Superior cervical ganglion

The superior cervical ganglion (SCG) is part of the autonomic nervous system (ANS), more specifically it is part of the sympathetic nervous system, a division of the ANS most commonly associated with the fight or flight response. The ANS is composed of pathways that lead to and from ganglia, groups of nerve cells. A ganglion allows a large amount of divergence in a neuronal pathway and also enables a more localized circuitry for control of the innervated targets. The SCG is the only ganglion in the sympathetic nervous system that innervates the head and neck. It is the largest and most rostral (superior) of the three cervical ganglia. The SCG innervates many organs, glands and parts of the carotid system in the head.The right sympathetic chain and its connections with the thoracic, abdominal, and pelvic plexuses.Superior cervical ganglionSympathetic connections of the ciliary and superior cervical ganglia.The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.The Sympathetic Trunk and SCG innervation of target organs in the head. The superior cervical ganglion (SCG) is part of the autonomic nervous system (ANS), more specifically it is part of the sympathetic nervous system, a division of the ANS most commonly associated with the fight or flight response. The ANS is composed of pathways that lead to and from ganglia, groups of nerve cells. A ganglion allows a large amount of divergence in a neuronal pathway and also enables a more localized circuitry for control of the innervated targets. The SCG is the only ganglion in the sympathetic nervous system that innervates the head and neck. It is the largest and most rostral (superior) of the three cervical ganglia. The SCG innervates many organs, glands and parts of the carotid system in the head. The SCG is located opposite the second and third cervical vertebrae. It lies deep to the sheath of the internal carotid artery and internal jugular vein, and anterior to the Longus capitis muscle. The SCG contains neurons that supply sympathetic innervation to a number of target organs within the head. The SCG also contributes to the cervical plexus. The cervical plexus is formed from a unification of the anterior divisions of the upper four cervical nerves. Each receives a gray ramus communicans from the superior cervical ganglion of the sympathetic trunk. The superior cervical ganglion is a reddish-gray color, and usually shaped like a football with tapering ends. Sometimes the SCG is broad and flattened, and occasionally constricted at intervals. It formed by the coalescence of four ganglia, corresponding to the upper four cervical nerves, C1-C4. The bodies of these preganglionic sympathetic neurons are specifically located in the lateral horn of the spinal cord. These preganglionic neurons then enter the SCG and synapse with the postganglionic neurons that leave the rostral end of the SCG and innervate target organs of the head. There are a number of neuron types in the SCG ranging from low threshold to high threshold neurons. The neurons with a low threshold have faster action potential firing rate, while the high threshold neurons have a slow firing rate. Another distinction between SCG neuron types is made via immunostaining. Immunostaining allows the classification of SCG neurons as either positive or negative for neuropeptide Y (NPY), which is found in a subgroup of high-threshold neurons. Low threshold, NPY-negative neurons are secretomotor neurons, innervating salivary glands. High threshold, NPY-negative neurons are pilomotor neurons, innervating blood vessels. High threshold, NPY-positive neurons are vasoconstrictor neurons, which innervate the iris and pineal gland. The SCG receives input from the ciliospinal center. The ciliospinal center is located between the C8 and T1 regions of the spinal cord within the intermediolateral column. The preganglionic fibers that innervate the SCG are the thoracic spinal nerves, which extend from the T1-T8 region of the ciliospinal center . These nerves enter the SCG through the cervical sympathetic nerve. A mature preganglionic axon can innervate anywhere from 50-200 SCG cells. Postganglionic fibers then leave the SCG via the internal carotid nerve and the external carotid nerve. This pathway of SCG innervation is shown through stimulation of the cervical sympathetic nerve, which invokes action potentials in both the external and internal carotid nerves. These postganglionic fibers shift from multiple axon innervation of their targets to less profound multiple axon innervation or single axon innervation as the SCG neurons mature during postnatal development. The SCG provides sympathetic innervation to structures within the head, including the pineal gland, the blood vessels in the cranial muscles and the brain, the choroid plexus, the eyes, the lacrimal glands, the carotid body, the salivary glands, and the thyroid gland. The postganglionic axons of the SCG innervate the pineal gland and are involved in Circadian rhythm. This connection regulates production of the hormone melatonin, which regulates sleep and wake cycles, however the influence of SCG neuron innervation of the pineal gland is not fully understood. The postganglionic axons of the SCG innervate the internal carotid artery and form the internal carotid plexus. The internal carotid plexus carries the postganglionic axons of the SCG to the eye, lacrimal gland, mucous membranes of the mouth, nose, and pharynx, and numerous blood-vessels in the head.