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Lab Exercise 13 Histology of Nervous Tissue Portland Community College BI 231 Major divisions of the nervous system • Central nervous system (CNS)- brain and spinal cord • Peripheral nervous system (PNS)comprises all nerves that connect the brain and spinal cord to muscles, glands and receptors. 2 Nerves • Cranial nerves are those that are connected to the brain • Spinal nerves are connected to the spinal cord. • Both contain sensory information from receptors and send motor signals. 3 Motor (Efferent) Neurons Efferent = Away from CNS • These are neurons that carry information from CNS to the body • Groups of axons running together are the Nerves when they are outside the CNS and Tracts inside the brain and spinal cord • The cell bodies are clustered in groups in the CNS and are called nuclei • Brain gray matter is made up of millions of nuclei. • It is gray because there is no myelin around the cell bodies • These axons exit the spinal cord on the ventral side 4 Motor (efferent) division of PNS • Somatic nervous system- contains efferent neurons extending from the CNS to skeletal muscle. • Autonomic nervous system- contains efferent neurons from CNS to smooth muscle, cardiac muscle and glands 5 Sensory (Afferent) Neurons Afferent = Toward the CNS • These carry sensory information from the body to the CNS (brain and spinal cord) • Their axons run in the same group as the motor neurons (nerves=groups of axons) • Their cell bodies are clustered outside of the spinal cord and are called ganglia • These axons enter the spinal cord on the dorsal side 6 Sensory (afferent) division • Afferent neurons that receive stimuli from somatic sensory receptors that detect general sensations • Receive stimuli from visceral sensory receptors • Special sensory receptors that detect special sensations (smell, taste, vision, hearing, equilibrium) 7 Organization of nervous system 8 Neuron 9 Myelin • Some axons are surrounded by a myelin sheath • Multilayered lipid and protein covering formed by Schwann cells around axons • Oligodendrocytes in the CNS • The covering is the plasma membrane of the Schwann Cell • The Schwann Cell can cover more than one axon • Insulates axon 10 Nodes of Ranvier • Areas between Schwann Cells that do not contain Myelin • Involved in saltatory conduction 11 Dendrit e Nucleu s Axon Hillock Neuron Cell Body Axon 12 Schwann Cell Axon Myelin Sheath Node of Ranvier Telodendria Axon Terminal (Synaptic end bulbs) 13 Classification • Sensory (afferent) neurons conduct nerve impulses from sensory receptors • Motor ( efferent) neurons conduct nerve impulses from the CNS • Interneurons form links between sensory and motor 14 Multipolar Neuron Cell Body Axon Dendrites (trigger zone) • Most common type of neuron • Interneurons and motor neurons 15 Anaxonic Neurons • A small number of multipolar neurons contain only dendrites or • Cannot distinguish dendrites from axons • Functions are poorly understood. 16 Bipolar Neuron Dendrite (trigger zone) Cell Body Axon • Location: special senses (smell, vision, hearing) 17 Unipolar Neuron Dendrite (trigger zone) Cell Body Axon • All are sensory afferent • Cell bodies are located in the dorsal root ganglia 18 Association or Interneurons • Neurons between the afferent and efferent neurons. • Are only in the CNS 19 Neuron Axon Myelin Sheath Node of Ranvier Perineurium Fascicle Epineurium 20 Glial Cells • • • • Associated with neurons Provide Supportive scaffolding Segregate and insulate neurons Outnumber neurons by 10 to 1 21 Supporting Cells in the CNS Astrocytes • Star Shaped • Many functions • Regulates levels of O2 , • & CO2 • • Exchanges between capillaries and neurons (blood-brain barrier) • Nutrient transfer 22 Supporting Cells in the CNS Microglia • Protect CNS from disease-causing organisms • Monitor the health of neurons • Act as phagocytes eating microorganisms and debris 23 Ependymal cells • These cells are modified epithelial cells that line the ventricles of the brain and central canal of spinal cord. • Facilitate circulation of CSF 24 Supporting Cells in the CNS Oligodendrocytes • Produce the myelin sheath which provides the electrical insulation for some neurons in the CNS 25 Supporting Cells in the PNS Schwann Cells • Form the myelin sheath around axons in the PNS 26 Satellite cells • Surround neuron cell bodies in peripheral ganglia and regulate levels of oxygen, carbon dioxide and nutrients. 27 The synapse • Axons generate action potentials which are transmitted across synapses • Formed by presynaptic membrane and postsynaptic membrane on an effector cell • The synaptic cleft is a narrow space that separates these 28 The End 29