Author: Adrian Rad BSc (Hons)•Reviewer: Elizabeth O. Johnboy, PhDLast reviewed: September 02, 2021Reading time: 6 minutes

Have you ever wondered why you immediately look in the direction of a sudden flash of light, or turn towards a startling sound, or as soon as someone calls your name? Although these actions take place a dozen times a day, they are so automatic and also common that you sindicate neglect them.

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These reflexive actions are mediated by 4 incredibly small swellings at the earlier of your brainstem. They are collectively referred to as the corpora quadrigemina. This article will describe these structures, concentrating on their afferent and also efferent relations, along with their attributes.


Contents
Superior colliculiInferior colliculi
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Characteristics

Corpora quadrigemina is the Latin terminology for the quadruple bodies, also well-known as the colliculi. These round eminences are situated on the posterior surface of the midbrain, simply below the thalamus. Tright here are 2 remarkable and also 2 inferior colliculi,through among each sitting on either side of the midline. The entire region, consisting of the four colliculi, is recognized as the tectum, or tectal plate. The superior colliculi play a vital function in the visual pathmethod, while the inferior colliculi are necessary in the auditory pathway.

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Superior colliculus (posterior view)

Each quadruple body is related to a bundle of nerve fibres referred to as the brachium. The premium brachium develops the link in between the two superior colliculi, the lateral geniculate body and also the optic tract. The inferior brachium web links the 2 inferior colliculi via the medial geniculate body, which in turn is linked to the auditory cortex. The geniculate bodies are relay centers which play a duty in vision and hearing. They job posteriorly from the pulvinar of the thalamus and contain sets of nuclei delivering the particular names.

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Inferior colliculus (posterior view)

Superior colliculi

Afferent connections

Overall, the afferent pathmethods getting to the superior colliculi start in the retina, inferior colliculi, spinal cord (spinotectal tract) and cortex. More particularly, the premium colliculi consist of alternating layers of gray and white issue which are arranged into salso layers from superficial to deep, as offered below:

Superficial grey - is composed of multipolar interneurons, hence it is the synapsing site of the corticotectal fibers.Optic - this layer receives fibers originating in the optic tract, more specifically the retina. They are specifically arranged in a certain pattern, causing a retinotopic map of the contralateral (opposite) field of vision.Intermediate grey - this layer receives fibers from a variety of resources. Firstly, it receives fibers largely from Brodmann location 18 (visual association cortex). Because of this, the zonal layer enables you to check out a picture, while the intermediate grey layer permits you to translate it. In addition, fibers from the spinal cord (spinotectal tract), the inferior colliculi, locus coeruleus and raphe nuclei also arrive in the intermediate grey layer.Deep grey - this layer, in addition to the deep white one develops the parabigeminal nucleus. The deep grey and the deep white are the major sites wright here efferent information leaves the remarkable colliculi.Deep whitePeriventricular strata

Before diving into the details, make certain you"ve mastered the basics! Check that your knowledge of the components of the brain is up to scratch via our totally free brain diagrams and quizzes.

Efferent connections

Generally speaking, the efferent pathways exiting the premium colliculi travel to the retina, pulvinar, lateral geniculate bodies (through the premium brachium), pretectum, brainstem and spinal cord. Two of the a lot of essential ones are the tectospinal and tectobulbar tracts.

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Lateral geniculate nucleus (superior view)

The tectospinal tract travels via the brainstem in cshed association via the medial longitudinal fasciculus, ending in the anterior white column of the cervical percent of the spinal cord. The tectobulbar tract travels cshed to the tectospinal one, finishing in the pontine nuclei of the pons and also motor nuclei of the cranial nerves.

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Tectospinal tract (axial view)

Functions

One of the a lot of essential features of the premium colliculi is in visual body reflexes. Such automatic and also involuntary motions include: scanning in the time of the act of reading, covering your eyes in incredibly bappropriate locations or turning your head in the direction of sudden and also unexpected visual stimuli.

Throughout these reflexes, the stimuli reach the exceptional colliculi via the visual pathway and also are relayed to the anterior gray column of the spinal cord and also the motor nuclei of the cranial nerves using the tectospinal and also tectobulbar tracts, respectively.

Inferior colliculi

Afferent connections

The inferior colliculus consists of a main nucleus of gray matter. The nucleus has two zones (dorsomedial and ventrolateral) that are surrounded by a dorsal cortex, written of 4 neuronal layers (I to IV), and also an external cortex. The inferior colliculi receive auditory information from the cochlear nuclei using the terminal nerve fibers of the lateral lemniscus.

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Anterior cochlear nucleus (posterior view)

Efferent connections

The majority of efferent fibers leaving the inferior colliculi take a trip with the inferior brachium and project onto the ipsilateral (exact same side of the body) medial geniculate body. A percentage of those synapse within the geniculate body, while others proceed straight via it. In the end, both sets take a trip to the auditory cortex in the remarkable temporal gyrus through the auditory radiation.

See more: Which Statement Explains The Difference Between Multiple Alleles And Polygenic Inheritance?

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Medial geniculate nucleus

Functions

The inferior colliculi are connected in the reflex component of the auditory pathway. This involvement is mediated by small efferent projections that travel via the exceptional colliculi, connecting via the tectospinal and tectobulbar tracts. Similar to the visual body reflexes, the auditory reflex is automatic and involuntary, permitting you to turn your head in the direction of unmeant acoustic stimuli, such as someone calling your name or a startling sound.