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ZOO 117 1.0
Histology
Nervous Tissue
Dr. Dinithi Peiris
Dept. of Zoology
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Nervous tissue
Nervous tissue
Two types of neural cells in the nervous system:
§  Neurons / Nerve cells - For processing,
transfer, and storage of information (nerve
impulses)
§  Neuroglia – Associate with neurons. For
support, regulation & protection of neurons
Two Anatomical Divisions
¨ 
Central nervous system (CNS)
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Brain
Spinal cord
Peripheral nervous system (PNS)
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All the neural tissue outside CNS
Afferent division (sensory input)
Efferent division (motor output)
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Somatic nervous system
Autonomic nervous system
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Development of Nervous
tissue
Nervous tissue
PNS
CNS
Brain
Sensory
division
Spinal
cord
Visceral
sensory
division
Somatic
sensory
division
Motor
division
Visceral
motor
division
Sympathetic
division
Somatic
motor
division
Parasympathetic
division
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Development of Nervous
tissue
Nervous tissue
§ 
Excitability (irritability): ability to respond to
environmental changes or stimuli.
§ 
Conductivity: respond to stimuli by initiating electrical
signals that travel quickly to other cells at distant
locations. Nerve impulse
§ 
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NS develops from the ectoderm
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Ectoderm along mid-dorsal side of the embryo
thickness to from the neural plate
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Cells of neural tube give rise to entire CNS
Secretion: Upon arrival of the impulse at a distant
location the neuron secretes a neurotransmitter at a
synapse that crosses the synaptic gap and
stimulates the next cell.
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Development of Nervous
tissue
Neuron
Two types of cells
• 
Consists of 3 parts
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Neurons: For processing transfer and storage
information
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Neuroglia: Support, regulation and protection of
neurons.
Cell body
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Cell processes
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Dendritie
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Axon
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Distal portion of the axon is branched.
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Neuron
Cell body
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• 
Contains large spherical nucleus & a prominent
nucleolus
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Major biosynthetic center
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Focal point for the outgrowth of neuronal processes
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There are no centrioles
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Well developed Nissl bodies (rough ER)
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Axon hillock – cone-shaped area from which axons
arise.
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Cell body
Dendrites
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• 
Usually there is only one
unbranched axon per neuron
• 
Rare branches, if present, are
called axon collaterals
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Axonal terminal – branched
terminus of an axon
Schwann cell
nucleus
Neurilemma
Long axons are called nerve fibers
Axoplasm
Axolemma
• 
Myelin sheath
Slender processes of uniform
diameter arising from the hillock
Short, tapering, and diffusely branched processes
• 
They are the receptive, or input, regions of the
neuron
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Electrical signals are conveyed as graded potentials.
(Not action potentials)
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Regions of the Brain & Spinal
Cord
Axons
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•  White matter – dense collections of myelinated
fibers
•  Gray matter – mostly soma and unmyelinated
fibers
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Structural Classification of
Neurons
•  Multipolar neuron
–  most common
•  Bipolar neuron
–  one dendrite/one axon
•  Unipolar neuron
–  Ex. sensory from skin to
spinal cord directly
•  Anaxonic neuron
–  many dendrites/no axon
–  Ex. help in visual processes
Functional Classification of
Neurons
•  Sensory neurons: Most unipolar, few bipolar
•  Transmit sensory information from receptors of PNS
towards CNS
•  Motoneurons : Multipolar
•  transmit motor information from the CNS to effectors
(muscles/glands/adipose tissue) in the periphery of the
body.
•  Internurons: Multipolar
•  transmit information between neurons within the CNS;
analyze inputs, coordinate outputs
•  Most common type of neuron (20 billion)
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Comparison of Neurons
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Comparison of Neurons
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Neuroglia (glial cells)
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Neuroglia Cells (CNS)
Neurons are out numbered by neuroglia (1:50)
CNS neuroglia
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Astrocytes
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Oligodendrocytes
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Microglia
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Ependymal cells
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PNS neuroglia.
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Schwann cells
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Satellite cells
Astrocytes
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most abundant glial cells form framework of CNS
Astrocytes with few long
processes – Fibrous ast.
Found in white matter
Ast. With many short
branched processes in grey
matter – Protoplasmic ast.
contribute to blood-brain
barrier and regulate
composition of brain tissue
fluid
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Neuroglia Cells (CNS)
Neuroglia Cells (CNS)
Ependymal cells
Oligodendrocytes
•  Low columnar or cuboidal cells
•  Create myelin sheath around
axons of neurons in the CNS.
•  Apical ends of some cells have cilia to facilitate the
movement of CSF
•  No basal lamina. Instead the basal ends are elongated &
extended branch processes
•  Myelinated axons transmit
impulses faster than
unmyelinated axons
Microglia
•  Brain macrophages
•  Phagocyte cellular wastes &
pathogens
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Myelin Sheath
Neuroglia Cells (PNS)
•  Whitish, fatty (protein-lipid), segmented sheath
around most long axons
•  Function:
•  Protection of the axon
Schwann cells
•  Surround all axons of neurons in the
PNS creating a neurilemma around
them. Neurilemma allows for potential
regeneration of damaged axons
•  Electrically insulating fibers from one another
•  creates myelin sheath around most
axons of PNS
•  Increase the speed of nerve impulse
transmission
Satellite cells
•  Support groups of cell bodies of
neurons within ganglia of the PNS
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Myelin Sheath
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CNS
Myelin sheath
of CNS
Myelin sheath
of PNS
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•  3 regions
•  Cerebrum
•  Cerebellum
•  Spinal cord
•  Show regions of grey & white matter
•  Cerebral cortex has 3 layers
•  Molecular layer: outer layer
•  Purkinje cells: very large neurons
•  Granule layer: inner layer
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CNS
Meninges
•  Between the skull & NS are membranes of
connective tissue called meninges.
•  3 layers
•  Dura matter: Thick external dense connective tissue
•  Arachnoid: Has 2 components. 1. A sheet of CT in
contact with dura matter. 2. System of loosely arranged
trabeculare containing fibroblast & collagens.
•  PIA matter: inner layer. Consist of flattened
mesenchymally dervied cells
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Blood Brain Barrier
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Choroid Plexus
•  Main structural component is capillary endothelium
•  Cells are tightly sealed together
•  Specialized tissue projects in to elaborate folds with
many villi.
•  Basal lamina of capillaries are enveloped by
preivascular feet of astrocytes.
•  Each villus contains a thin layer of well vascularized
pia matter covered by cuboidal epithelial cells.
•  BBB allows stable composition & constant balance
of ions and fluid
•  Main function of choroid plexus is to remove water
from blood and release it as CSF
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PNS
Nerve Fibers
•  Consist of axons enclosed within a
sheath.
•  3 components
•  Nerves: bundles of nerve fibers surrounded by
glial cells and CT
•  Ganglia
•  P. nerves contains groups of nerve
fibers; where axons are sheathed by
Schwann cells.
•  Axons of small diameter are
unmyelinated nerve fibers.
•  Nerve endings
•  Thicker axons are sheathed by
numerous concentric wrappings of
enveloping cells forming myelin sheath.
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Nerves
Ganglia
•  Nerve fibers are grouped into bundles
to form nerves.
•  Ovoid structures containing neural cell bodies & glial cells
supported by CT
•  Axon & Schwann cells are enclosed
within concentric layers of nerve fibers.
•  2 types
•  Sensory ganglia
•  Receive afferent impulses
•  Associated with dorsal root of the spinal & cranial
nerves
•  Autonomic ganglia
•  Consists of 3 layers
•  Epineruium: dense fibrous coat
•  Perineurium: surrounds each nerve
fiber bundle
•  Effects the activity of skeletal muscles
•  Endoneurium: consists of spare
layer of loose CT
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