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THE NERVOUS SYSTEM PART 1 CHAPTER 11. Nervous System Figure 11.1.

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Presentation on theme: "THE NERVOUS SYSTEM PART 1 CHAPTER 11. Nervous System Figure 11.1."— Presentation transcript:


2 Nervous System Figure 11.1

3 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

4 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

5 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 5 Levels of Organization

6 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 Peripheral Nervous System (PNS): Two Functional Divisions

7 Somatic nervous system Conscious control of skeletal muscles Autonomic nervous system (ANS) Regulates smooth muscle, cardiac muscle, and glands Divisions – sympathetic and parasympathetic Motor Division: Two Main Parts

8 sensory nerves axons of motor nerves somatic subdivision (motor functions) autonomic subdivision (visceral functions) sympathetic Peripheral Nervous System para- sympathetic Central Nervous System brain spinal cord AFFERENT EFFERENT

9 Autonomic nervous system (ANS)

10 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 Histology of Nerve Tissue

11 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 Supporting Cells: Neuroglia

12 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 Astrocytes

13 Figure 11.3a

14 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 Microglia and Ependymal Cells

15 Figure 11.3b, c

16 Oligodendrocytes – branched cells that wrap CNS nerve fibers Schwann cells (neurolemmocytes) – surround fibers of the PNS Satellite cells surround neuron cell bodies with ganglia Oligodendrocytes, Schwann Cells, and Satellite Cells

17 Figure 11.3d, e Oligodendrocytes, Schwann Cells, and Satellite Cells

18 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 Neurons (Nerve Cells)

19 blood vessels outer connective tissue of one nerve unsheathed node axon myelin sheath many neurons bundled together inside a connective tissue sheath axon of one neuron

20 axon axon endings cell body dendrites axon cell body axon ending peripheral axon receptor endings Sensory Neuron Motor Neuron Interneuron cell body

21 Neurons (Nerve Cells) Figure 11.4b

22 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) Has well-developed Nissl bodies (rough ER) Contains an axon hillock – cone-shaped area from which axons arise Nerve Cell Body (Perikaryon or Soma)

23 Armlike extensions from the soma Called tracts in the CNS and nerves in the PNS There are two types: axons and dendrites Processes

24 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) Dendrites of Motor Neurons

25 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 Axons: Structure

26 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 Axons: Function

27 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 Myelin Sheath

28 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 Myelin Sheath and Neurilemma: Formation


30 Schwann cell

31 Myelin Sheath and Neurilemma: Formation Figure 11.5a-c

32 Gaps in the myelin sheath between adjacent Schwann cells They are the sites where axon collaterals can emerge Nodes of Ranvier (Neurofibral Nodes)

33 A Schwann cell surrounds nerve fibers but coiling does not take place Schwann cells partially enclose 15 or more axons Unmyelinated Axons

34 Amyotrophic Lateral Sclerosis ALS

35 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

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

37 Structural: Multipolar three or more processes Bipolar two processes (axon and dendrite) Unipolar single, short process Neuron Classification

38 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

39 Comparison of Structural Classes of Neurons Table

40 Comparison of Structural Classes of Neurons Table

41 Comparison of Structural Classes of Neurons Table

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