The brain is the main organ of the nervous system, receiving information and coordinating movement, thought and many internal body functions. It lies within the cranial cavity, the space enclosed by the skull, and continues into the spinal cord through an opening at the skull’s base called the foramen magnum.
Where is the brain located, and what surrounds it?
The brain occupies the cranial cavity above the vertebral canal, which contains the spinal cord. Its lower surface is related to the skull base, with meninges and cerebrospinal fluid intervening, while its upper and outer surfaces follow the curved inner surface of the skull.
The meninges are protective membranes surrounding the brain and spinal cord. They comprise the tough outer dura mater, the middle arachnoid mater and the delicate inner pia mater, which closely follows the brain’s surface. Cerebrospinal fluid, a clear fluid surrounding the central nervous system, occupies the subarachnoid space between the arachnoid mater and pia mater.
Folds of dura mater separate major regions. The falx cerebri lies between the cerebral hemispheres, the left and right halves of the cerebrum. The tentorium cerebelli separates the cerebellum from the overlying posterior parts of the cerebrum.
What are the main parts of the brain?
The cerebrum forms the largest part of the brain. The diencephalon lies deep between its hemispheres, and the brainstem extends inferiorly from the diencephalon, while the cerebellum lies behind the brainstem.
| Region | Position and structure | Main functions |
|---|---|---|
| Cerebrum | Paired hemispheres with a folded outer layer | Conscious sensation, voluntary movement, language, memory and thought |
| Diencephalon | Deep central region containing the thalamus and hypothalamus | Relaying information and regulating internal body conditions |
| Brainstem | Midbrain, pons and medulla oblongata between the cerebrum and spinal cord | Conducting signals and supporting breathing, circulation and cranial nerve functions |
| Cerebellum | Behind the brainstem, beneath the posterior cerebrum | Coordinating movement, posture and balance |
The medulla oblongata is the lowest part of the brainstem and becomes continuous with the spinal cord. The thalamus relays much sensory information to the cerebrum. The hypothalamus, below the thalamus, links nervous activity with hormonal regulation through its connections with the pituitary gland.
What are the brain’s surfaces and lobes?
Each cerebral hemisphere has an outer superolateral surface, an inward-facing medial surface and an inferior surface facing the skull base. Raised folds are called gyri, and the grooves between them are called sulci. The cerebral cortex is the outer layer of grey matter, tissue containing many nerve-cell bodies; deeper white matter contains mainly nerve fibres connecting different regions.
The four main surface lobes are named after the overlying cranial bones: frontal, parietal, temporal and occipital. The insula is a further region buried within the lateral sulcus, the groove separating the temporal lobe from the frontal and parietal lobes.
The central sulcus separates the frontal and parietal lobes. Immediately in front of it, the left precentral gyrus contains the primary motor cortex, a major source of signals for voluntary movement. Immediately behind it, the left postcentral gyrus contains the primary somatosensory cortex, which receives information about touch and body position.
What are the ventricles of the brain?
Ventricles are connected cavities within the brain containing cerebrospinal fluid. Most of this fluid is produced by the choroid plexus, specialised vascular tissue within the ventricles.
The left lateral ventricle lies within the left cerebral hemisphere, with a corresponding ventricle on the right. Each communicates with the third ventricle, a narrow midline cavity within the diencephalon. Fluid then passes through the cerebral aqueduct, a channel in the midbrain, into the fourth ventricle between the brainstem and cerebellum.
Openings in the fourth ventricle allow fluid to enter the subarachnoid space. It circulates around the brain and spinal cord and returns to venous blood, including through arachnoid granulations, projections of the arachnoid mater into venous channels.
How does blood reach and leave the brain?
The paired internal carotid artery and vertebral artery provide the principal arterial supply. The vertebral arteries unite to form the basilar artery along the front of the pons. Connections between these arterial systems form the cerebral arterial circle at the brain’s base.
The major cerebral arteries supply broadly distinct territories:
- The anterior cerebral artery supplies much of the medial frontal and parietal surfaces.
- The middle cerebral artery supplies much of the outer surface of each hemisphere.
- The posterior cerebral artery supplies the occipital region and inferior temporal areas.
Superficial and deep cerebral veins drain into dural venous sinuses, blood-filled channels within the dura mater. Blood ultimately leaves the skull mainly through the internal jugular vein. Brain tissue lacks conventional lymphatic vessels, but lymphatic vessels in the dura mater contribute to drainage towards deep cervical lymph nodes in the neck.
What does the brain do, and how is it connected?
Brain functions depend on connections between regions rather than isolated centres. Sensory pathways carry incoming information, while motor pathways carry signals involved in movement. Cranial nerves connect the brain with structures mainly in the head and neck; most attach to the brainstem.
The cerebrum supports conscious perception, language and planning. The left hippocampus, within the medial temporal region, contributes to forming new memories. The cerebellum helps adjust the timing and accuracy of movement, while the hypothalamus regulates processes such as temperature, hunger and thirst.
How can you explore the brain in the 3D model?
In the 3D model next to this article, select the brain and isolate it, then rotate and zoom to view it from different directions and at different magnifications. If surrounding structures obscure it, hide or fade them. A sagittal section divides left from right, a coronal section divides front from back, and a transverse section divides upper from lower parts; use these planes to orient your study.