Tuesday, July 10, 2018

Connections and function of Thalamus

The thalamus, which is a thick cluster of neurons located in the base of the brain, lies between the sensor tracts in the tegmentum mesencephali and the cerebral cortex. In other words, it connects afferent nerve impulses that come from the sense organs with the cerebrum. The thalamus also sends and receives myelinated fibers from the hypothalamus. Function: it works as a relay station for several sensory tracts which transmit sensation of pain, touch, muscle sense, and temperature up to the postcentral gyrus of the cerebral cortex, which is a sensory area. It is in the thalamus where the primitive analysis of all these stimuli take place before they are further conveyed into the cortex.

Sunday, July 8, 2018

Supraorbital and supratrochlear arteries

The supraorbital and the supratrochlear arteries are two oxygen-rich blood vessels that arise in the eye orbit from the ophthalmic artery. They come out onto the forehead, following a parallel course to the supraorbital and supratrochlear nerves. Then they run up across the forehead to supply the anterior and posterior aspects of the scalp, next to the supraorbital and supratrochlear veins.

Below, an image of the two arteries mentioned above.

Wednesday, July 4, 2018

Internal Structure of Cerebellum

The internal structure of the cerebellum is made up of the corpus medullare (white substance) and the peripheral cortex (grey matter). The corpus medullare in each lateral hemisphere is thicker than in the median vermis and consists of myelinated fibers that go and come from the cortex. On the other hand, the cortex has a more uniform thickness and is folded up, forming sulci (deep fissures). In a sagittal section in the mesal plane of the cerebellum, the white core can be seen to divide into two main branches; anterior ramus and posterior ramus. In turn, these main branches further divide and subdivide into a series of medullary laminae, which are surmounted by the foliated cortex, giving the characteristic appearance known as arbor vitae cerebelli.

Within the white matter of the cerebellum, there is a series of four isolated nuclei composed of grey matter. They are the dentate nucleus (or dentatum); the nucleus emboliformis (or embolus); nucleus globosus (or globulus); nucleus fastigii (or fastigatum).

Tuesday, June 26, 2018

Layers and cells of the cerebellum

The cerebellum, like the cerebrum, is made up of two types of cells; the parenchyma cells, which are neurons, and the supportive cells. The parenchyma cells in turn are constituted by four types of neurons; 1) the Purkinje cell, which is located in the upper, molecular layer of the cerebellum cortex and is densely branched, being the characteristic nerve cell of this central nervous system organ; 2) the basket cell, which is also situated in the molecular layer, with their axons enmeshing the body of the Purkinje cell; 3) the Golgi cell, which is an inhibitory neuron found slightly below the Purkinje cell in the granular layer, having short axons and using GABA as their neurotransmitter; 4) granular cell, which is also found in the granular layer of the cerebellum immediately below the Purkinje cell, with which it establishes connection, receiving inputs from the brainstem and spinal cord.

The neuroglia cell is the supportive cell of the cerebellum tissue and is located in the molecular layer.

This schematic view of the cerebellum shows the different cells that make up the its tissue. There you can see the lacation of both parenchyma cells (neurons) and supportive tissue cells (neuroglia) lacation in the cerebellum

Nuclei of Afferent Cranial Nerves

The nuclei of the cranial nerves afferent fibers are located in the brainstem (midbrain, pons, medulla oblongata). The vagus nerve afferent axons originate from the neurons in the jugular ganglion and ganglion nodosum (ganglion of the trunk), whereas the glossopharyngeal afferent axons emerge from the nerve cells in its ganglion superius and ganglion petrosum. The root fascicles of both nerves goes into the medulla oblongata along its dorsolateral groove, and the axons then bifurcate into ascending and descending rami, similar to those of the dorsal roots of the spinal nerves.

The ascending rami end in the nucleus alae cinereae nucleus vagi et glossopharyngeal); the descending rami come together to form a compact bundle called the tractus solitarius or trineural fasciculus, and terminating in a gray cell column called the nucleus of the solitary tract, which is a caudal prolongation of the nucleus alae cinereae. Both tract and nucleus become attenuated caudal, to disappear in the fourth cervical segment.

Down below, a sideview of the nuclei of cranial nerves sensory fibers

Friday, June 22, 2018

Vagal trigone (nucleus ala cinerea)

The nucleus ala cinerea, commonly known as the vagal trigone, is the nucleus of the ascending afferent vagus nerve axons, which arise from the nerve cells in the jugular (superior) ganglion and the ganglion nodosum (ganglion of the trunk). The vagal trigone lies in the lower closed portion of the dorsal (posterior) aspect of the medulla oblongata, right behind the dorsal motor nucleus. It receives sensory information from the external auditory meatus and from the taste buds from the root of the tongue via these ganglia, respectively (auditory impulses via the jugular ganglion, and taste information via the ganglion nodosum).

Down below, an image of the vagal trigone in the dorsal side of medulla

Tuesday, June 19, 2018

Why alcohol is bad for you. Physiological reasons

The physiological reasons why ethanol alcohol is bad for you lie in acetaldehyde, which is the ethanol first metabolic product when it is processed in the liver. When someone drinks alcoholic beverages, such as beer or whiskey, ethanol is absorbed in the duodenum and then goes to the liver through the portal system. With the intervention of alcohol dehydrogenase and zinc, it is broken down to acetaldehyde in this organ. Before it is further broken down into acetate, this extremely toxic product gets into tissue cells, especially into hepatocytes and neurons, where it wreaks havoc on the Golgi apparatus and especially on the mitochondria, inducing the cell apoptosis (death).

In the liver, apoptosis of hepatocytes means fibrogenesis and fibrosis; in other words cirrhosis. In the brain, apoptosis of neurons means brain shrinkage and the thinning of its fasciculi, which can be translated into loss of mental awareness and memory. But sometimes acetaldehyde-damaged mitochondria do not induce cell apoptosis but activate an oncogene in the cell nucleus DNA, and the normal cell becomes into a cancer cell.

Ethanol-derived acetaldehyde also affects brain functions in several ways. Being a depressant of the central nervous system, it inhibits and alters normal brain activities, impairing body movements and speech. It is a depressant because it alters the amount of gamma aminobutyric acid (GABA) and glutamate, which are two important neurotransmitters, disrupting the balance between inhibitory and excitatory activities of neurons as it increases inhibitory functions. You have to bear in mind that GABA is an inhibitory neurotransmitter. Thus, according to the amount of alcohol you have drunk, ethanol depressant effect ranges from drowsiness to blackout or death.

The other reason why ethanol is bad for you is because it activates an enzyme called aromatase, which is present in every tissue. Aromatase converts testosterone into estradiol, which is a feminine hormone.

To sum up, alcohol does not make you smart, but stupid, as you lose your mental capacity to discriminate (see the differences between things and persons in your surrounding reality. Thus, from being bright and sharp, you become dimmed and obtuse.  Nor does it make you manly but less virile as you lose your libido and masculine drive.