Kharkov National Medical University Department of Histology, cytology and embryology LECTURE for dentistry students Nervous Tissue consists of 2 types of cells Neurons- Neuroglia- Embryogenesis Neural tube Neural crest – cranial, spinal, autonomic ganglia, neuroendocrine cells (APUD), Shwann cells of neuroglia Monoblast – microglia Neurons. Structure Slide 4 Neurons = nerve cells Specialized to perception, excitement and transmition messages Cell body Processes – that extend from the cell body (dendrites and axons) Nerve endings (synapses and others) Neuron Slide 5 Cell body Neurofibrils: A network of neurofibrils is in the perikaryon and in the dendrites and axon. Is unique to neurons. Support, drainage. Nissl body clumps of basophilic material is unique to neurons. an aggegation of the rough endoplasmic reticulum and free ribosomes. Neuron processes Slide 8 Extensions outside the cell body Dendrites – conduct impulses toward the cell Axons – conduct impulses away from the cell (only 1!) dendrite axon Classifications of neurons According to amount of processes – structural classification: Unipolar neurons Pseudounipolar neurons Bipolar neurons Mutipolar neurons Slide 11 (2) Functional Classification 1. Sensory (afferent) neurons Carry impulses from the sensory receptors 2. Motor (efferent) Carry impulses from the central nervous system 3. Interneurons (association) -99,9% In the central nervous system Connect sensory and motor neurons (2). Neuron Classification Support Cells (Neuroglia) Macroglia Microglia Ependymal cells Astrocytes Schwann cells Nerve fibers – processes, covered by sheaths 1. Unmyelinated 2. Myelinated Unmyelinated nerve fiber Processes are invaginated in Schwann cell cytoplasm nucleus cytoplasm N.c. process N.c. process Myelinated nerve fibers 2 sheaths: myelin and Schwann (neurilemma) nucleus nucleus cytoplasm cytoplasm process process process myelin The Nervous Tissue Nerve endings I. Synapses Peripheral: II. Sensory III. Motor NERVOUS System Nervous system consists of: Central nervous system (CNS) --Brain --Spinal cord Peripheral (PNS): - ganglia - nerves Nervous system consists of: Somatic – innervates skeletal muscles Autonomic – innervates viscera: - sympathetic - parasympathetic PNS Ganglia are aggregations of nerve cells Sensory ganglia lie on the dorsal root of the spinal cord, contain sensory neurons Autonomic ganglia lie near or inside organs, contain motor neurons PNS Nerves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nerve = bundle of myelinated and un- myelinated fibers Structure of a Nerve Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.20 Connective tissue in the nerve: individual nerve fibres are covered by loose connective tissue - endoneurium. Bundles of Nerve fibres, fascicles, are surrounded by perineurium. The entire nerve is surrounded by a thick layer of dense connective tissue, the epineurium. PNS ganglia are surrounded by a c.t. capsule, Neurons N.fibers * consists of Gray and white matters. Gray matter – neurons and unmyelinated fibers white matter – fibers – Clusters of neurons form Nuclei CNS Spinal Cord- participates in formation of reflex arcs and connects body with the brain cortex Nerves begin from: Dorsal root Ventral root Spinal Cord grey matter Dorsal horn Ventral horn white mater – conduction tracts Anterior horn: two motor nuclei: medial and lateral The axons of motor neurons form anterior root Posterior horn two integrative (intercalated) nuclei of somatic nervous system: proper nucleus and Klark’s nucleus. Lateral horn medial and lateral nuclei intercalated neurons of ANS (mostly SNS) Somatic reflex arc 1-st neuron – sensory ganglion 2-d neuron – dorsal horn 3-d neuron – ventral horn Target – skeletal muscle Testing Patellar Reflex Somatic reflex arc Sympathetic reflex arc 1-st: sensory neuron - in the spinal ganglion) 2-d: intercalated (preganglionic) neuron – in the lateral horn of the thoracic and upper lumbar segment of spinal cord. Its axon is called preganglionic fiber. 3-d, motor (efferent) neuron is located in the sympathetic ganglion. The axon of the ganglion cell is called the postganglionic fiber, carries impulse to the effector Parasympathetic reflex arc 1-st: sensory neuron (in the spinal ganglion) 2-d neuron: is in the sacral spinal cord segments and in the brain stem. 3-d neuron is in the parasympathetic ganglia, which lie close to the viscera or into wall of viscera. Cerebellum Two hemispheres form ’’arbor vitae’’ Provides involuntary coordination of body movements Cerebellum Cerebellar cortex 1)Molecular layer 2)Purkinje cells layer – main, Receive all infor- mation 3)Granular layer Cerebral cortex Trough spinal cord receives all the information, analyzes it, forms respond Cerebral cortex = grey matter Cerebral cortex 1)molecular layer 2)external granular layer 3 )pyramidal layer 4)internal granular layer 5)ganglionic layer 6)multiform layer Main =Pyramidal cells the biggest Betz cells Structural unit – module = vertical column = processes of neurons around neuroglial cell