Human Brain: Definition, Function, Anatomy and Cranial Nerves

It is an organized structure, divided into many components that fulfill specific and essential functions.

The central nervous system consists of the brain and the spinal cord. The peripheral nervous system consists of the extensions of neuronal structures beyond the central nervous system and includes somatic and autonomic divisions.


The brain constitutes only about 2% of the human body. However, it is responsible for all body functions.

It controls the thoughts, the memory and the speech, the movements of arms and legs, and the function of many organs within the body. It also determines how people respond to stressful situations by regulating heart rate and breathing.

Anatomy of the human brain

In short, the brain is divided into the brain, brainstem, and cerebellum.

The brain’s base is the brainstem, which extends from the upper cervical spinal cord to the brain diencephalon. The brainstem is divided into the medulla, the swell, and the mesencephalon. Posterior to the brainstem is the cerebellum.

The brain is divided into right and left hemispheres. The corpus callosum is the collection of white matter fibers that bind to these hemispheres.


Each of the cerebral hemispheres is divided into four lobes:

  • The frontal lobe is named for its location in the front and top of the brain. It is associated with the highest levels of human thinking and behavior, such as planning, judgment, decision making, impulse control, and attention.
  • The parietal lobe is in the upper part of the brain and behind the frontal lobe. This lobe is responsible for taking in sensory information. The parietal lobe is responsible for understanding the position of someone in their environment.
  • The temporal lobe is in the lower frontal part of the brain. This lobe is associated with visual memory, language, and emotion.
  • Finally, the occipital lobe is in the back of the brain. The occipital lobe processes what a person sees.

The brain is divided into the telencephalon and the diencephalon. The telencephalon consists of the cortex, the subcortical fibers, and the basal nuclei. The diencephalon consists mainly of the thalamus and the hypothalamus.

The brain telencephalon is disproportionately developed in humans compared to other mammals.

Cranial nerves:

Twelve pairs of nerves originate in the brain itself. These nerves are responsible for particular activities and are named and numbered as follows:

  • Olfactory: Odor.
  • Optics: visual fields and ability to see.
  • Oculomotor: eye movements; the opening of the eyelid.
  • Trochlear: eye movements.
  • Trigeminal: facial sensation.
  • Abducent: eye movements.
  • Facial: eyelid closure; facial expression; taste sensation
  • Auditory/vestibular: Hearing; feeling of balance.
  • Glossopharyngeal: the sense of taste; swallow
  • Vagus: swallowing; taste sensation
  • Accessory: control of neck and shoulder muscles.
  • Hypoglossal: movement of the tongue.

Cortex and subcortical fibers:

The brain’s outermost layer is the cortex, which has a slightly gray appearance, hence the term ” gray matter .” The crust has a folded structure; Each fold is called a turn, while each groove between the folds is called a groove.

Under the cortex, there are axons, which are long fibers that emanate and connect neurons. Axons are isolated by myelin, which increases driving speed. Myelin is what gives the white aspect to these brain fibers, hence the term “white matter.”

Limbic system:

It is a grouping of cortical and subcortical structures involved in forming memory and emotional responses.

The limbic system allows complex interactions between the cortex, the thalamus, the hypothalamus, and the brainstem.

The limbic system is not defined by strict anatomical limits but incorporates several vital structures. Limbic structures conventionally include the amygdala, the hippocampus, the fornix, the mammillary bodies, the cingulate gyrus, and the parahippocampal gyrus.

Basal nuclei (ganglia):

The basal nuclei (formerly known as basal ganglia) comprise the caudate nucleus, the putamen, the pale globe, the subthalamic nucleus, and the substantia nigra. The pairs of these structures carry different names. The combined putamen and pale world form the lentiform nuclei.

The combined putamen and caudate nucleus form the striated body. The striated body derives its name from the striped appearance of gray matter connections that pass through the internal capsule.

The basal nuclei are tightly integrated with the motor cortex, the premotor cortex, and the motor nuclei of the thalamus and play a crucial role in the modulation of movements.

The primary entry to the basal nuclei comes from the direct motor and the premotor cortex and consists mainly of the pyramidal cells in the cortical layer V.

These exciting projections lead mainly to the fluted. The striatum also receives information from the dopaminergic cells of the substantia nigra.

The striatum sends inhibitory projections to the outer and inner pale globe. The pale external world sends inhibitory projections to the subthalamic nucleus, which sends excitatory projections to the pale inner planet. The internal globus pallidus, in turn, projects to the anterior ventral and lateral ventral nuclei of the thalamus.

Certain movement disorders can be attributed to pathologies in the basal nuclei, the most notable being Parkinson’s disease, which is related to the deficiencies of the dopaminergic cells of the substantia nigra.

Huntington’s disease is an inherited disorder involving degeneration of the striatum and leads to unequal or choreiform progressive movement.


Positioned between the brainstem and the telencephalon, the diencephalon comprises the thalamus, the epithelium, the subthalamus, and the hypothalamus.

The thalamus serves as a relay station for the ascending entrance to the cortex and receives information from each cardinal direction (except smell). It is believed that the thalamus serves as a gateway to information leakage. The thalamus consists of multiple nuclei.

The left and right sides of the thalamus are divided by the third ventricle. Each side is divided by the internal medullary lamina into anterior nuclei, ventrolateral nuclei, and medial nuclei. Smaller hearts are found within these regions, which number perhaps more than 100.

The anterior thalamic nuclei are functionally associated with the limbic system and share reciprocal connections with the cingulate gyrus and the mammillary bodies. The medial nuclei project to the frontal association cortex and the premotor cortex, with standard connectivity.

The ventrolateral nuclei can be further divided into the ventral anterior (VA), ventral lateral (VL), ventral posterolateral (VPL), and ventral posteromedial (VPM) nuclei.

The VA and VL nuclei share the entrance of the pale globe and the projections to the motor cortex. The VPL and VPM serve as sensory relays on the body and face.

The lateral nuclei are divided into lateral dorsal and posterior-lateral nuclei, with projections of the cingulate gyrus and parietal cortex, respectively.

Other thalamic structures not included in the anterior anatomical divisions have the medial and lateral geniculate bodies, which process auditory and visual information, respectively. Pulvinar connects reciprocally with the parietal and occipital association cortex.

The intralaminar nuclei within the internal medullary lamina obtain input from the brainstem, cerebellum, and other thalamic nuclei and project to basal nuclei and other thalamic nuclei.

Among intralaminar nuclei, the centromedian core is a part of the reticular activation system, which plays a role in maintaining cortical excitation.


The epithalamus is formed by the habenula, the habenular commissure, the posterior commissure, and the pineal gland.


Located between the mesencephalon and the thalamus, the subthalamus contains the subthalamic nucleus, the red nucleus, and the substantia nigra. The subthalamic structures are tightly integrated with the basal nuclei and play a role in the modulation of movement.


Your hypothalamic nuclei lie in the walls of the third ventricle above. The hypothalamus mediates endocrine, autonomic, visceral, and homeostatic functions. It can be roughly divided into anterior, posterior, and middle nuclei groups.

The previous nuclei include the preoptic, supraoptic, and paraventricular cores. The posterior nuclei have the supramammilar nucleus, the mammillary nucleus, the intercalated nucleus, and the posterior nucleus. The intermediate hearts include the infundibular, tubular, dorsomedial, ventromedial, and lateral cores.

The parasympathetic control can be attributed to the anterior and medial nuclear groups, while the sympathetic control can be attributed to the posterior and lateral atomic groups.

Satiation can be localized to the stimulation of the medial nuclei, and hunger can be localized to the inspiration of the lateral nuclei. Other hypothalamus functions include regulating body temperature, heart rate, blood pressure, and water balance.

The hypothalamus has close connections with the cingulate gyrus, frontal lobe, hippocampus, thalamus, brainstem, spinal cord, basal nuclei, and pituitary gland.