dorsal root ganglia

Examples of dorsal root ganglia in the following topics:

• Spinal Cord Grey Matter and Spinal Roots

  • Each segment of the spinal cord is associated with a pair of ganglia, called dorsal root ganglia, which are situated just outside of the spinal cord.
  • The dorsal root ganglia lie along the vertebral column by the spine.
  • The dorsal root ganglia develops in the embryo from neural crest cells, not the neural tube.
  • The axons of dorsal root ganglion neurons are known as afferents.
  • Two distinct types of mechanosensitive ion channels have been found in the dorsal root ganglia.

• Autonomic Ganglia

  • The dorsal root ganglia lie along the vertebral column by the spine and develop in the embryo from neural crest cells, not neural tube.
  • A dorsal root ganglion (or spinal ganglion) is a nodule on a dorsal root of the spine that contains the cell bodies of nerve cells (neurons) that carry signals from the sensory organs towards the appropriate integration center.
  • The axons of dorsal root ganglion neurons are known as afferents.
  • Unlike the majority of neurons found in the central nervous system, an action potential in a dorsal 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 in the dorsal horn of the spinal cord.
  • The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli.

• Somatic Sensory Pathways to the Cerebellum

  • The ventral and dorsal spinocerebellar tracts convey proprioceptive information from the body to the cerebellum.
  • It is part of the somatosensory system and runs in parallel with the dorsal spinocerebellar tract.
  • The dorsal spinocerebellar tract does not decussate, or cross sides, at all through its path.
  • The axon runs via the fila radicularia (nerve rootlets) to the dorsal horn of the gray matter.
  • Proprioceptive information is taken to the spinal cord via central processes of the dorsal root ganglia (where first order neurons reside).

• Trigeminal (V) Nerve

  • The trigeminal ganglion is analogous to the dorsal root ganglia of the spinal cord, which contain the cell bodies of incoming sensory fibers from the rest of the body.
  • From the trigeminal ganglion, a single large sensory root enters the brainstem at the level of the pons.
  • Immediately adjacent to the sensory root, a smaller motor root emerges from the pons at the same level.
  • Schematic illustration of the trigeminal nerve (labeled Sensory root above) and the structures it innervates in the face and mouth.

• Sensory and Motor Tracts

  • Somatosensory organization is divided into the dorsal column–medial lemniscus tract (the touch/proprioception/vibration sensory pathway) and the anterolateral system, or ALS (the pain/temperature sensory pathway).
  • In both pathways, primary sensory neuron cell bodies are found in the dorsal root ganglia, and their central axons project into the spinal cord.

• General Organization of the Somatosensory System

  • The cell body of the primary neuron is housed in the dorsal root ganglion of a spinal nerve or, if sensation is in the head or neck, the ganglia of the trigeminal or cranial nerves.

• Parasympathetic (Craniosacral) Division

  • Parasympathetic ganglia are the autonomic ganglia of the parasympathetic nervous system that lie near or within the organs they innervate.
  • Parasympathetic ganglia are the autonomic ganglia of the parasympathetic nervous system, blue fibers).
  • Most are small terminal ganglia or intramural ganglia, so named because they lie near or within (respectively) the organs they innervate.
  • Each has three roots entering the ganglion (motor, sympathetic, and sensory roots) and a variable number of exiting branches.
  • The sensory root carries general sensory fibers (general somatic afferent fibers) that also do not create a synapse in the ganglion.

• Shingles

  • Varicella zoster virus can become latent in the nerve cell bodies and less frequently in non-neuronal satellite cells of dorsal root, cranial nerve or autonomic ganglion, without causing any symptoms.
  • The virus may spread from one or more ganglia along nerves of an affected segment and infect the corresponding dermatome (an area of skin supplied by one spinal nerve) causing a painful rash.

• Overview of the Spinal Nerves

  • Each spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord.
  • The dorsal roots carry afferent sensory axons, while the ventral roots carry efferent motor axons.
  • The dorsal ramus contains nerves that serve the dorsal portions of the trunk; it carries visceral motor, somatic motor, and somatic sensory information to and from the skin and muscles of the back (epaxial muscles).
  • Its anterior root helps form the coccygeal plexus.
  • Spinal nerves arise from a combination of nerve fibers from the dorsal and ventral roots of the spinal cord.

• The Role of the Basal Ganglia in Movement

  • Currently popular theories hold that the basal ganglia play a primary role in action selection.
  • One of the most intensively studied functions of the basal ganglia is their role in controlling eye movements.
  • Dopamine is used by the projection from the substantia nigra pars compacta to the dorsal striatum and also in the analogous projection from the ventral tegmental area to the ventral striatum (nucleus accumbens).
  • This diagram shows the main circuits of the basal ganglia.
  • Two coronal slices have been superimposed to include the involved basal ganglia structures.