5_Form_and_function - Central Nervous System: brain and...

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Unformatted text preview: Central Nervous System: brain and spinal cord Peripheral Nervous System: neurons that convey sensory input to the CNS, and motor output from the CNS Autonomic Nervous System: information from organs of the body, and control of those organs Amazing Brain Numbers 100 billion neurons 1 trillion glial cells 1.000 trillion connections Amazing Brain Numbers • About 1.4 kg • < 2.5% of body weight • 78% water (10% fat, 8% protein) 1 Amazing Brain Numbers BASIC ASPECTS of the CNS 2% of our body mass 1. ELEMENTS: cells uses 20% of the energy 25% of the oxygen 70% of the total glucose 2. STRUCTURE: brain 3. FUNCTION: transmission of information The nerve cell, or neuron Two types of “braincells”: 3 major elements: cell body, dendrites (afferent), axon (efferent) 1. Neurons 2. Glial cells 2 The Neuron: Parts of the Neuron The basic unit of the nervous system Three Types of Neurons: Afferent or sensory: run from sense organs to central nervous system. Efferent or motor: run from the central nervous system to the muscles. Interneurons: have multiple connections to other neurons. Cell Body- The part of the neuron containing the nucleus and the organelles Axon- Conducts information from the neuron cell body to the synaptic terminals transmission. Dendrites- All of the fibrous extensions of the cell body except the axon. Myelin- A fatty sheath of insulation that covers larger axons. Synapse- Points of functional contact between axon terminals and other cells. Chemical Synapse Electrical Synapse afferent Nissl Bodies - groups of ribosomes used for protein synthesis. Endoplasmic reticulum (ER) - system of tubes for transport of materials within cytoplasm. Microtubules/Neurofibrils - system of transport for materials within a neuron and may be used for structural support. Nucleus - contains genetic material (chromosomes, DNA) Nucleolus - produces ribosomes necessary for translation of genetic information into proteins Golgi Apparatus - membranous structure important in packaging peptides and proteins (including neurotransmitters) into vesicles. efferent Mitochondria - produce energy to fuel cellular activities. 3 Myelin De location of the cell body of the neuron determines the type of neuron reception conduction transmission of information Motor neuron Sensory neuron Different types of NEURONS The myelin sheath improves transmission within the neuron 4 Networking Endoneurium: around axon Periaround fascicule Epiaround nerve Convergence Divergence of impulses Nerve Conduction Within the Neuron When the neuron is resting (not conducting impulses) it is polarized. Between Neurons When depolarization reaches the terminal buttons, neurotransmitters are released into the synapse The cell is invaded by Na ions and expulses K ions => depolarization => either excite or inhibit the following cell (an electrical process) (a chemical process) 5 Four types of messengers 1. Neurotransmitters: released by terminal buttons of neurons and detected by receptors in the membrane of another cell at short distance 2. Neuromodulators: neurotransmitters released in large amounts from the terminal buttons, but diffuse, affecting many neurons at distance (e.g. serotonin) 3. Hormones: produced by endocrine glands, released into blood. Stimulate different cells, including neurons 4. Pheromones: chemicals released into the environment through sweat, urine or secretions of special glands. Most receptors in nose of animals Synaps-es Glial cells -pavement of ventricles and canal -BBB -can form neural stem cells -fagocytosis (defensive function) -communication with immune cells Glial cells have a structural and a functional significance 6 Astrocyts are more than just supporting cells Like neurons, astrocytes in V1 can respond to visual stimuli, with distinct spatial receptive fields and sharp tuning to visual stimulus features including orientation and spatial frequency. Shummers L. et al. Science 2008, 320, 1638-43 Real cells: neurons and astrocyt Some principles of Nervous System Function 1: Information-Processing Sequence in the Brain: “In – Integrate – Out” 2: Sensory and Motor Functions Throughout the Nervous System Are Separated 3: Inputs and Outputs to the Brain Are Crossed 4: Brain Anatomy and Function Display Both Symmetry and Asymmetry 5: The Nervous System Works Through Excitation and Inhibition 6: The Nervous System Functions on Multiple Levels 7: Brain Components Operate Both Hierarchically and in Parallel A microglial cell is going to destroy a bacterium (phagocytosis). Microglial cells attack the central nervous system in multiple sclerosis. 8: Functions in the Brain Are Both Localized in Specific Regions and Distributed 7 Intermezzo: stamcellen Ovocyst – enucleation Embryo, Fetus (pluripotent) Blastocyst: outer layer(=> placenta) and inner cell mass (embryo) 8 Kunnen uitgroeien tot een compleet mens Stamcellen Embryo (blastocyst) Progenitorcel Kunnen alle celtypes van de 3 kiembladen vormen (maar geen placenta meer; dus geen nieuw mens) Voor aanmaak van cellen met specifieke functie. Maar ook: Transdifferentiatie: bv somatische stamcellen uit beenmerg kunnen neuronale cellen vormen (turning blood into brain) Stamcellen -houden zichzelf in stand (self-renewal) -genereren dochtercellen die zich verder ontwikkelen tot meer gedifferentieerde celtypes In het volwassene CZS blijken ook nog stamcellen voor te komen !!! (in subventriculaire zone, hippocampus en langs centraal kanaal van ruggenmerg) ⇒ toch (beperkte) neuronale regeneratie mogelijk TNN 2004, 105, 130-137 Toepassing Stem cells Fetal cells enter mothers brain !!! foetale stamcellen This astonishing finding in 2005 opens new therapeutic perspectives in treating brain disorders ! Identifying the molecules typical of fetal cells that enter the brain and become nervous system cells could help find similar cells from sources other than fetuses. Stem Cells, 2005, August 10 9 2007: Engeland geeft groen licht voor hybride embryo onderzoek 6 september 2007 NB: Humanimal? Hybride embryo’s In Engeland is toestemming verleend om een combinatie van mensdierlijke embryo’s te maken. Deze zogenaamde hybride embryo's worden gemaakt door menselijk erfelijk materiaal in de eicellen van koeien of konijnen te brengen. De kern van een somatische cel wordt in een ontkernde diercel gebracht. Al het genetische materiaal is dus humaan behalve het mitochondriaal DNA. Daarom worden deze hybriden cytoplasmatisch genoemd. Het zijn dus geen “echte” hybriden. Er is verschillend gereageerd op deze ontwikkeling. Tegenstanders vinden het onacceptabel dat menselijk en dierlijk materiaal gecombineerd wordt in een embryo. Voorstanders verwijzen naar vele voordelen in de gezondheidszorg. 2008: Britse vorsers maken embryo's uit mens en dier Britse onderzoekers van de universiteit van Newcastle zijn erin geslaagd hybride embryo's te maken door genetisch materiaal van menselijke huidcellen te injecteren in eicellen van koeien. Na drie dagen zijn de hybride embryo's vernietigd. Up to the adult brain De katholieke kerk en organisaties voor de bescherming van ongeboren kinderen eisen een verbod op dergelijke onderzoeken. 10 Brain Structures: Brain Structures: 2 hemispheres, 4 cortical lobes, fissures and sulci, gyri 2 hemispheres, 4 cortical lobes, fissures and sulci, gyri longitudinal fissure right hemisphere corpus callosum left hemisphere cerebral commisures fissura gyrus sulcus lateral fissure central fissure lateral fissure Lateral view Lateral view of the left hemisphere 11 Medial view Medial view of the left hemisphere Paramedian sagital vieuw CORTEX CEREBRI The cerebral cortex has a laminar structure with regional changes => cytoarchitecture (Brodmann) 12 Different cytoarchitecture Areas of Brodmann Different cytoarchitecture e.g. in the temporal lobe Lateral view Medial view Areas of Brodmann Areas of Brodmann 13 Lateral view Some primary areas: -motor -sensible (tactile) -visual -auditive Medial view => sensation (gewaar worden) The motor and somatosensory primary areas in more detail topography somatotopy 14 topograpgy somatotopy Primary somatosensory cortex Homunculus (Penfield) Primary motor cortex The myelinated fiber tracts form the white matter White matter (fiber tracts) 15 Myelinated fiber tracts form the white matter: association (U) fibers projection fibers commissural fibers • Most of the integrative power resides in the cerebral cortex of the two cerebral hemispheres Right cerebral hemisphere Left cerebral hemisphere Corpus callosum Structures connecting both hemispheres Structures connecting both hemispheres: corpus callosum commissura anterior commissura posterior corpus callosum commissura commissura anterior posterior 16 The lobes Frontal Lobe Location: Before the (Rolandic) central fissure, above the (Sylvian) lateral fissure Main functions: M1, M2 (motor) Broca in dominant hemisphere (expressive language) PFC (prefrontal cortex) multimodal association cortex (personality, emotion and “behavior”) DLPFC Cingulate cortex M1, the primary motor cortex => central or first motor neuron, pyramidal tract M2, the secondary motor cortex (premotor, supplementary motor, cingulate motor areas) is involved in the programming of specific patterns of movement after more general instructions from the DLPFC. M1 the primary motor cortex => central or first motor neuron, pyramidal tract M2 the secondary motor cortex (premotor, supplementary motor, cingulate motor areas) is involved in the programming of specific patterns of movement after more general instructions from the DLPFC. 17 Major areas of the prefrontal cortex Cingulate cortex Orbitofrontal Anterior cingulate M2 dorsolateral premotor cortex: handling inspired by external cues supplementary motor cortex: planning and executing complex motor sequencess (generated internally) Noradrenerg Histaminerg Dopaminerg Projections from different subcortical zones to the prefrontal cortex. PFC (prefrontal cortex) 1. Dorso-lateral prefrontal cortex (DLPFC) Executive functions*, working memory dopamine lesion: executive and memory dysfunctions 2. Orbito-frontal cortex Integration of (limbic)emotional and behavioral responses serotonin lesion: dysfunctions of mood and personality disorders 3. Anterior cingulate cortex Motivational behavior noradrenaline lesion: obsessive-compulsive disorders *The ability to think abstractly and to plan, initiate, sequence, monitor, and stop complex behaviour 18 Parietal Lobe Location: After the (Rolandic) central fissure, above the (Sylvian) lateral fissure Main functions: S1, S2 (somatosensory) visual attention, visuospatial processing, control of goal directed voluntary movement multimodal association: integrates different senses to allow a single concept. Major areas of the parietal cortex Posterior parietal cortex (PPC) •Sensory guidance of movement Projections to premotor cortex Projections directly to M1 Damage can cause deficits in visually guided reaching (Balint’s syndrome) and, or apraxia •Part of the dorsal visual stream (the Where route) Occipital Lobe Postcentral gyrus Location: Located at the most posterior pole of the brain Supramarginal gyrus Main functions: V1 Some interpretation of visual information Angular gyrus Superior parietal lobule 19 Occipital Lobe Occipital Lobe => visual information -Primary visual cortex (V1) (retinotopic organization) -Segregation of visual information processing: form, color, motion, depth, etc. Retinotopic organization Occipital Lobe Segregation of visual information processing: form, color, motion, depth, etc. 20 SPL The When path Temporal Lobe Location: inferior to the lateral fissure (Sylvius) Main functions: Lateral: - auditory sensation (A1) - Wernicke in dominant hemisphere (receptive language) A third pathway The when pathway: using time information to identify objects (e.g. determining when objects appeared or disappeared). Medial: - memory (hippocampus) - emotional and sexual behavior (limbic system) is lateralized in the right hemisphere. comes from V1 to the temporoparietal junction (TPJ) Pole: - role in social and emotional processes Trends in Cognitive Sciences, 2007, 204-210 The temporal pole (BA 38) Scheme showing the anatomical relationship of the temporal pole to the posterior orbital frontal cortex and the amygdala (in reality the amygdala is buried under the cortex) Olson, I. R. et al. Brain 2007 130:1718-1731 The temporal pole has some role in both social and emotional processes, including face recognition and theory of mind (beyond semantic memory). The temporal pole binds complex, highly processed perceptual inputs to visceral emotional responses. Because perceptual inputs remain segregated into auditory, olfactory and visual streams, the integration of emotion with perception is channel specific. Olson, I. R. et al. Brain 2007 130:1718-1731 21 The hippocampus (medial part of temporal lobe) The hippocampus Location: On the medial side of the temporal lobe ('seahorse‘), three layered archicortex Functions: Memory - encodes memories and then finds them when you want to remember - ultimate station to determine whether a new memory should go into longterm storage or be deleted Affect and emotion Deep brain structures Diencephalon Basal ganglia Diëncephon Thalamus: gate to the cortex gate for attention (selection) Hypothalmus: visceral regulation (hunger, thirst…) Epithalamus: pineal gland (melatonin) Limbic system: MOVE 22 Thalamus Thalamus Location: The thalamus is a large mass of gray matter located deep on either side of the hemisphere of the forebrain Functions: Information from all sensory receptors (except smell) is processed in the thalamus before being sent to the cerebral cortex (sort of a requisite 'last pit stop' for information going to cortex) Contains four groups of nuclei: anterior, ventral, dorsal, posterior. Project and receive fibers from the cerebral cortex => (therefore) function in selection of attention Hypothalamus Thalamus: “gateway” to the cerebral cortex Location: The hypothalamus is a midline structure, below the thalamus It connects to the pituitary gland The connection between thalamus and cerebral cortex is made in the 29th week of gestation. Medical (and ethical) practice: before that period, pain can not be feeled. => a foetus does not feel pain during the first 6 months Functions: The hypothalamus has many regulating functions The autonomic nervous system: pupils, body temperature, hunger, thirst, sleep-waking cycles, blood pressure, water balance, respiration and food intake. Controls the release of hormones: ADH, growth hormone, prolactin, thyroid, corticotropin and gonadotropins Role in emotions and behavior, in regulating complex moods such as anger and placidity. Role in memory (corpora mammillaria) (Rosen, 2005) 23 Hypothalamus Hypothalamus - ADH oxitocin thyroid adrenal gonads hormones Hypothalamus Hypothalamus: Corticotroop Releasing Factor Stress Hypothalamushypophysisadrenal axis Hypofyse: Adreno-CorticoTroop Hormoon Adrenal: cortisol, (nor)adrenaline various organs negative FEEDBACK 24 Hypothalamus Hypothalamus is less sensitive to negative feedback in women than in men Hypocretins (orexins) = peptides produced by a group of neurons in the hypothalamus ⇒ response to stress is stronger and longer ⇒ biological reason for -gender difference in depression and anxiety -premenstrual dysphoria Hypocretins play a part in the regulation of various functions including arousal, regulation of feeding behaviour vegetative functions and… addiction The Lancet Neurology, 2005, 4,673-82 Neuron, 2006. See section on biorhythms Hypothalamus Ghrelin and cognition Ghrelin secreted by an empty stomach - triggers hunger (via hypothalamus) - interact with hippocampus (memory) (better not to study after a copious meal) Evolutionary: A hungry animal needs extra brainpower to find the next meal. Perhaps the cognitive brain is a side-effect of hunger? Horvath T. Nature Neuroscience, DOI:10.1038/nn1656 Hypothalamus ‘Special parts’: -Corpora mammillaria -Hypophysis -Mammillary bodies Small, paired nuclei bulging anteriorly from the hypothalamus Relay stations for olfactory pathways Role in memory -Infundibulum (stalk of the hypophysis) connecting to the pituitary gland 25 Intermezzo: The biological clock Epithalamus Most dorsal portion of the diencephalon, forms roof of the third ventricle. Pineal gland secretes melatonin, a hormone involved with sleep regulation, sleep-wake cycles, and mood. Intermezzo: The biological clock The circadian clock is located in the in the suprachiasmatic nucleus of the hypothalamus pineal gland Absence of light Production of melatonin by the pineal gland is stimulated by darkness and inhibited by light (via the hypothalamus) 26 (of the hypothalamus) peak during darkness Intermezzo: The biological clock Recent research proposes a rhythm of 24 hours and 11 minutes (as well in elder as in younger persons) (of the hypothalamus) The suprachiasmatic nucleus, via an inhibitory projection to the paraventricular nucleus, controls the sympathetic output to the pineal gland that is responsible for melatonin secretion. Neurology, 2008, 594-8 Back to the anatomy The limbic system s.s. and the “limbic lobe” a primitive structure deep in the temporal lobe MOVE Memory Olfaction Visceral Emotion 27 The limbic system is a term referring to several brain parts, including the hippocampus and the amygdala. The limbic system s.s. and the “limbic lobe” for the regulation of memory (hippocampus), olfaction (olfactory bulb), visceral (hippocampus) and emotion (amygdala). ant cingulate cortex ant cingulate cortex brainstem nuclei orbitofrontal cortex hypothalamus and basal forebrain Important zones for emotions Frontal: orbitofrontal cortex anterior cingulate cortex Temporal: amygdala (limbic S) hypothalamus Brainstem: some nuclei 28 Basal Ganglia Deep structures Diencephalon Basal ganglia Location: surrounds the thalamus Functionally includes: caudate, putamen, nucleus accumbens, globus pallidus, substantia nigra, subthalamic nucleus Functions: Controls voluntary movement (and posture), and cognition. Striatum Basal Ganglia Basal Ganglia 29 1 Substantia nigra 2 Projects to striatum 3 2 (putamen, nu caudatus, gl pallidus) 1 3 Projects to prefrontal cortex The Brain Stem - Midbrain (mesencephalon) - Pons - Medulla oblongata (bulbus) 2 Putamen, nucleus caudatus 3 Prefrontal cortex 1 Substantia nigra Brainstem - mesencephalon - pons - medulla oblongata (bulbus) nuclei of cranial nerves nuclei for emotion centers: ARAS swallow, cough … vital centers Midbrain Location: At the top of the brainstem Here, corticospinal pathway crosses => each hemisphere of the brain controls the opposite side of the body Functions: Nuclei for cranial nerves III and IV (eye movements) ARAS: reticular formation (basic life support system) Substania nigra: a large black nucleus involved in movement Periaqueductal grey: role in emotion 30 Pons Medulla Oblongata Location: Lies between mesencephalon and medulla oblongata. Many axons cross sides within this region (bridge). Three peduncles link the pons to the cerebellum. Location: Lower part of the brainstem before reaching the spinal cord. Functions: Nuclei for cranial nerves (V, VI, VII, VIII) ARAS: arousal, sleep Relays information between the brain and the cerebellum. Function: Nuclei for cranial nerves (IX, X, XI, XII) Centers for cough, gag, swallow and vomit ARAS and vital centers (cardiac center, respiratory center) . ARAS ARAS in the brainstem 31 Twelfe pairs of cranial nerves Cerebellum Location: Two hemispheres at the base of the brain, overlying the pons Convolutions similar to those of the cerebral cortex (but much smaller, "little brain"): outer cortex, inner white matter and deep nuclei Functions: Coordinates and fine tunes motor activity Cognitive functions (performance, verbal working memory, procedural memory) Mental functions (e.g. autism) 32 Formation and circulation of CSF Filled with CSF (cerebro-spinal fluid) 33 CSF: resorbtion at the vertex Spinal tap 4 cerebropetal arteries 34 Cerebral vasculature A. vertebralis MR Angiography Cerebral Vasculature 35 BLOOD VOLUME The total volume remains constant Regional differences (in function of brainactivity) When pCO2 diminishes (eg.by hyperventilation) => vasoconstriction BLOOD-BRAIN-BARRIER Lets pass O2, glucose… Barrier for some products Blood-brain-barrier (BBB) Blood-brain-barrier (BBB) 36 ...
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This note was uploaded on 05/28/2010 for the course GE BIOL020000 taught by Professor Luccrevits during the Spring '10 term at Ghent University.

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