The nervous system is a complicated and elaborate system which helps the body in functioning. It is divided in to the central and preipheral nervous system. The central nervous system consists of the brain and spinal cord. The brain is further divided into the Fore brain, Mid brain and Hind brain. While the Fore brain controls the functions such as thought reasoning, voluntary movement, language, it is the Mid brain that controls the auditory, Eye movement, vision and body movement. The brain stem comprises of different parts like pons or metencephalon, medulla oblongata and myelencephalon and the mid brain or mesencephalon. Crossing the pon’s dorsal surface is placed the cerebellum while the cranial nerves nuclei span the length of the brain stem.
A short stem which serves the function of being a path between the fore brain and the hind brain is mid brain. Its upper portion forms corpora quadrigemina and its remainder forms the peduncles of brain. The overall cavity of mid brain is displayed by fine canal, aqueduct of sylvius or the iter and goes further up to the fourth ventricle and opens in the heart’s third ventricle.
Small and rounded eminences called as quadrigemina are present on the upper surface of mid brain which is separated by crucial groove from one another. These are arranged as superior and anterior pairs and are associated with sense of sight. The other two arranged inferior or posterior are related to hearing sense. Brachium is a strand of rounded fibers which passes outwards from each side and this brachium rises into the external geniculate body partially and its other portion goes further ahead inside the optic tract. The inferior brachium moves further into the little swelling of internal geniculate. The lateral as well as the inferior mid brain surfaces is made up of crura cerelbri which are further divided into upper portion called as tegmentum and the lower portion termed as crusta. The division is indicated by a groove- the lateral sulcus present on the surface.
The most important portion of internal midbrain structure is grey matter which is arranged in four groups:
The superior colliculi are placed in the anterior side of the midbrain partially. Midbrain is not differentiated distinctively but the nuclei of midbrain shows gray and white layers that look like cerebral cortex. Superior colliculi is functionally divided into deep superficial layers which perform some different functions altogether. The inferior colliculus mainly involved with analyzing as well as detecting auditory stimuli is organized tonotopically. In tonotopical arrangement neurons are organized in laminar pattern and represent various auditory frequency bands. The inferior colliculus helps to localize and analyze the sources of various sounds and help in correlating them.
The various functions which involve brainstem mechanism are controlling the respiratory muscles, controlling the vocal cords enabling a person to phonate, controlling pharyngeal, oral as well as nasal passages that are known to cause resonance effect and controlling the palate, tongue, lips and mandible which are involved in articulation control. These all functions are controlled by midbrain periqueductal gray and the cranial nerves 12, 10, 9, 5 & 7. The coordinated activities of laryngeal and oral facial tissues are controlled by the midbrain periaqueductal gray due to which it has control over the way we laugh and cry. That is the reason why even if the remaining brain is dead, a person can still laugh and cry. Monamine neurotransmitters are manufactured by midbrain’s nuclei and neurons which are called as dopamine or DA and this DA is more profusely produced inside the midbrain substantia nigra as well as the tegmentum. This Dopamine plays an important role in motor and cognition functioning and the DA transmitter system disturbances are correlated with the development of Parkinson’s disease as well as psychotic abnormalities.