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Nervous System
Myelin sheath in H and E slides
Spinal cord
Myenteric ganglion
Pacinean Corpuscle
Nervous Tissue:
The organization of cells in nervous tissue
The organization of organelles in neurons.
Nervous System Organisation:
-Central nervous system (CNS)
-Brain & spinal cord
-Peripheral nervous system (PNS)
-Outside CNS
-Cranial & spinal nerves and associated ganglia
- PNS
> sensory
> motor - somatic: impulses transmitted
directly to skeletal muscle via one
neuron
- autonomic: impulse  one neuron
 autonomic ganglion  SM, CM,
glands
Cells of the nervous system:
Glia
Neurons
- perikaryon (soma, cell body)
- dendrites
- axon
- axon terminals
Neurons:
- many shapes (unipolar, bipolar, pseudounipolar,
multipolar)
Usually polarized
- cell body
- dendrites
- axon
- axon terminal
Dendrites:
Receive and integrate synaptic signals.
**Dendritic spines**
Some neurons have many dendrites.
Some dendrites have many branches.
Ultrastructure similar to cell body.
Axon: one process, some have collateral branches.
-can be long in the PNS
-NO ribosomes
-Yes, neurofilaments, microtubules, mitochondria
> believed to serve in regulation of diameter
Axon ensheathing cells are glia.
o Oligodendrocytes in the CNS.
o Schwann cells in the PNS.
Ensheathing cells responsible for maintaining myelin
sheath
In the CNS,
white matter contains myelinated axons
gray matter, no myelination
Other types of glia (neuroglia):
Astrocytes:
protoplasmic - gray matter
fibrous - white matter
- regulate ions and other molecules around neurons
- release glucose from glycogen
- have processes around blood vessels
- form scar tissue
astrocyte
Oligodendrocytes: smaller than astocytes
-some produce myelin
Microglia: small phagocytic cells
-originate from bone marrow
Ependymal cells:
- cuboidal or low columnar simple epith.
- line the ventricles
Astrocytes – green
Microglia – red
Morphological reactions of injured axons in the PNS: PAGE 216
Chromatolysis: may last several months.
•Nissl bodies disperse, peripheral nucleus.
•Soma producing: Free ribosomes, protein, RNA and
other molecules.
•The axon and myelin sheath distal to the lesion
degenerates as far as the axon collateral
•sprouting of the axon into endoneurium
•guiding by proliferating Schwann cells toward the
target
•regeneration in the presence of macrophages,
fibroblasts, Schwann cells and basal lamina. These
express growth factors, cytokines, up-regulate
expression signal receptors.
Chromatolysis cont’d
Schwann cells form a sheath that guides the sprout to the target
Sprout makes synaptic contact with target
Other sprouts degenerate
If no synaptic contact is made, the target cell degenerates.
Need connective tissue sheaths for the regeneration.
These are absent in the CNS generally, no regeneration
In the CNS, microglia phagocytose the injured cells
Glial scar occupies the space.
Location of synapses:
Axodendritic synapses
Axosomatic synapses
Axoaxonic synapses
Dendrodendritic synapses
Ultrastructure of neurons:
Cell body
- nucleus
- rER and polyribosomes (Nissl bodies)
- Golgi complex
- mitochondria
- lipofuscin granules (considered ‘aging’
pigment)
- cytoskeleton: neurofilaments,
microtubules
Axon hillock - no rER
Pacinian Corpuscle
Nerve ending