Nervous Tissue PDF

ILOs  Describe the LM & EM structure of the neuron  Classify different types of neurons  Describe the microscopic structure of myelinated nerve fiber and the process of myelination  Describe the microscopic structure of peripheral nerve trunk  List neuroglia and describe their microscopi...

ILOs  Describe the LM & EM structure of the neuron  Classify different types of neurons  Describe the microscopic structure of myelinated nerve fiber and the process of myelination  Describe the microscopic structure of peripheral nerve trunk  List neuroglia and describe their microscopic structure  Mention the definition & classification of synapses  Describe LM structure of different types of ganglia  Relate the structure of nervous tissue to its function  The nervous tissue is one of the 4 basic tissues of the body  It consists of 2 cell types (neuron & neuroglia)  It is the basic component of nervous system Nervous System is divided into: 1) The central nervous system (CNS) Brain & spinal cord 2) The peripheral nervous system (PNS) Cranial nerves, spinal nerves & ganglia Functionally it is divided into: Sensory or afferent Motor or efferent Interneuron Structure of Neuron: - Is the structural & functional unit of the nervous system - Composed of: - Cell body - Its processes including: axon dendrites Cell body (perikaryon, soma, cyton) RER LM: Nucleus: Large, rounded, central, vesicular, prominent nucleolus Cytoplasm: basophilic (Nissl granules) stained by toluidine blue EM: SER * RER& polyribosomes: (Nissl granules) * Golgi complex: juxtanuclear (synthesis of neurotransmitters) * Numerous scattered mitochondria * SER * Cytoskeleton: neurofibrils (microtubules, intermediate filaments, microfilaments) * Inclusions: melanin, lipofuscin & lipid droplet * One centriole (vestigial structure) Cell processes: Include: axon dendrites Axon (nerve fiber): - Single, arise from the axon hillock (hillock is a pyramidal area contains no Nissl granules) - Thin& long (sometimes has axon collateral) - Constant diameter& smooth contour axolemma - Terminal arborization - It has an axolemma and axoplasm axoplasm - Contains neurofibrils, SER, mitochondria but no Nissl granules Dendrites: - Arising from the cell body - Multiple, short, extensive branching - Irregular contour (thick origin, thin apex) - Contain Nissl granules, mitochondria, SER, neurofibrils Classification of neurons: * According to polarity (number of processes) into: 1- Unipolar neuron: flask, single process (not in human) 2- Pseudounipolar neuron: single process divides into: central branch as axon & peripheral branch as dendrite (sensory neurons) 3- Bipolar neuron: spindle, has two opposite poles (retina) 4- Multipolar neurons: have several processes containing: I- Polygonal, stellate neurons (anterior horn cells) I II III II- Pyriform neurons (Purkinje cell, cerebellum) III- Pyramidal neurons (cerebral cortex) * According to the length of their axons into: Golgi type I (long axon) Golgi type II (short axon) * According to axonal diameter & myelin sheath thickness: - Type A fibers: Larger diameter, heavily myelinated - Type B fibers: Smaller diameter, moderately myelinated - Type C fibers: Smallest diameter, unmyelinated Neurolemmal sheath: (Shwann cells) - Cellular tube of Schwann cell around p. nerves - Each cell is related to an inter-nodal segment - Support , regeneration, myelin formation Myelin sheath: - Myelin forms a tubular covering around the axon - It is interrupted at (nodes of Ranvier) - It is formed of lipids (derived from cell membrane) - Not stained by H& E & stained by osmic acid (black circles) - Protective insulation of the nerve - Travelling of nerve impulses Myelin formation (myelination) - Schwann cell warps its membrane around the axon > 50 turns - Cytoplasm between rings is squeezed back into the body of Schwann cell, making the cytoplasmic surfaces of the membrane in contact - N.B: Schwann cell is responsible for myelination in PNS - Oligodendrocyte is responsible for myelination in CNS Peripheral nerve trunk & its CT: -TS shows varying number of nerve fibers grouped in bundles of different sizes - Nerve fiber is acidophilic by H&E stain CT investment of peripheral nerve: - Each fiber are surrounded by endoneurium; thin layer of loose CT - Each bundle is surrounded by perineurium; dense CT - Whole trunk is covered by epineurium; thicker dense collagenous CT Function of CT: * Supplies blood vessels & nerves * Supportive and protective Neuroglial cells: CT of the NS :Astrocyrtes -1 :A- Protoplasmic astrocytes Large branching cells (many thick wavy, branching processes) - One or more of these ends (perivascular feet) - Large rounded to oval nuclei - Granular cytoplasm - :B- Fibrous astrocytes Its processes are longer, thinner, less branching - Less granular cytoplasm - Both contain Intermediate filaments (glial fibrillary acidic protein, GFAP) - Both functioning as: support, nutrient & maintaining blood brain barrier - Neuroglial cells :Oligodendrocytes -2 Small cells, oval nucleus - Few, short, less branching processes - - Myelin production in CNS 3- Microglial cells: Small cells, oval nucleus - Thin cytoplasmic processes with spines - Mononuclear phagocytic cell (brain macrophage) - All mentioned neuroglial types are present in CNS - :Schwann cell is considered as PNS neuroglia - Myelin formation, regeneration & support of neurons :Synapses The site of contact between 2 neurons where nerve impulses are transmitted from one neuron to the other - It has 3 parts: presynaptic, postsynaptic membranes & synaptic cleft :Morphology (contact sites) Axo-dendritic: between axon & dendrite -1 Axo-somatic: between axon & soma -2 Axo-Axonic: between 2 axons -3 Dendro-dendritic: between 2 dendrites -4 :Type of transmission Chemical: neurotransmitters released from vesicles in pre-synaptic membrane -1 Electrical: as gap junction, channels allow charges (ions) to flow -2 Ganglia: nodular structure, aggregation of neuronal bodies in PNS covered by C.T capsule (spinal & sympathetic) Sympathetic Spinal Ganglia Sympathetic chain Dorsal root of spinal nerve Site * All of small size Generally large neurons * Neuronal * Multipolar with Pseudounipolar (rounded) * bodies eccentric nuclei with central nuclei * Surrounded by less * Surrounded by many satellite cells satellite cells * Numerous * Few in number * Scattered Arranged in groups * Scattered * Bundles * Nerve fibers  Spinal Sympathetic  A B C A- Pyriform nerve cells B- Pyramidal nerve cells C- Nerve trunk