Fundamentals of the Nervous System and Nervous Tissue

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Chapter 11

• Fundamentals of the Nervous System and Nervous
  Tissue

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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

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Organization of the Nervous System
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Organization of the Nervous System
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Organization of the Nervous System
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Histology of Nervous Tissue

• Neurons excitable cells that transmit
  electrical signals
• Neur, neuri, neuro nervous sys
• Supporting cells Neuroglia or glial cells
• Surround and wrap neurons
• 6 types

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Neuroglial in the CNS

• Astrocytes
• Star-shaped
• Most abundant
• Anchor neurons to nutrient supply
• Guide migration of young neurons
• Control chemical (ions) environment

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Neuroglial in the CNS

• Microglia
• Small ovoid
• Long thorny processes
• Monitor neuron health
• Turn into phagocytes
• Gets rid of debris or invading microorganiams

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Neuroglial in the CNS

• Ependymal
• Squamous, columnar
• Line the cavities of brain and spinal cord
• Cilia circulate cerebrospinal fluid

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Neuroglial in the CNS

• Oligodendrocytes
• Wrap several CNS nerve fibers (axons) myelin
  sheaths

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Neuroglial in the PNS

• Schwann cells
• Wrap PNS nerve fibers (axons) myelin sheaths
• Satellite cells
• Surround neruon cell bodies within ganglia

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• Oli the goat w dandruff and the swan

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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

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Neurons

• Cell Body
• Soma
• Contains nucleus, nucleolus
• Is the major biosynthetic center
• Is the focal point for the outgrowth of neuronal
  processes
• Cytoplasm with usual organelles, no centrioles
• Well developed Nissl bodies rough ER
• Axon hillock - cone-shaped area from which axons
  arise

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Neurons

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

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Processes

• Dendrites
• Short, tapered, branch diffusely
• Contain all organelles
• They are the receptive, or input, regions of the
  neuron
• Convey incoming messages toward cell body

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Axon Structure

• Slender process of uniform diameter arising from
  the hillock
• Long axons are called nerve fibers
• Usually there is only one unbranched axon per
  neuron
• Axonal terminals - terminal branches

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Axon Functions

• Generates and transmits action potentials
• Secrete neurotransmitters from the axonal
  terminals
• No Nissl bodies or Golgi bodies

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Myelin Sheaths

• Whitish, fatty, segmented sheaths
• Protect the axon
• Electrically insulate fibers from one another
• Increase the speed of nerve impulse transmission

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Myelin Sheaths in PNS

• Formed by 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

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Myelin Sheaths in PNS

• Neurilemma remaining nucleus and cytoplasm of a
  Schwann cell

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Nodes of Ranvier

• Gaps in the myelin sheath between adjacent
  Schwann cells
• Sites where axon collaterals can emerge

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Unmyelinated Fibers in PNS

• Schwann cells surround, but do not coil around,
  fiber
• Schwann cells partially enclose 15 or more axons
• Typically thin fibers

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Myelinated and Unmyelinated Fibers in CNS

• Both myelinated and unmyelinated fibers are
  present
• Myelin sheaths are formed by oligodendrocytes
• Nodes of Ranvier are widely spaced
• There is no neurilemma

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Regions of the Brain and Spinal Cord

• White matter dense collections of myelinated
  fibers
• Gray matter mostly soma and unmyelinated fibers

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Structural Classification

• Multipolar three or more processes
• Most common

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Classification of Neurons

• Bipolar two processes (axon and dendrite)
• retinal of eye , olfactory mucosa of nasal area

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Classification of Neurons

• Unipolar single, short process
• ganglia in PNS

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Classification of Neurons

• Functional Classification
• Sensory, afferent
• Transmit impulses toward the CNS
• Most are unipolar
• Motor, efferent
• Carry impulses away from CNS
• Multipolar
• Interneurons or association neurons
• shuttle signals through CNS pathways

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Neurophysiology of Neurons

• Are highly irritable
• When stimulated will generate and conduct an
  electrical impulse (AP) along its axon
• AP is always the same, regardless of stimulus
• The underlying functional feature of the nervous
  system