Tectum and Tegmentum

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Tectum and Tegmentum

The mesencephalon or midbrain joins the pons to the prosencephalon (forebrain), and along with the hindbrain, it constitutes the brain stem. Midbrain creates the shortest portion of the brainstem. The tectum, the cerebral aqueduct, the tegmentum, and the cerebral peduncles make up the bulk of the midbrain. Anatomically, the midbrain is divided into the tegmentum (floor) and the tectum (roof). Here, let us learn more about the tectum and tegmentum of the midbrain.

Tectum of Midbrain

It forms the dorsal side of the mesencephalon or midbrain. The midbrain tectum is formed by two structures:

  • Superior colliculus
  • Inferior colliculus.

Superior Colliculus

The superior colliculus is a tiny structure that serves as a key reflex hub. The superior colliculus, via the tectospinal tract, regulates the motions of the eyes, head, trunk, and limbs in response to visual signals. The efferent fibres of the superior colliculus travel to the nucleus of the third cranial nerve and cause the pupil to constrict during the light reflex. Additionally, it also aids in the integration of the optical and postural responses.

Inferior Colliculus

The inferior colliculus is made up of a single layer of neurons to which the lateral lemniscus (auditory fibres) synapses. It acts as the centre for auditory reflexes. Reflex vocalisation is also produced when it is stimulated.

See more: Function of Pons

Tegmentum of Midbrain

The midbrain tegmentum runs horizontally from the substantia nigra to the cerebral aqueduct. Three decussations (crossovers) and a red nucleus make up the tegmentum.

  • The superior cerebellar peduncle is made up of fibres connecting the cerebellum to other CNS areas. Most of these fibres are efferent fibres from the dentate nucleus of the cerebellum. Fewer fibres come from other cerebellar nuclei, such as the globose nucleus and emboliform nucleus.
  • Meynert decussation, which is caused by the crossing of the medial longitudinal bundle, is made up of the efferent fibres of the third, fourth, and sixth cranial nerves.
  • Forel decussation is caused by the crossing of the rubrospinal tracts from either side.

The superior colliculus and the hypothalamus are separated by a huge grey mass known as the red nucleus, which is either oval-shaped or spherical. It controls muscle tone and complex muscle movements. The substantia nigra lies beneath the red nucleus. Substantia nigra is a component of the basal ganglia.

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Frequently Asked Questions

Q1

What are the regions of the midbrain?

The tectum, tegmentum, cerebral aqueduct, and cerebral peduncles are the main areas of the midbrain. The midbrain connects to the diencephalon rostrally and the hindbrain caudally.
Q2

What is pontine tegmentum?

The pontine tegmentum, or dorsal pons, is one of two portions of the pons. It is a region involved in a variety of activities, such as sensory and motor control, levels of arousal and alertness, management of sleep stages and some elements of respiratory control.
Q3

What are some functions of the red nucleus?

The red nucleus is involved in the regulation of the upper arm and shoulder muscles. It also has a significant part in the regulation of ocular movements through its efferent connections with the nuclei of the third, fourth, and sixth cranial nerves.
Q4

What is the function of the tectum?

The tectum contributes to several reflex actions in reaction to auditory or visual stimuli. It regulates eye movements, avoidance and approach movements through its connections to premotor regions.

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