Histology
Lab-6-
Ass. Lec.
Wafaa H. M. Alhashimy
Dentistry College
Second Stage
Peripheral nervous system(PNS)
consists of neurons , nerves and axons that are located outside the CNS . these
include cranial nerves from the brain and spinal nerves from the spinal cord , along
with their associated ganglia
Ganglia (singular , ganglion) are small accumulations of neurons that are located
outside the CNS and are surrounded by a connective tissue capsule .
* Paravertebral ganglia (sensory ganglion): are an interconnected chain of
ganglia that are located parallel to the vertebral column , near the junction of the
dorsal and ventral roots of the spinal nerves .
* Peripheral ganglia (autonomic ganglion ): are located distally from the vertebral
near visceral organs .
Supportive cells in the PNS
The supportive cells in the PNS are the myeline – forming neurolemmocytes
(Schwann cells) and the satellite cells . satellite cells are small cells that surround the
neuronal cells in paravertebral and peripheral ganglia .
Connective tissue layers in the PNS
A peripheral nerve is composed of numerous axons of various sizes surrounded by
several layers of connective tissue that partition the nerve into several nerve (axon)
bundles or fascicles .
Epinerium : . the outermost connective tissue layer , which consists of dense
irregular connective tissue that completely surrounds the peripheral nerve .
Perineurium :a thinner connective tissue layer, extends into several and surrounds
numerous nerve fascicles . within each fascicle are individual axon and their
supporting cells , the neurolemmocytes (Schwann cells) .
Endonerium : each exon is surrounded by a loose connective tissue layer of thin
reticular fibers .
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Peripheral nervous system(PNS) divided in to :
 Somatic Nervous System
The somatic nervous system consists of peripheral nerve fibers that control of body
movements via skeletal muscles.
consists of efferent nerves responsible for stimulating muscle contraction that send
sensory information to the central nervous system and motor nerve fibers that project
from CNS to skeletal muscle.
 Autonomic Nervous System (ANS)
autonomic nervous system controls cardiac muscle , smooth muscle of the viscera
(internal organs) and glands .The ANS is classically divided into two subsystems:
sympathetic nervous system(SNS): The ganglia of SNS called Sympathetic
ganglia or paravertebral ganglia, are located just ventral and lateral to the spinal cord .
They deliver information to the body about stress and impending danger, and are
responsible for the familiar fight-or-flight response.
parasympathetic nervous system(PSNS) : ( rest stage) The main nerves are the tenth
cranial nerves, the vagus nerves. They originate in the medulla oblongata.
Not :Sympathetic and parasympathetic divisions typically function in opposition to
each other. But this opposition is better termed complementary in nature .
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Note : the somatic nervous system has only one neuron between the central nervous
system and the target organ while the autonomic nervous system uses two neurons. ).
It also differs from the sensory-somatic system is using two groups of motor neurons
to stimulate the effectors instead of one .
Note:
1. In the CNS, collections of neurons are called nuclei. In the PNS,
collections of neurons are called ganglia.
2. In the CNS, collections of axons are called tracts. In the PNS, collections
of axons are called nerves.
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