Histology SSN
October 16, 2002
Sara Nash (sas2007@columbia.edu) and Sue Lee (sjl2005@columbia.edu)
Nerve Tissue
I. The Neuron (slide #85, H&E; see Ross Fig. 11.1, p258)
A. Basics
-the neuron is the structural and functional unit of the nervous system
-highly polarized cells: dendrites are neuronal processes that receive stimuli from other nerve
cells, and axons comprise the transmitting end of the neuron (note that dendrites, containing rER
and ribosomes, hold the Nissl stain; axons, lacking these features, do not stain with Nissl)
-neurons synapse on cell bodies, dendrites, or axons of other neurons
-neurons integrate, conduct, and transmit coded information
B. Cell Body (Perikaryon)
-contains the nucleus, ribosomes, ER, Golgi apparatus, and other cellular organelles
-the ER synthesizes neurotransmitter and contains the ribosomal RNA that retains the Nissl stain
C. Axon
1. Axon Hillock: responsible for action potential integration
2. Myelin Sheath: lipid wrapping that facilitates saltatory conduction of action potentials
-in the CNS, oligodendrocytes form the myelin sheath
-in the PNS, Schwann cells form the myelin sheath
-does not retain H&E stain
3. Nodes of Ranvier: channels that allow Na+ entry, which leads to depolarization
-seen as small breaks in the myelin sheath
-in saltatory conduction the action potential “jumps” between nodes of Ranvier
4. Axon Terminal: Site of vesicular storage and calcium-induced neurotransmitter
release
II. The Central Nervous System
The CNS consists of the brain and spinal cord.
A. Key Features
1. The Meninges (described as move from outer to inner layers)
a) dura mater: hard, outermost connective tissue (collagen) covering
b) arachnoid mater: delicate sheet of connective tissue that extends delicate
trabeculae into the pia mater; CSF is found beneath this layer in the subarachnoid space
c) pia mater: delicate connective tissue layer resting upon the brain and spinal cord
2. Supporting Cells
a) oligodendrocytes: form myelin sheet around CNS neurons
b) astroglia: physical and metabolic support for neurons and blood vessels,
responsible for the blood brain barrier
c) microglia: phagocytotic cells responsible for waste disposal in the CNS
B. Spinal Cord (see Ross, plate 44, p300)
1. The spinal cord can be divided into 2 parts:
a) white matter (myelinated axons and glial cells; mostly oligodendrocytes)
b) gray matter (neuronal cell bodies and dendrites; looks like a butterfly)
-in the white matter axons will be oriented in cross section (as fibers are running to and from the
brain) whereas in the gray matter axons will appear in plane of section
2. The gray matter can be further subdivided:
a) dorsal horn (more pointy)
-dorsal horn neurons are responsible for somatosensation, temperature
sensation and pain sensation (innervate the skin)
b) ventral horn (more rounded)
-ventral horn neurons are responsible for movement (innervate skeletal
muscle)
C. The Brain
1. Cerebral Cortex (slide #108, Nissl stain)
-consists of 6 different layers
-large pyramidal cells, which are responsible for movement, can be found in the
deeper parts of the cortex
2. Cerebellum (slide #86, Nissl stain; Ross plate 43, p298)
a) brain structure that enables motor coordination
b) the gray matter of the cerebellum consists of two major cell layers:
(i) molecular layer: the pale staining layer containing mostly axons and
dendrites, and some neuronal and support cell bodies; outside of granular layer
(ii) granular layer: darker, basophilic layer that contains more cell bodies
c) the white matter of the cerebellum is the innermost layer (inside the granular
layer)
c) thin layer of Purkinje cells (flask shaped, eosinophilic) is found between the
two layers; these cells convey output from the cerebellum
III. Peripheral Nervous System
The peripheral nervous system includes the somatic nervous system, the autonomic
nervous system, and the enteric nervous system.
Key Features
1. Fibroblasts- produces collagen necessary for connective tissue
2. Connective Tissue- provides stability to peripheral nerve
3. Satellite Cells- cuboidal cells that provides peripheral insulation, but does not make
myelin
4. Schwann Cells- forms myelin sheath that insulates axon and makes myelin
5. Histocytes- macrophages of the PNS
A. Autonomic Nervous System: Thoracic Ganglion (slide #83, H&E)
The autonomic nervous system innervates the smooth muscle and glands. It is responsible for
organ function.
1. Autonomic Ganglion- Thoracic Ganglion (slide #83, H&E)
a) ANS contains ganglia or clusters of neurons and supporting cells. NOT found in
CNS
b) Satellite cells surround the cell bodies of the ganglia;
(i) Responsible for maintaining a stable chemical microenvironment around the
neuron.
(ii) Very similar to Schwann cells, except they don’t make myelin.
B. Somatic Nervous System
The somatic nervous system innervates skeletal muscle and is responsible for movement.
1. Peripheral Nerve- Sciatic Nerve Slide (#81 H&E)
a) Peripheral Nerve = a bundle of nerve fibers held together by connective tissue.
b) A major PNS feature is connective tissue, classified in the following way.
(i) ENDONEURIUM: Vascular connective tissue around an individual nerve fiber
(ii) PERINEURIUM: Connective tissue that arranges groups of axon fibers into
fascicles
(iii) EPINEURIUM: Connective tissue that binds nerve fascicles into nerve bundles
(see p. 260 in Ross for comparison with muscle tissue)
C. The Enteric Nervous System (slide #35, H&E)
The gut has its own independent nerve supply. Throughout the peripheral nervous system, you’ll
see smooth muscle is innervated by peripheral nerve.
1. Difference between nerve and smooth muscle.
a) Nerve tissue tends to be more compact, enclosed by the connective tissue layers
mentioned above
b) Nerve is less eosinophilic whereas smooth muscle is more diffuse with a more intense
eosinophilic hue.
c) Peripheral nerves are wavy and bubbly because there are lots of non-staining regions
where myelin has leaked out.
Final note: Most of the time, CNS structures are stained with a Nissl stain whereas PNS
substances are stained with H&E.
Important Skills:
-Know the characteristic features of both the CNS and PNS
-Be able to distinguish nerve tissue from muscle and dense, irregularly arranged connective
tissue. This will enable you to recognize nerve tissue present in various organs.
-Know the features of the neuron. Correlate light micrograph structures with electron
micrograph structures.