated* axons ▪The differentiation of the neural tube determines the size, location and shape of its adult derivatives. ▪ You should be able to follow the shape of the ventricular system based on these principles. The peripheral nervous system (PNS, purple) Aggregations of nerve cell bodies = Ganglia ▪Collection of nerve fibers (axons) = (Peripheral) nerves ▪Located outside the dural sac. ▪Ganglia are either sensory (dorsal root ganglia and certain sensory ganglia associated with some cranial nerves) ▪Or motor ganglia (autonomic ganglia) located in the head and other parts of the body.  What are pathways? Pathway*: a series of neurons, responsible for carrying a specific type of information. The following attributes may vary: ▪ Type of information carried (by definition). ▪ Length of a pathway (as to how many synapses are involved and actual physical length). ▪ Chemical coding of pathways = the type of neurotransmitter ▪ Whether the information reaches the level of conscious perception or not  Examples of descending or ascending long tracts of central nervous system There are functional systems* based on distinct pathways. For example, the anterolateral system*, dorsal column-medial lemniscus system*, corticospinal system* Clinically, these are called long tracts because they traverse many levels, and their damage produces repeatable patterns of lesion signs.  What are reflexes? Reflex* = involuntary response to a certain type of input It is automatic and involuntary even when a skeletal muscle target is involved. The most commonly examined type of reflex: myotatic or stretch reflex (also called deep tendon reflexes) Clinical terms: Areflexia*, hyporeflexia*, hyperreflexia*. Reflexes use pathways: An interaction between sensory and motor pathways! Note that all reflexes use pathways but not all pathways code reflexes.  Drawing of neurons and synapses, a reflex arc and a pathway Objective: Draw and/or May be a long interpret distance schematic representations of pathways in the central nervous system.  Nervous system block diagram The nervous system is topographically divided: central and peripheral components Functionally: Sensory, Motor, and Integrative components. → From this we get the concepts of reflexes, reflex arc. Visceral nervous system Also conceptualized as: somatic and visceral nervous systems. Based on the targets of motor innervation. Spinal cord at a typical thoracic level The simplest model of nervous system organization. You have already encountered this in the study of Gross Anatomy. Image in “Anatomical or histological orientation”. Ventral side is facing the observer. Spinal cord at a typical thoracic level Ganglia (e.g. sensory or dorsal root ganglia) Posterior (dorsal) Peripheral nerve (spinal nerve) motor and sensory fibers are mixed Anterior (ventral) Sensory and motor components Central processing inside spinal gray matter Helps you understand afferents “sensory”. E.g. Ia afferent (red) Central processing efferents “motor” (toward a target) The concept of afferent and efferent “Afferent” and “efferent” are relational terms to describe that something is running to or from a reference point. We have discussed afferent and efferent as sensory and motor, respectively. This is true regarding spinal nerves and spinal cord because the spinal cord is the link between PNS and higher centers. Let us apply the terms “Afferent” and “Efferent” in a series of neurons: We can do this regardless whether the information is sensory, motor or integrative. Nucleus A is sending its efferents to Nucleus B. The tract is an “output” of Nucleus A. From the perspective of Nucleus B, you would consider the tract a collection of afferents because they are going toward it. This can also be called an “input“ to Nucleus B. Using Nucleus B a reference point now, “B” is receiving afferents from “A “ and is sending efferents to “C”. Regions of the central nervous system  Spinal cord Spinal cord links PNS to brain. Spinal nerve roots are attached to its segments. Organizes reflex activity. Its white matter has ascending and descending tracts to communicate with the brain and between various Spinal cord levels of spinal cord itself. Cross section Brainstem: medulla oblongata, pons, midbrain Infratentorial: below tentorium cerebelli. ▪ Medulla oblongata – rostral continuation of spinal cord, has ascending and descending tracts, cranial nerve nuclei, Brainstem cardiorespiratory centers ▪ Pons – has cranial nerve nuclei, pontine nuclei link cortex to cerebellum. ▪ Midbrain - has cranial nerve nuclei. Made up by a central core and a base. ▪ In addition to cranial nerve nuclei, the brainstem has chemically coded, widespread connections, participating in integrative functions. Midbrain  Cerebellum Infratentorial: below tentorium cerebelli. ▪ Topographically, the cerebellum is positioned close to brainstem but is considered as a separate unit. ▪ Receives highly processed sensory input. ▪ Modulates motor output by acting on spinal cord and forebrain motor centers. Inputs and outputs of ▪ Anatomically, it has a foliated outer cerebellum. region, the cerebellar cortex, and a We will study the deep white matter and cerebellar cerebellum as a nuclei. system later. ▪ Important for sensorimotor integration  Forebrain Above tentorium cerebelli(supratentorial) Diencephalon – divided into several components. Has many groups of neurons called nuclei. Important link between brainstem and cerebral hemispheres. Cerebral hemispheres – composed of cerebral cortex and subcortical gray matter (basal ganglia). White matter tracts are located just beneath cortex (e.g. corona radiata, internal capsule).  Cranial Nerves Numbered from I to XII I (olfactory) and II (optic) are tracts of the central nervous system III through XII are attached to the brainstem and act as true nerves, going to the periphery. They range from purely sensory, purely motor or mixed nerves. Some cranial nerves have autonomic (visceral motor) components. These belong to the cranial division of the parasympathetic outflow. Regional and Systemic Studies Can be viewed from a hierarchical Systems and perspective. pathways, like roads, often E.g. going up from spinal cord traverse several to brainstem regions. then into forebrain.  Systemic and Regional Neurobiology (Neuroanatomy) Somatosensory A somatic system, carrying two motor types of sensory system information Important neuroanatomical/neuroscientific key words: ▪ Central nervous system ▪ Peripheral nervous system ▪ Ipsilateral - contralateral ▪ Commissure (a connection between left and right sides of the brain of the same territories ▪ Decussation (a pathway crossing the midline at a certain point) ▪ Nerve fibers = axons ▪ Projection (a neuron sending its axon, typically to contact another neuron) ▪ Synapse ▪ White and gray matter ▪ Lobe, gyrus, sulcus, fissure (visible features of cerebral cortex) ▪ Nucleus ▪ Tract ▪ Afferent and efferent ▪ Modality (mainly in sensory systems, describing various classes of information) ▪ Somatotopic maps Our First Look At Functional Systems Motor and sensory pathways. Most of them are topographically organized. (They display somatotopic maps) Motor systems: Upper motor neuron cell bodies Main motor pathways Corticospinal tract critical for fine, voluntary, fractionated movements of limbs Aka pyramidal tract Contains the upper and lower motor neurons. Most of its fibers decussate in the pyramidal decussation at the spinomedullary junction. Lesions of it cause contralateral (opposite sided) weakness. axons Other motor pathways will also be discussed later with brainstem-spinal cord projecting systems. The primary motor and somatosensory areas of the cortex are somatotopically organized Homunculi: recruitment of neuronal activation patterns in cortex according to body parts (contralateral) * * Figure 2.13 Somatotopic Maps in the Cortex Somatosensory homunculus in postcentral gyrus of left hemisphere and motor homunculus in precentral gyrus of right hemisphere. Motor output is regulated by basal ganglia and cerebellum. They primarily influence upper motor neurons via loops of neurocircuitry. We will discuss these systemically. What you need to know now is that basal ganglia are important for movement initiation and program selection whereas cerebellum establishes sensorimotor integration and coordination of movement. Both regulate posture and locomotion to be expressed harmoniously. Main sensory systems: Somatosensory (general sensation from body) Sensation from face oral, nasal cavities is carried by the trigeminal nerve (cranial nerve V) These are carried via distinct pathways, in a modality specific manner. The pathways cross the midline so lesion signs in cases of tract damage above the decussation cause Figure 2.18 Posterior Figure 2.19 Spinothalamic contralateral sensory Column Sensory Pathway: Sensory Pathway: Pain and deficit. Vibration and Joint Position Temperature Sense Primary somatosensory information processing in thalamus and cortex Thalamus acts a gateway to cerebral cortex * Postcentral gyrus of parietal lobe Relay of somatosensory information occurs in the VPL (ventral posterolateral nucleus) of thalamus. Neurons of this nucleus project to postcentral gyrus.