NERVOUS SYSTEM Lecture 1

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NERVOUS SYSTEMLecture 1

• OVERVIEW
• and
• NEUROHISTOLOGY

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ANATOMICAL ORGANIZATION of the NERVOUS SYSTEM
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Central Nervous System (CNS)

• Definition
• Unpaired, bilaterally symmetrical structures
  extending along the longitudinal axis of the
  midsagittal plane of the body.
• Structures arising directly from the neural
  tube.
• Includes
• Brain
• Spinal cord

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Peripheral Nervous System (PNS)

• Definition
• Made up of transmission pathways carrying
  information between the CNS and
  external/internal environments.
• Afferent (sensory) pathways
• Carry information to the CNS.
• Efferent (motor) pathways
• Carry information from the CNS.

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Peripheral Nervous System (PNS)

• Includes
• Cranial nerves (12 pairs).
• Spinal nerves (31 pairs).

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Autonomic Nervous System (ANS)

• May be considered a subdivision of the PNS.
• Entirely motor.
• Innervates smooth muscle and glands (viscera).

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ANS Subdivisions

• Sympathetic system (fight or flight)
• Also called thoracolumbar.
• Parasympathetic system (feed or breed)
• Also called craniosacral.

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Parts of a Neuron

• Cell body
• Trophic unit
• Perikaryon
• Dendrites
• Receptive unit
• Axon
• Conductive unit

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Cell Body Definition

• That part of a neuron that encloses the nucleus
  and other organelles necessary to maintain and
  repair the neuron.

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Cell Body Organelles

• Nucleus
• Golgi apparatus
• RER
• Ribosomes (Nissl substance)

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Dendrites (Characteristics)

• Branches off the cell body that carry information
  to the cell body.
• Usually several to many.
• Relatively short.
• Often branched.
• Have receptors for neurotransmitters.
• Conduct local potentials.

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Axon Characteristics

• Carries information to another neuron or muscle
  cell.
• Often relatively long.
• Single (one per neuron).
• Conducts action potential

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Axon Characteristics

• Ends in short branched processes called
  telodendria.
• May have collateral branches.
• Cell membrane ( axolemma).
• Cytoplasm (axoplasm).

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Axon Characteristics

• Covered by neurolemma
• Made up of Schwann cells.
• Often myelinated
• Myelin is formed by Schwann cells.
• Note axon is the only part of a neuron that is
  ever myelinated.

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Axon Organelles

• Mitochondria
• Neurofilaments
• Neurotubules

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Axonal Transport

• Anterograde
• Transports vesicles from cell body to end of
  axon.
• Kinesin
• Retrograde
• Transports vesicles from end of axon toward
  cell body.
• Cytoplasmic dynein

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Axonal Transport

• Slow transport
• 1-5 mm/day
• Fast transport
• 200-400 mm/day

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General Terminology

• Nerve
• Bundle of fibers in the PNS.
• Tract
• Bundle of fibers in the CNS.
• Commissure
• Tract in the CNS that crosses from one side to
  the other.

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General Terminology

• Nucleus
• Aggregation of dendrites and nerve cell bodies
  in the CNS.
• Ganglion
• Aggregation of dendrites and nerve cell bodies
  in the PNS.

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General Terminology

• White matter
• Areas of myelinated axons.
• Gray matter
• Areas of unmyelinated axons, cell bodies, and
  dendrites.

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Synapse

• Definition
• Composite structure that allows two neurons or a
  neuron and a muscle cell to talk to each other.

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Synapse Components

• Presynaptic membrane
• With synaptic vesicles filled with
  neurotransmitters.
• Synaptic cleft
• Postsynaptic membrane
• With receptors for neurotransmitters.
• Monosynaptic pathways.
• Polysynaptic pathways.

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Reflex Arc

• Afferent (sensory) pathways
• Somatic.
• Visceral (splanchnic).
• Efferent (motor) pathways
• Somatic.
• Visceral (splanchnic).
• Association neurons (interneurons).

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Neuroglial Cells

• Schwann cells
• Astrocytes
• Microglial cells
• Oligodendrocytes
• Ependymal cells

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Schwann Cells

• Derived from neural crest cells.
• Myelinate axons in the PNS.

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Astrocytes

• Derived from neural crest cells.
• Function to physically support neurons.
• Channel materials between capillaries and neurons
  ( Blood-brain barrier).
• Support and guide neurons during embryonic
  building of cerebral cortex.
• Act as sinks for ions (i.e., K).
• Remove neuroactive and potentially toxic
  substances.

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Microglial Cells

• Derived from embryonic mesenchyme.
• May transform into phagocytes within CNS.

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Oligodendrocytes

• Derived from neural crest cells.
• Function to myelinate axons within CNS.

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Ependymal cells

• Derived from neural crest cells.
• Line ventricles of brain.