Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb 11 Fundamentals of the Nervous System and Neural Tissue Part A

Nervous System Figure 11.1

Divisions of the Nervous System

CNS PNS Efferent (motor) neurons Afferent (sensory) neurons ANSSomatic Sympathetic Parasympathetic

 Provide scaffolding for neurons  Segregate & insulate neurons  Guide growing neurons to proper connections  Promote health & growth of neurons  Cell types  Astrocytes  Microglial cells  Ependymal cells  Oligodentrocytes  Schwann cells  Satellite cells Neuroglia – Supporting Cells

 Abundant, versatile, and highly branched CNS cell  Cover capillaries  Support & brace neurons  Anchor neurons to their nutrient supplies  Guide migration of young neurons  Control the chemical environment Astrocytes

 Microglia – small, ovoid cells with spiny processes  Phagocytic  Monitor health of neurons Microglial Cells

Ependymal Cells  Squamous or columnar cells lining ventricles of brain and spinal cord

 Branched cells that wrap CNS nerve fibers (axons) Oligodendrocytes

Schwann Cells and Satellite Cells  Schwann cells surround axons of PNS neurons  Satellite cells surround bipolar neuron cell bodies in ganglia

 Whitish, fatty (protein-lipid), segmented sheath around most long axons sphingomyelin  Formed by:  Schwann cells in the PNS  Oligodendrocytes in CNS  Functions to:  Protect axons  Electrically insulate fibers  Increases speed of impulse transmission Myelin Sheath and Neurilemma Formation

 A Schwann cell:  Encloses the axon with its plasma membrane  Concentric layers of membrane make up the myelin sheath  Neurilemma  Nucleus and cytoplasm of a Schwann cell

 Functional units of neurons  Composed of a body, axon, and dendrites  Long-lived, amitotic, and have a high metabolic rate  Plasma membrane functions in:  Electrical signaling  Cell-to-cell signaling during development Neurons (Nerve Cells)

 Generate and transmit action potentials  Secrete neurotransmitters from termini  Intracellular movement along axons  Anterograde — toward terminus  Retrograde — away from terminus, toward soma Axon Function

 Both myelinated and unmyelinated fibers are present  Myelin sheaths are formed by oligodendrocytes  Nodes of Ranvier are widely spaced  There is no neurilemma Axons of the CNS

 White matter – dense collections of myelinated fibers  Gray matter – mostly soma and unmyelinated fibers Regions of the Brain and Spinal Cord

 Structural:  Multipolar - three or more processes  Bipolar - two processes (axon and dendrite)  Unipolar - single process diverges into 2 conductive regions  Functional:  Sensory (afferent) — transmit impulses toward the CNS  Motor (efferent) — carry impulses away from the CNS  Interneurons (association neurons) — shuttle signals through CNS pathways Neuron Classification

Structural Classes of Neurons