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Posterior Commissure
The posterior commissure (also known as the epithalamic commissure) is a rounded band of white fibers crossing the middle line on the dorsal aspect of the rostral end of the cerebral aqueduct. It is important in the bilateral pupillary light reflex. It constitutes part of the epithalamus. Its fibers acquire their medullary sheaths early, but their connections have not been definitively determined. Most of them have their origin in a nucleus, the ''nucleus of the posterior commissure'' (nucleus of Darkschewitsch), which lies in the periaqueductal grey at rostral end of the cerebral aqueduct, in front of the oculomotor nucleus. Some are thought to be derived from the posterior part of the thalamus and from the superior colliculus, whereas others are believed to be continued downward into the medial longitudinal fasciculus The medial longitudinal fasciculus (MLF) is a prominent bundle of nerve fibres which pass within the ventral/anterior portion of periaqueductal gray of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saggital Plane
The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse plane, transverse and coronal plane, coronal planes. The plane may be in the center of the body and divide it into two equal parts (mid-sagittal plane, mid-sagittal), or away from the midline and divide it into unequal parts (para-sagittal). The term ''sagittal'' was coined by Gerard of Cremona. Variations in terminology Examples of sagittal planes include: * The terms ''median plane'' or ''mid-sagittal plane'' are sometimes used to describe the wikt:sagittal plane, sagittal plane running through the midline. This plane cuts the body into halves (assuming bilateral symmetry), passing through midline structures such as the navel and Vertebral column, spine. It is one of the planes which, combined with the umbilical plane, defines the Quadrant (abdomen), four quadrants of the human abdomen. * The term ''parasagi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Human Brain
The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activities of the human body, body, processing, integrating, and coordinating the information it receives from the sensory nervous system. The brain integrates sensory information and coordinates instructions sent to the rest of the body. The cerebrum, the largest part of the human brain, consists of two cerebral hemispheres. Each hemisphere has an inner core composed of white matter, and an outer surface – the cerebral cortex – composed of grey matter. The cortex has an outer layer, the neocortex, and an inner allocortex. The neocortex is made up of six Cerebral cortex#Layers of neocortex, neuronal layers, while the allocortex has three or four. Each hemisphere is divided into four lobes of the brain, lobes – the frontal lobe, frontal, pa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cerebral Aqueduct
The cerebral aqueduct (aqueduct of the midbrain, aqueduct of Sylvius, Sylvian aqueduct, mesencephalic duct) is a small, narrow tube connecting the third and fourth ventricles of the brain. The cerebral aqueduct is a midline structure that passes through the midbrain. It extends rostrocaudally through the entirety of the more posterior part of the midbrain. It is surrounded by the periaqueductal gray (central gray), a layer of gray matter. Congenital stenosis of the cerebral aqueduct is a cause of congenital hydrocephalus. It is named for Franciscus Sylvius. Anatomy The cerebral aqueduct is roughly circular in transverse section, and measures 1-2 mm in diameter. It is 15 mm long and is commonly subdivided into a pars anterior antrum, and pars posterior. Relations Rostrally, it is continuous with the third ventricle, commencing just inferior to the posterior commissure. Caudally, it is continuous with the fourth ventricle at the junction of the mesencephalon and pons. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pupillary Light Reflex
The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity ( luminance) of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness. A greater intensity of light causes the pupil to constrict ( miosis/myosis; thereby allowing less light in), whereas a lower intensity of light causes the pupil to dilate ( mydriasis, expansion; thereby allowing more light in). Thus, the pupillary light reflex regulates the intensity of light entering the eye. Light shone into one eye will cause both pupils to constrict. Terminology The pupil is the dark circular opening in the center of the iris and is where light enters the eye. By analogy with a camera, the pupil is equivalent to aperture, whereas the iris is equivalent to the diaphragm. It may be helpful to consider the ''Pupillary reflex'' as an Iris ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Epithalamus
The epithalamus (: epithalami) is a posterior (dorsal) segment of the diencephalon. The epithalamus includes the habenular nuclei, the stria medullaris, the anterior and posterior paraventricular nuclei, the posterior commissure, and the pineal gland. Functions The function of the epithalamus is to connect the limbic system to other parts of the brain. The epithalamus also serves as a connecting point for the dorsal diencephalic conduction system, which is responsible for carrying information from the limbic forebrain to limbic midbrain structures. Some functions of its components include the secretion of melatonin from the pineal gland (circadian rhythms), regulation of motor pathways and emotions, and how energy is conserved in the body. A study has shown that the lateral habenula, in the epithalamus, produces spontaneous theta oscillatory activity that was correlated with theta oscillation in the hippocampus. The same study also found that the increase in theta waves in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Periaqueductal Gray
The periaqueductal gray (PAG), also known as the central gray, is a brain region that plays a critical role in autonomic function, motivated behavior and behavioural responses to threatening stimuli. PAG is also the primary control center for descending pain modulation. It has enkephalin-producing cells that suppress pain. The periaqueductal gray is the gray matter located around the cerebral aqueduct within the tegmentum of the midbrain. It projects to the nucleus raphe magnus, and also contains descending autonomic tracts. The ascending pain and temperature fibers of the spinothalamic tract send information to the PAG via the spinomesencephalic pathway (so-named because the fibers originate in the spine and terminate in the PAG, in the mesencephalon or midbrain). This region has been used as the target for brain-stimulating implants in patients with chronic pain. Role in analgesia Stimulation of the periaqueductal gray matter of the midbrain activates enkephalin-r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oculomotor Nucleus
The fibers of the oculomotor nerve arise from a nucleus in the midbrain, which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From this nucleus the fibers pass forward through the tegmentum, the red nucleus, and the medial part of the substantia nigra, forming a series of curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial side of the cerebral peduncle. The nucleus of the oculomotor nerve does not consist of a continuous column of cells, but is broken up into a number of smaller nuclei, which are arranged in two groups, anterior and posterior. Those of the posterior group are six in number, five of which are symmetrical on the two sides of the middle line, while the sixth is centrally placed and is common to the nerves of both sides. The anterior group consists of two nuclei, an antero-medial and an antero-lateral. The nucleus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thalamus
The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, known as the thalamocortical radiations, allowing hub (network science), hub-like exchanges of information. It has several functions, such as the relaying of sensory neuron, sensory and motor neuron, motor signals to the cerebral cortex and the regulation of consciousness, sleep, and alertness. Anatomically, the thalami are paramedian symmetrical structures (left and right), within the vertebrate brain, situated between the cerebral cortex and the midbrain. It forms during embryonic development as the main product of the diencephalon, as first recognized by the Swiss embryologist and anatomist Wilhelm His Sr. in 1893. Anatomy The thalami ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superior Colliculus
In neuroanatomy, the superior colliculus () is a structure lying on the tectum, roof of the mammalian midbrain. In non-mammalian vertebrates, the Homology (biology), homologous structure is known as the optic tectum or optic lobe. The adjective form ''tectum, tectal'' is commonly used for both structures. In mammals, the superior colliculus forms a major component of the midbrain. It is a paired structure and together with the paired inferior colliculi forms the corpora quadrigemina. The superior colliculus is a layered structure, with a pattern that is similar in all mammals. The layers can be grouped into the superficial layers (retinal nerve fiber layer, stratum opticum and above) and the deeper remaining layers. Neurons in the superficial layers receive direct input from the retina and respond almost exclusively to visual stimuli. Many neurons in the deeper layers also respond to other modalities, and some respond to stimuli in multiple modalities. The deeper layers also conta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Medial Longitudinal Fasciculus
The medial longitudinal fasciculus (MLF) is a prominent bundle of nerve fibres which pass within the ventral/anterior portion of periaqueductal gray of the mesencephalon (midbrain). It contains the interstitial nucleus of Cajal, responsible for oculomotor control, head posture, and vertical eye movement. The MLF interconnects interneurons of each abducens nucleus with motor neurons of the contralateral oculomotor nucleus; thus, the MLF mediates coordination of horizontal (side to side) eye movements, ensuring the two eyes move in unison (thus also enabling saccadic eye movements). The MLF also contains fibers projecting from the vestibular nuclei to the oculomotor and trochlear nuclei as well as the interstitial nucleus of Cajal; these connections ensure that eye movements are coordinated with head movements (as sensed by the vestibular system). The medial longitudinal fasciculus is the main central connection for the oculomotor nerve, trochlear nerve, and abduce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pretectal Area
In neuroanatomy, the pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system. Through reciprocal bilateral projections from the retina, it is involved primarily in mediating behavioral responses to acute changes in ambient light such as the pupillary light reflex, the optokinetic reflex, and temporary changes to the circadian rhythm. In addition to the pretectum's role in the visual system, the anterior pretectal nucleus has been found to mediate somatosensory and nociceptive information. Location and structure The pretectum is a bilateral group of highly interconnected nuclei located near the junction of the midbrain and forebrain. The pretectum is generally classified as a midbrain structure, although because of its proximity to the forebrain it is sometimes classified as part of the caudal diencephalon (forebrain). Within vertebrates, the pretectum is located directly anterior to the superior col ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
