Pretectum
Encyclopedia
The pretectum, also known as the pretectal area, is a region of neuron
s found between the thalamus
and midbrain. It receives binocular
sensory
input from retinal ganglion cells
of the eye
s, and is the region responsible for maintaining the pupillary light reflex.
in the midbrain,
The Edinger-Westphal nucleus projects onto the ciliary ganglion
, whose output controls pupillary constriction (miosis
).
The Edinger-Westphal nucleus controls the Pupillary sphincter muscle (used in situations of bright light to reduce the exposure of the retina) and the Ciliary muscle
(used for eye focusing and accommodation
).
The Cilio-Spinal Nucleus projects onto the superior cervical ganglion, and controls the Pupillary dilator muscle (used in situations of near dark, to increase the exposure of the retina)
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s found between the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
and midbrain. It receives binocular
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
sensory
Sensory system
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic...
input from retinal ganglion cells
Ganglion cell
A retinal ganglion cell is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells...
of the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
s, and is the region responsible for maintaining the pupillary light reflex.
Outputs
The pretectum, after receiving binocular input, outputs to the Edinger-Westphal nucleusEdinger-Westphal nucleus
The Edinger-Westphal nucleus is the accessory parasympathetic cranial nerve nucleus of the oculomotor nerve , supplying the constricting muscles of the iris...
in the midbrain,
- to the Cilio-spinal nucleus (Budge), which is located in the VIII cervical and I, II thoracic vertebral segments,
- and to the nucleus of the posterior commissurePosterior commissureThe posterior commissure is a rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. It is important in the bilateral pupillary light reflex....
.
The Edinger-Westphal nucleus projects onto the ciliary ganglion
Ciliary ganglion
The ciliary ganglion is a parasympathetic ganglion located in the posterior orbit. It measures 1–2 millimeters in diameter and contains approximately 2,500 neurons. Preganglionic axons from the Edinger-Westphal nucleus travel along the oculomotor nerve and form synapses with these cells...
, whose output controls pupillary constriction (miosis
Miosis
Miosis is the constriction of the pupil of the eye to two millimeters or less...
).
The Edinger-Westphal nucleus controls the Pupillary sphincter muscle (used in situations of bright light to reduce the exposure of the retina) and the Ciliary muscle
Ciliary muscle
The ciliary muscle is a ring of striated smooth muscle in the eye's middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm's canal. It changes the shape of the lens within the eye not the size of the pupil which is...
(used for eye focusing and accommodation
Accommodation (eye)
Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image on an object as its distance changes....
).
The Cilio-Spinal Nucleus projects onto the superior cervical ganglion, and controls the Pupillary dilator muscle (used in situations of near dark, to increase the exposure of the retina)
External links
- http://www.indiana.edu/~pietsch/neuro20labels500.jpg
- http://isc.temple.edu/neuroanatomy/lab/atlas/papc/