The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.
Mydriasis is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of drugs.
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The oculomotor nerve is the third cranial nerve. It enters the orbit through the superior orbital fissure and innervates extrinsic eye muscles that enable most movements of the eye and that raise the eyelid. The nerve also contains fibers that innervate the intrinsic eye muscles that enable pupillary constriction and accommodation. The oculomotor nerve is derived from the basal plate of the embryonic midbrain. Cranial nerves IV and VI also participate in control of eye movement.
The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness. A greater intensity of light causes the pupil to constrict, whereas a lower intensity of light causes the pupil to dilate. Thus, the pupillary light reflex regulates the intensity of light entering the eye. Light shone into one eye will cause both pupils to constrict.
The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscle in the eye's middle layer, uvea or. It controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm's canal. It also changes the shape of the lens within the eye but not the size of the pupil which is carried out by the sphincter pupillae muscle and dilator pupillae.
The otic ganglion is a small parasympathetic ganglion located immediately below the foramen ovale in the infratemporal fossa and on the medial surface of the mandibular nerve. It is functionally associated with the glossopharyngeal nerve and innervates the parotid gland for salivation.
The pterygopalatine ganglion is a parasympathetic ganglion found in the pterygopalatine fossa. It is largely innervated by the greater petrosal nerve ; and its axons project to the lacrimal glands and nasal mucosa. The flow of blood to the nasal mucosa, in particular the venous plexus of the conchae, is regulated by the pterygopalatine ganglion and heats or cools the air in the nose. It is one of four parasympathetic ganglia of the head and neck, the others being the submandibular ganglion, otic ganglion, and ciliary ganglion.
The ciliary ganglion is a bundle of nerve parasympathetic ganglion located just behind the eye in the posterior orbit. It is 1–2 mm in diameter and in humans contains approximately 2,500 neurons. The ganglion contains postganglionic parasympathetic neurons. These neurons supply the pupillary sphincter muscle, which constricts the pupil, and the ciliary muscle which contracts to make the lens more convex. Both of these muscles are involuntary since they are controlled by the parasympathetic division of the autonomic nervous system.
The iris dilator muscle, is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike arrangement of modified contractile cells called myoepithelial cells. These cells are stimulated by the sympathetic nervous system. When stimulated, the cells contract, widening the pupil and allowing more light to enter the eye.
The iris sphincter muscle is a muscle in the part of the eye called the iris. It encircles the pupil of the iris, appropriate to its function as a constrictor of the pupil.
The greater petrosal nerve is a nerve in the skull that branches from the facial nerve; it forms part of a chain of nerves that innervate the lacrimal gland. The preganglionic parasympathetic axons of this nerve synapse in the pterygopalatine ganglion.
The ophthalmic nerve (V1) is one of three divisions of the trigeminal nerve (CN V). It has three branches that provide sensory innervation to the eye, skin of the upper face and anterior scalp.
The nasociliary nerve is a branch of the ophthalmic nerve, itself a branch of the trigeminal nerve. It is intermediate in size between the other two branches of the ophthalmic nerve, the frontal nerve and lacrimal nerve.
The cardiac plexus is a plexus of nerves situated at the base of the heart that innervates the heart.
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 long ciliary nerves, two or three in number, are given off from the nasociliary nerve as it crosses the optic nerve. The nasociliary nerve that the long ciliary nerves branch from is itself a branch of the ophthalmic branch (V1) of the trigeminal nerve (CN V).
The submandibular ganglion is part of the human autonomic nervous system. It is one of four parasympathetic ganglia of the head and neck..
The tympanic nerve is a branch of the glossopharyngeal nerve found near the ear. It gives sensation to the middle ear, the Eustachian tube, the parotid gland, and mastoid air cells. It gives parasympathetic to supply to the parotid gland via the otic ganglion and the auriculotemporal nerve.
The ciliary ganglion is a parasympathetic ganglion located just behind the eye in the posterior orbit. Three types of axons enter the ciliary ganglion but only the preganglionic parasympathetic axons synapse there. The entering axons are arranged into three roots of the ciliary ganglion, which join enter the posterior surface of the ganglion.
