Midbrain, Anatomy, location, parts, definition
The midbrain is the smallest portion of the brainstem (about 1.5 cm) and its most cranial structure. It is in the brainstem between the pons caudally (mesencephalic-pons groove) and the diencephalon, which includes the thalamus, the hypothalamus, the epithalamus, and the subthalamus. Read the article to know more.
Nivedita Dar14 Nov, 2024
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The Midbrain: Structure, Development and Function
Midbrain, also called Mesencephalon, is a vital segment of the brainstem that houses many important centers for proper functioning of the human body which include various important nuclei ( collection of cell bodies of neurons) for motor control, sensory processing, and autonomic functions. It also serves as a conduit for numerous white matter( collections of nerve fibers of neurons) pathways. Midbrain is divided anatomically into two principal regions of the Tectum and the Tegmentum. The tectum is situated dorsally in midbrain and comprises the superior and inferior colliculi.The Superior and Inferior colliculi
The superior colliculi plays the role of processing of visual inputs through the retina and helps us perform reflexive eye movements, while the inferior colliculi help in processing of auditory information and localization of the place from where sound is coming from.Tegmentum
Tegmentum is located in the ventral side and has important structures like the red nucleus, the substantia nigra and the periaqueductal gray matter. Red nucleus mediates motor coordination, particularly control of limb movements. The substantia nigra, the famous structure due its infamous relation with the infamous disease of Parkinson. It plays a pivotal role in voluntary motor activities through its dopaminergic outputs. The degeneration of neurons in the substantia nigra pars compacta is notably associated with Parkinson’s disease. The cerebral aqueduct of Sylvius is an important connection between the third and fourth ventricle ,for the flow of cerebrospinal fluid. This duct passes through the midbrain. Around this duct the periaqueductal gray is an area of gray matter helping in pain modulation and autonomic regulation.Development
Midbrain formation starts early in gestation by the segmentation of the neural tube ( a very important tube-like structure which forms early in gestation and gives rise to different segments of the brain). The neural tube undergoes segmentation into three primary brain vesicles: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain). The mesencephalon is the middle segment and remains a single, unpaired structure throughout its development, unlike the other primary vesicles, which further divide.Functions
The midbrain serves as a central hub for processing auditory and visual information. The superior colliculi are crucial for visual tracking and coordinating eye movements for example like rapid redirection of the gaze called the saccades . The inferior colliculi are fundamental for auditory signal processing, contributing to the localization of the direction from where the sound is coming from and interpretation of sounds. Motor control is another vital function of the midbrain, with the substantia nigra playing a significant role. Dopaminergic neurons in the substantia nigra pars compacta project to the higher centers of the brain, facilitating the initiation and regulation of movement. Dysfunction in this pathway is central to the mechanism of development of Parkinson’s disease, characterized by symptoms such as tremors, rigidity and slow movements. The red nucleus is integral to motor coordination. While its role in humans is somewhat diminished compared to other species, it remains important for fine motor control and coordination.Midbrain FAQs
What are the clinical features of Parkinsonism?
Clinical features include Bradykinesia leading to slowness in initiation and execution of movements. Rigidity meaning increased muscle tone leading to stiffness .Tremors usually a resting tremor.
What is Weber syndrome?
Lesions of Weber syndrome is a vascular lesion due to disruption of blood supply. It is characterized by same sided oculomotor nerve palsy and opposite side weakness of muscles due to damage to the nerve.
What is drug induced Parkinsonism?
Certain medications, particularly antipsychotics and antiemetics that block dopamine receptors, can induce parkinsonism. Thus having the same features of Parkinsonism but symptoms go away after discontinuing drugs.
What is aqueductal atresia?
Aqueductal atresia refers to a congenital( present by birth)condition characterized by the complete or partial obstruction of the cerebral aqueduct, which is the narrow channel that connects the third and fourth ventricles in the brain. This obstruction impedes the flow of CSF, leading to a buildup of CSF within the ventricles, causing hydrocephalus.
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