Chapter 10, Section 2

Neurons and Neuroglia

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Structural Classification of Neurons

A multipolar neuron contains many dendrites and 1 axon. • Includes most neurons in the brain and motor neurons

A bipolar neuron contains 1 dendrite and 1 axon• Includes some sensory neurons such as

photoreceptors and olfactory neurons

A unipolar neuron contains a single process extending from the soma• Example includes the cells of the dorsal root ganglion

Peripheral Process – conducts information from PNS Central Process – conducts information to CNS

structural classifications of neurons

Functional Classification of Neurons

An afferent or sensory neuron conducts information from the PNS to CNS• Dendrites may act as receptors (eyes, ears, touch)• Most afferent neurons are unipolar, and some are bipolar

An efferent or motor neuron conducts impulses from CNS to PNS

Voluntary Control – in somatic nervous systemInvoluntary control – in autonomic nervous system

An interneuron or association neuron is located completely within the CNS. Interneurons link neurons together in the CNS, and they also connect sensory neurons to motor neurons.

Functional Classification of Neurons

Figure 10.7. Neurons classified by their functions. Sensory, Motor, and Interneurons.

Neuroglia in the CNS are different from those in the PNS

Astrocytes “star-shaped” attach blood vessels to neurons.

Astrocytes aid in metabolism, strengthen synapses, and participate in the blood-brain-barrier

Ependymal cells line the central canal of the spinal cord and the ventricles of the brain.

Ependyma regulate the composition of cerebral spinal fluid (CSF)

Neuroglia in CNS

Neuroglia in CNS

Microglia are normally small cells, but they enlarge into macrophages during an infection.

• Phagocytize bacteria and cell debris

Oligodendrocytes form the myelin sheath in the CNS

Figure 10.8. Types of neuroglia in the CNS. Neuroglia compose half of the brain’s volume

Neuroglia of the PNSSchwann Cells form the myelin sheath in the PNS.

Satellite Cells support clusters of cell bodies, called ganglia in PNS.

Multiple Sclerosis (MS) The immune system attacks neurons in the CNS, destroying the

myelin sheath of neurons.

The damaged myelin sheath is replaced with Connective tissue, leaving behind scars (scleroses)

Scars block the transmission of underlying neurons, so muscles no

longer receive stimulation and begin to whither (atrophy).

Disorders of Neuroglia

End Section 2, Chapter 10