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The Nervous System

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Title: The Nervous System


1
The Nervous System
2
The Nervous System
  • The master controlling and communication system
    of
  • the body

3
Three Overlapping Functions
  • Sensory Input
  • Monitors internal and external stimuli (Changes)
  • Afferent pathway to the brain
  • receptors
  • Integration
  • Processes and interprets information
  • Decides the appropriate response
  • Motor Output
  • Efferent pathway to effector organs (muscles or
    glands), effects a response

4
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5
Organization of the Nervous System
  • Central Nervous System (CNS)
  • Brain and spinal cord
  • Dorsal body cavity
  • Integrating command center
  • Peripheral Nervous System (PNS)
  • Nerves to and from brain and spinal cord
  • Communication links to the CNS
  • Spinal nerves and cranial nerves

6
Peripheral Nervous System
  • Sensory Afferent Division
  • Impulses to the brain and spinal cord (CNS)
  • Monitors internal and external changes
  • Somatic afferent
  • Skin, skeletal muscle, joints
  • Visceral afferent
  • Organs within ventral body cavity

7
Peripheral Nervous System
  • Motor Efferent Division
  • From CNS to effector muscle, organs, and glands
  • Somatic efferent nervous system
  • Voluntary nervous system
  • Autonomic nervous system
  • Involuntary
  • Visceral motor nerve fibers (to smooth and
    cardiac muscle and glands)
  • Sympathetic (emergency situations)
  • Parasympathetic (conserves energy, nonemergency
    functions)

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9
Classification
  • P. 224

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11
Nervous System
  • THE CELLS OF THE NERVOUS SYSTEM

12
Nervous Tissue-Types of Cells
  • Two Principal Cell Types-
  • Neurons excitable nerve cells
  • Supporting cells Neuroglia Nerve Glue
  • Support, insulate, and protect neurons by
    surrounding and wrapping neurons.
  • Central nervous system supporting cells
  • Astrocytes
  • Microglia
  • Ependymal cells
  • Oligodendrocytes
  • Peripheral nervous system supporting cells
  • Satellite cells
  • Schwann cells

13
Neuroglia-Supporting Cells of CNS
14
Astrocytes
  • Most abundant Star-shaped
  • Radiating processes cover neurons and anchor them
    to adjacent blood vessels
  • Controls exchange between blood vessels and
    neurons
  • Determines capillary permeability

15
Astrocytes (Cont)
  • Controls chemical environment around neurons
  • Cleans up leaked potassium and recycling released
    neurotransmitter
  • Guide migration of young neurons

16
Microglia
  • Small, ovoid cells, with thorny processes
    (spider-like)
  • Branches monitor health of neurons
  • Migrate toward injured neuron
  • Transform into a macrophage when invading
    microorganisms or dead neurons are present and
    dispose of debris
  • Protective role because cells of immune system
    are denied access to CNS

17
Ependymal cells
  • Simple squamous to columnar in shape
  • Line the cavities of the brain and spinal cord
  • Beating of their cilia circulates cerebrospinal
    fluid that cushions brain and spinal cord

18
Oligodendrocytes
  • Wrap cytoplasmic extensions around neurons and
    form myelin sheaths in CNS
  • Insulates and protects

19
Supporting Cells of the PNS
  • Satellite cells
  • Surround neuron cell bodies within ganglia
  • Protective and cushioning cells
  • Schwann cells
  • Surround and form myelin sheaths around larger
    nerve fibers
  • Functionally similar to oligodendrocytes

20
Neurons
  • Highly specialized to transmit nerve impulses

21
Neurons
  • Nerve cells
  • Structural units of the nervous system
  • Special characteristics of neurons
  • Conduct nerve impulses
  • Extreme longevity
  • Amiotic (exceptions olfactory and hippocampus)
    (become injured and do not regenerate)
  • High metabolic rate requires abundant oxygen and
    glucose
  • All Neurons have cell bodies and processes, plus
    three functional components receptive or input
    region, conducting component, and secretory or
    output component.

22
Cell Body
  • Metabolic center
  • No centrioles
  • Ribosomes and rough ER (Nissl Substance)most
    active of any cell in the body
  • Plasma membrane acts as part of the receptive
    surface
  • Most located within the CNS (called nuclei)
  • Cell body collections in the PNS are called
    ganglia

23
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24
Cell Processes
  • Brain and spinal cord (CNS) contain both cell
    bodies and their processes
  • The PNS consists chiefly of neuron processes
  • Bundles of neuron processes are called tracts
    (CNS) and nerves (PNS).
  • Dendrites
  • Short, tapering, hundreds/cell
  • Receptive (input) region convey incoming
    messages(electrical signals) toward the cell body
  • Large surface area

25
Cell Processes
  • Axon (conducting component)
  • One Axon (Single process) per neuron
  • Axon arises from axon hillock of cell body
  • Generates nerve impulses and transmits them away
    from the cell body
  • Long axons called nerve fibers
  • Axon terminals created where the axon branches
    at the terminal end
  • 100-1000 terminal branches per axon
  • Axon terminals are the secretory portionsecretes
    neurotransmitters

26
Myelin Sheath (neurilemma)
  • Myelin whitish, fatty material covering long
    nerve fibers has waxy appearance
  • Protects and provides an electrical insulation
    covering for large and long nerve fibers
  • Increases speed of transmission of nerve impulses
  • Unmyelinated fibers conduct impulses slowly
  • Associated only with axons Dendrites always
    unmyelinated
  • Formed by Schwann cells in PNSmade of concentric
    layers of cell membranes (no channel or carrier
    proteins) called the neurilemma

27
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28
Myelin (Cont)
  • Nodes of Ranvier are the gaps between Schwann
    cellsregularly spaced
  • Oligodendrocytes form CNS myelin sheathscoils
    around 60 fibers at the same timeno neurilemma
    because of the absence of coiling of cells
  • Regions of the brain and spinal cord with
    myelinated fibers called white matter.
  • Gray matter contains mostly cell bodies and
    unmyelinated fibers

29
Classification of Neurons
  • Structural Classification
  • Multipolar neurons
  • Bipolar neurons
  • Unipolar Neurons
  • Functional Classification
  • Sensory (afferent) neurons
  • Motor (efferent) neurons
  • Association (interneurons) neurons

30
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33
Nervous Tissue Structures
  • p. 227

CELL BODY
DENDRITE
34
Nervous Tissue Structures
AXON
AXON TERMINAL
35
Nervous Tissue Structures
SCHWANN CELLS
NODES OF RANVIER
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