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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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Do Check:
- Forebrain: Overview, Functions and FAQs
- Short Notes on Hindbrain
- Hypothalamus Function
- Difference between Forebrain, Midbrain and Hindbrain
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