Figure 112

Diagram illustrating different types of neurons. The cell bodies of pseudounipolar (unipolar), bipolar, and postsynaptic autonomic neurons are located outside the CNS. Integrative neurons are restricted to the CNS; many of them have elaborate dendritic arborizations that facilitate their identification, a, axon.

Motor neurons and interneurons are multipolar

Interneurons constitute most of the neurons in the nervous system. The direction of impulses is from dendrite to cell body to axon or from cell body to axon. Thus, functionally, the dendrites and cell body of multipolar neurons are the receptor portions of the cell, and their plasma membrane is specially adapted for impulse generation. The axon is the conducting portion of the cell, and its plasma membrane is specialized for impulse conduction. The terminal portion of the axon, the synaptic ending, contains various neurotransmitters, i.e., small molecules whose release at the synapse affects other neurons as well as muscle cells and glandular epithelium.

Sensory neurons are unipolar

The cell body of a sensory neuron is situated in a dorsal root ganglion close to the CNS (Fig. 11.3); one ax-onal branch extends to the periphery, and one extends to the CNS. The two axonal branches are the conducting units. Functionally, impulses are generated in the peripheral arborizations (branches) of the neuron; these arborizations are the receptor portion of the cell. Unipolar neurons are also sometimes called pseudounipolar because during development they exist as bipolar neurons. They become unipolar as their processes migrate around the cell body and fuse into a single process as the cell matures.

Nissl bodies pyramidal cell -

large motor neuron presynaptic autonomic neuron interneurons postsynaptic .autonomic \ neuron

Purkinje cell striated (skeletal) muscle smooth muscle of intestine blood vessels epineurium sensory neuron

Schwann cell

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