Transcript ANATOMICAL ORGANIZATION of the NERVOUS SYSTEM

NERVOUS SYSTEM
Lecture 1
OVERVIEW
and
NEUROHISTOLOGY
ANATOMICAL ORGANIZATION of the
NERVOUS SYSTEM
Nervous
System
CNS
PNS
ANS
BRAIN
CRANIAL
NERVES
SYMPATHETIC
SPINAL
CORD
SPINAL
NERVES
PARASYMPATHETIC
Central Nervous System (CNS)
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Definition:
Unpaired, bilaterally symmetrical structures
extending along the longitudinal axis of the
midsagittal plane of the body.
Structures arising directly from the neural tube.
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Includes:
Brain
Spinal cord
Peripheral Nervous System (PNS)
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Definition:
Made up of transmission pathways
carrying information between the CNS and
external/internal environments.
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Afferent (sensory) pathways:
Carry information to the CNS.
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Efferent (motor) pathways:
Carry information from the CNS.
Peripheral Nervous System (PNS)
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Includes:
Cranial nerves (12 pairs).
Spinal nerves (31 pairs).
Autonomic Nervous System (ANS)
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May be considered a subdivision of the
PNS.
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Entirely motor.
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Innervates smooth muscle and glands
(viscera).
ANS Subdivisions
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Sympathetic system (fight or flight):
Also called thoracolumbar.
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Parasympathetic system (feed or breed):
Also called craniosacral.
Parts of a Neuron
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Cell body:
Trophic unit
Perikaryon
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Dendrites:
Receptive unit
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Axon:
Conductive unit
Cell Body Definition
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That part of a neuron that encloses the
nucleus and other organelles necessary to
maintain and repair the neuron.
Cell Body Organelles
Nucleus
 Golgi apparatus
 RER
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Ribosomes (=Nissl substance)
Dendrites (Characteristics)
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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.
Axon Characteristics
Carries information to another neuron or
muscle cell.
 Often relatively long.
 Single (one per neuron).
 Conducts action potential

Axon Characteristics
Ends in short branched processes called
telodendria.
 May have collateral branches.
 Cell membrane (= axolemma).
 Cytoplasm = (axoplasm).
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Axon Characteristics
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Covered by neurolemma:
Made up of Schwann cells.
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Often myelinated:
Myelin is formed by Schwann cells.
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Note: axon is the only part of a neuron that
is ever myelinated.
Axon Organelles
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Mitochondria
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Neurofilaments
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Neurotubules
Axonal Transport
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Anterograde:
Transports vesicles from cell body to end of
axon.
Kinesin
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Retrograde:
Transports vesicles from end of axon toward
cell body.
Cytoplasmic dynein
Axonal Transport

Slow transport:
1-5 mm/day
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Fast transport:
200-400 mm/day
General Terminology
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Nerve:
Bundle of fibers in the PNS.
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Tract:
Bundle of fibers in the CNS.
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Commissure:
Tract in the CNS that crosses from one side
to the other.
General Terminology

Nucleus:
Aggregation of dendrites and nerve cell
bodies in the CNS.
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Ganglion:
Aggregation of dendrites and nerve cell
bodies in the PNS.
General Terminology
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White matter:
Areas of myelinated axons.
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Gray matter:
Areas of unmyelinated axons, cell bodies,
and dendrites.
Synapse
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Definition:
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Composite structure that allows two neurons
or a neuron and a muscle cell to “talk” to each
other.
Synapse Components
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Presynaptic membrane:
With synaptic vesicles filled with
neurotransmitters.
Synaptic cleft:
 Postsynaptic membrane:
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With receptors for neurotransmitters.
Monosynaptic pathways.
 Polysynaptic pathways.
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Reflex Arc
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Afferent (sensory) pathways:
Somatic.
Visceral (splanchnic).
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Efferent (motor) pathways:
Somatic.
Visceral (splanchnic).
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Association neurons (interneurons).
Neuroglial Cells
Schwann cells
 Astrocytes
 Microglial cells
 Oligodendrocytes
 Ependymal cells
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Schwann Cells
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Derived from neural crest cells.
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Myelinate axons in the PNS.
Astrocytes
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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.
Microglial Cells
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Derived from embryonic mesenchyme.
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May transform into phagocytes within
CNS.
Oligodendrocytes
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Derived from neural crest cells.
Function to myelinate axons within CNS.
Ependymal cells
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Derived from neural crest cells.
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Line ventricles of brain.