Nervous tissue is composed of neurons and support cells. Schwann cells in the peripheral nervous system wrap their cell membrane around axons to form an insulating myelin sheath. Between Schwann cells are gaps called nodes of Ranvier that enhance nerve impulse conduction. Oligodendrocytes perform myelination in the central nervous system. Support cells include astrocytes in the CNS and Schwann cells and satellite cells in the PNS.

1. Histology Review Supplement 3
cells, in particular, are responsible for wrapping their cell
Nervous Tissue Review membrane jelly-roll style around axons and dendrites to form
From the PhysioEx main menu, select Histology Atlas. Click an insulating sleeve called the myelin sheath.
on the white Sort By drop-down menu and select Histology
Click slide 5.
Review from the list. Refer to the slides in the Nervous Tis-
sue Slides folder as you complete this worksheet. Because Schwann cells are aligned in series and myelinate
Nervous tissue is composed of nerve cells (neurons) and only a small segment of a single axon, small gaps occur be-
a variety of support cells. tween the myelin sheaths of adjacent Schwann cells. The
gaps, called nodes of Ranvier, together with the insulating
Click slide 1. properties of myelin, enhance the speed of conduction of
Each nerve cell consists of a cell body (perikaryon) and one electrical impulses along the length of the axon. Different
or more cellular processes (axon and dendrites) extending support cells and myelinating cells are present in the central
from it. The cell body contains the nucleus, which is typi- nervous system (CNS).
cally pale-staining and round or spherical in shape, and the
usual assortment of cytoplasmic organelles. Characteristi- What is the general name for all support cells within the
cally, the nucleus features a prominent nucleolus often de- CNS?
scribed as resembling the pupil of a bird’s eye (“bird’s eye”
or “owl’s eye”).
Click slide 2.
The cytoplasm of the cell body is most often granular in ap- Name the specific myelinating cell of the CNS.
pearance due to the presence of darkly stained clumps of ri-
bosomes and rough endoplasmic reticulum (Nissl bodies/
Nissl substance). Generally, a single axon arises from the cell
body at a pale-staining region (axon hillock) devoid of Nissl In the PNS, connective tissue also plays a role in provid-
bodies. The location and number of dendrites arising from ing support and organization. In fact, the composition and or-
the cell body varies greatly. ganization of the connective tissue investments of peripheral
Axons and dendrites are grouped together in the periph- nerves are similar to those of skeletal muscle.
eral nervous system (PNS) to form peripheral nerves.
Click slide 3.
What is the primary unit of function in nervous tissue? Each individual axon or dendrite is surrounded by a thin and
delicate layer of loose connective tissue called the en-
doneurium (not shown.) The perineurium, a slightly thicker
layer of loose connective tissue, groups many axons and den-
drites together into bundles (fascicles). The outermost
Name the pale-staining region of the cell body from which epineurium surrounds the entire nerve with a thick layer of
the axon arises. dense irregular connective tissue, often infiltrated with
adipose tissue, that conveys blood and lymphatic vessels to
the nerve. There is no connective tissue component within
the nervous tissue of the CNS.
The support cells of the nervous system perform extremely
important functions including support, protection, insulation, What is the relationship of the endoneurium to the myelin
and maintenance and regulation of the microenvironment sheath?
that surrounds the nerve cells.
Click slides 3, 4.
In the PNS, support cells surround cell bodies (satellite cells)
and individual axons and dendrites (Schwann cells). Schwann