NERVOUS TISSUE (Neuroglia, Ganglia) PDF

HNU Faculty of Medicine Histology & Cell Biology Department Year 1 Principle of Human Body Structure HBS-101 NERVOUS TISSUE (PART 2) Ganglia, Neuroglia & brain barriers Objective 1.Recognize types of ganglia. 2...

HNU Faculty of Medicine Histology & Cell Biology Department Year 1 Principle of Human Body Structure HBS-101 NERVOUS TISSUE (PART 2) Ganglia, Neuroglia & brain barriers Objective 1.Recognize types of ganglia. 2.Differentiate between spinal & sympathetic ganglia. 3.Describe the histological structure of chemical synapses 4.Describe histological structure & functions of neuroglial cells. 5.Define blood brain barriers - CNS: Brain & spinal cord. - PNS: Nerve fibers (nerve trunk) , ganglia & nerve endings. The nervous tissue → ectodermal in origin -Two cell types: *Neurons → functioning cells. *Glial cells →supporting tissue. Extra*-CNS: brain & spinal cord. -PNS: nerve fibres (nerve trunk) , ganglia & nerve endings. The nervous tissue →ectodermal in origin -Two cell types: *Neurons → functioning cells *Glial cells →supporting tissue  Ganglia They are collection of nerve cells outside the CNS. They are of 2 types; 1- Sensory (spinal) & 2- Autonomic (sympathetic & parasympathetic).  located close to and on either side of the spinal cord in long chains outside the V COULMN & SUPPLY THE ORGANS. Spinal ganglia Sympathetic ganglia  Spinal Ganglion Sympathetic Ganglion 1) Covered by a thick C.T. Capsule. 1) Covered by a thin C.T. capsule 2) Contains NO synapses 2) Contains synapses 3) Contains Pseudo-unipolar 3)Contains multipolar stellate neurons neuron 4) Nerve cells are small, medium- 4) Nerve cells are small & sized or large uniform size.  Spinal Ganglion Sympathetic Ganglion 6) Nerve cells are arranged in 6) Nerve cells are scattered. group of rows, separated by nerve and C.T 7) Nerve cells are capsulated by 7) Satellite cells are few. satellite cells 8) Nerve fibers may become 8) No glomeruli are formed by convoluted forming glomeruli. the nerve fibers. 9) Nerve fibres are myelinated 9) Non myelinated 10) Poor blood supply 10) Rich blood supply. Sympathetic G Spinal G  Synapse Histologically: formed of: 1.Presynaptic side: rich in mitochondria & vesicles of chemical transmitter (in chemical synapse). It shows separate zones of dense cytoplasm. 2.Synaptic cleft: 20-30 nm in width. It shows delicate fibers or granules. 3. Postsynaptic side: - Has receptors for the chemical transmitter. - It shows a continuous zone of dense cytoplasm which is associated with a network of filaments called synaptic web. ❖ Classification: 1) According to method of transmission of nerve impulse: A-Chemical: - most common, conduction of impulses takes place by release of neurotransmitters. B-Electrical: - Contain gap junctions that allow movement of ions between cells & so permit spread of electric current. - They have been demonstrated in cerebellum. ❖ Classification: 2) According to the site of contact of the axon: 1- Axosomatic: axon forms synapse with cell body. 2- Axodendritic: axon forms synapse with a dendrite. 3- Axo-axonic: axon forms synapse with an axon  NEUROGLIA Glial cells are 10 times more abundant in the mammalian brain than neurons. They surround the cell bodies and processes of neurons.  Types of Neuroglia Types CNS Peripheral nervous system Microglia Oligodendroglia Astrocyte Ependymal cells Schwann cells 1- Astrocytes (Macroglia): - large star shaped cells with multiple processes. - Have large pale nucleus. - Have centrioles so can divide &form tumors. By E/M, show bundles of intermediate filaments that keep their shape. Ectodermal in origin. In grey matter & white matter. Astrocytes (Macroglia): Functions: 1. Blood brain barrier: have processes with expanded end feet linked to endothelium of blood capillaries so can control metabolic exchanges between nerve cell & blood. 2.Structural support. 4.Repair process by formation of scar tissue. There are 2 types: Fibrous astrocytes Cytoplasmic astrocytes In white matter. In grey matter. Cytoplasm is fibrillary. Cytoplasm is granular. Few long processes. Many short processes. Oligodendrocytes Have few processes with dark nucleus. Have Centrioles. Dense dark cytoplasm rich in endoplasmic reticulum, Golgi body, ribosomes & mitochondria. Ectodermal in origin. Present in both grey & white matter. Function: 1-Formation of myelin sheath in CNS. 2- Electric insulation 3- Support nerve cells Microglia (mesoglia): Small cells with many branches. The cell body & the branches are decorated by spines. Oval dark nucleus. Cytoplasm is scanty rich with lysosome. No Centrioles. Mesodermal in origin. In grey & white matter. Phagocytic cells (stained by vital stains as trypan blue). Ependymal cells Line central canal of spinal cord & ventricles of brain. They form simple cuboidal or columnar epithelium that may be ciliated in places. Cilia may be involved in propulsion of CSF. Ectodermal in origin. Schwann cells In peripheral nervous system. Responsible for myelin production, electric insulation & regeneration. Ectodermal in origin. Satellite cells Low cuboidal cells, In peripheral nervous system. Around nerve cells in ganglia.  Functions of neuroglia cells Main functions Glial cell type 1. Metabolic exchange. Astrocytes 2. Blood- brain barrier. 3. Structural support. 4. Repair processes. Myelin production in CNS , electric Oligodendrocytes insulation. Phagocytic activity Microglia Myelin production in PNS, electric Schwann cells insulation, regeneration. Lining cavities of central nervous Ependymal cells system  BRAIN BARRIARS There are 3 types of brain barriers: 1- Blood Brain Barrier 2- Blood CSF Barrier 3- Arachnoid Barrier 1-Blood brain barrier: Definition: It is the barrier between blood & nerve cells. Structure: formed of A- Tight junction between non fenestrated endothelium lining capillaries. B-Thick continuous basement membrane (Basal lamina). C- End feet of astrocytes firmly applied on capillaries. Function: 1- Prevents harmful materials from reaching the nerve cells. 2- Allows nutrients and precursors of neurotransmitters to pass by facilitated diffusion and active transport. 2- Blood CSF Barrier: Definition: it is the barrier that separates blood from CSF. Structure: it is formed of: 1- Endothelium of choroidal capillary. 2- Basement membrane of choroidal capillary. 3- Basement membrane of ependymal cells forming choroid plexus. 4- Tight junctions between ependymal cells forming the choroid plexus, Function: Protection. Selection of substances to pass From blood to CSF. Maintenance and constancy of CSF 3- Arachnoid barrier: Definition: It is the barrier between extra-cerebral capillaries & subarachnoid space. Structure: Formed of cells joined by tight junctions & desmosomes. Function: block substances leaving extra-cerebral capillaries from reaching subarachnoid space, brain tissue & ventricles  Test yourself 1.Which of the following cells have defense mechanism against invading bacteria in CNS ? a) Oligodendroglia. b) Microglia c) Schwann cells d) Ependymal cells 2. Which of the following is TRUE concerning sympathetic ganglia ? a) Have pseudo-unipolar neuron. b) Poor in blood supply c) The neurons are arranged in groups d) Have multipolar neurons 3. Which of the following cells share in structure of blood CSF barrier? a) Ependymal cells. b) Astrocyte c) Cells of arachnoid layer d) Schwann cells Reference 37