Optic tract
Fiona Rowe in Visual Fields via the Visual Pathway, 2016
The retinal nerve fibres after having passed through the optic chiasm travel posteriorly toward the lateral geniculate body by way of the two optic tracts. The optic tracts sweep laterally from the optic chiasm, passing around the ventral portion of the midbrain and encircling the hypothalamus posteriorly. The majority of retinal nerve fibres terminate in the lateral geniculate body. A smaller number continue to the pretectal area (pupillary reflexes), hypothalamus and superior colliculi.
Discussions (D)
Terence R. Anthoney in Neuroanatomy and the Neurologic Exam, 2017
Without stating so explicitly, most authors of recent neuroanatomy texts seem to place the pretectal area solely in the mesencephalon (midbrain), as its description is usually contained in a section on mesencephalic structures (e.g., B&K, p. no; C&S, p. 424–4251, CH&L, p. 235–237; W&W, p. 942).2 An exception in this regard is Martinez Martinez, who describes the pretectal area as extending into the diencephalon 1982, p. 218).
ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
A midbrain structure immediately anterior to the SUPERIOR COLLICULUS. It controls reflex constriction of the PUPIL: GANGLION CELLS in the RETINA project to the pretectum, which in turn projects to PREGANGLIONIC NEURONS in the EDINGER- WESTPHAL NUCLEUS. These neurons send axons to the OCULOMOTOR NERVE (the third cranial nerve; see CRANIAL NERVES) via the CILIARY GANGLION.
Per1 mutation enhances masking responses in mice
Published in Chronobiology International, 2022
Nemanja Milićević, Arthur A. Bergen, Marie-Paule Felder-Schmittbuhl
Masking responses are mediated by classical photoreceptor input involving rods and cones (Thompson et al. 2008) and melanopsin (Opn4) positive, intrinsically photosensitive retinal ganglion cells (ipRGCs)(Mrosovsky and Hattar 2003). IpRGCs project to the central clock in suprachiasmatic nuclei (SCN) and to other brain areas via retinal projections, including the retinohypothalamic tract (RHT) (Berson et al. 2002). The RTH projections are necessary for masking responses (Li et al. 2005), but the role of the SCN is still debated (Li et al. 2005; Redlin and Mrosovsky 1999). Other brain regions modulate masking responses such as the dorsal lateral geniculate nucleus (Edelstein and Mrosovsky 2001), the visual cortex (Redlin et al. 2003) and the intergeniculate leaflet (Langel et al. 2014; Redlin et al. 1999) among others. The circadian system can, in turn, modulate masking responses in both diurnal and nocturnal species (Shuboni et al. 2012; Smale et al. 2003). The neural underpinnings of this link are not well understood, but extensive work on the Nile grass rat revealed that many brain regions play important roles, such as: the ventral subparaventricular zone (Gall et al. 2016), the olivary pretectal area (Gall et al. 2017; Langel et al. 2014), the superior colliculus (Gall et al. 2020), among others (reviewed in detail by (Yan et al. 2020)).
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
Contrast Acuity and the King-Devick Test in Huntington’s Disease
Published in Neuro-Ophthalmology, 2020
Ali G. Hamedani, Tanya Bardakjian, Laura J. Balcer, Pedro Gonzalez-Alegre
The pupillary light reflex is a polysynaptic reflex arc that involves retinal photoreceptor activation and ganglion cell depolarisation; conduction through the optic nerve, chiasm, and tract; signalling across the pretectum to the Edinger-Westphal nucleus; and pupillary constriction via the third cranial nerve. Consequently, it can be affected by abnormalities at either the afferent or efferent level. In both symptomatic and presymptomatic patients with autosomal dominant Alzheimer’s disease, subtle differences in pupillary light reflex have been identified19, consistent with the cholinergic deficit observed in that disease. We did not observe any differences in pupillary function in HD, which may help to explain why the benefit from cholinesterase inhibitors for cognitive function or chorea in HD has been minimal.32 Because pupillometry was performed under scotopic (dark-adapted) conditions using mixed-wavelength white light, afferent activation was driven primarily by rod photoreceptors, and subtle cone or intrinsically photosensitive retinal ganglion cell dysfunction may not have been captured using this method. Future studies of pupillometry in HD would benefit from both photopic (light-adapted) and scotopic testing at different ranges of light wavelength.
Related Knowledge Centers
- Circadian Rhythm
- Forebrain
- Midbrain
- Neuroanatomy
- Nociception
- Retina
- Somatosensory System
- Visual System
- Pupillary Light Reflex
- Optokinetic Response