Introduction to Neurohistology PDF

(002) INTRODUCTION TO NEUROHISTOLOGY DR. STEVE S. ARELLANO | 30/09/2020 OUTLINE III. CLASSIFICATION OF NEURONS I. INTRODUCTION...

(002) INTRODUCTION TO NEUROHISTOLOGY DR. STEVE S. ARELLANO | 30/09/2020 OUTLINE III. CLASSIFICATION OF NEURONS I. INTRODUCTION According to NUMBER OF NEURITES II. NERVE TISSUE − Unipolar Neurons III. CLASSIFICATION OF NEURONS − Bipolar Neurons A. BASIC PARTS OF A NEURON − Multipolar Neurons B. NERVE CELL BODY C. CELL TRANSPORT D. RESTING STATE OF A NEURON E. SYNAPSE IV. NEUROGLIA V. REACTION OF A NEURON TO INJURY I. INTRODUCTION Cell - Basic building blocks of living tissues - Basic structures of all living organisms - Take nutrients from food, & carry out functions - Human body is composed of TRILLION of cells CELLS 🡪 TISSUES 🡪 ORGANS 🡪SYSTEMS🡪 ORGANISMS Types of Cells Fig.1 Types of Neurons − Nerve Cell 1. UNIPOLAR NEURONS − Muscle Cells − single neurite that divides a short distance from the cell body − Bone Cell into 2 branches: − Gland Cell one branch proceeding to some peripheral − Blood cells (e.g. RBCs, lymphocyte, monocyte, structure neutrophil, eosinophil, basophil) other branch entering CNS − Reproductive cell (e.g. sperm cell, egg cell) − branches of this neurite have the structural & functional characteristics of an axon II. NERVE TISSUE − terminal branches are referred to as the dendrites − ex. Posterior root ganglion Nerve Tissue 2. BIPOLAR NEURONS − Consists of numerous varieties of neurons, which are − Elongated cell body, from each end of which a single structurally & functionally supported by Glial Cells of several neurite emerges different types. − ex. Retinal bipolar cells, cells of the sensory cochlear & vestibular ganglia Other Associated cells − Ependymal Cells (ventricular cavities) 3. MULTIPOLAR NEURONS − Satellite Cells (sensory &autonomic ganglia − Several neurites arising from the cell body − Schwann Cells (peripheral nerve myelin) − With exception of the long process, the axon, the remainder of the neurites are dendrites NEURONS (NERVE CELLS) − ex. Most neurons of the brain & SC - Basic functional unit of the nervous system - Excitable cells that are specialized for the reception of stimuli & conduction of nerve impulse - Information is processed & encoded by electrical or chemical steps that occur very rapidly (in MS) - Nerve cells serving a common function, often with common target are grouped together into NUCLEI - Nerve cells with common form, function & common target are grouped outside the CNS are called GANGLIA - If it is destroyed by trauma or disease, it is not replaced - Incapable of undergoing cell division PREPARED AND EDITED BY: LUMAYAG, J., MANLONGAT, A., MOJICA, S., PRUDENCIO, J., PUZON, M., QUIAMBAO, C., QUILALA, E  (002) INTRODUCTION TO NEUROHISTOLOGY DR. STEVE S. ARELLANO | 30/09/2020 A. BASIC PARTS OF A NEURON According to SIZE − Golgi type I Neurons − Golgi Type II Neurons CELL BODY − Amacrine Neurons − Project one or more processes called neurites − 5 um to 135 um diameter − Neurites may extend over >1 meter Fig. 2 Golgi type 1 Neurons 1. GOLGI TYPE I NEURON − 1 m long axon Examples: − Long fiber tracts (brain & SC) Fig. 4 Parts of a Neuron − Purkinje cells (cerebellum) NEURITES − Nerve fibers (peripheral nerves) 1. Dendrites − Pyramidal cells (cerebral cortex) − Short processes of the cell body − Motor cells (SC) − diameter tapes as they extend from the cell body & often branch profusely 2. GOLGI TYPE II NEURONS − many neurons bear large number of dendritic projections − Short axon (DENDRITIC SPINES) − Terminates in the neighborhood of the cell body − responsible for receiving information & conducting it toward − Outnumber the Golgi type I neurons the cell body − Star-shaped in appearance − Cerebellar & cerebral cortex 2. Axon − Inhibitory in function − Single long tubular neurite that conducts impulses away from the cell body 3. AMACRINE NEURONS − Commonly branch profusely before their terminal end − Unusual neuron type − Distal end often enlarged, called Terminals − Lack axon − Some axons (autonomic nerves) have series of swellings near their termination resembling a string of beads, called Varicosities − Length varies (0.1 mm to 3 meters long) Diameter varies: − Larger conducts impulse rapidly − Smaller conducts impulse very slowly Initial segment of the axon: − first 50 to 10 um after it leaves the axon hillock − most excitable part of the axon − origin of the action potential (AP) Fig. 3 Amacrine cells − conducts impulse away from the cell body (exemptions: axons of sensory DRG cells) PREPARED AND EDITED BY: LUMAYAG, J., MANLONGAT, A., MOJICA, S., PRUDENCIO, J., PUZON, M., QUIAMBAO, C., QUILALA, E  (002) INTRODUCTION TO NEUROHISTOLOGY DR. STEVE S. ARELLANO | 30/09/2020 Axolemma 4. Nissl Substance − Plasma membrane bounding the axon − Basophilic Axoplasm − Composed of rough ER − Cytoplasm of the axon − Synthesizes proteins which replaces the proteins that are − Devoid of Nissl granules or Golgi complex broken down during cellular activity − Devoid of RNA & ribosomes − Fatigue or neuronal damage causes the Nissl substance to move & get concentrated in the periphery of the cytoplasm leading to the phenomenon Chromatolysis. B. NERVE CELL BODY − Granules are distributed throughout the cytoplasm of the cell body, except at the region close to the axon (Axon Hillock) − Present at the proximal parts of the dendrites 5. Golgi Complex − Network of irregular way threads around the nucleus − Made of smooth surfaced ER − CHON by the Nissl substance is transferred to the cis side of the Golgi complex 6. Mitochondria − Spherical or rod shaped − Scattered all throughout the cell body, axon, & dendrites Fig. 4 Parts of a Nerve Cell Body − Possess many enzymes, that take part of tricarboxylic acid cycle and the cytochrome chains − Mass of cytoplasm in which a nucleus is embedded of respiration − Bounded externally by a plasma membrane − Important in production of energy − Small as 5 um to 135 um in diameter 7. Neurofibrils 1. Nucleus − Bundles of neurofilaments − Stores the genes − Each filament = 10 nm in diameter − Centrally located, large & rounded − Neurofilaments form the main component of the − Chromosomes no longer duplicate; function only in gene cytoskeleton expression − Chromosome: uncoiled state 8. Microfilaments − Single prominent nucleolus, concerned with ribosomal RNA − about 3 to 5 nm in diameter (rRNa) synthesis & ribosome subunit assembly − formed by actin − In females, one of the 2x-chromosomes is compact & is − concentrated at the periphery of the cytoplasm known as Barr Body (composed of sex chromatin at the inner − Role: formation of new cell processes, & the surface of the nuclear envelope) retraction of old ones − Assist the microtubules in axon transport 2. Nuclear Envelope − Special portion of the rough endoplasmic reticulum (ER) 9. Microtubules − Double layered, & has fine nuclear pores, where materials can − 25 nm in diameter diffuse into & out of the nucleus − Provide a stationary track which permits specific organelles to move by molecular motors 3. Cytoplasm − Rich in granular & agranular ER 10. Lysosomes − Contains organelles & inclusions: − Membrane-bound vesicles, 8 nm in diameter − Acting as intracellular scavengers a. Nissl substance e. Microtubules b. Golgi complex f. Lysosomes − Contain hydrolytic enzymes c. Mitochondria g. Centrioles − Formed by the building off of Golgi apparatus d. Microfilaments h.Lipofuscin,melanin, glycogen, 3 forms of Lysosomes: & lipid a. Primary Lysosomes − Have just been formed b. Secondary Lysosomes − Contains partially digested material (Myelin Figures) PREPARED AND EDITED BY: LUMAYAG, J., MANLONGAT, A., MOJICA, S., PRUDENCIO, J., PUZON, M., QUIAMBAO, C., QUILALA, E  (002) INTRODUCTION TO NEUROHISTOLOGY DR. STEVE S. ARELLANO | 30/09/2020 c. Residual Bodies − Enzymes are inactive D. RESTING STATE OF A NEURON − Evolved from digestible materials such as pigment & lipid 1. Unstimulated State − K+ ions diffuse through the plasma membrane from the cell to 11. Centrioles cytoplasm to the tissue fluid − Hollow cylinder whose wall is made up of bundles − Permeability of the membrane to K+ ions is much greater than microtubules that to Na+ ions − Found in immature, dividing nerve cells − Passive efflux of K+ ions is > than influx of Na+ − Also found in mature nerve cells, involved in the − Result to a steady potential difference of -80nmV maintenance of microtubules − Inside of the membrane is negative with respect to the outside − Potential is known as Resting Potential 12. Lipofuscin (pigment material) − Yellowish granules within the cytoplasm − Formed as a result of lysosomal activity 2. Excitation of the Plasma Membrane of the Nerve Cell Body − Represents a harmless metabolic by product Nerve cell is stimulated by electrical, mechanical, or chemical means − Accumulates with age 13. Melanin Granules Change in membrane permeability to Na+ ions − Catecholamine-synthesizing ability of a neuron whose neurotransmitter is Dopamine. − Found in the cell cytoplasm (substantia nigra of the Na+ ion diffuse through the plasma membrane into the cell midbrain) cytoplasm from the tissue fluid 14. Plasma Membrane − Continuous external boundary of the cell body & its Membrane becoming progressively depolarized processes − Site for the initiation & conduction of the nerve impulse Sudden influx of Na+ ions followed by altered polarity − 8 nm thick − Composed of an inner & outer layer of loosely arranged Protein molecules (about 2.5 nm) separated by a middle layer of lipid (3 nm) ACTION POTENTIAL +40 mV (5msec) Lipid layer − Made up of 2 rows of phospholipid molecules Increased membrane permeability for Na+ ions ceases 🡪 K+ ions − Hydrophobic ends are in contact with each other permeability increases 🡪 K+ ions start to flow from the cell cytoplasm 🡪 − Polar ends are in contact with the protein layer Return to Resting State − CHO molecules are attached to the outside of the plasma membrane & are linked to the Protein or the lipids forming the Cell − once generated, AP spreads over the plasma membrane Coat or Glycocalyx away from the site of initiation − conducted along neurite as the NERVE IMPULSE − impulse is self-propagated C. CELL TRANSPORT − size & frequency do not alter − once the nerve impulse has spread over a given region of plasma membrane, another AP cannot be elicited − Movement of membrane organelles, secretory materials, immediately synaptic precursor membranes, large dense core vesicles, mitochondria & smooth ER − duration of this non excitable state is called REFRACTORY PERIOD 2 kinds of Cell transport − Rapid Cell Transport (100 to 400 mm per day) − Slow Cell Transport (0.1 to 3 mm per day) E. SYNAPSES − site where two neurons come into close proximity 1. Rapid Cell Transport − functional inter- neuronal communication occurs − By 2 motor CHON associated with microtubule − most neurons make synaptic connections to a 1,000 or more ATPase sites: other neurons − Kinesin for anterograde movement (away from the cell) − communication takes place in one direction only − Dynesin for retrograde movement They may be: − Chemical (neurotransmitter) or − Electrical (ion channels) PREPARED AND EDITED BY: LUMAYAG, J., MANLONGAT, A., MOJICA, S., PRUDENCIO, J., PUZON, M., QUIAMBAO, C., QUILALA, E  (002) INTRODUCTION TO NEUROHISTOLOGY DR. STEVE S. ARELLANO | 30/09/2020 TYPES OF SYNAPSE TYPES OF NEUROGLIAL CELLS − CNS − Ependymal cells − Oligodendrocytes − Astrocytes − Microglia − PNS − Satellite cells − Schwann cells ASTROCYTES − Small bodies with branching processes Processes are interwoven in the outer & inner surface of the CNS forming the: − Outer Glial Membrane − beneath the pia matter − Inner Glia Limiting Membrane Fig. 5 Different Types of Synapse − Beneath the ependyma lining the ventricles (brain) & central canal (SC) 1. Axodendritic Synapse − Most common type − 2 Types of Astrocytes − Between an axon of a neuron on a dendrite of the next − Fibrous Astrocytes neuron − Protoplasmic Astrocytes 2. Axosomatic Synapse − Dendrite or axon synapse on the initial segment of another 1. Fibrous Astrocytes axon − Found in white matter, where their processes pass between 3. Axoaxonic Synapse the nerve fibers − Synapses between axon terminal expansions from different − Each process is long, slender, smooth, & not much branched neurons − Most brain tumors are astrocytoma derived from fibrous astrocytes. These are distinguished pathologically by their glial fibrillary acid protein (GFAP) in the proximal processes. IV. NEUROGLIA − Non-excitable cells that support the neurons of the CNS 2. Protoplasmic Astrocytes − Smaller in size, but outnumbered the neurons 5-10X − Found in gray matter, where their processes pass between − Comprises the 50% of the total volume of the brain & SC the nerve cell bodies − No axons, nor do axon terminals synapse upon them − Processes are shorter, thicker, & more branched FUNCTIONS OF ASTROCYTES 1. Supporting framework for the nerve cells & nerve fibers 2. Scaffolding for the migration of immature neurons (embryonic stage) 3. Electrical insulators preventing axon terminals from influencing neighboring & unrelated neurons 4. Barriers for the spread of NT substances released at synapses. 5. Absorbs GABA & glutamic acid secreted by the nerve terminals & limiting their influence 6. Store glycogen within their cytoplasm 7. Absorb excess K+ ions from ECF during repetitive firing of a neuron 8. Phagocytes by taking up degenerating synaptic axon terminals 9. Proliferate & fill in the space previously occupied by a dead neuron (Replacement Gliosis) 10. Conduit for the passage of metabolites or raw materials from blood capillaries to the neurons through their perivascular feet 11. Produce substances that have trophic influence on neighboring neurons. Fig. 6 Different types of Neuroglial Cells PREPARED AND EDITED BY: LUMAYAG, J., MANLONGAT, A., MOJICA, S., PRUDENCIO, J., PUZON, M., QUIAMBAO, C., QUILALA, E  (002) INTRODUCTION TO NEUROHISTOLOGY DR. STEVE S. ARELLANO | 30/09/2020 FUNCTIONS OF THE EPENDYMAL CELLS OLIGODENTROCYTES 1. Assists in the circulation of CSF − Have small cell bodies & delicate processes 2. Absorptive function (microvilli) − No filaments in their cytoplasm 3. Transport chemical substances (by Tancytes) from the CSF to the − Found in rows along myelinated nerve fibers & nerve cell hypophyseal portal system bodies 4. Play a part in the control hormone production by the anterior lobe of the pituitary 5. Involved in the production & secretion of CSF (choroidal epithelial FUNCTIONS OF OLIGODENDROCTYES cells) 1. Formation of myelin sheath of nerve fibers in the CNS -One Oligodendrocyte can form 60 internodal segments of myelin on the same or different axon V. REACTION OF A NEURON TO INJURY − FIRST reaction of a nerve cell to injury is LOSS OF (Schwann Cells form the myelin sheath of nerve fibers in the PNS) FUNCTION − Whether the cell recovers or dies will depend on the severity MYELINATION & duration of the damaging agent − Begins at 16th week (4 months) of intrauterine life & − Morphological evidence of cell injury requires a minimum 6 to continues post-natally up to the time child is walking 12 hours of survival o Nerve cell becomes swollen & rounded off MICROGLIA o Nucleus swells & displaced to the periphery of the − Not related to the other neuroglial cells cell − Derived from macrophages outside the NS o Nissl granules dispersed toward the periphery of − Smallest of the neuroglial cells the cytoplasm − Resembles connective tissue macrophages − Phagocytic activity is performed by: − Migrated into the nervous system during fetal life o Microglia in the CNS − Increase in number in the presence of damaged nervous o Reticuloendothelial System in the PNS (is a tissue (many are monocytes that have migrated from the component of the immune system) blood) − Inactive in a normal brain & SC (Resting Microglial Cells) ASTROCYTES − Astrocytosis (GLIOSIS) FUNCTIONS OF MICROGLIAL CELLS − Proliferation of astrocytes 1. Migrate to the site of a lesion during inflammation or degeneration of − Reaction of neuroglial cells to injury is by hyperplasia & the CNS hypertrophy of the astrocytes, which become fibrous 2. Proliferate & phagocytized lipids & cell remnants − Gliotic Star − Dense feltwork of astrocytic processes that occurs in the same neuronal degeneration EPENDYMA − Line the cavities of the brain & the central canal of the SC OLIGODENTROCYTES − Single layer of cells − Respond to injury by expanding & showing vacuolation of − Cuboidal or columnar in shape their cytoplasm − Have microvilli & cilia for the movement of CSF − Nuclei become pyknotic − Base lie in the Internal Glial Limiting Membrane − Severe damage would result to DEMYELINATION 3 GROUPS OF EPENDYMAL CELLS MICROGLIA 1. Ependymocytes − Retract their process and migrate to the site of the lesion − Line the ventruicles of the brain & central canal of the SC (in o Proliferate/actively phagocytic contact with CSF) − They are joined in their scavenger activity by Monocytes 2. Tanycytes − Line the floor of the 3rd ventricle overlying the median eminence of the hypothalamus AXONAL REACTION AND AXONAL DEGENERATION 3. Choroidal Epithelial Cells − Changes that takes place in a nerve cell when its axon is cut − Cover the surface of the choroid plexuses or injured − Start to appear in 24 to 48 hours after injury, & reach its maximum in 12 days − In the PNS − Injury is a followed by regeneration − Reparative changes take place in the cell body − In the CNS − Degeneration is not followed by regeneration PREPARED AND EDITED BY: LUMAYAG, J., MANLONGAT, A., MOJICA, S., PRUDENCIO, J., PUZON, M., QUIAMBAO, C., QUILALA, E  (002) INTRODUCTION TO NEUROHISTOLOGY DR. STEVE S. ARELLANO | 30/09/2020 CEREBRAL EDEMA TEST YOUR KNOWLEDGE − Clinical condition that can follow head injury, cerebral infections, or tumors − Abnormal increase in the water content of the tissues of the 1. A node of Ranvier is CNS − Sequelae: a. the point of near-contact between the processes of two neurons − Flattening of cerebral gyri = Herniation of the brain b. characteristic of unmyelinated fibers = Death c. a constriction of the axon d. a nerve receptor 3 FORMS OF CEREBRAL EDEMA e. a junction between two Schwann cells 1. Vasogenic Edema 2. The cells that are responsible for forming myelin in the central − Most common type nervous system are the − Accumulation of tissue fluid in the ECS after a damage to the vascular capillary walls or the presence of new capillaries a. Schwann cells without fully formed BBB b. satellite cells − Causes: infection, trauma, or tumors c. microglia d. astroglia 2. Cytotoxic Edema e. oligodendroglia − Accumulation of fluid within the cells of nervous tissue, resulting in cellular swelling 3. Nissl substance in nerve cell bodies is associated with − Failure in the plasma membrane ATP Na-pump mechanism − Causes: toxic, metabolic a. spread of stimulus b. synaptic junctions 3. Interstitial Edema c. axons − Occurs in obstructive hydrocephalus d. protein synthesis − Rise in CSF pressure forces the fluid out of the ventricular e. myelin formation system into the ECS. NEOPLASM OF NEUROGLIA 4. Myelination of peripheral nerves is accomplished by − Account for 40 to 50% of intracranial tumors a. astrocytes. − Tumors are referred to as GLIOMAS b. oligodendrocytes. Astrocytoma (Glioblastoma) c. Schwann cells. − Most commonly encountered d. neural crest cells. − Tumors of astrocytes e. basket cells. Ependymoma & tumor − of the neuroglia are highly invasive. 5. What are the scavenger cells of the CNS? a. Astrocytes b. Microglial cells c. Oligodendrocytes d. Schwann cells 6. Which of the following collective term is not applied in the CNS: a. Tracts b. Nuclei c. Nerves d. Oligodendrocytes 7. A report from a hospital pathology lab indicates that a microscope slide with a small specimen of neural tissue contains "numerous GFAP-positive" cells. What is the most likely source of this specimen? a. A region of white matter b. A sensory ganglion c. An autonomic ganglion d. A region of gray matter e. Pia mater E, E, D, C, B, C, D PREPARED AND EDITED BY: LUMAYAG, J., MANLONGAT, A., MOJICA, S., PRUDENCIO, J., PUZON, M., QUIAMBAO, C., QUILALA, E