Chapter 10, Section 2
Neurons and Neuroglia
Structural Classification of Neurons Multipolar neuron – 1 axon and many dendrites • Includes most neurons in the brain • Motor neurons and interneurons Bipolar Neuron – 1 axon and 1 dendrite • Some sensory neurons are bipolar • Includes photoreceptors of retina and olfactory nerves Unipolar Neurons Single process extending from soma • Peripheral Process – conducts information from PNS • Central Process – conducts information to CNS • Example: Dorsal root ganglion
Figure 10.6. structural types of neurons
Functional Classification of Neurons Afferent – Sensory • Conducts information from PNS to CNS • Dendrites may act as receptors (eyes, ears, touch) • Most are unipolar, and some are bipolar Efferent – Motor • Conducts impulses from CNS to PNS • Controls Effectors (muscles or glands) •Voluntary Control – in somatic nervous system • Involuntary control – in autonomic nervous system
Interneurons • located within CNS • links neurons in CNS together • multipolar
Functional Classification of Neurons
Figure 10.7. Neurons classified by their functions. Sensory, Motor, and Interneurons.
Neuroglia in CNS Astrocytes “star-shaped” • • • •
Attach blood vessels to neurons Aid in metabolism Strengthen synapses Role in blood Brain barrier
Ependymal Cells • Cuboidal or columnar epithelium • Line central canal of spinal cord and ventricles of brain • Regulate Cerebral Spinal Fluid (CSF)
Neuroglia in CNS Microglia “small cells” • Phagocytize bacteria and cell debris • Proliferate with inflammation or infection of CNS
Oligodendrocytes • Forms Myelin sheath in CNS • 1 Oligodendrocytes covers several axons
Figure 10.8. Types of neuroglia in the CNS. Neuroglia compose half of the brain’s volume
Neuroglia of the PNS Schwann Cells • Forms Myelin Sheath in PNS
Satellite Cells • Support cluster of cell bodies in PNS, called ganglia
Disorders of Neuroglia 1. Multiple Sclerosis (MS) – immune system attacks neurons in the CNS • Myelin sheath is destroyed, leaving behind scars (scleroses) •
Scars block transmission of underlying neurons
•
Muscles no longer receive stimulation from neurons and may whither (atrophy)
Disorders of Neuroglia 2.
Brain tumors • most brain tumors are from neuroglia, not neurons
3. Huntington’s Disease • May be caused by activation of microglia in CNS • Microglia release neurotoxins, causing the degeneration of neurons
End Section 2, Chapter 10