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Warm-Up

Outline pages 222-230. Warm-Up. The Nervous System. Chapter 7. Master controlling and communicating system of the body Monitor changes (stimuli) both inside and outside of the body Gathered information is called sensory input

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Warm-Up

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  1. Outline pages 222-230 Warm-Up

  2. The Nervous System Chapter 7

  3. Master controlling and communicating system of the body • Monitor changes (stimuli) both inside and outside of the body • Gathered information is called sensory input • Processes and interprets the sensory input and makes decisions about what should be done at every moment • This is called integration Functions

  4. Effects a response by activating muscles or glands (effectors) via motor output

  5. Does not work alone to regulate and maintain body homeostasis • Endocrine system is a second important regulating system • Produces hormones • Typically brings about its effects in a more leisurely way

  6. Structural Classification • Central nervous system (CNS) • Brain and spinal cord • Occupy the dorsal body cavity and act as the integrating and command centers of the nervous system • Interpret incoming sensory information • Issue instructions Organization of the Nervous System

  7. Peripheral nervous system (PNS) • Parts of the nervous system that are outside of the CNS • Consists mainly of the nerves that extend from the brains and spinal cord • Spinal nerves carry impulses to and from the spinal cord • Cranial nerves carry impulses to and from the brain • Serve as communication lines

  8. Concerned only with PNS structures • 2 subdivisions • Sensory (afferent) division • Consists of nerve fibers that convey impulses to the CNS from sensory receptors located through the body • Somatic (afferent fibers) – impulses from the skin, skeletal muscles and joints • Visceral fiber (visceral afferents) – impulses from the visceral organs Functional Classification

  9. Motor (efferent) division • Carries impulses from the CNS to effector organs, the muscles and glands • Effect a motor response • Two subdivisions • Somatic nervous system – voluntary nervous system • Autonomic nervous system (ANS) – involuntary nervous system • Sympathetic • Parasympathetic

  10. Nervous Tissue: Structure and Function

  11. Two Principal Types of Nervous Cells • Supporting cells • Neurons Background Information

  12. Neuroglia – supporting cells in the CNS that are “lumped together” • Many types of cells that support, insulate and protect the neurons • Glia – different types of neuroglia that have a special function Supporting Cells

  13. Astrocytes • Star shaped • Account for nearly half of the neural tissue • Form a living barrier between capillaries and neurons and play a role in making exchanges between them • Help control the chemical environment in the brain • Microglia • Spiderlike phagocytes • Dispose of debris Types of Glial

  14. Ependymal • Line the cavities of the brain and the spinal cord • Helps circulate the cerebrospinal fluid • Oligodendrocytes • Wrap their flat extensions tightly around the nerve fibers • Produce fatty insulating covering called the myelin sheaths • Glia do not transmit nerve impulses • Never lose their ability to divide • Most brain tumors are gliomas

  15. Supporting Cells in the PNS come in two major varieties • Schwann cells • Form the myelin sheaths around the nerve cells that are found in the PNS • Satellite cells • Act as protection, cushioning cells

  16. Also called nerve cells • Highly specialized to transmit messages • Have a cell body containing the nucleus and is the metabolic center of the cell • No centrioles • Very abundant are the • Nissl substances – specialized RER • Neurofibrils – intermediate filaments that are important in maintaining cell shape Neurons

  17. Extending from the cell body there are one or more slender processes (fibers) • Vary in length • Dendrites – convey incoming messages (electrical signals) towards the cell body • May have hundreds of branching dendrites • Axons – generate nerve impulses and typically conduct them away from the cell body • Only has one • Arise from the axon hillock • Occasionally branch to give off a collateral branch • Branch profusely at their terminal end to form the axon terminals

  18. Terminals contain the neurotransmitters in tiny vesicles which are released when stimulated • Synaptic cleft separates the one neuron for the next • The functional gap is the synapse • Myelin – whitish, fatty material with a waxy appearance surrounds most nerve fibers • Protects and insulates the fibers along with increasing the transmission rate

  19. Outside the CNS, the myelination is done by Schwann cells • A myelin sheath results from the myelination • Most of the Schwann cell cytoplasm ends up just beneath the outermost part of its plasma membrane and is called the neurilemma • Remains intact (for the most part) when a peripheral nerve fiber is damages, it plays an important role in fiber regeneration • Nodes of Ranvier form where there are gaps between the adjacent Schwann cells • In the CNS, the oligodendrocytes form the myelin sheaths. • Coil around as many as 60 different nerve fibers at a time • Lack neurilemma

  20. Clusters of neuron cell body and collections of nerve fibers • In the CNS, the cell body clusters are called nuclei • Protected in the skull and vertebral column • Do not routinely undergo cell division • Carries out most of the metabolic functions • In the PNS, small collections of cell bodies are called ganglia • Found in few sites • In the CNS, bundles of nerve fibers are called tracts • White matter – dense collections of myelinated tracts • Gray matter – mostly unmyelinated fibers and cell bodies • In the PNS, bundles of nerve fibers are called nerves

  21. Functional • Groups neurons according to the direction the nerve impulse is traveling relative to the CNS • Sensory (afferent) neurons – carry impulses from sensory receptors to the CNS • Cell bodies are always found in a ganglion outside the CNS • Keep use informed about what is happening both inside and outside the body • Dendrite endings are usually associated with specialized receptors that are activated by specific changes occurring nearby. Neuron Classification

  22. Complex receptors may be discussed later; we will focus on the simpler type of sensory receptors found in the skin (cutaneous sense organs), muscles and tendons (proprioceptors). • The pain receptors (which are bare dendrite endings) are the least specialized cutaneous receptors as well as the most numerous. • Proprioceptors detect the amount of stretch (tension) skeletal muscles, their tendons and joints • These allow the body to make the proper adjustments to maintain balance and normal posture.

  23. Motor (efferent) neurons carry impulses from the CNS to the viscera and/or muscles and glands • The cell bodies of motor neurons are always located in the CNS • Association neurons (interneurons) connect the motor and sensory neurons in neutral pathways • Their cell bodies are always located in the CNS

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