ANATOMY OF THE BRAIN

Anatomy of the brain

The human nervous system is basically composed of central nervous system and the peripheral nervous system. The central nervous system comprises the brain and the spinal cord whereas, peripheral nervous system is composed of spinal nerves that branch from the spinal cord and cranial nerves that branch from the brain.

Anatomy of brain:

Brain is the most complex organ in the human body comprising of three sections:

1.      Cerebrum

2.      Cerebellum

3.      Brain stem

Cerebrum:

It is the largest component of the human brain and is divided into right and left hemispheres which are joined together by a collection of white matter of fibers, termed as Corpus callosum.

Each of the cerebral hemispheres is further divided into four lobes: the frontal lobe, the parietal lobe, the temporal lobe and the occipital lobe. All of these lobes are different from each other with structural variations, as the frontal lobe id different from the parietal lobe by the central sulcus in their structure. In the same way the frontal and parietal lobes are distinguished anteriorly from the temporal lobe by means of the lateral salcus.

The cerebrum is further divided into telencephalon and diencephalon. The telecephalon is further divided into the cortex, the sub cortical fibers and basal nuclei. Whereas, the diencephalon is composed of the thalamus and hypothalamus.

Cortex and sub cortical fibers:

The cortex is the outermost layer of the cerebrum, due to the gray color it is termed as gray matter. The cortex has a folded structure called as gyrus and the grove in the gyrus is termed as sulcus.

Below the cortex are present cortical fibers, they make a connection with the neurons. Axons are covered by myelin sheath which increases the tendency and the speed of  the conduction. Myelin is what gives the name of white matter to the cortex. The cortical and the subcortical group together to form a limbic system which is responsible formation of memory and emotional responses. The limbic system allows an interaction between the cortex, the thalamus, the hypothalamus,, and the brain stem. limbic system also have the structures of the hippocampus, the amygdala, the fornix, the mammillary bodies.

Basal nuclei:

The basal nuclei comprises of caudate nucleus, Globus pallidus, putamen, subthalmic and substantia nigra. The basal nuclei are closely integrated with motor cortex, premotor cortex and motor nuclei of the thalamus, hence plays a role in the movements in the body.

Thalamus:

Thalamus, which is the part of the  play an important role in receiving the information from senses except the sense of smell. A third ventricle divides the left and right side of the thalamus. Each side of the thalamus is further divided into a series of anterior nuclei by means of a medullary lamina.

Epithalamus:

Another part of the diencephalon, epithalamus  is composed of habenula, the habenular and the posterior commissure, and the pineal gland.

Subthalamus:

It is located between the site of  midbrain and the thalamus, and it contains the subthalamic and the red nucleus, and the substantia nigra. Subthalamic structures play a role in modulation of movement.

Hypothalamus:

The hypothalamic nuclei have a position on the walls of the third ventricle.

Brain stem and the cranial nerves:

Structurally, the brain stem is composed of the medulla oblongata, Pons and midbrain.

Medulla:

Medulla also called as medulla oblongata is the lowest part of the brain and also the lowest part of the brain stem. It is connected to the mid brain via Pons and is continuous posteriorly with the spinal cord. Medulla also consists of both gray and white matter in its structure just like cerebellum and cerebrum.

Pons:

Pons lies superior to the medulla, having a ventral surface which is characterized by the band of horizontal fibers. These fibers enter the area of contralateral middle cerebellar peduncle and thus, finally entering the cerebellum.There are bulges on the other side of the Pons which are produced by the descending corticospinal tracts.

Mid-brain:

Mid-brain which is also termed as encephalon is the most superior aspect of the brainstem.it is present in between the forebrain and hind brain. It has reticular formation in it, which forms a part of the tagamentum which is responsible for the influence on the motor function of the brain. On the ventral side of the midbrain there are two bundles that diverge to form cerebral peduncles. The third cranial nerve can be seen between the cerebral peduncles. On the posterior side of the midbrain, there are two pairs of protrusions, which are the superior and inferior colliculi.

Cranial nerves:

There are 12 pairs of the cranial nerves whose function is to send the motor signals to and from the head and neck.(1)

Cerebellum:

The cerebellum occupies the portion of posterior fossa, which is located dorsally to the Pons and Medulla. It involves in the management of motor control thus maintaining the function of the body movement. The cerebellum has structures like finer Folia and fissures just like the Gyri and Sulci in the cerebrum.

A cerebellum is composed of two hemispheres which are connected I the center by means of a midline structure, Vermis. The cerebellar cortex has basically three layers:molecular, purkenjie, and granular. There are four deep cerebral nuclei in the cerebellum termed as the fastigial, globose, emboliform, and dentate nuclei. There are also efferent and afferent pathways in the cerebellum within the three peduncles.

Besides these three structures there are also some other structures in the anatomy of the brain like meninges, ventricles and cerebrospinal fulids.(2)

Meninges:

There are three layers of meningies which cover the brain and the spinal cord. These are:

·         Pia matter

·         Arachanoid layer

·         The dura matter

The innermost of the layers is Pia meter, which tightly encloses the brain. This layer is really rich in blood vessels. Arachanoid layer is outside the Pia matter, and looks like a thin web like material. Between these two layers is arachnoid space which contains cerebrospinal fulid in it.

Cerebro-spinal fluid:

The brain is completely immersed in the cerebrospinal fluid contained in the cavities termed as ventricles. The structures which are responsible for the release of the cerebrospinal fluid lie within the ventricles and are termed as Chroid Plexus. (3)

References:

1. Regina Bailey (). Anatomy of the Brain. [ONLINE] Available at: http://biology.about.com/od/humananatomybiology/a/anatomybrain.htm

2. (2006). anatomy of the brain . [ONLINE] Available at: http://www.aans.org/Patient%20Information/Conditions%20and%20Treatments/Anatomy%20of%20the%20Brain.aspx.

3. interactive tour of the brain. [ONLINE] Available at: http://www.braintumor.org/patients-family-friends/about-brain-tumors/brain-anatomy.html.