Histology of Nervous Tissue:
Neuroglial Cells & Neurons
Chapter 9: Nervous System
Unit 3: Integration and Coordination
Nervous tissue consists of two types of
2. Neuroglial cells
Neuroglial Cells fill spaces, provide structural
framework, produce myelin, and carry on
Name derives from histoligsts believeing they were
the “glue” that held nervous tissue together.
In the CNS, they constitute about 1/2 the volume.
CNS neuroglial cells: Microglial Cells,
Oligodendrocytes, Astrocytes, &Ependymal
PNS neuroglial cells: Schwann cells, & satellite
Microglial cells are scattered throughout
the central nervous system.
They support neurons and phagocytize
bacterial cells and cellular debris.
Oligodendrocytes occur in rows along
They provide insulating layers of myelin
around axons within the brain and spinal cord
Astrocytes are commonly found between
neurons and blood vessels, providing
They also join parts by numerous cellular
processes, and help regulate the
concentrations of nutrients and ions within
Astrocytes also form scar tissue that fills
spaces following injury to the CNS.
Ependymal cells form an epithelial-like
membrane that covers specialized brain
Also forms the inner linings that enclose
spaces within the brain (ventricles) and spinal
cord (central canal).
Schwann cells help to form a covering
called a Myelin Sheath around axons of
the periphreal nervous system.
We’ll talk more about those is a second!!
Neurons vary considerably in size and shape,
but they all have common features.
Cell body - contains nucleus & organelles for
Dendrites (little trees) - receiving or input parts of a
Axons - conduct impulses towards another neuron,
muscle, or gland
The axons of most neurons are surrounded by a
many-layered covering called a myelin sheath.
Myelin is produced by Schwann cells (PNS) and
Schwann cells wrap around the axon many times,
surrounding the axon with many layers of cell
This membrane is made of a lipoprotein called Myesin.
The portions of these cells that contain most of the
cytoplasm and the nuclei remain outside the myelin
sheath and comprise the Neurolemma.
Narrow gaps in the myelin sheath between schwann
cells are celled Nodes of Ranvier.
Axons with myelin sheaths are called
Myelinated and those that lack sheaths
are called Unmyelinated.
Masses of myelinated axons form the White
Matter in the CNS.
Unmyelinated axons and neurons bodies form
Grey Matter within the CNS.
Myelin sheaths begin forming during the 4t
mo of fetal development and continue into
the teenage years.
Clinical Connection: Multiple Sclerosis
Multiple Sclerosis (MS) is a progressive autoimmune
destruction of myelin sheaths of neurons in the CNS.
Myelin sheaths deteriorate to scleroses (scars) in
Afflicts about 1/2 million peopld in the US and 2 million
Appears between the ages of 20-40, affecting females
twice as often as males
Symptoms: Heaviness & weakness in the muscles,
abnormal sensations, double vision, loss of
Treatment: Therapies that slow recurrence of
Differences in Neurons
Neurons can vary in a number of ways:
1. Structure, size, and shape of cell body
2. Length and size of their axons and
3. Number of connections neurons make with
Classification of Neurons
On of the basis of structural
differences, neurons are classified into
the following three major groups:
1. Bipolar Neurons
2. Unipolar Neurons
3. Multipolar Neurons
The cell body of a bipolar neuron only
has two processes, arising from each
One process is an axon, the other is a
dendrite (even though they look the same).
Neurons within specialized parts of the eyes,
nose, and ears are bipolar.
Unipolar neurons have a single process
extending from its cell body.
The process divides into two branches, that
both function as a single axon.
One branch (peripheral process) is associated
with dendrites near a peripheral body part.
The other branch (central process) enters the
brain or spinal cord.
The cell bodies of some unipolar neurons
aggregrate in specialized masses of nervous
tissue called Ganglia.
Multipolar neurons have many
processes arising from their cell bodies.
Only one process of each neuron is an
axon, the rest are dendrites.
Most neurons whose cell bodies lie within the
brain or spinal cord are multipolar.
Classification of Neurons Continued
On the basis of functional differences,
neurons are grouped as follows:
1. Sensory Function
3. Motor Neurons
Sensory neurons carry nerve impulses
from peripheral body parts into the brain
or spinal cord.
Sensory neurons either have specialized
Receptor Ends at the tips of their
dendrites, or they have dendrites that are
closely associated with Receptor Cells in
the skin or in sensory organs.
Most sensory neurons are unipolar, although
some are bipolar.
Interneurons lie entirely within the brain or
They are multipolar and link other neurons.
Interneurons transmit impulses from one part of
the brain or spinal cord to another.
Motor neurons are multipolar and carry
nerve impulses out of the brain or spinal
cord to effectors.
Motor impulses stimulate muscles to contract.
Stimulate glands to release secretions.