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Nervous Tissue

Nervous Tissue. Chapter 9 . 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

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Nervous Tissue

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  1. Nervous Tissue Chapter 9

  2. 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

  3. Nervous System Figure 11.1

  4. Organization of the Nervous System • Central nervous system (CNS) • Brain and spinal cord • Brain contains 100 billion neurons • Function: Integration and command center • Peripheral nervous system (PNS) • Paired spinal and cranial nerves • Cranial nerves – twelve pairs emerge from the base of the brain • Function: Carries messages to and from the spinal cord and brain

  5. Nerve • Nerve is a bundle of thousands of axons (from a neuron) and its associated connective tissue and blood vessels

  6. Spinal Cord • Spinal cord – contains about 100 million neurons and is protected by the vertebral column. • Spinal nerves – 32 pairs emerge from the spinal cord, each serving a region of the right and left side of the body. • Ganglia – are small masses of nervous tissue that are located outside the brain and spinal cord

  7. Sensory receptors • Sensory receptors are either the dendrites of sensory neurons or other specialized cells that monitor changes. • Help you to respond to a change in the environment

  8. Functions of the NS • Sensory Fxn – using sensory receptors your nervous system is able to detect changes in the environment but within your body and externally. • Sensory neurons or afferent neurons carry the information to the brain or spinal cord • 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

  9. Function of the NS • Integrative Fxns – the nervous system processes sensory information by analyzing and storing the information and then making appropriate responses to that information • Interneurons – are the neurons that are responsible for this function • Short axons and connect to nearby neurons in the brain or spinal cord

  10. Function of the NS • Motor Functions • Motor (efferent) division • Transmits impulses from the CNS to effector organs

  11. PNS – 3 main division • Somatic nervous system (SNS) • Conscious control of skeletal muscles • Autonomic nervous system (ANS) • Regulates smooth muscle, cardiac muscle, and glands • Divisions – sympathetic and parasympathetic • Enteric Nervous System (ENS) • Sensory receptors of the gastrointestinal tract

  12. 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

  13. Supporting Cells: Neuroglia • The supporting cells: • Provide a supportive scaffolding for neurons • Segregate and insulate neurons • Guide young neurons to the proper connections • Promote health and growth

  14. Astrocytes • Most abundant, versatile, and highly branched supporting 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

  15. Astrocytes Figure 11.3a

  16. 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

  17. Microglia and Ependymal Cells Figure 11.3b, c

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

  19. Oligodendrocytes, Schwann Cells, and Satellite Cells Figure 11.3d, e

  20. 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

  21. Neurons (Nerve Cells) Figure 11.4b

  22. Nerve Cell Body • 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

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

  24. 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)

  25. 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

  26. 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

  27. 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

  28. 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

  29. Nodes of Ranvier • Gaps in the myelin sheath between adjacent Schwann cells • They are the sites where axon collaterals can emerge

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

  31. 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

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

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

  34. 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

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