Tectum

The tectum (Latin: roof) is a region of the brain, specifically the dorsal (top) part of the midbrain (mesencephalon). The position of the tectum is contrasted with the tegmentum, which refers to the region ventral (lower) to the ventricular system. The tectum is responsible for auditory and visual reflexes.Tectum2° (Spinomesencephalic tract → Superior colliculus of Midbrain tectum) The tectum (Latin: roof) is a region of the brain, specifically the dorsal (top) part of the midbrain (mesencephalon). The position of the tectum is contrasted with the tegmentum, which refers to the region ventral (lower) to the ventricular system. The tectum is responsible for auditory and visual reflexes. The optic tectum projects through the reticular formation and interacts with motor neurons in the brainstem. These connections are important for the recognition and reaction to various sized objects which is facilitated by excitatory optic nerve transmitters like L-glutamate. Recent lesion studies have suggested that the tectum has no influence over higher-order motion responses like OMR or OKR, but may be more integral to lower-order cues in motion perception like in the identification of small objects. The tectum is derived in embryonic development from the alar plate of the neural tube. The optic tectum is the visual center in the non mammalian brain which develops from the alar plate of the mesencephalon. It has a laminar organization which allows for different cell types to be present on corresponding layers . One example of the layer specificity is the deep laminae which send output signals away from the tectum toward the motor neurons, specifically the pontine nucleus. The pontine nucleus is located in the basal pons and is responsible for sharing information between the cerebrum and cerebellum (Pontine nucleus). Another example is the superficial laminae which receive input from retinal ganglion cells. In adult humans, the tectum only consists of the inferior and the superior colliculi. Both colliculi also have descending projections to the paramedian pontine reticular formation and spinal cord, and thus can be involved in responses to stimuli faster than cortical processing would allow. Collectively the colliculi are referred to as the corpora quadrigemina. The structure is supplied by quadrigeminal artery (a branch of posterior cerebral artery), and superior cerebellar artery. Disrupting visual experience early on in Zebrafish development results in a change in tectal activity. Changes in tectal activity resulted in an inability to successfully hunt and capture prey. Hypothalamus inhibitory signaling to the deep tectal neuropil is important in tectal processing in zebrafish larvae. The tectal neuropil contains structures including periventricular neurons axons and dendrites. The neuropil also contains GABAergic superficial inhibitory neurons located in stratum opticum. Instead of a large cerebral cortex, Zebrafish have a relatively large tectum that is hypothesized to carry out some of the visual processing that the cortex performs in mammals. The term 'tectal plate' (or 'quadrigeminal plate') is used to describe the junction of the gray and white matter in the embryo. (ancil-453 at NeuroNames)