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Flashcards in May: neurohisto Deck (26):

What are the 2 classes of cells in the CNS?

1. Neurons - specialized for:
a. excitation (or inhibition)
b. impulse conduction

2. Neuroglia (Glia) - interstitial cells
a. Astrocytes
b. Oligodendrocytes
c. Microglia (mesoglia)
d. Ependymal cells


What is gray matter? Where is it found?

Gray matter - Cell bodies of neurons embedded in a neuropil made up of unmyelinated cell processes plus glial cells. A group or cluster of nerve cell bodies with similar function
is termed a nucleus. Outside the CNS, a similar structure would be termed a ganglion.
a. central part of spinal cord
b. brain stem (portions)
c. cortical tissue (of brain)


What is white matter?

White Matter - Long processes of neurons (predominantly myelinated) plus glial cells.
Functionally related processes are grouped in “TRACTS”.


What are the "mixed areas"?

Mixed Areas - Neuron cell bodies plus myelinated cell processes plus glial cells. Includes portions of brain stem (medulla, pons, midbrain.)


Does the CNS have CT fibers?

No C.T. fibers except some associated with capillaries.


What are the general characteristics of a neuron cell body (perikaryon)?

-size: 4μm to 135 μm
- usually central except for the neurons of the autonomic nervous system (have eccentrically placed nuclei).
- chromatin almost entirely extended (lots of euchromatin).
- single, large nucleolus near the center of the nucleus.
-Nissl substance
- identified at the light microscopic level as blue patches (With H & E stain).
- stacks of flattened cisternae of rough E.R. mixed with lots of free ribosomes.
- chromatolysis: following nerve injury, there is a dissolution of Nissl substance.
- located in the perikaryon and dendrites (NOT in axons).
-contains Golgi, mitochondria, microfilaments, microtubules.
-various pigments; esp.:
- lipofuscin (increases with age of cell).
- melanin: abundant in the substantia nigra of the midbrain.


What are the general characteristics of a neuron axon?

a. size varies from a fraction of a mm to several feet.
b. many have collateral branches which leave at right angles
- some have recurrent collaterals that curve back along originating
c. axon hillock - proximal part of axon; a little thicker in diameter.
d. axolemma - plasmamembrane of axon
e. axoplasm - cytoplasm of axon. Lacks Golgi and rER. Free ribosomes
are rare.


What are the general characteristics of a neuron's dendrites?

a. much shorter than axons
b. branch dichotomously at right angles
c. contain ribosomes, Nissl, filaments, mitochondria, etc.
d. dendritic transport occurs but little is known of details


What are multipolar neurons?

-many dendritic processes + 1 axon
-includes most neurons


What are bipolar neurons?

-two processes: 1 dendrite + 1 axon
-location: inner ear, retina of eye


What are Unipolar neurons?

-1 axon only
-location: retina of eye


What are pseudounipolar neurons?

-modified unipolar: axonal process + dendritic process
-somatic sensory fibers


What are the characteristics of Golgi Type 1 Neurons? Examples?

LARGE (Golgi Type I)
1) perikaryon to 135μm diameter
2) axons to several feet
3) examples:
i. Pyramidal cells (cerebral cortex)
ii. Purkinje cells (cerebellar cortex)
iii. lower motor neurons


What are pyramidal cells?

LARGE (Golgi Type I)
Pyramidal cells (cerebral cortex)
* pyramid-shaped
* apical dendrite (extends towards cortical surface)
* several basal (horizontal) dendrites
* axon arises from base
* Betz cells of motor area of cerebral cortex


What are Purkinje cells?

LARGE (Golgi Type I)
Purkinje cells (cerebellar cortex)
* flask-shaped
* 1 or 2 dendrites extend towards surface (lots of branching.
* axon from base of perikaryon passes deep into the


What are lower motor neurons?

LARGE (Golgi Type I)
lower motor neurons
* location:
- ventral horns of spinal cord
- motor nuclei of cranial nerves


What are Golgi Type 2 cells? Examples?

SMALL (Golgi Type II)
1) perikaryon as small as 5μm
2) axons - a fraction of a mm. (usually unmyelinated)
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3) vastly outnumber the Golgi type I cells
4) includes interneurons (internuncials)
5) examples:
i. Stellate cell (cerebral cortex)
ii. Cell of Martinotti
iii. Granule cell
iv. Horizontal cell


What are stellate cells?

SMALL (Golgi Type II)
Stellate cell (cerebral cortex)
* cerebral cortex
* axon ends on one or more cells in the area


What are cells of martinotti?

SMALL (Golgi Type II)
Cell of Martinotti
* cerebral cortex
* resembles stellate except it has a longer axon which is
directed towards the cortical surface


What are granule cells?

SMALL (Golgi Type II)
Granule cell
* located in deepest of three layers of cerebellar cortex


What are horizontal cells?

SMALL (Golgi Type II)
Horizontal cell
* cerebral cortex
* long axis is parallel to cortical surface
* also located in the retina


What are oligodendrocytes?

Part of Neuroglia
1. Nucleus is spherical with medium to dense chromatin.
2. Numerous cytoplasmic processes project from the cells to wrap around
* The continued wrapping of the cytoplasmic processes forms a
myelin sheath in much the same manner as Schwann cells myelinate peripheral nerves.
* Each process projects to a different axon.
* Thus a single oligodendrocyte wraps portions of several axons and
a single axon is wrapped by several oligos.
3. In white matter, the oligodendrocytes are disposed in rows between the
axons while in gray matter they appear to be randomly located.


What are astrocytes?

Part of neuroglia
1. nuclei are larger than other glial cells. Also, somewhat irregular in shape.
2. contain many processes that project in several directions.
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3. the ends of the processes widen and spread over the surfaces of neurons and capillaries as Astrocyte Feet. Most capillaries are completely ensheathed by the astrocytic feet.
4. contain lots of microfilaments (for rigidity)
5. Function:
a. support
b. chemical transport (between capillaries and neurons).
6. Types:
a. fibrous - present in white matter
b. protoplasmic - present in gray matter


What are ependymal cells?

Part of neuroglia
1. Location: Line the ventricles of the brain and the central canal of the spinal cord.
2. Structure:
a. cuboidal to columnar in shape
b. ependyma is ciliated in the ventricles and non-ciliated elsewhere


What are microglia?

Part of neuroglia
1. small cells with dark, flattened nuclei.
2. origin & function are controversial: May said they were phagocytic


What is Neuropil?

A. Light microscopic level - neuropil appears as a fine mottled area between
cell bodies of neurons.
B. Electron Microscopic level
1. conglomerate of cell bodies & cell processes of astrocytes along w/processes of neurons (mostly unmyelinated).
2. fine intercellular spaces between cells and their processes.
3. glycosaminoglycans (hyaluronic acid, chondroitin and heparin sulfates) present in spaces. Similar to ground substance of C.T.