Fundamentals of the Nervous System and Nervous Tissue PART 2 Fundamentals of the Nervous System and Nervous Tissue

Classification of Neurons Structural classification Multipolar – possess more than two processes Numerous dendrites and one axon Bipolar – possess two processes Rare neurons Found in some special sensory organs Unipolar (pseudounipolar) – possess one short, single process Start as bipolar neurons during development Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Neurons Classified by Structure Figure 12.10a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Neurons Classified by Structure Figure 12.10b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Neurons Classified by Structure Figure 12.10c Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Functional Classification of Neurons Functional classification is According to the direction the nerve impulse travels Sensory (afferent) neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Functional Classification of Neurons Transmit impulses toward the CNS Virtually all are unipolar neurons Cell bodies in ganglia outside the CNS Short, single process divides into The central process – runs centrally into the CNS The peripheral process – extends peripherally to the receptors Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Functional Classification of Neurons Motor (efferent) neurons Carry impulses away from the CNS to effector organs Most motor neurons are multipolar Cell bodies are within the CNS Form junctions with effector cells Interneurons (association neurons) – most are multipolar Lie between motor and sensory neurons Confined to the CNS Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Neurons Classified by Function Figure 12.11 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Six types of supporting cells Four in the CNS Two in the PNS Provide supportive functions for neurons Cover nonsynaptic regions of the neurons Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Neuroglial in the CNS Neuroglia Glial cells have branching processes and a central cell body Outnumber neurons 10 to 1 Make up half the mass of the brain Can divide throughout life Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Astrocytes are the most abundant glial cell type Neuroglia in the CNS Astrocytes are the most abundant glial cell type Sense when neurons release glutamate Extract blood sugar from capillaries for energy Take up and release ions in order to control environment around neurons Involved in synapse formation in developing neural tissue Produce molecules necessary for neuronal growth (BDTF) Propagate calcium signals involved with memory Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Neuroglia in the CNS Figure 12.12a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Microglia – smallest and least abundant glial cell Neuroglia in the CNS Microglia – smallest and least abundant glial cell Phagocytes – the macrophages of the CNS Engulf invading microorganisms and dead neurons Derive from blood cells called monocytes Figure 12.12b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Oligodendrocytes – have few branches Neuroglia in the CNS Ependymal cells Line the central cavity of the spinal cord and brain Bear cilia – help circulate the cerebrospinal fluid Oligodendrocytes – have few branches Wrap their cell processes around axons in CNS Produce myelin sheaths Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Neuroglia in the CNS Figure 12.12c, d Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Satellite cells – surround neuron cell bodies within ganglia Neuroglia in the PNS Satellite cells – surround neuron cell bodies within ganglia Schwann cells (neurolemmocytes) – surround axons in the PNS Form myelin sheath around axons of the PNS Figure 12.13 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings