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HISTOLOGY OF NERVOUS SYSTEM

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Presentation on theme: "HISTOLOGY OF NERVOUS SYSTEM"— Presentation transcript:

1 HISTOLOGY OF NERVOUS SYSTEM
DR. Nabil Khouri

2 NERVOUS SYSTEM The most complex system in the human body
10/09/2018 The most complex system in the human body Formed by network more than 100 million neuron Each neuron has a thousand interconnection  a very complex system for communication Nerve tissue is distribute throughout the body, anatomically divide into : CNS & PNS Structurally consist : Nerve cells & Glial cells

3 Anatomically divided in to :

4 Functional Organization of the Nervous System
Peripheral Nervous System Histology Lecture 2004 Michael Hortsch Functional Organization of the Nervous System Somatic (conscious afferent* and efferent, voluntary motor control) Autonomic (unconscious efferent, involuntary motor control of internal organs to maintain homeostasis) Sympathetic – thoracolumbar division Parasympathetic – craniosacral division * Somatic afferents = sensory fibers from skin, muscle, joints, tendons. Visceral afferents = sensory fibers from visceral organs; some result in conscious sensations, but others do not. However, they are not considered part of the autonomic nervous system, which is entirely efferent. These functional divisions of the nervous system are used to convey an organizational scheme that is based on certain neuroanatomical and neurophysiological properties, although the scheme is incomplete (visceral afferents are left out) and over simplified.

5 Function of the nervous system
sensory input sensory receptor motor input effector Function of the Nervous System integration

6 CONTENTS Cells of nervous system nerve cells and Neuralgia
10/09/2018 CONTENTS Cells of nervous system nerve cells and Neuralgia Synaptic communication Central nervous system & Peripheral nervous system & associated structure

7 Cellular Components of the Nervous System
Peripheral Nervous System Histology Lecture 2004 Michael Hortsch Neurons Cellular Components of the Nervous System Wheater’s Functional Histology; 5th edition, 2006, Young, Lowe, Stevens and Heath; Nervous tissue is the third of the four basic tissue types. Neurons have many cytoplasmic processes, and are best appreciated with special stains that employ heavy metal impregnation. These classic neuronal stains were developed by the pioneers of neuroanatomy: Ramon y Cajal and Golgi. Both neurons and supporting glia arise from the embryonic neuroectoderm. Glia (support cells)

8 Nervous Tissue: Support Cells
Support cells in the Central Nervous System (CNS) are grouped together as neuroglia Neuroglia literally means “nerve glue” The function of neuroglia is to support, insulate, and protect the delicate neurons of the brain

9 Neuroglial Cells Half of the volume of the CNS
Smaller cells than neurons 50X more numerous Cells can divide rapid mitosis in tumor formation (gliomas) 4 cell types in CNS Astrocytes Microglia Ependymal oligodendrocytes 2 cell types in PNS Schwann satellite cells

10 Types of Neuroglia in CNS
Astrocytes Star-shaped cells Half of all brain tissue Brace neurons; they keep the neurons in contact with their blood supply (capillaries) Control the chemical environment of the brain by mopping up leaked ions

11

12 Types of Neuraglia in CNS
Microglia Spiderlike phagocytes (white blood cells) Dispose of debris like dead brains cells and bacteria

13 Types of Neuroglia in CNS
Ependymal cells Lines the cavities of the brain and spinal cord Circulate cerebrospinal fluid by beating their cilia Cerebrospinal fluid fills the space the brain does not take up and forms a protective cushion around the brain and spinal chord

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15 Types of Neuroglia in CNS
Oligodendrocytes Wrap around nerve cells in the brain and spinal chord Produce myelin sheaths Myelin is a fatty, insulation covering the nerve cells; allows for the electrical signal to transmit faster (like wire coating)

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17 Neuroglial Cells in the PNS
2 cell types in PNS Schwann satellite cells

18 Types of Neurolgia in PNS
Satellite cells Protects neuron cell bodies which is where the nucleus of the cell if found

19 Schwann cells Form myelin sheath in the peripheral nervous system (nerves of the body; not nerves of the CNS

20

21 Schwann cells

22 Myelin sheath — whitish, fatty material covering axons
protects/insulates the cells and increases the transmission rate of nerve impulses Schwann cells — produce myelin Nodes of Ranvier — gaps in myelin sheath along the axon

23 The process of myelination

24 Nodes of Ranvier in a longitudinal nerve section
Peripheral Nervous System Histology Lecture 2004 Michael Hortsch Color Atlas of Histology; 1992; Erlandsen and Magney; Mosby Book; Fig. 9-13 Nodes of Ranvier in a longitudinal nerve section

25

26 So what’s a Neuron? Neurons = nerve cells
Cells specialized to transmit messages Major regions of neurons Cell body — nucleus and metabolic center of the cell (main part of nerve cell) Processes — fibers that extend from the cell body can be microscopic or up to 3-4 feet in length

27 So what’s a Neuron? Neurons = nerve cells
Cells specialized to transmit messages Major regions of neurons Cell body — nucleus and metabolic center of the cell (main part of nerve cell) Processes — fibers that extend from the cell body can be microscopic or up to 3-4 feet in length

28

29 STRUCTURE OF NEURON Principle cells of Nervous Tissue
Consist of 3 parts : CELL BODY (perikaryon/soma) A single AXON Multiple DENDRITES ø µm

30 Neurons Functional unit of nervous system Cell body Nissl bodies
Neurofilaments Microtubules Lipofuscin pigment clumps Cell processes Dendrites Axons Functional unit of nervous system Have capacity to produce action potentials electrical excitability Cell body single nucleus with prominent nucleolus Nissl bodies (chromatophilic substance) rough ER & free ribosomes for protein synthesis neurofilaments give cell shape and support microtubules move material inside cell lipofuscin pigment clumps (harmless aging) Cell processes = dendrites & axons Lecutre 8: Nervous System

31 FUNCTION OF NEURON Receptive Integrative Motor
Receptor receive stimuli and tranduce into nerve impulse and transferro to other neuron Integrative Processing impulse on the higher center Motor Initiating motor respons and tranduse impulse to the effector

32 CELL BODY (PERIKARYON)
Central portion of the cell Generally are polygonal Different shape and size  characteristic regions of nervous system Contain : Nucleus Perinuclear cytoplasm

33 ULTRASTRUCTURE OF NEURON
Nucleus : large, spherical to ovoid and centraly located a single prominent nucleolus finely dispersed chromatin  trancriptionaly active Cytoplasm : Abundant of R.E.R Polyribosomes Basic dyes (a+b) Nissl Bodies lots of S.E.R. Golgi bodies (perikaryon) protein secreting cell 10/09/2018

34 ULTRASTRUCTURE OF NEURON
Cytoplasm Many mitochondria, most abundant in axon terminal extensive cytoskeleton  axonal transport One centriole  do not undergo cell divisions 10/09/2018

35 Dendrites Conducts impulses towards the cell body
Typically short, highly branched & unmyelinated Surfaces specialized for contact with other neurons Contains neurofibrils & Nissl bodies

36 Axons Conduct impulses away from cell body
Long, thin cylindrical process of cell Arises at axon hillock Impulses arise from initial segment (trigger zone) Side branches (collaterals) end in fine processes called axon terminals Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters

37 Structural Classification of Neurons
Based on number of processes found on cell body multipolar = several dendrites & one axon most common cell type bipolar neurons = one main dendrite & one axon found in retina, inner ear & olfactory unipolar neurons = one process only(develops from a bipolar) are always sensory neurons

38 Structural Classification of Neurons

39 NEURONS CLASSIFICATION :

40 NEURONS CLASSIFICATION :
According to their function : Sensory Neuron (afferent ) Receive sensory input  conduct impulses to CNS Motor Neuron (Efferent) CNS  conduct impulses to muscles, glands and other neurons Interneuron In the CNS as interconnectors, establish neuronal circuit between sensory and motor neuron

41 NEURON GROUPING CORTEX NUCLEI GANGLION
Neuron form six layers on the cerrebrum Form three layers on the cerrebellum NUCLEI In subcortical region (thalamus, midbrain, brainstem and spinal cord) neuron form irregular cluster  nuclei GANGLION Cluster of neuron outside the CNS 10/09/2018

42 THE CNS Covered by meninges Consist of :
Cerebrum Cerebellum Spinal cord No connective tissue soft, gel like When sectioned : White matter Gray matter Covered by meninges 10/09/2018

43 Gray and White Matter White matter = myelinated processes (white in color) Gray matter = nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (gray color) White matter = myelinated processes (white in color) Gray matter = nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (gray color) In the spinal cord = gray matter forms an H-shaped inner core surrounded by white matter In the brain = a thin outer shell of gray matter covers the surface & is found in clusters called nuclei inside the CNS Lecutre 8: Nervous System

44 NERVE FIBERS Consist of axons enveloped by a special sheath
Group of fibers constitute the peripheral nerve Two types : Myelinated fiber Unmyelinated fiber 10/09/2018

45 NERVE FIBERS Myelinated fibers Unmyelinated fibers
A single Schwann cell wraps around single axon form myelin sheath  nodes of Ranvier Unmyelinated fibers A single Schwann cell envelopes several axon Fibers enveloped within simple clefts of Schwann cells 10/09/2018

46 CONNECTIVE TISSUE INVESTMENTS
Epineureum Dense collagenous Con. Tissue with thick elastic fiber Prevent damage by overstreching Perineureum Dense con. Tissue Layers of epithelioids Isolates neural environment (blood-nerve barrier) Endoneureum Loose con. Tissue Regulation of microenvironment of nerve fiber 10/09/2018

47 Peripheral Nervous System Histology Lecture 2004 Michael Hortsch
Connective tissue layers in a peripheral nerve. Tight junctions between perineurium cells form a important isolating barrier. Epineurium Basic Histology – Text & Atlas; 10th edition, 2003; Junqueira and Carneiro, Lange McGraw-Hill; Fig 9-34 Endoneurium surrounds individual axons (nerve fibers) within a fascicle, perineurium surrounds bundles (fascicles) of nerve fibers, epineurium surrounds fascicles and forms a denser sheath around the entire nerve. Perineurial cells are derived from fibroblasts. Perineurium

48 PERIPHERAL NERVE

49 AUTONOMIC NERVOUS SYSTEM
SYMPHATETIC SYSTEM PARASYMPHATETIC SYSTEM The nuclei located in the thoracic and lumbar segment of spinal cord Preganglionic fibers leave the CNS by way of ventral roots The chemical mediator postganglionic fibers is norepinephrine The nuclei located in the medulla and midbrain and in the sacral portion of spinal cord Pre ganglionic fibers leave the CNS trough cranial nerve III, VII, IX and X and also trough II, III, IV sacral nerve The ganglion located near the effector organs The chemical mediator pre and postganglionic fibers is acethilcholine 10/09/2018

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