What is the anatomy of the brain?

From the Guidelines

The human brain's anatomy is complex, with 12 paired cranial nerves emerging from the brain, providing specialized sensory and motor innervation to the head and neck region, as described in the 2022 update of the ACR Appropriateness Criteria1. The brain's structure can be divided into several major regions, including the cerebrum, diencephalon, brainstem, and cerebellum.

• The cerebrum is the largest part of the brain, consisting of two hemispheres connected by the corpus callosum, and is divided into four lobes: frontal, parietal, temporal, and occipital.
• The diencephalon includes the thalamus and hypothalamus, which play crucial roles in sensory relay and homeostasis regulation, respectively.
• The brainstem, comprising the midbrain, pons, and medulla oblongata, controls vital functions like breathing and heart rate.
• The cerebellum coordinates movement and balance. The 12 paired cranial nerves, designated by numbers I-XII, emerge from the brain and are responsible for various sensory and motor functions, including:
• Olfactory (CN I) and optic (CN II) nerves, which are actually tracts formed from the telencephalon and diencephalon, respectively.
• The remaining cranial nerves, including oculomotor (CN III), trochlear (CN IV), trigeminal (CN V), abducens (CN VI), facial (CN VII), vestibulocochlear (CN VIII), glossopharyngeal (CN IX), vagus (CN X), spinal accessory (CN XI), and hypoglossal (CN XII) nerves, which are responsible for various sensory and motor functions. The anatomy of the brain and its associated cranial nerves is essential for understanding various neurological conditions and developing effective treatment strategies, as highlighted in the 2022 update of the ACR Appropriateness Criteria1.

From the Research

Brain Structure

The human brain is a complex organ composed of various anatomical regions, each contributing uniquely to its overall functionality 2. It is made up of billions of neuronal and non-neuronal cells that are organized into distinct anatomical and functional regions 3. Some of the key features of the brain include:

• A protective brain-blood barrier
• High-energy demand
• Electrical activity
• Unique diversity of components, including neurons and astrocytes, that vary greatly even across brain regions 4

Brain Regions

The brain can be divided into distinct functional compartments, including:

• Cerebrum: responsible for processing sensory information, controlling movement, and managing higher-level cognitive functions
• Cerebellum: plays a critical role in motor control and motor learning, and is also involved in nonmotor cognitive and affective functions 5
• Brainstem: connects the cerebrum to the spinal cord and regulates basic functions such as breathing, heart rate, and blood pressure

Cellular Composition

The brain is composed of a diverse range of cell types, including:

• Neurons: responsible for transmitting and processing information
• Glia: provide support and maintenance functions for neurons
• Astrocytes: play a critical role in maintaining the health and function of neurons 4
• Other non-neuronal cell types, such as oligodendrocytes and microglia, that are involved in various aspects of brain function and maintenance 3

Development and Function

The brain develops and functions through a complex interplay of genetic and environmental factors, including:

• Dynamic processes that shape brain areas and circuit connectivity 6
• Specialized connectivity maps and characteristic gross external morphologies that reflect dedicated functions 6
• Regional heterogeneity and temporal dynamics that can be influenced by factors such as age, sex, and ethnic background 2