[NEURO]LEC_002_NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA.pdf

(002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 - A very complex form of communication OUTLINE...

(002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 - A very complex form of communication OUTLINE TWO TYPES OF CELLS IN NERVOUS SYSTEM I. NEUROBIOLOGY OF NEURONS AND o Nerve Cells - Neurons NEUROGLIAL CELLS o Neuroglial Cells - Glial/ Supporting Cells A. Basic Organization of Nervous System C. Neurons Basic structure and functional unit of the nervous system B. Nervous System Receptive- receive stimuli and transduce into nerve C. Neurons impulses for transfer to another neurons D. Neuronal Bodies or Soma Groups/ Integrative- processing impulse on the higher center Clustering Motor- initiating motor response and transduce the impulse to an effector E. Definition >100 years of living F. Axons and Axonal Transport Amitotic II. NEUROPHYSIOLOGY High metabolic rate A. Structure and Function of Biomolecules STRUCTURE OF NEURONS B. Metabolism Neurons - Neurons are excitable cells that are C. Molecular Genetics specialized for the reception of stimuli and the conduction III. NERVE VS. TRACTS of the nerve impulse. They vary considerably in IV. PATELLAR REFLEX size and shape, but each possesses a cell body from which one or more processes called neurltes project. A. Knee jerk/patellar reflex Cell Body (Perikaryon/ Soma) B. Synaptic reflex o The expanded portion that contains nucleus V. THE NEUROGLIAL CELLS o The nucleus contains chromosomal DNA and nucleolus A. Neuroglial Cells o Neurofilaments, neurofibrils (structural proteins B. Cells in the Central Nervous System within the nerve cell) C. Cells in the Peripheral Nervous System o Nuerotubules (responsible for cellular transport) o No centrioles, incapable of cell division o Stains basophically due to the abundance of RER and polyribosomes ▪ Clumps of RER and Ribosomes: NISSL BODIES I. NEUROBIOLOGY OF NEURONS AND o The Nissl substance is responsible for synthesizing protein, which flows along the NEUROGLIAL CELLS dendrites and the axon and replaces the proteins A. Basic Organization of Nervous System that are broken down during cellular activity. - Central Nervous System Fatigue or neuronal damage causes the Nissl a. Brain and Spinal Cord with their associated tracts substance to move and become concentrated at and nuclei the periphery of the cytoplasm. o Major biosynthetic center - Peripheral Nervous System Single Axon (Efferent) a. All cranial and spinal nerves and their associated o Typically one neuron roots or nerves and ganglia. o Covered in myelin sheath which acts as insulation of the nerve NOTE: o Nodes of Ranvier- gaps between the myelin Clusters of Nerve Cell Bodies sheath which allows jumping conduction of nerve CNS - Nuclei (eg: Basal Ganglia/ Thalamus) impulse (Saltatory conduction) PNS - Ganglia (eg: Trigeminal o Generate nerve impulses (Action Potentials) away Ganglia/ Dorsal Root) from soma Bundles of Axons o Originate from axon hillock to distal portion – axon terminal – end bulbs – synapse with another CNS - Tracts (eg: Corpus callusum/ neuron Corticospinal Tract) o Axon hillock is also called initial segment PNS - Nerves (eg: Ulnar Nerve) o Devoid of ribosome o When bundled together B. Nervous System ▪ CNS: Tracts (Corpus callusum/ Corticospinal - the most complex system in human body Tract) - A network of approximately 100 billion neurons ▪ PNS: Nerves (Ulnar Nerve) a. Neurons density differs in different region of the o Synaptic Bouton/Presynaptic junction – endpoint brain. Counting neurons in a high density part of of the axon branch the brain might lead to a high estimate while o The single long tubular neurite that conducts counting those in lower density region might lead impulses away from the cell body. to an excessively low estimate. o Dendrites and axons are commonly referred to as - Each neuron has thousands of interconnections nerve fibers. PREPARED AND EDITED BY: TRANS GROUP 6  (002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 Multiple Dendrites (Afferent) o Short tapering, diffusely branched processes o Receptive input region o Electrical signals are conveyed as Graded Potential o Always unmyelinated o With cytoplasm devoid of golgi complex o Contain Nissl bodies in their proximal parts and thus the initial portions of dendrites stain basophically o Often have small protrusion (Dendritic Spines) that expand the dendritic surface area and serves as sites of synaptic contact with the axon of another neuron o Dendritic Spines: point synapse with other neurons' o Neurites responsible for receiving information and conducting it toward the cell body. STRUCTURE OF SYNAPSE Synapse o Junction between two neurons o Axodendritic- axon endings of one nerve cell interacts with the dendrites of another o Axosomatic- axon endings of one nerve cell interacts with cell body o Axoaxonic – axon endings of one nerve cell interacts with another axon o The nervous system consists of a large number of neurons that are linked together to form functional conducting pathways. The site where two neurons (or a neuron and a skeletal muscle or gland cell) come Into close proximity and functional intemeuronal communication occurs. 2 Types of Junctions between Neurons Chemical Synapse o uses substance called neurotransmitters which are released from presynaptic neuron & diffused NEUROMUSCULAR JUNCTION across a small gap to bind to receptors in postsynaptic neuron Electrical Synapse o has a direct connection between two cells (gap junction) o eg. found in smooth muscle & cardiac muscle STRUCTURE OF CHEMICAL SYNAPSE PREPARED AND EDITED BY: TRANS GROUP 6  (002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 A neuromuscular junction (or myoneural junction) is a F. Axons and Axonal Transport chemical synapse between a motor neuron and a muscle Axons fiber. o Lacks Nissl bodies It allows the motor neuron to transmit a signal to the muscle o Axons are either fiber, causing muscle contraction. - Myelinated - surrounded by a fatty insulating Muscles require innervation to function—and even just to sheath that speeds conduction of the electrical maintain muscle tone, avoiding atrophy. impulse It is the site for the transmission of action potential from - Non-myelinated - lacking of myelin sheath and nerve to the muscle. It is also a site for many diseases and thus conduct impulses slowly) a site of action for many pharmacological drugs. Axonal Transport Neuromuscular junction can be divided into three main o Myelin Production – makes transmission faster; parts: a presynaptic part (nerve terminal), the postsynaptic insulator part (motor endplate), and an area between the nerve - CNS - Oligodendrocytes terminal and motor endplate (synaptic cleft). - PNS - Schwann Cells o Myelin sheath gaps between adjacent Schwann Cell, 1. Action potential arrives at synaptic bouton occur at regular intervals. 2. Calcium influx 3. Fusion of vesicles containing acetylcholine in the presynaptic membrane 4. Exocytosis releases Ach in synaptic cleft 5. combination of Ach with post-synaptic receptors (nicotinic acetylcholine) II. NEURON PHYSIOLOGY 6. Opening of Na+ /K+ channels (cation channels). NODES OF RANVIER (NEUROFIBRIL NODES) 7. postsynaptic membrane depolarization 8. Muscle action potential. Sites where axon collaterals can emerge Unmyelinated axons – Schwann cells enclose axons but no myelin present. D. Neuronal Bodies or Soma Clustering Cortex o 6 layers in Cerebral Cortex o 3 layers in Cerebellar Cortex Nuclei o Subcortical Region ▪ Thalamus ▪ Basal Ganglia ▪ Midbrain ▪ Brainstem ▪ Spinal Cord o Cell Bodies form irregular clusters Ganglia o Found in dorsal root of Ganglia o Autonomic Ganglias o Cranial Nerve Ganglia SYNAPSES: CHEMICAL TRANSMISSION o Question: Where to find nerve cell bodies with their Dendrites? - Axondendritic Synapse 1) Cerebral Cortex - Axomatic Synapse 2) Inner Gray of Spinal Cord (Dorsal and Ventral Horns) - Axoaxonic Synaps 3) Clusters (Relay Stations): a. CNS: Nuclei (Basal Ganglia/ Thalamus) b. PNS: Ganglia (Terminal Ganglia/ Dorsal Root NEURONAL TRANSMISSION SIGNALING Ganglia) Electrical Transmission (IONIC) E. Tracts and Nerves One-way transmission along the cell membrane Tract (dendrite-body-axon) o Bundle of axons within the CNS Flow of ions along the length of a membrane o Found in white matter/ Spinal Cord (Corpus Callosum/ Graded potential (along dendrites towards the soma) Corticospinal Tract) Action potential (along Axons) o Connective tissue is absent Nerves SYNAPTIC TRANSMISSION (NEUROTRANSMITTER) o Bundles of axons that extend out from the brain as cranial nerves and from the spinal cord as spinal nerves more diffuse/diffuse across space (PNS) chemical transmission (E, NE, ACH) o Surrounded by connective tissue sheaths cell to cell/ signal between cells PREPARED AND EDITED BY: TRANS GROUP 6  (002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 Axon terminals (Axodendritic/Neurotransmitter junction) 2. Motor - related innervation of muscle, glands, etc. activation SYNAPTIC TRANSMISSION - Mostly Axodentritic of these neurons leads to some motor event (ie., contraction of a muscle) - Motor (precentral gyrus) cortex - Conducts impulses from the CNS to the muscles and glands 3. Interneurons - neither motor or sensory - connects sensory and motor cortex - neurons responsible for the various spinal reflexes, SYNAPTIC TRANSMISSION - Neuromuscular Junction connecting the neurons in the posterior horn (sensory) to the anterior horn (motor) of the spinal cord - interconnectors - establishes neuronal circuit between sensory and motor neurons Dendrites (Receptive/Graded Potential) Soma/Body (Integration) ANATOMICAL CLASSIFICATION (BY THE NUMBER OF PROCESSES) Axons (Conductive/Action Potential) 1. Multipolar Neurons - interneurons (integrates motor and sensory impulses in the CNS) - motor neurons (efferent pathway from CNS to effector muscles or glands Axon terminal synapse (chemical transmission) - (axodentric/ - efferent neurons axosomatic/ axoaxonic) - have a number of neurites arising from the cell body. With the exception of the long process, the axon, the remainder Via Peripheral nerve (chemical transmission) – of the neurites are dendrites. Most neurons of the brain and neuromuscular junction - muscle spinal cord are of this type. NOTE: 2. Unipolar/Pseudounipolar Ionic Transmission - in the nerve cell along the Cell - primary/first order sensory neurons (Plasma) Membrane -sensory ganglia: dorsal root ganglia or cranial nerve Synaptic Transmission - occurs between cell to cell ganglias - no dendrites - afferent neurons - have a single neurite that divides a short distance from TYPES OF NEURONS the cell body into two branches, one proceeding to some peripheral structure and the other entering the central Functional Classification nervous system (CNS). The branches of this single neurite 1. Sensory have the structural and functional characteristics of an - related to the transfer of sensory information (ie pain, axon. In this type of neuron, the fine terminal branches touch, temperature, pressure, vibration) found at the peripheral end of the axon at the receptor site - Sensory (Post central gyrus) cortex are often referred to as the dendrites. Examples of this - Neurons of dorsal root ganglia form of neuron are found in the posterior root ganglion. - receive sensory input - conduct impulses towards the CNS 3. Bipolar - sensory neurons PREPARED AND EDITED BY: TRANS GROUP 6  (002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 - Afferent pathway from visual/olfactory inputs towards the Dorsal root glial is made up of nerve cell bodies and the CNS interconnection in synapse and that neuron send another - afferent neurons axon of spinal cord to sensory cortex of brain. Again goes -have an elongated cell body, with a single neurite to the white membrane to ventral root that travels to same emerging from each end. Examples of this type of neuron nerves and the motor never fibre passes to same nerves to are found in the retinal bipolar cells and the cells of the muscles and it takes inorder to affect the action. sensory cochlear and vestibular ganglia. NOTE: - Neurons may also be classified according to size. Golgi Both motor and sensory fiber will pass though the same nerve type I neurons have a long axon that can stretch 1 m or but on a different fiber of axon. more in length. In extreme cases. The axons of these neurons form the long fiber tracts of the brain and spinal - Sensory fibers pass through the nerve and goes to dorsal cord and the nerve fibers of peripheral nerves. The horn. pyramidal cells of the cerebral cortex, the Purkinje cells of - Motor fibers pass through nerve and goes to ventral horn. the cerebellar cortex, and the motor cells of the spinal cord are good examples. Golgi type II neurons have a short axon that terminates in the neighborhood of the cell body or is entirely absent. They greatly outnumber the Golgi type I neurons. The short dendrites that arise from these neurons give them a star-shaped appearance. These neurons are numerous in the cerebral and cerebellar cortex and are often Inhibitory in function summarizes neuronal classification. III. NERVE VS TRACT Definition 1. NERVES Bundle of axons that extends out from the brain as cranial I. EPINEURIUM nerves and from the spinal cord as (PNS) and it’s Covering the whole neurons. surrounded by connective tissue. II. PERINEURIUM Covering the fascicle (nerve fibre) 2.TRACTS III. ENDONEURIUM Covering the single nerve fibre (axon) Bundle of axons within central nerves system, found in white matter of brain (corticospinal nerve) Connective tissue is absent EXAMPLE: Pinching the skin Information travels to single nerve fibre (axon) and then next goes to CNS passes to sensory glial. PREPARED AND EDITED BY: TRANS GROUP 6  (002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 Pain and temperature Example: touching hot water. THREE ORDERS OF NEURON ▪ First order of neurons is connected in dorsal root ganglia ▪ Second order of neurons is connected in the thalamus ▪ Third order of neurons is connected in primary sensory cortex IV. PATELLAR REFLEX A. KNEE JERK/PATELLAR REFLEX Tracts Bundle of axons in the CNS Found in the white matter of brain and spinal cord. Examples Corticospinal tract Spinothalamic tract Dorsal column Example: Numbfeel hitted with harmmer Maintain poster imbalance, if this doesn’t happens it indicates disorder in nerves system. CORTICOSPINAL TRACT When patellar tendon stretch decidated by muscle spindle stimulate the sensory neurons. Nerve cell body of those action located in pre-central gyrus. It starts and travel white matter of brain to B. SYNAPTIC REFLEX posterior limb of internal capsule which is also It is connected between sensory neurons and made of nerve fibres and goes to pyramided motor neurons. dissocation White matter of the spinal cord as the The motor neurons sends out the message to a laternal corticospinal tract, travels to ventricle horn and muscle. ventricle column of spinal cord. Sensory neurons stimulate the inhibitory So, this is the reason why Left side of brain is interneurons. The hamstring to the muscle travel controlled by right side of the body. Right side of the impulse through SENSORY NEURONS-CNS-PNS. brain is controlled by left side of the body. DORSAL COLUMN Pathway for light touch/proprioception Example: Applause - The information to is sent to the thalamus and then to the primary somatosensory cortex. SPINOTHALAMIC TRACT PREPARED AND EDITED BY: TRANS GROUP 6  (002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 V. NEUROGLIAL CELLS A. Neuroglial cells - Glial cells/ Supporting cells - Offers metabolic and mechanical support for neurons - 10x more abundant than neurons - In contrast to neurons, they undergo mitosis because of the presence of centrioles - capable of reproduction/ mitosis - when control over this capacity is lost, primary brain tumors (originate mainly from neuroglial cells/ supporting cells, not from the nerve cell) result > Glioblastomas (PNET- primitive neuroectodermal tumor) > Gliomas (ex.Astrocytoma/Oligodendroglioma/Ependym oma/Ganglioglioma) Grade I (best prognosis)-IV(worst) Amongst the most deadly/malignant form of PRIMARY BRAIN CANCER CLASSIFICATION OF NEUROGLIAL CELLS - according to location CNS - astrocytes, oligodendrocytes, ependymal cells, microglial cells PNS - Schwann cells, Satellite cells (supporting cells) B. Cells in the Central Nervous System Astrocytes - Greek word Astron: a star - most abundant, largest, versatile, highly branched glial cells - cling to neurons and cover capillaries - pedicles wraps capillaries and binds to the pia matter to form PREPARED AND EDITED BY: TRANS GROUP 6  (002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 - Glial Limitans - forms the Blood-Brain Barrier o Myelin is an electrical insulator which speeds up - prevent toxins/certain drugs from conduction entering the brain o Responsible for the formation of the myelin sheath of - not all drugs can enter the brain nerve fibers in the CNS, much as the myelin of - Functions: peripheral nerves is formed from Schwann cells. This - support and braces neurons formation and maintenance of myelln around many - anchor neurons to their nutrient supplies CNS axons provides them with an insulating coat and (capillaries) greatly increases the speed of nerve conduction along - guide migration of young neurons during them (seep. 47). Because oligodendrocytes have development several processes, unlike Schwann cells, they can - control the chemical/ ionic environment each form several intermodal segments of myelin on - responsible for scar formation (after the same or different axons. A single oligodendrocyte trauma/stroke) can form as many as 60 internodal segments. Note - energy metabolism that, unlike Schwann cells in the peripheral nervous - forms the blood brain barrier (one of the most system (PNS), oligodendrocytes and their associated important functions) axons are not surrounded by a basement membrane. - Astrocytes, with their branching processes, form a supporting framework for the nerve cells and nerve fibers. Their processes are frictionally coupled at gap junctions. In the embryo, they serve as a scaffolding for the migration of immature neurons. By covering the synaptic contacts between neurons, they may serve as electrical insulators preventing axon terminals from influencing neighboring and unrelated neurons. Microglial Cells - “policemen” of the Nervous system - immune effector cells - smallest and rarest glial cell, ovoid with spines - Phagocytes (neuronal debris, microorganisms)> part of the inflammatory response - scattered throughout CNS clearing any debris - protection from viruses and microorganisms - In inflammatory disease of the CNS, they become the immune effector cells. They retract their processes and migrate to the site of the lesion. Here, they proliferate and become antigen- presenting cells, which, together with the invading C. Cells in the Peripheral Nervous System T lymphocytes, confront Invading organisms. They are also actively phagocytic; their cytoplasm Schwann Cells becomes filled with lipids and cell remnants. The - lemmocytes microglial cells are joined by monocytes from - analogue of the oligodendrocytes in the PNS neighboring blood vessels. - wraps around an individual segment of a single axon Ependymal Cells - wrap individually around the shaft of peripheral - line cerebrospinal fluid-filled cavities axons, forming a layer or myelin sheath along - low columnar ciliated epithelial cells segments of the axon - line the ventricles of the brain and central brain of the - Saltatory conduction via Nodes of Ranvier – spinal cord jumping of impulse from node to node - forms the Choroid plexus in the lateral ventricles - Schwann cell membrane, which forms the myelin - main production of cerebrospinal fluid sheath, is composed primarily of lipids; the lipids - facilitates distribution of CSF serve as insulator thereby speeding the - Ependymocytes assist in CSF circulation within the transmission rate of action potentials along the cavities of the brain and the central canal of the spinal axon cord by the movements of the cilia. The microvilli on the free surfaces of the ependymocytes indicate that Basal Lamina/ Neurilemma they also have an absorptive function. - remnants of the nucleus/ cytoplasm of Schwann cells Oligodendrocytes o analog of the Schwann cells (PNS) in the CNS - allows axonal repair in the PNS o responsible for forming the myelin sheaths in the CNS - absent in the CNS (white matter fiber tracts) axons - repair is not possible in the CNS o around brain and spinal cord axons - cannot reattach in the brain and spinal cord Satellite Cells PREPARED AND EDITED BY: TRANS GROUP 6  (002) NEUROBIOLOGY OF NEURONS AND THE NEUROGLIA DR. VIADO | 09/23/2020 - analog of astrocytes in the PNS Dorsal - wraps around nerve cell bodies in the sensory Root (dorsal root ganglia) and autonomic (Sympathetic Ganglion and parasympathetic) ganglias - regulates the microenvironment in these ganglias - nutrient supply/ structural function. 4. The conducting portion of a nerve cell is a. Dendrite b. Axon c. Soma d. None of the above 5. Myelinated axons facilitates faster conduction compared with unmyelinated axons a. True b. False 6. Action potentials generated by the soma begins at what structure of the neuron? a. Axon Terminals b. Node of Ranvier c. Axon Hillock d. RER 7. Match the following characteristics/function with the specific type of Neuroglial cell 1. Oligodendrocytes a. May develop into brain tumor 2. Astrocytes b. Lemmocytes TEST YOURSELF 3. Ependymal cells c. Scar formation (Gliosis) 1. Collection of cell bodies in the CNS are collectively called Ganglia 4. Schwann cells d. Central Canal of the spinal cord a. True 5. Microglial cells e. Forms myelin sheath in CNS b. False 6. All of the above f. Active phagocytic cells 2. Bundle of axons (Fibers) in the CNS are collectively called Nuclei a. True b. False Answers: 1. False (Nuclei), 2. False (Tracts), 3. Bipolar neuron – olfactory cell, fused dendrite and a single axon, retina; Pseudounipolar/Unipolar neuron – Dorsal 3. Match the following cells/characteristics/function with the specific root ganglion; Multipolar neuron – pyramidal cell, 4. Axon, 5. True, 6, Axon Hillock, 7. Oligodendrocytes – E; Astrocytes – C; Ependymal cells – D; Schwann cells – B; structural type of Neuron Microglial cells – F; All of the above – may develop into brain tumor Bipolar Pseudounipolar/Unipolar Multipolar Neuron Neuron Neuron Olfactory cell Pyramidal cell Fused dendrite and a single axon Retina PREPARED AND EDITED BY: TRANS GROUP 6