| Dorsal root ganglion | |
|---|---|
 A dorsal root ganglion (DRG) from a chickenembryo (around stage of day 7) after incubation overnight inNGF growth medium stained with anti-neurofilamentantibody. Neurites growing out of the ganglion are visible. | |
 A spinal nerve with its ventral and dorsal roots. The dorsal root ganglion is the "spinal ganglion", following the dorsal root. | |
| Details | |
| Precursor | Neural crest |
| Identifiers | |
| Latin | ganglion sensorium nervi spinalis |
| MeSH | D005727 |
| TA98 | A14.2.00.006 |
| TA2 | 6167 |
| FMA | 5888 |
| Anatomical terminology | |
Adorsal root ganglion (orspinal ganglion; also known as aposterior root ganglion[1]) is a cluster ofneurons (aganglion) in adorsal root of aspinal nerve. The cell bodies of sensory neurons known asfirst-order neurons are located in the dorsal root ganglia.[2]
Theaxons of dorsal root ganglion neurons are known asafferents. In theperipheral nervous system, afferents refer to the axons that relay sensory information into thecentral nervous system (i.e. thebrain and thespinal cord).
The neurons comprising the dorsal root ganglion are of thepseudo-unipolar type, meaning they have a cell body (soma) with two branches that act as a single axon, often referred to as adistal process and aproximal process.
Unlike the majority of neurons found in thecentral nervous system, anaction potential in posterior root ganglion neuron may initiate in thedistal process in the periphery, bypass the cell body, and continue to propagate along theproximal process until reaching thesynaptic terminal in theposterior horn of spinal cord.
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 thedistal process is encapsulated as such are,Meissner's corpuscles, which render thedistal processes of mechanosensory neurons sensitive to stroking only, andPacinian corpuscles, which make neurons more sensitive to vibration.[3]
The dorsal root ganglia lie in theintervertebral foramina. The anterior and posterior spinal nerve roots join just beyond (lateral) to the location of the dorsal root ganglion.
The dorsal root ganglia develop in the embryo fromneural crest cells, notneural tube. Hence, the spinal ganglia can be regarded as gray matter of the spinal cord that became translocated to the periphery.
Proton-sensing G protein-coupled receptors are expressed by DRG sensory neurons and might play a role in acid-inducednociception.[4]
The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli.[5] In these sensory neurons, a group ofion channels thought to be responsible forsomatosensory transduction have been identified. Compression of the dorsal root ganglion by a mechanical stimulus lowers the voltage threshold needed to evoke a response and causesaction potentials to be fired.[6] This firing may even persist after the removal of the stimulus.[6]
Two distinct types ofmechanosensitive ion channels have been found in the posterior root ganglion neurons. The two channels are broadly classified as either high-threshold (HT) or low threshold (LT).[5] 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.[5] 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 channels have a possible role innociception. 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.[5] 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.[5][6][7]
The presynaptic regulation of the dorsal nerve ending discharge in the spinal cord can occur through certain types ofGABAA receptors but not through the activation ofglycine receptors which are absent from these types of terminals. ThusGABAA receptors but notglycine receptors can presynaptically controlnociception andpain transmission.[8]
