Power Point Lecture Slides prepared by Vince Austin

Power. Point® Lecture Slides prepared by Vince Austin, University of Kentucky Fundamentals of the Nervous System and Nervous Tissue Part A Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings 11

Nervous System § The master controlling and communicating system of the body § Functions § Sensory input – monitoring stimuli occurring inside and outside the body § Integration – interpretation of sensory input § Motor output – response to stimuli by activating effector organs Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Nervous System Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings Figure

Organization of the Nervous System § Central nervous system (CNS) § Brain and spinal cord § Integration and command center § Peripheral nervous system (PNS) § Paired spinal and cranial nerves § Carries messages to and from the spinal cord and brain Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Peripheral Nervous System (PNS): Two Functional Divisions § Sensory (afferent) division § Sensory afferent fibers – carry impulses from skin, skeletal muscles, and joints to the brain § Visceral afferent fibers – transmit impulses from visceral organs to the brain § Motor (efferent) division § Transmits impulses from the CNS to effector organs Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Motor Division: Two Main Parts § Somatic nervous system § Conscious control of skeletal muscles § Autonomic nervous system (ANS) § Regulates smooth muscle, cardiac muscle, and glands § Divisions – sympathetic and parasympathetic Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Histology of Nerve Tissue § The two principal cell types of the nervous system are: § Neurons – excitable cells that transmit electrical signals § Supporting cells – cells that surround and wrap neurons Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Supporting Cells: Neuroglia § The supporting cells (neuroglia or glial cells): § Provide a supportive scaffolding for neurons § Segregate and insulate neurons § Guide young neurons to the proper connections § Promote health and growth Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Astrocytes § Most abundant, versatile, and highly branched glial cells § They cling to neurons and their synaptic endings, and cover capillaries § Functionally, they: § Support and brace neurons § Anchor neurons to their nutrient supplies § Guide migration of young neurons § Control the chemical environment Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Astrocytes Figure 11. 3 a Copyright © 2004 Pearson Education, Inc. , publishing as

Microglia and Ependymal Cells § Microglia – small, ovoid cells with spiny processes § Phagocytes that monitor the health of neurons § Ependymal cells – range in shape from squamous to columnar § They line the central cavities of the brain and spinal column. § Main function is to help move the fluid that protects the brain and spinal cord. Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Microglia and Ependymal Cells Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin

Oligodendrocytes, Schwann Cells, and Satellite Cells § Oligodendrocytes – branched cells that wrap CNS nerve fibers § Schwann cells (neurolemmocytes) – surround fibers of the PNS to protect the axon of a nerve fiber. § Satellite cells surround neuron cell bodies with ganglia Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Oligodendrocytes, Schwann Cells, and Satellite Cells Copyright © 2004 Pearson Education, Inc. , publishing

Neurons (Nerve Cells) § Structural units of the nervous system § Composed of a body, axon, and dendrites § Long-lived, amitotic, and have a high metabolic rate § Their plasma membrane functions in: § Electrical signaling § Cell-to-cell signaling during development Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Neurons (Nerve Cells) Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Nerve Cell Body (Perikaryon or Soma) § Contains the nucleus and a nucleolus § Is the major biosynthetic center § Is the focal point for the outgrowth of neuronal processes § Has no centrioles (hence its amitotic nature) § Contains an axon hillock – cone-shaped area from which axons arise Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Processes § Processes are the pojections or growths that come off of a cell body. § The cell body is the focal point for the outgrowth of neuronal processes. § The CNS contains both cell bodies and processes, the PNS contains mostly just processes. § Bundles of nuerons in the CNS are called tracts, in the PNS they are called nerves. Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Dendrites of Motor Neurons § Short, tapering, and diffusely branched processes § They are the receptive, or input, regions of the neuron § Electrical signals are conveyed as graded potentials (not action potentials) Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Axons: Structure § Slender processes of uniform diameter arising from the hillock § Long axons are called nerve fibers § Usually there is only one unbranched axon per neuron § Rare branches, if present, are called axon collaterals § Axonal terminal – branched terminus of an axon Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Axons: Function § Generate and transmit action potentials § Secrete neurotransmitters from the axonal terminals § Movement along axons occurs in two ways § Anterograde — toward axonal terminal § Retrograde — away from axonal terminal Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Myelin Sheath § Whitish, fatty (protein-lipoid), segmented sheath around most long axons § It functions to: § Protect the axon § Electrically insulate fibers from one another § Increase the speed of nerve impulse transmission Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Myelin Sheath and Neurilemma: Formation § Formed by Schwann cells in the PNS § A Schwann cell: § Envelopes an axon in a trough § Encloses the axon with its plasma membrane § Has concentric layers of membrane that make up the myelin sheath § Neurilemma – remaining nucleus and cytoplasm of a Schwann cell Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Myelin Sheath and Neurilemma: Formation Figure 11. 5 a-c Copyright © 2004 Pearson Education,

Nodes of Ranvier (Neurofibral Nodes) § Gaps in the myelin sheath between adjacent Schwann cells § They are the sites where axon collaterals can emerge PLAY Inter. Active Physiology®: Nervous System I: Anatomy Review Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Unmyelinated Axons § A Schwann cell surrounds nerve fibers but coiling does not take place § Schwann cells partially enclose 15 or more axons Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Axons of the CNS § Both myelinated and unmyelinated fibers are present § Myelin sheaths are formed by oligodendrocytes § Nodes of Ranvier are widely spaced § There is no neurilemma Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Regions of the Brain and Spinal Cord § White matter – dense collections of myelinated fibers § Gray matter – mostly soma and unmyelinated fibers Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Neuron Classification § Structural: § Multipolar — three or more processes § Bipolar — two processes (axon and dendrite) § Unipolar — single, short process Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings

Neuron Classification § Functional: § Sensory (afferent) — transmit impulses toward the CNS § Motor (efferent) — carry impulses away from the CNS § Interneurons (association neurons) — shuttle signals through CNS pathways Copyright © 2004 Pearson Education, Inc. , publishing as Benjamin Cummings