Transcript Nervous Tissue

Nervous Tissue
Graduate Microanatomy Spring
1999
Sandra H. Bolanos
Central Nervous System
• Brain
• Spinal Cord
Brain
• Cranium (brain case)
• Cortex
Gray matter
Nerve cell bodies
• Interior Portion
White matter
Axons
Ventricles
CSF
Spinal Cord
• Occupies two-thirds
of the vertebral canal
• Enveloped by
meninges
• Cervical and lumbar
enlargements
• Gray matter centrally
located
Meninges
• 3 layers of connective
tissue membranes
• Surround and protect
brain and spinal cord
Pia Mater
Arachnoid
Dura Mater
Peripheral Nervous System
• Nerves that emerge from central nervous system:
12 pairs of cranial nerves
31 pairs of spinal nerves
Autonomic Nervous System
Sympathetic
Parasympathetic
Cellular Composition of CNS
• Neurons and
their processes
• Support cells:
Astrocytes
Oligodendrocytes
Ependymal cells
Microglia
Astrocytes
• In developing NS, form
structural framework to guide
migration of developing
neurons
• In developed NS, form
structural scaffolding for
more specialized neural
elements
• Clear ECM of by-products
of neural activity and
contain glycogen reserves
• Extend foot processes around
blood capillaries
Blood Brain Barrier
• Capillaries of the CNS not
fenestrated and have
intercellular tight junctions
between endothelial cells
• Highly resistant to passage of
ions or small molecules
• Do not exhibit
transendothelial transport in
small vesicles
• Astrocytes may influence
capillaries to express these
unique properties
Oligodendrocytes
• Produce myelin within
CNS
• Each cell sends out several
processes and myelinates
several nearby axons
Ependymal Cells
• Epithelial-like
• Ciliated
• Line cavities of brain ventricles and central canal of spinal
cord forming sheets of cuboidal cells in contact with CSF
Microglia
• Specialized macrophages
• In areas of injury, proliferate
and become actively
phagocytic in clearing
cellular debris and ingesting
damaged myelin
Composition of PNS
• Ganglia - a peripheral collection of nerve cell bodies
together with efferent and afferent axons and support
cells
• Nerves - a collection of axons linked together by
support tissue into an anatomically defined trunk
Ganglia
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Sensory (spinal sensory ganglia)
Non-sensory (sympathetic or parasympathetic)
Dorsal root ganglia, cranial ganglia, autonomic ganglia
Neuron cell bodies, support cells, loose fibrocollagenous tissue
Nerves
• Motor
Innervate skeletal muscle (CNS)
Innervate smooth muscle (PNS)
• Sensory
• Myelinated or Non-myelinated
• Axons, Schwann cells, fibroblast cells, blood
vessels
- 3 types of support tissue in a nerve trunk:
• Endoneurium
Surrounds individual axons, their associated Schwann cells, and
capillary blood vessels
• Perineurium
Surrounds groups of axons and endoneurium to form fascicles
• Epineurium
binds individual nerve fascicles into a
nerve trunk
• Endoneurium
Collagen fibers that are longitudinally oriented
ECM rich in GAGs and sparse fibroblasts
• Perineurium
7-8 concentric layers of epithelium-like flattened cells separated by
layers of collagen and joined by junctional complexes
Each layer of cells surrounded by an external lamina
• Epineurium
Outer sheath of loose fibrocollagenous tissue
May also include adipose tissue and muscular artery that supplies the nerve trunk
Peri
Epi
Fascicle
Endo
Schwann Cells
• PNS
• Myelinate only one axon
Neurons
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Gather information from sensory receptors
Process information and provide a memory
Generate appropriate signals to effector cells
Cell body, dendrites, axon, and synaptic bouton
Cell Body
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Pale-staining
Conspicuous nucleolus
Little heterochromatin
Nissl bodies
Golgi complex
Mitochondria
Lysosomes
Neurofilaments
Microfilaments
Microtubules
Dendrites
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Radiating processes of the cell body
Receive signals (synapses) from other neurons
Broader than axons
Extensive branching increases cell surface available for receiving
signals from other neurons
• Organelles similar to those of the perikaryon (no Golgi bodies)
• As distance from cell body increases, smooth ER and NFs reduced
but MTs and mitochondria still prominent
Axons
• A single long process capable of generating a nerve
impulse
• More slender and usually longer than dendrites
• Branch at right angles
• Can be quite long (spinal motor neurons that supply
foot muscles 40 inches in length)
• Axon Hillock is conical extension of cell body from
which axon arises
• Axoplasm lacks Nissl bodies
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Branches as it approaches its end forming small expansions
Terminal boutons contact other cells to form a synapse
At synapse, chemicals or electrical signals pass from one neuron to
another cell known as the effector cell
Neurotransmitters act rapidly and locally to activate their target cells and
neuromodulators that regulate these events
Neuron Shapes
Neuron Types
Myelin
• Insulation
minimizes leakage of current from membrane
speeds up conduction along axons
• Reduction of electrical capacitance
wide axons lower capacitance than narrow ones
increases diameter of axons
increases speed of nerve conduction
• Myelin-producing cells
Oligodendrocytes (CNS)
Schwann cells (PNS)
• Nodes of Ranvier
space between each unit of myelin
increase efficiency of nerve conduction
Myelin
Synapses
• Specialized region of contact where NT released from axon to
stimulate another cell
Axonal Transport
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Anterograde or retrograde
Fast or slow
Microtubules
Motor proteins
Ca2+
ATP
Minus end
Kinesin
Plus end
Dynein