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A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of
neurons A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

neurons
(a
ganglion A ganglion is a group of neuron cell bodies in the peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In biology Biology is the natural science that studies li ...

ganglion
) in a
dorsal root The dorsal root of spinal nerve (or posterior root of spinal nerve or sensory root) is one of two "roots" which emerge from the spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue Nervous tissue, also call ...
of a
spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...

spinal nerve
. The cell bodies of sensory neurons known as
first-order neurons The somatosensory system is a part of the sensory nervous system The sensory nervous system is a part of the nervous system responsible for processing sense, sensory information. A sensory system consists of sensory neurons (including the sen ...
are located in the dorsal root ganglia. The
axons An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, tha ...
of dorsal root ganglion neurons are known as afferents. In the
peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, ...
, afferents refer to the axons that relay sensory information into the
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
(i.e. the
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tis ...

brain
and the
spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the spinal cord, which contain ...

spinal cord
).


Structure

The neurons comprising the dorsal root ganglion are of the pseudo-unipolar type, meaning they have a cell body (soma) with two branches that act as a single axon, often referred to as a ''distal process'' and a ''proximal process''. Unlike the majority of neurons found in the
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
, an
action potential In physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...

action potential
in posterior root ganglion neuron may initiate in the ''distal process'' in the periphery, bypass the cell body, and continue to propagate along the ''proximal process'' until reaching the
synaptic terminal Synaptic may refer to: * Synapse In the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmitting act ...
in the
posterior horn of spinal cord The posterior grey column (posterior cornu, dorsal horn, spinal dorsal horn, posterior horn, sensory horn) of the spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblonga ...
.


Distal section

The distal section of the axon may either be a bare nerve ending or encapsulated by a structure that helps relay specific information to nerve. Two examples where the nerve ending of the ''distal process'' is encapsulated as such are,
Meissner's corpuscles Tactile corpuscles or Meissner's corpuscles are a type of mechanoreceptor discovered by anatomy, anatomist Georg Meissner (1829–1905) and Rudolf Wagner. This corpuscle is a type of nerve ending in the skin that is responsible for sensitivity to li ...
, which render the ''distal processes'' of mechanosensory neurons sensitive to stroking only, and
Pacinian corpuscles Pacinian corpuscle or lamellar corpuscle or Vater-Pacini corpuscle; is one of the four major types of mechanoreceptors A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanor ...
, which make neurons more sensitive to vibration.


Location

The dorsal root ganglia lie in the
intervertebral foramina The intervertebral foramen (also called neural foramen, and often abbreviated as IV foramen or IVF), is a :wikt:foramen, foramen between two spinal vertebrae. Cervical vertebrae, Cervical, thoracic vertebrae, thoracic, and lumbar vertebrae all ...
. The anterior and posterior spinal nerve roots join just beyond (lateral) to the location of the dorsal root ganglion.


Development

The dorsal root ganglia develop in the embryo from
neural crest Neural crest cells are a temporary group of cells unique to vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingd ...

neural crest
cells, not
neural tube In the developing chordate A chordate () is an animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that function ...

neural tube
. Hence, the spinal ganglia can be regarded as gray matter of the spinal cord that became translocated to the periphery.


Function


Nociception

Proton-sensing G protein-coupled receptors in response to activation of GPR65, TDAG8 G protein-coupled receptor by low pH. Data from Wang et al., "TDAG8 is a proton-sensing and psychosine-sensitive G-protein-coupled receptor". Proton-sensing G protein-coupled receptors are membrane receptor ...
are expressed by DRG sensory neurons and might play a role in acid-induced
nociception Nociception (also nocioception, from Latin ''nocere'' 'to harm Harm is a moral A moral (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was original ...
.


Mechanosensitive channels

The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli. In these sensory neurons, a group of
ion channel Ion channels are pore-forming membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane ...

ion channel
s thought to be responsible for
somatosensory The somatosensory system is a part of the sensory nervous system The sensory nervous system is a part of the nervous system In biology, the classical doctrine of the nervous system determines that it is a Complex system, highly comple ...
transduction have been identified. Compression of the dorsal root ganglion by a mechanical stimulus lowers the voltage threshold needed to evoke a response and causes
action potential In physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...

action potential
s to be fired. This firing may even persist after the removal of the stimulus. Two distinct types of
mechanosensitive ion channelMechanosensitive channels, mechanosensitive ion channels or stretch-gated ion channels (not to be confused with mechanoreceptors). They are present in the membranes of organisms from the three domains of life: bacteria, archaea, and eukarya. They ar ...
s have been found in the posterior root ganglion neurons. The two channels are broadly classified as either high-threshold (HT) or low threshold (LT). As their names suggest, they have different thresholds as well as different sensitivities to pressure. These are cationic channels whose activity appears to be regulated by the proper functioning of the cytoskeleton and cytoskeleton associated proteins. The presence of these channels in the posterior root ganglion gives reason to believe that other sensory neurons may contain them as well.


High-threshold mechanosensitive channels

High-threshold channels have a possible role in
nociception Nociception (also nocioception, from Latin ''nocere'' 'to harm Harm is a moral A moral (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was original ...
. These channels are found predominantly in smaller sensory neurons in the dorsal root ganglion cells and are activated by higher pressures, two attributes that are characteristic of nociceptors. Also, the threshold of HT channels was lowered in the presence of PGE2 (a compound that sensitizes neurons to mechanical stimuli and mechanical hyperalgesia) which further supports a role for HT channels in the transduction of mechanical stimuli into nociceptive neuronal signals.


Presynaptic control

The presynaptic regulation of the dorsal nerve ending discharge in the spinal cord can occur through certain types of but not through the activation of
glycine receptor Glycine The glycine receptor (abbreviated as GlyR or GLR) is the receptor of the amino acid Amino acids are organic compounds that contain amino (–NH2) and Carboxylic acid, carboxyl (–COOH) functional groups, along with a Substituent, si ...
s which are absent from these types of terminals. Thus but not
glycine receptor Glycine The glycine receptor (abbreviated as GlyR or GLR) is the receptor of the amino acid Amino acids are organic compounds that contain amino (–NH2) and Carboxylic acid, carboxyl (–COOH) functional groups, along with a Substituent, si ...
s can presynaptically control
nociception Nociception (also nocioception, from Latin ''nocere'' 'to harm Harm is a moral A moral (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was original ...
and
pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society A learned societ ...
transmission.


See also

*
Anterior root of spinal nerve In anatomy and neurology, the ventral root or anterior root is the efferent nerve, efferent motoneuron, motor root of a spinal nerve. At its distal end, the ventral root joins with the dorsal root to form a mixed spinal nerve. Additional images ...
* Knee jerk


References


Additional images

File:Medulla spinalis - Section - English.svg, Medulla spinalis File:Spinal nerve.svg, The formation of the spinal nerve from the posterior and anterior roots File:Gray799.svg, Scheme showing structure of a typical spinal nerve.


External links

* *
Photo of model
at
Ohio State University The Ohio State University, commonly Ohio State or OSU, is a public In public relations Public relations (PR) is the practice of deliberately managing the release and spread of information between an individual or an organization ...

Diagram
at webanatomy.net

at uwlax.edu {{Authority control Back anatomy Peripheral nervous system