17 External Brain Anatomy
The human brain is a complex three-dimensional organ with distinct regions visible from its external surface. Understanding external brain anatomy provides the foundation for exploring how different brain areas contribute to behavior and cognition. This chapter examines the major divisions of the brain, including the cerebral lobes and their specialized functions, as well as the non-cerebral components that support essential life functions.
Gross Anatomy Components
The brain is comprised of the cerebrum, cerebellum, and brainstem. The cerebrum is the most prominent region of the brain. It is divided into left and right hemispheres. The hemispheres have many of the same functions, for example, each perceives touch on one side of the body, but some functions, like language, demonstrate laterality, meaning they are primarily controlled on one side of the brain. The cerebral hemispheres in humans have many folds to increase the surface area of the brain. The ridges are called gyri and the grooves are called sulci. Large sulci are often called fissures.
The four lobes of the brain are each responsible for specific functions
Frontal Lobe
The cerebral hemispheres of the brain are divided into four lobes. The frontal lobes are the most rostral, located in the front of the brain and are responsible for higher-level executive functions, like attention, critical thinking, and impulse control. They are the last brain region to fully develop, not completing development until individuals reach their 20s. The frontal lobes are also the location of the primary motor cortex, the region of the brain responsible for executing voluntary movement. The primary motor cortex is located in the precentral gyrus.
View the frontal lobe using the BrainFacts.org 3D Brain
Parietal Lobe
The central sulcus lies caudal to the frontal lobe and divides the frontal lobes from the parietal lobes. The parietal lobes are important for processing sensory information. The primary somatosensory cortex is located in the postcentral gyrus of the parietal lobe and is responsible for the perception of touch and pain. The parietal lobes also perform higher-level visual processing.
View the parietal lobe using the BrainFacts.org 3D Brain
Temporal Lobe
The temporal lobes are located on the side of the brain, separated from the frontal and parietal lobes by the lateral fissure. Like the parietal lobe, the temporal lobe plays a role in sensory processing, specifically with hearing, smell, and higher-level visual processing. The temporal lobe is also important for speech and memory. Beneath the cerebral cortex, deep in the temporal lobes, lie the hippocampus and amygdala, two regions of the limbic system, a circuit important for emotion and memory.
View the temporal lobe using the BrainFacts.org 3D Brain
Occipital Lobe
The last lobes are the occipital lobes, the most caudal lobes located in the back of the brain. The occipital lobes’ primary function is processing of visual information.
View the occipital lobe using the BrainFacts.org 3D Brain
Non-Cerebral Components
The cerebellum lies inferior to the occipital lobes. The cerebellum is also divided into two hemispheres, like the cerebral cortex. The cerebellum is best known for its role in the regulation and control of movement, but it also contributes to cognitive functions, including emotion. These non-motor roles are less well understood than the cerebellum’s motor functions and are an active area of ongoing research.
The brainstem is located between the cerebrum and the spinal cord. It is important for regulating critical functions like heart rate, breathing, and sleep. Most cranial nerves enter or exit the brain at the level of the brainstem.
The spinal cord, which is part of the central nervous system but not part of the brain, is responsible for receiving sensory information from the body and sending motor information to the body. Involuntary motor reflexes are also a function of the spinal cord, indicating that the spinal cord can process information independently from the brain.
View the brainstem using the BrainFacts.org 3D Brain
View the cerebellum using the BrainFacts.org 3D Brain
Landmarks on the brain can be seen from different planes of view
Dorsal View
Viewing the brain from above shows the bilateral symmetry of the left and right cerebral hemispheres, which are separated by the longitudinal fissure. The frontal, parietal, and occipital lobes can be seen. Similar to the lateral view, the central sulcus divides the frontal lobe from the parietal lobe. The precentral gyrus, which is the location of the primary motor cortex, sits rostral to the central sulcus, whereas the postcentral gyrus, which is the location of the primary somatosensory cortex, lies caudal to the central sulcus.
Ventral View
Underneath the brain, the frontal and temporal lobes are visible, as is the cerebellum. Like the dorsal view, the longitudinal fissure divides the cerebrum into right and left hemispheres. The pons and medulla, components of the brainstem, connect the cerebrum to the spinal cord.
Cranial nerves are also visible on the ventral surface of the brain. The olfactory tract leads out to the olfactory bulb, which connects to the olfactory nerve. The optic tract crosses the midline at the optic chiasm, and then the optic nerve projects to the retina. Other cranial nerves enter or leave the brain at the level of the brainstem. The hypothalamus is located rostral to the pons, and the mammillary bodies project out from the hypothalamus.
Conclusion
External brain anatomy reveals the organization of neural structures that support human cognition and behavior. The specialized lobes of the cerebral cortex, combined with the cerebellum and brainstem, create an integrated system capable of complex processing while maintaining essential life functions. Understanding these anatomical relationships is crucial for appreciating how brain structure relates to function.
Key Takeaways
- The frontal lobe governs executive function and voluntary movement; the parietal lobe processes somatosensory information; the temporal lobe processes hearing and memory; the occipital lobe processes vision.The four lobes of the cerebral cortex each have specific functions
- The cerebral cortex has gyri and sulci to increase the surface area
- The cerebral cortex, underlying structures, cerebellum, brainstem, and spinal cord form the central nervous system
Important Terms
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The region of the brain located between the cerebrum and the spinal cord. It connects the cerebrum to the spinal cord and is critical for regulating functions like heart rate, breathing, and sleep. Most cranial nerves enter or exit the brain at the level of the brainstem.
The groove that divides the frontal lobe from the parietal lobe. The precentral gyrus lies rostral to it, and the postcentral gyrus lies caudal to it.
A structure located posterior and inferior to the cerebrum, divided into two hemispheres like the cerebral cortex. The cerebellum regulates and controls movement and also contributes to cognitive functions, including emotion.
The largest and most prominent region of the brain, divided into left and right hemispheres with a folded surface of gyri and sulci.
The most rostral of the four cerebral lobes, responsible for higher-level executive functions such as attention, critical thinking, and impulse control. It contains the primary motor cortex in the precentral gyrus and is the last brain region to fully develop.
A ridge on the folded surface of the cerebral cortex. Gyri increase the surface area of the brain.
A structure located rostral to the pons that regulates the stress response, reproduction, sleep, thirst, hunger, and other homeostatic functions. The mammillary bodies project from the hypothalamus.
The tendency for a function to be primarily controlled by one cerebral hemisphere rather than both.
A prominent groove separating the temporal lobe from the frontal and parietal lobes; the secondary somatosensory cortex and the primary auditory cortex are located near or within it. Also called the lateral fissure.
A circuit of brain structures, including the hippocampus and amygdala, important for emotion and memory.
The groove that separates the left and right cerebral hemispheres.
Paired structures projecting from the hypothalamus, visible on the ventral surface of the brain.
A component of the brainstem, located between the pons and the spinal cord, that connects the cerebrum to the spinal cord.
The most caudal of the four cerebral lobes. Its primary function is processing visual information.
A structure that connects to the olfactory tract and receives input from the olfactory nerve, the cranial nerve that carries smell information.
The cranial nerve that carries smell information, connecting to the olfactory bulb and olfactory tract.
The white matter pathway leading from the olfactory bulb, visible on the ventral surface of the brain.
The point at the midline where the optic tracts cross.
The cranial nerve that projects from the optic chiasm to the retina.
The pathway that crosses the midline at the optic chiasm, connecting the optic nerve to the diencephalon.
One of the four cerebral lobes, located caudal to the frontal lobe and separated from it by the central sulcus. The parietal lobe processes sensory information, including touch and pain through the primary somatosensory cortex, and performs higher-level visual processing.
A component of the brainstem, located between the cerebrum and the medulla, that connects the cerebrum to the spinal cord.
The gyrus caudal to the central sulcus that contains the primary somatosensory cortex.
The gyrus rostral to the central sulcus that contains the primary motor cortex.
The region of the brain responsible for executing voluntary movement, located in the precentral gyrus of the frontal lobe.
The region of the brain responsible for the perception of touch and pain, located in the postcentral gyrus of the parietal lobe.
A groove on the folded surface of the cerebral cortex. Large sulci are often called fissures.
One of the four cerebral lobes, located on the side of the brain and separated from the frontal and parietal lobes by the lateral sulcus. The temporal lobe processes hearing, smell, and higher-level vision, and supports speech and memory.
