The CNS is 1) enclosed by the bones (skull and spine) with the exception of the retina that has the same embryological origin, 2) is not washed by the blood stream, even if covered by blood vessels, the blood-brain barrier prevents the contact of blood with neurons. 3) It is enclosed by three layers of membranes called meninges so as not to impact directly the soft tissue of the CNS against the hardness of bone. Just below the bone is
dura mater that has the consistency of leather, below this the ' arachnoid and pia mater finally , soft and follows the shape of the grooves of the CNS and is fully participating. Between the pia mater el'aracnoide there is a gap that sub-arachnoid space adapting the form of two different brains. Between the dura mater is a el'aracnoideo subdural space.
Under the meninges, if you look at the brain, there is the gray matter (somata) and then the white matter (axons), conversely, in the spinal cord, there is the white matter and gray matter then .
In sub-arachnoid space containing the cerebrospinal fluid or cerebrospinal fluid (CSF) and is similar to blood plasma and the extra-cellular fluid. The LCS also fills the cavities of the CNS Call ventricles and communicates with the sub-arachnoid space. All
LCS is located inside the blood-brain barrier amounts to 125 and is fully reciprocated every 6-7 hours.
The ventricles
The ventricle is composed of two large lateral ventricles that extend the length of the brain. Communicate with the third ventricle (found in medial position), which in turn communicates through ' cerebral aqueduct with the fourth ventricle . This communicates with the spinal canal that runs through the spinal cord.
The CSF is produced by the choroid plexus the height of the ventricles and then reabsorbed by the arachnoid villi sub-arachnoid space that filters the blood. The LCS
replaces the replaces the blood within the blood-brain barrier and plays an important mechanical function, in fact, the brain floats inside the skull nell'LCS. The liquid absorbs the acceleration and reduces the overall weight from 1500g to 100g, so the base of the brain is not liable to be crushed.
The development of SN
the early stages of development, the SN is composed of a tube that grows two-dimensionally. The embryo differentiates three cell layers: ectoderm , mesoderm and endoderm which will bring different structures.
Dall'endoderma develop the internal organs and the alimentary canal; mesoderm from the bones, skeletal muscles, circulatory system and kidneys; dall'ectoderma the nervous system and skin.
Three weeks after conception the ectoderm folds on itself to form the neural groove and then closes to form the neural tube . The remaining portion of the ectoderm on the side of the tube gives rise to neural crest they carry dorsally. From
neural tube is formed by the CNS and the neural crest SNP. In the following weeks are formed from three vesicles that arise from rostral to caudal, the forebrain, the midbrain and hindbrain . The rest of the neural tube give rise to the spinal cord .
From the forebrain vesicle, which differs in telencephalon and diencephalon , will form the rostral olfactory bulbs, cerebral hemispheres the side of the forebrain, optic vesicles and . From the midbrain superior and inferior colliculi , from the hindbrain cerebellum The bridge and bulb. Optic vesicles are different from the optical stem from which derive the optic nerve and optic cup which will form the retina . Subsequently, the midbrain will differ in thalamus, the center of sensory afferents, and hypothalamus.
Up to this point, the embryo, neurons are the same as any other cell type. Soon, however, will differ in the forebrain areas occupied by gray matter and white matter (the cortical white matter the corpus callosum, the internal capsule ).
Very soon you'll see the ventricles, the two sides in the telencephalon, the third in the diencephalon, the cerebral aqueduct in the midbrain and fourth ventricle in the hindbrain.
The spinal cord is contained in the spine and begins and ends with the first cervical to the twelfth thoracic. In addition to the twelfth thoracic spinal cord continues cauda aequina .
the height of each vertebra out a pair of spinal nerves. There are three layers of meninges and the arrangement of white and gray matter is opposite to that of the brain.
The gray matter becomes an H-shaped bundles of axons and the substance white running from caudal to rostral or caudal to rostral. But the internal structure of the spinal cord varies depending on the distance of the brain, showing the height of the swelling of the limbs. There is the presence of specialized nuclei.
sensory fibers emerge dorsally in the dorsal root ganglia and dorsal root contains the soma of sensory neurons, whereas the motor fibers emerge ventrally and are called the ventral roots and somata lie within the gray matter of the spinal cord.
In the "H" of the gray matter can be distinguished dorsal horn, where do the sensory afferents, the ventral horn , home of the somata of motor neurons, and the intermediate zone where they are located for pre-ganglionic neurons of the ANS.
traits that run along the axon in the spinal white matter are called columns (dorsal column, lateral column and ventral column). Those senses are drawn upward, while the descenders are the main drivers. Ventral position in the white matter is commissure that connects the right side with the left.
The spinal nerves are divided into: cervical (8), thoracic (12), lumbar (5), sacral (5) and a coccygeal nerve .
hindbrain and midbrain
The hindbrain, distinct from the fourth ventricle, is divided into:
or bulb or medulla oblongata
is adjacent to the spinal cord and is crossed by the same bundles of axons in the spinal cord.
contains numerous nuclei involved in functions such as control of breathing, heart rate, salivation and vomiting, and cough reflexes.
is also involved in various sensory functions (hearing, touch, taste).
depart from it many of the cranial nerves.
or Cerebellum
accounts for 10% by weight of the brain, but contains 50% of all neurons.
It is involved in fine motor function and learning of new motor skills.
It is divided into two cerebellar hemispheres.
or Bridge
contains bundles of fibers that connect the two cerebellar hemispheres.
contains a structure called the reticular formation responsible for the state of general activation of the SN, such as the sleep-wake cycle.
The midbrain, which is distinct from the aqueduct of the brain, is divided into:
or
roof consists of the inferior colliculus (hearing) and superior colliculus (vision) that are also called the optical roof. The latter is particularly well developed in birds and in lower vertebrates as presiding over the most visual drawing. In humans, the visual processing is mainly performed by the cortex of the occipital lobe.
or
tegmentum contains many important structures such as the substantia nigra involved in motor control, affected by Parkinson's disease.
forebrain
The Diencephalon is located at the third ventricle and is divided into:
or Talamo
is a set of nuclei as an important processing station for all sensory information.
Various nuclei project to areas of the cerebral cortex deputies to the analysis of each sensory modality.
is involved in motor control. Emerge from the thalamus of the internal capsule fibers that link the thalamus and cortex. There is a right and left thalamus (equivalent structure).
or Hypothalamus
is located rostral to the thalamus and presides over the control of the entire organism by regulating homeostasis.
Since it depends on the temperature regulation, hunger, thirst, sleep, sleep, sexual behavior and expression of emotions such as aggression and fear. Check
activation of SNA.
Through the pituitary controls the release of Most of hormones by the various endocrine glands.
bulb, cerebellum, bridge, midbrain, thalamus and hypothalamus are the brain stem .
Telencephalon
is the most rostral portion of the brain and its development is characteristic of mammals, especially primates.
It is distinguishable from the lateral ventricles and is divided into:
or
cerebral hemispheres is the most cumbersome and consists of the brain outside the cerebral cortex , which has a thickness of 2-4 mm and is about 2000cmq (45x45cm), three times the size inside the skull. The convex part are called revolutions and troughs and furrows, the grooves are deeper fissures said.
The hemispheres are divided into lobes . The frontal lobe ventral and is bordered by the parietal lobe which is rostral. This is adjacent to the temporal lobe , caudal, dorsal and occipital lobe . The fissure of Rolando
or central sulcus separates the frontal lobe and parietal lobe. The fissure of Silvio
or lateral sulcus separates the frontal lobe from temporal lobe. The two hemispheres are separated
the fissure interemispheric .
widening the gap can be seen the lateral cortex of the insula between the temporal lobe and frontal lobe.
widening the fissure is observed interemispheric corpus callosum and the cingulate gyrus . The central sulcus separates the
precentral gyrus (frontal lobe) that is called the primary motor cortex and postcentral gyrus (parietal lobe) that primary somatosensory cortex. In the primary motor cortex and primary somatosensory cortex are ordered maps of body surface and motor homunculus homunculus somatosensory .
Brodmann in 1909 created a map cyto-architecture of the cortex, which is based on the characteristics of the tissue. Discriminated 49 different areas, is still valid and called Brodmann areas.
Areas 1,2 and 3 correspond to the primary somatosensory cortex (frontal and parietal lobe). The area 17, striate cortex, for example, is delegated the primary visual area (temporal lobe). The primary area all'uditiva 17 (temporal lobe). The fourth area is the primary motor (frontal lobe).
or Telencephalon baseline or subcortical structures
The basal ganglia are the caudate nucleus The globus pallidus and putamen involved in movement control.
L ' amygdala el' hippocampus are part of the limbic system which is involved in emotion and learning.
The blood circulation in the brain
The brain is crossed by two pairs of large arteries. The two internal carotid arteries supply blood to the rostral part of the brain, while the two vertebral arteries the caudal portion, but at deck join in ' basilar artery then divide again. The carotid arteries divide into anterior cerebral artery , which waters also the insula cortex, and middle cerebral artery . The vertebral arteries in a rteria posterior cerebral artery and superior cerebellar . Ventrally, near the optic chiasm the carotid arteries and vertebral arteries are pooled in the circle of Willis .
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