Secrets of the Brain: An Introduction to the Brain Anatomical Structure and Biological Function (1906.03314v1)

Abstract: In this paper, we will provide an introduction to the brain structure and function. Brain is an astonishing living organ inside our heads, weighing about 1.5kg, consisting of billions of tiny cells. The brain enables us to sense the world around us (to touch, to smell, to see and to hear, etc.), to think and to respond to the world as well. The main obstacles that prevent us from creating a machine which can behavior like real-world creatures are due to our limited knowledge about the brain in both its structure and its function. In this paper, we will focus introducing the brain anatomical structure and biological function, as well as its surrounding sensory systems. Many of the materials used in this paper are from wikipedia and several other neuroscience introductory articles, which will be properly cited in this article. This is the first of the three tutorial articles about the brain (the other two are [26] and [27]). In the follow-up two articles, we will further introduce the low-level composition basis structures (e.g., neuron, synapse and action potential) and the high-level cognitive functions (e.g., consciousness, attention, learning and memory) of the brain, respectively.

• The paper highlights the evolution from diffuse nerve nets to centralized brains through detailed comparative neuroanatomy.
• It systematically maps human brain regions—brainstem, cerebellum, diencephalon, and cerebrum—detailing their distinct functions.
• The study integrates sensory pathways with anatomical frameworks to support advancements in computational models, neuromodulation, and neuroprosthetics.

Comprehensive Overview of Brain Anatomical Structure and Biological Function

This paper presents a systematic introduction to the anatomical organization and biological functions of the brain, emphasizing comparative neuroanatomy, hierarchical structure, and the integration of sensory systems. The discussion is grounded in established neurobiological principles and provides a detailed mapping from evolutionary origins to fine-grained human cortical organization.

Comparative Nervous System Architecture

The paper begins by situating the brain within the broader context of animal nervous systems, highlighting the evolutionary trajectory from simple nerve nets in cnidarians to the highly organized central nervous systems of vertebrates. The transition from diffuse neural networks to centralized brains is illustrated through comparative anatomy, emphasizing the emergence of specialized regions for sensory integration and motor control.

Figure 1: Examples of nervous system complexity across animal taxa, from nerve nets in jellyfish to centralized brains in vertebrates.

The vertebrate brain is shown to develop from three primary embryonic swellings—forebrain, midbrain, and hindbrain—which differentiate into specialized regions. The evolutionary expansion of the forebrain, particularly the cerebral hemispheres, is underscored as a key driver of advanced cognitive capabilities in mammals and birds.

Figure 2: Early vertebrate brain structure, showing the tripartite organization that underlies subsequent specialization.

Figure 3: Evolutionary comparison of vertebrate brains, highlighting the disproportionate growth of cerebral hemispheres in mammals and birds.

Human Brain Macroanatomy

The human brain is anatomically partitioned into the brainstem, cerebellum, diencephalon, and cerebrum, each with distinct structural and functional roles.

Brainstem

The brainstem, comprising the midbrain, pons, and medulla oblongata, is responsible for autonomic functions, cranial nerve integration, and basic life-support mechanisms such as cardiac and respiratory regulation.

Figure 4: Anatomical illustration of the brainstem, showing its continuity with the spinal cord and its role in vital functions.

Cerebellum

The cerebellum is essential for motor coordination, precision, and timing, integrating sensory inputs to fine-tune voluntary movements. It also contributes to motor learning and certain cognitive processes.

Figure 5: The cerebellum, highlighting its layered structure and connectivity with motor and sensory systems.

Diencephalon

The diencephalon includes the thalamus (sensory relay), hypothalamus (homeostasis and endocrine regulation), epithalamus (circadian rhythm), and subthalamus (motor modulation). The pituitary gland, regulated by the hypothalamus, orchestrates hormonal control over diverse physiological processes.

Figure 6: Diencephalon structure, showing the thalamic nuclei and hypothalamic regions.

Figure 7: Pituitary gland anatomy, illustrating its anterior and posterior lobes and their distinct developmental origins.

Cerebrum

The cerebrum encompasses the cerebral cortex and subcortical structures (hippocampus, basal ganglia, olfactory bulb). It is the locus of sensory perception, voluntary motor control, memory, and higher-order cognition.

Figure 8: Human cerebrum, showing the division into hemispheres and major subcortical structures.

The cortex is subdivided into four lobes—frontal, parietal, occipital, and temporal—each associated with specialized functions.

Figure 9: Cerebral lobes, color-coded to indicate functional domains.

Motor and Sensory Cortices

The motor cortex, located in the frontal lobe, is somatotopically organized, with disproportionate representation for fine motor control regions such as the hands and face.

Figure 10: Motor homunculus in the primary motor cortex, illustrating the cortical allocation for different body parts.

The parietal lobe houses the somatosensory cortex, which receives tactile input and is similarly organized by receptor density.

Brodmann Areas

Cortical cytoarchitecture is formalized in the Brodmann area scheme, which divides the cortex into 52 regions based on histological features. These areas correspond to functional domains such as primary sensory and motor cortices, language centers, and association areas.

Figure 11: Brodmann area map, showing lateral and medial cortical surfaces with numbered regions.

Sensory System Integration

The paper provides a detailed account of the major sensory systems—vision, audition, somatosensation, taste, olfaction, and vestibular function—emphasizing the anatomical pathways and receptor types involved in transducing environmental stimuli into neural signals.

Visual System

The visual system processes light via photoreceptors in the retina, relaying information through the optic nerve to cortical and subcortical centers for image formation, object recognition, and spatial analysis.

Figure 12: Visual system architecture, from the eye to cortical processing centers.

Figure 13: Visual pathway, detailing the anterior and posterior segments from retina to visual cortex.

Auditory System

Auditory processing begins with mechanical transduction in the cochlea, followed by neural relays through the brainstem and thalamus to the primary auditory cortex.

Figure 14: Auditory pathway, showing peripheral and central processing stages.

Somatosensory System

Mechanoreceptors in the skin and deeper tissues encode touch, pressure, vibration, and proprioception, with signals transmitted to the somatosensory cortex.

Figure 15: Cutaneous mechanoreceptors, illustrating their distribution and functional specialization.

Taste and Olfactory Systems

Taste buds and olfactory epithelium contain chemoreceptors that transduce chemical stimuli into neural activity, with central processing in the gustatory and olfactory cortices.

Figure 16: Papillae types on the tongue, each containing taste buds for different modalities.

Figure 17: Peripheral olfactory system, showing the nasal cavity and olfactory epithelium.

Figure 18: Central olfactory system, mapping the olfactory bulb and associated cortical regions.

Vestibular System

The vestibular apparatus, comprising semicircular canals and otolithic organs, encodes rotational and linear accelerations, supporting balance and spatial orientation.

Figure 19: Semicircular canal system, demonstrating the orthogonal arrangement for three-dimensional motion detection.

Implications and Future Directions

The anatomical and functional mapping provided in this paper establishes a foundation for understanding the neural basis of perception, cognition, and behavior. The hierarchical organization and specialization of brain regions underscore the complexity of neural integration required for adaptive function. The comparative approach highlights evolutionary constraints and innovations that inform both basic neuroscience and translational research.

From a practical perspective, this detailed anatomical framework is essential for the development of biologically inspired computational models, neuroprosthetics, and brain-machine interfaces. The delineation of sensory pathways and cortical areas provides targets for neuromodulation, rehabilitation, and the design of artificial sensory systems.

Theoretically, the mapping of cytoarchitectonic regions to functional domains supports ongoing efforts in connectomics and systems neuroscience to elucidate the principles of neural computation and information processing. Future research will benefit from integrating molecular, cellular, and network-level data to refine our understanding of brain function and its disorders.

Conclusion

This paper offers a comprehensive, technically rigorous overview of brain anatomical structure and biological function, integrating evolutionary, anatomical, and sensory perspectives. The systematic mapping of brain regions and sensory systems provides a critical reference for neuroscientists and related disciplines, facilitating both theoretical inquiry and practical application in the paper of neural systems.