The Nervous System

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The Nervous System
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The Nervous System

• The master controlling and communication system
  of
• the body

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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

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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

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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

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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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Classification

• P. 224

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Nervous System

• THE CELLS OF THE NERVOUS SYSTEM

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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

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Neuroglia-Supporting Cells of CNS
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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

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Astrocytes (Cont)

• Controls chemical environment around neurons
• Cleans up leaked potassium and recycling released
  neurotransmitter
• Guide migration of young neurons

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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

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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

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Oligodendrocytes

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

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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

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Neurons

• Highly specialized to transmit nerve impulses

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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.

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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

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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

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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

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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

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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

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Classification of Neurons

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

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Nervous Tissue Structures

• p. 227

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