NERVOUS SYSTEM (cont.)

GANGLIA = collection of cell bodies outside of CNS

1) Spinal Ganglia (Dorsal Root Ganglia) = collection of cell bodies of sensory neurons entering spinal cord; contain pseudounipolar neurons; cell bodies grouped into fascicles

- Cell bodies surrounded by delicate collagen fibrils, fibroblasts and satellite cells =
flattened cells continuous with neurilemma of axons, function in support and may
regulate metabolite exchange between cells and blood
- Spinal ganglion covered with dense irregular CT capsule with septa extending into
interior




2) Autonomic Ganglia = cell bodies of visceral motor neurons
Locations:

a) Lateral Chain Ganglia (sympathetic) = near and parallel to spinal cord; segmented
and connected into chain (except in primitive vertebrates)
b) Collateral Ganglia (sympathetic) = distal to vertebral column
c) Terminal Ganglia (parasympathetic) = in or near wall of innervated organ

- Multipolar neurons, stellate appearance of cell body
- Satellite cells present but incompletely surround cell body due to multipolarity
- No fascicles present, but possess dense irregular CT capsule with septa


CENTRAL NERVOUS SYSTEM

I. SPINAL CORD -- See Handout for Structure

- Central Canal = filled with cerebrospinal fluid (derived from plasma); functions in
CNS metabolism and in protection from trauma
- Ependymal Cells = line central canal; non-neural cells composing simple cuboidal
epithelium (ciliated); secrete cerebrospinal fluid and monitor CSF composition
- Meninges = CT membranes covering CNS

1. Pia Mater = innermost, vascular loose CT, adheres to surface of CNS, lined by
simple squamous epithelium on outside
2. Arachnoid = thin, delicate non-vascular membrane with trabeculae extending
inwardly, contains collagen and elastic fibers; covered on outside by simple
squamous epithelium
3. Dura Mater = outermost, dense CT protective covering of collagen fibers + some
elastic fibers

- Subarachnoid Space separates pia and arachnoid, filled with CSF
- Subdural Space separates arachnoid and dura, filled with lymph-like fluid


II. CEREBRUM = responsible for consciousness, intelligence, thought, interpretation
of
sensations
- Gray Matter organized into six somewhat indistinct layers of nerve cell bodies. Lies on
outside in brain.

1) Molecular Layer
2) Granular Layer
1 & 2 composed of relatively small association neurons, involved in
communication between intracortical neurons
3) Pyramidal Cell Layer = neurons with pyramid-shaped cell body, function as
association and projection neurons
4) Inner Granular Layer = relatively small association neurons, myelinated fibers
5) Inner Pyramidal Cell Layer = contains pyramidal cells and small neurons
6) Polymorphic Cell Layer = polymorphous neurons - small neurons with spindle-
shaped cell body and branching dendrites; function as association and projection
neurons
(see handout)
- Lined by meninges on outside, ependymal cells on inside lining ventricles of brain;
contains many neuroglia cells in addition to neurons

III. CEREBELLUM = coordination of motor movements
- Composed of superficial cortex of gray matter covering a deeper body of white matter
- Cortex folded into many transverse ridges (folia cerebelli)
- Each ridge has a core of white matter (stains pink in H&E) and cortex (blue-staining)
of 3 layers:

1) Molecular Layer = outermost; contains glial cells, dendrites and many
unmyelinated
axons; also contains stellate cells and basket cells. Both are
considered to be inhibitory interneurons that modify actions of cortical neurons
2) Purkinje Layer = middle layer composed of a single layer of large flask-shaped
purkinje neurons with a few major branched dendrites extending into molecular layer.
Purkinje axons leave cortex and project to nuclei (collection of cell bodies w/in
CNS) in medullary regions. Purkinje cells convey motor impulses from cortex which
inhibit function of medullary nuclei.
3) Granular Layer = innermost; contains cell bodies of small neurons, granule cells
(multipolar neurons with small dark round nucleus, little cytoplasm and no Nissl
bodies; relay impulses from body to Purkinje cells) and Golgi cells (large multipolar
neurons with prominent nucleus and Nissl bodies; function as inhibitory neurons
modifying impulses passing to Purkinje cells).
(see handout)


NEUROGLIA CELLS = modified nerve cells, arise embryonically from neural crest
tissue

1) Astrocyte - 2 Types:

a) Fibrous = occurs in white matter of brain, have smaller number of cell processes
so take on star- like appearance, processes are generally straight; some are
attached to blood vessels
b) Protoplasmic = occur in gray matter, have large number of highly branched
processes so take on mossy appearance; processes often terminate in expanded foot
on blood vessels, or bind pia mater to CNS

- Astrocytes may regulate movement of metabolites, ions, fluids and gases between
blood, CSF and CNS

2) Oligodendroglia = present in both gray and white matter; box-like cell body with
short processes that wrap around nearby axons, responsible for myelination in CNS
(See Handout)
3) Microglia = tiny cells; may be rod-shaped, oval and indented, or bent; mainly found
in gray matter near blood vessels and nerve cell bodies; upon CNS damage
become motile and phagocytic; believed to be derived from monocytes (therefore from
mesoderm rather than neural crest)


BLOOD-BRAIN BARRIER = functions to keep harmful compounds that may gain
access to blood out of the brain
Components:

1) Capillaries within brain lined by endothelium with entire perimeter of each cell
bounded by tight junctions which restricts passage of dissolved molecules from
capillary to brain tissue
2) Pinocytotic transfer of fluid across endothelium is restricted
3) Capillaries also surrounded by extra thick basement membrane
4) Outer surface of capillaries covered with astrocyte feet which may further regulate
passage of molecules

To Lecture 13