Kharkov National Medical University LECTURE for dentistry students Department of Histology, cytology and embryology

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 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) Slide 4

Neuron Cell body Slide 5

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 Extensions outside the cell body dendrite Extensions outside the cell body Dendrites – conduct impulses toward the cell Axons – conduct impulses away from the cell (only 1!) axon Slide 8

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) Support Cells (Neuroglia) Macroglia Microglia Ependymal cells Astrocytes Schwann cells

processes, covered by sheaths Nerve fibers – processes, covered by sheaths 1. Unmyelinated 2. Myelinated

Unmyelinated nerve fiber Processes are invaginated in Schwann cell cytoplasm cytoplasm N.c. process nucleus N.c. process

Myelinated nerve fibers 2 sheaths: myelin and Schwann (neurilemma) process nucleus process cytoplasm cytoplasm nucleus 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 Nerve = bundle of myelinated and un- myelinated fibers Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structure of a Nerve Figure 7.20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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. CNS consists of Gray and white matters. Gray matter – neurons and unmyelinated fibers white matter – fibers – Clusters of neurons form Nuclei

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 white mater – conduction tracts Dorsal horn Ventral horn

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

Trough spinal cord receives all the information, 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