Dr. Ammar Ganim Alhaaik, BVMS, MSc, PhD Scientific degree (Assist. Prof.), Department of Anatomy College of Veterinary Medicine, University of Mosul, Mosul, Iraq https://orcid.org/0000-0002-1473-7631 https://www.researchgate.net/profile/Ammar_Alhaaik4 Course name | Histology Part I | 2nd year 2019
Supporting cells of nervous tissue Neuroglia or glial cells: the neurons are supported by a special kind of connective tissue within the brain and spinal cord that is called neuroglia; it also located in the PNS.
• Neuroglia: Within the central nervous system: 1- Oligodendrocytes 2-astrocytes 3-microglia 4-ependymal cells Out of the central nervous system: Schwann cell (lemmocyte)
Astrocytes ❖ Star shape and most numerous type ❖ provide physical support for neurons ❖ store glycogen ❖ isolate synaptic areas from one and other ❖ In the brain, processes abut against the basement membrane of capillary endothelium (pedicles) forming the blood-brain barrier ❖ other processes are closely applied to neurons (pedicles) ❖ may form a conduit for nutrients from blood vessels to neurons Two types of astrocytes 1. Protoplasmic astrocytes ❖ granular cytoplasm, many branches on short processes ❖ found mainly in gray matter 2. Fibrous Astrocytes
Histology P1 | Nervous tissue 1 | Dr. Ammar Alhaaik Page | 1 ❖ have longer slender processes ❖ found mainly in white matter (but also occur in gray matter).
Ependymal cells ❖ ciliated cells forming single layer of simple cuboidal to low columnar epithelium that lines the entire neurocoel ❖ Epithelial cells that line ventricles and central cavities of brain and spinal cord-secrete CSF ❖ ciliary action acts to circulate cerebral spinal fluid.
The Synapse Concept: Synapses are highly specialized intercellular junctions which link the neurons of each nervous pathway. Similar intercellular junctions link neurons and their effector cells such as muscle fibers; where neurons synapse with skeletal muscle they are referred to as neuromuscular junction or motor end plate.
Classification of synapses: axodendritic synapse axosomatic synapse axoaxonal synapse dendro-axonic dendro-dendritic somato-somatic synapse somato-dendritic synapse
Elements of synapse 1- synaptic bottom and vesicles 2- presynaptic membrane 3- synaptic cleft (gap) 4- postsynaptic membrane
Connective tissue fascia of nerve trunk 1. Nerves are surrounded by a thick connective tissue sheath composed of collagenous fibers and fibroblasts and containing small blood vessels that is called the Epineurium.
2. Each bundle (or facicle) of axons is surrounded by a layer of connective tissue called the Perineurium 3. Each axon within each bundle is individually surrounded by a layer of reticular connective tissue called the Endoneurium
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Myelin is a lipid-rich (fatty) substance formed in the central nervous system (CNS) by glial cells called oligodendrocytes, and in the peripheral nervous system (PNS) by Schwann cells. Myelin protects nerve cell axons to increase the speed at which information travels from one nerve cell body to another (as in the CNS) or from a nerve cell body to a muscle (as in the PNS).
Schwann cell (lemmocyte) : supporting cell in PNS responsible for formation of myelin sheath of nerve fibers.. A Schwann cell surrounds nerve fibers but coiling does not take place. Schwann cells partially enclose 15 or more axons The lemmocyte wraps around the nerve fiber (axon) several times producing a membranous sheath that varies in thickness depending on the number of times the lemmocyte wraps around the axon.
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Nodes of Ranvier (Neurofibral Nodes) Gaps in the myelin sheath between adjacent Schwann cells. They are the sites where axon collaterals can emerge PLAY
Histology P1 | Nervous tissue 1 | Dr. Ammar Alhaaik Page | 4 Ganglia: group of neurons and nerve fibers surrounded by capsule of C.T. there are 2 types: 1- Sympathetic ganglia ……..motor 2- Spinal ganglia ………sensory
Spinal Autonomic (sympathetic)
Spinal ganglia Autonomic ganglia
(sympathetic)
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Motor end plate (motor nerve ending)
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