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 • 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• 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)(CSF)

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

Neuroglia in CNS

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

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

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