Discuss the anatomical features of the extraocular muscles
Nathaniel Knox Cartwright, Petros Carvounis in Short Answer Questions for the MRCOphth Part 1, 2018
Important relations of the extraocular muscles are as follows. Each oblique muscle passes below its corresponding rectus muscle. Levator palpebrae superioris runs above superior oblique and the two have fascial connections, facilitating coordinated movement. The optic nerve and ophthalmic artery enter the orbit within the tendinous ring. The ciliary ganglion lies between the optic nerve and lateral rectus. Part of the tendinous ring overlies the superior orbital fissure and (from superior to inferior) the superior division of the oculomotor nerve, the nasociliary nerve, the inferior division of the oculomotor nerve and the abducent nerve enter the orbit through this part. The lacrimal, frontal and trochlear nerves, together with the superior ophthalmic vein, pass above and the inferior ophthalmic vein passes below.
Anatomy and Physiology of the Autonomic Nervous System
Kenneth J. Broadley in Autonomic Pharmacology, 2017
The preganglionic parasympathetic fibres synapse in ganglia, which unlike sympathetic ganglia lie very close to or within the organ that they innervate. The postganglionic parasympathetic fibres are therefore short and non-myelenated. Often the cell bodies of the postganglionic neurones are distributed throughout the tissue so that no discrete ganglia occur but instead they form a network of interconnecting fibres known as a plexus. For example, the cardiac ganglia of the vagus nerve form a plexus around the great vessels or in the atrial wall which give rise to the postganglionic fibres to the heart. Also running through this plexus are sympathetic postganglionic fibres and sensory afferents. The vagus nerve also contains somatic motor fibres which innervate the striated muscle of the pharynx and larynx, which controls swallowing. The ciliary ganglion lies behind the eyeball, receiving preganglionic fibres from the oculomotor nerve, and innervates the ciliary muscle and smooth muscles of the sphincter pupillae (circular muscle) of the iris.
Cranial nerves
Ibrahim Natalwala, Ammar Natalwala, E Glucksman in MCQs in Neurology and Neurosurgery for Medical Students, 2022
Regarding clinical abnormalities of the pupils, which of the following are true and which are false? Horner’s syndrome is caused by a lesion to the parasympathetic pathway and causes a unilateral constricted pupil with associated ptosis.In a relative afferent pupillary defect (RAPD), the consensual light reflex is weaker than the direct light reflex.Argyll Robertson pupils are small, accommodate to near objects but are unreactive to light.Denervation of the ciliary ganglion can lead to a dilated pupil that reacts slowly to bright light.The Edinger-Westphal nucleus responsible for pupillary constriction is located in the midbrain at the level of the superior cerebellar peduncle.
Transient anisocoria after a traumatic cervical spinal cord injury: A case report
Published in The Journal of Spinal Cord Medicine, 2020
Paul Overdorf, Gary J. Farkas, Natasha Romanoski
The sympathetic innervation to the eye is from the superior cervical ganglion (Fig. 1). The superior cervical ganglion lies anterior to the transverse processes of the second and third cervical vertebra. Anterior to the ganglion lies the carotid sheath with the internal carotid artery, internal jugular vein, and vagus nerve, while the longus capitis muscle is found posterior to the ganglion. Postganglionic sympathetic fibers from the superior cervical ganglion are distributed onto the internal carotid artery and help to form the internal carotid nerve plexus, which ascends on the internal carotid artery into the carotid canal to enter the cranial cavity (Fig. 1).11 Once in the cranial cavity, postganglionic fibers from the internal carotid nerve plexus travel on the nasociliary nerve of the ophthalmic division of the trigeminal nerve, while other fibers continue from the internal carotid nerve plexus as the sympathetic root of the ciliary ganglion.12 The sympathetic root of the ciliary ganglion traverses the ciliary ganglion without synapsing (Fig. 1). These nerves then travel on the short ciliary nerves of the ciliary ganglion to the eye where they innervate the dilator pupillae muscle. Some of these postganglionic sympathetic fibers also travel on the long ciliary nerve, a nerve branch of the nasociliary nerve, to reach the eye (Fig. 1). Sympathetic activation of the dilator pupillae muscle dilates the pupil.11,12
Factors affecting the prevalence, severity, and characteristics of ocular surface pain
Published in Expert Review of Ophthalmology, 2023
Victor Sanchez, Noah K Cohen, Elizabeth R Felix, Anat Galor
The high density of nerve fibers in the cornea may contribute to the frequency of ocular surface pain in the general population. In fact, the corneal surface is among the most densely innervated regions within the human body [27]. Most of these are sensory fibers [28], which travel from the ophthalmic branch (V1) of the trigeminal nerve, through the nasociliary branch and into the ciliary ganglion. The ciliary ganglion gives rise to ciliary nerves which circumferentially innervate the cornea and surrounding anterior bulbar conjunctiva [29]. Estimates in animals suggest that between 50 and 450 trigeminal ganglion neurons supply the cornea, accounting for 2% of all trigeminal ganglion neurons [29–32]. The majority of sensory fibers innervating the cornea are polymodal nociceptors, which are activated over a wide range of stimulus intensities including noxious mechanical energy, heat, chemical irritants, as well as endogenous chemical mediators released by damaged corneal tissues [33–35]. Mechanistically, reduced tear secretion, rapid tear evaporation, or abnormal tear composition can lead to epithelial cell damage and production of inflammatory mediators that activate polymodal neurons, generating ocular surface pain [36,37].
Amplitude of Accommodation in Patients with Multiple Sclerosis
Published in Current Eye Research, 2019
Bekir Küçük, Mehmet Hamamcı, Seray Aslan Bayhan, Hasan Ali Bayhan, Levent Ertuğrul Inan
When the target distance is changed, the lens power must be altered to clearly view it; this is known as ocular accommodation.25 The accommodation reflex starts in the retinal ganglion cells with the light reflex. These impulses are sent through the optic nerve, the optic chiasma, and the optic tract. Most optic tract fibers go to the pretectal area, although some fibers synapse with the second-order neurons in the lateral geniculate nucleus of the thalamus. Then, second-order neurons carry the impulses through the optic radiation to the visual cortex. Impulses pass from the visual cortex to the prefrontal cortex, and fibers pass through the internal capsule to reach the midbrain. Then, the fibers in the midbrain synapse with the oculomotor nucleus and the Edinger-Westphal nucleus.26 The motor fibers are carried by the oculomotor nerve from the oculomotor nucleus to the medial rectus muscle, where both eyes converge. The efferent fibers of the Edinger-Westphal nucleus (which is the parasympathetic autonomic nucleus) accompany the oculomotor nerve and synapse in the ciliary ganglion. Then, the postganglionic fibers of the ciliary ganglion pass the short ciliary nerves to supply the sphincter pupillae muscle and the ciliary muscle, which allows the lens to thicken27 (Figure 1). This mechanism is controlled by the autonomic nervous system.23
Related Knowledge Centers
- Autonomic Nervous System
- Ciliary Muscle
- Iris Sphincter Muscle
- Otic Ganglion
- Pterygopalatine Ganglion
- Ganglion
- Parasympathetic Nervous System
- Orbit
- Neuron
- Submandibular Ganglion