ganglion

Examples of ganglion in the following topics:

• Parasympathetic (Craniosacral) Division

  • Nerves that supply parasympathetic fibers to the parasympathetic ganglia of the head include the oculomotor nerve (ciliary ganglion); the facial nerve (pterygopalatine ganglion, submandibular ganglion); the glossopharyngeal nerve (otic ganglion); the vagus nerve (no named ganglion); and the pelvic splanchnic nerves (no named ganglion).
  • These paired ganglia supply all parasympathetic innervation to the head and neck: ciliary ganglion (spincter pupillae, ciliary muscle), pterygopalatine ganglion (lacrimal gland, glands of nasal cavity), submandibular ganglion (submandibular and sublingual glands), and otic ganglion (parotid gland).
  • Each has three roots entering the ganglion (motor, sympathetic, and sensory roots) and a variable number of exiting branches.
  • The nerves that supply parasympathetic fibers to the parasympathetic ganglia of the head include the oculomotor nerve (ciliary ganglion), the facial nerve (pterygopalatine ganglion, submandibular ganglion), the glossopharyngeal nerve (otic ganglion), the vagus nerve, and the pelvic splanchnic nerves.
  • Pre- and post-ganglionic fibers and targets are depicted.

• Postganglionic Neurons

  • In the autonomic nervous system, fibers from the ganglion to the effector organ are called postganglionic fibers.
  • In the autonomic nervous system, fibers from the ganglion to the effector organ are called postganglionic fibers.
  • The chromaffin cells of the adrenal medulla are analogous to post-ganglionic neurons—the adrenal medulla develops in tandem with the sympathetic nervous system and acts as a modified sympathetic ganglion.
  • In all cases, the axon enters the paravertebral ganglion at the level of its originating spinal nerve.
  • After this, it can then either create a synapse in this ganglion, ascend to a more superior ganglion, or descend to a more inferior paravertebral ganglion and make a synapse there, or it can descend to a prevertebral ganglion and create a synapse there with the postsynaptic cell.

• Autonomic Ganglia

  • An example of parasympathetic ganglion is the ciliary ganglion, involved in pupil constriction and accommodation.
  • 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.
  • The chain extends from the upper neck down to the coccyx, forming the unpaired coccygeal ganglion.
  • The postganglionic fibers travel from the ganglion to the effector organ.

• Sympathetic Nervous System

  • This response is also known as the sympathetico-adrenal response because the pre-ganglionic sympathetic fibers that end in the adrenal medulla—like all sympathetic fibers—secrete acetylcholine.
  • An example of a sympathetic ganglion in a thoracic nerve is shown in . ganglia contain approximately 20000–30000 nerve cell bodies and are located close to and on either side of the spinal cord in long chains.
  • The chain extends from the upper neck down to the coccyx, forming the unpaired coccygeal ganglion.
  • There are usually 21 or 23 pairs of these ganglia: 3 in the cervical region, 12 in the thoracic region, 4 in the lumbar region, 4 in the sacral region and a single, unpaired ganglion lying in front of the coccyx called the ganglion impar.
  • This intercostal nerve shows the sympathetic ganglion at the top left.

• Preganglionic Neurons

  • In the autonomic nervous system (ANS), fibers from the central nervous system to the ganglion are known as preganglionic fibers.
  • The prevertebral ganglia celiac ganglion, aorticorenal ganglion, superior mesenteric ganglion, inferior mesenteric ganglion.
  • Pre- and post-ganglionic fibers and targets are depicted.

• Trigeminal (V) Nerve

  • The three branches converge on the trigeminal ganglion that is located within the trigeminal cave in the brain; it contains the cell bodies of incoming sensory nerve fibers.
  • 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.
  • Motor fibers pass through the trigeminal ganglion on their way to peripheral muscles, but their cell bodies are located in the nucleus of the trigeminal nerve, deep within the pons.

• Spinal Cord Grey Matter and Spinal Roots

  • The axons of dorsal root ganglion neurons are known as afferents.
  • The nerve endings of dorsal root ganglion neurons have a variety of sensory receptors that are activated by mechanical, thermal, chemical, and noxious stimuli.
  • Compression of the dorsal root ganglion by a mechanical stimulus lowers the voltage threshold needed to evoke a response and causes action potentials to be fired.
  • The presence of these channels in the dorsal root ganglion gives reason to believe that other sensory neurons may contain them as well.
  • 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.

• Somatic Sensory Pathways

  • The somatosensory pathway is composed of three neurons located in the dorsal root ganglion, the spinal cord, and the thalamus.
  • The first always has its cell body in the dorsal root ganglion of the spinal nerve.
  • Sensory nerves of a dorsal root ganglion are depicted entering the spinal cord.

• Facial (VII) Nerve

  • The facial nerve forms the geniculate ganglion prior to entering the facial canal.

• Transduction of Light

  • Visual signals leave the cones and rods, travel to the bipolar cells, and then to ganglion cells.
  • In the absence of light, the bipolar neurons that connect rods and cones to ganglion cells are continuously and actively inhibited by the rods and cones.
  • The now-active bipolar cells in turn stimulate the ganglion cells, which send action potentials along their axons (which leave the eye as the optic nerve).
  • Amacrine cells can distribute information from one bipolar cell to many ganglion cells.