The brain is a three-pound organ that is responsible for taking in information about the world around us, interpreting it, remembering it, and recalling it when making decisions or putting new information into context. It’s a huge job for a relatively small object! And within the folds of this gray and pink mess of thoughts, feelings, and directives are many parts with specific functions. By studying the parts of the brain, neuroscientists hope to understand how the brain works, what parts of the brain could be responsible for certain diseases, and how we can heal the brain after illness or injury.
This page will organize and direct you to our multiple pages on the parts of the brain. Keep an eye out as this page may change and add new links. Like the brain itself, this page will change and evolve!
What Are the Different Parts of the Brain?
There are many ways to organize the different parts of the brain, but for the sake of this page, we will start by dividing the brain into three parts: the forebrain, midbrain, and hindbrain. Each part of the brain contains many subparts and structures responsible for different functions.
Here is how this page will be divided:
- The Forebrain
- Frontal lobe
- Parietal lobe
- Temporal lobe
- Occipital lobe
- Insula brain
- Olfactory bulb
- Basal ganglia
- Pituitary Gland
- Limbic System
- The Midbrain
- The Hindbrain
When you think of the big, pink, wrinkly part of the brain, you are likely thinking of the forebrain. The forebrain, or prosencephalon, is the forward-most part of the brain. It also is 85% of the brain, so there are many ways to break down and organize the forebrain based on location and function.
There are two main regions of the forebrain: the telencephalon and the diencephalon. The telencephalon develops first in utero and becomes the cerebrum. The cerebrum is the largest part of the forebrain - it covers both cerebral hemispheres.
The telencephalon contains structures including the cerebrum, basal ganglia, and olfactory bulb. These are complex structures within themselves - for example, the telencephalon also contains the basal forebrain, a structure near the base of the telencephalon that plays a role in temperature regulation, sleep-wake control, and other functions. Within the basal forebrain is the nucleus accumbens.
On this page, we will focus on the most important areas of the telencephalon: the cerebrum, the olfactory bulb, and the basal ganglia.
What Is the Cerebrum?
The cerebrum is the largest part of your brain, which covers two hemispheres and five lobes. Its outermost layer is called the cerebral cortex. The cerebral cortex consists of neural tissue (gray matter) holding approximately 15 billion neurons, allowing processes such as consciousness, attention, perception, emotions, thought, language, and memory.
The five lobes of the cerebrum are the
The frontal lobe is the largest lobe of the cerebrum. It contains sections like the prefrontal cortex, at the very front of the lobe, that help us make decisions and conduct higher-level thinking.
The frontal lobe is divided into four sections which contain their own gyrus, or ridge on the surface of the brain. The four sections are the lateral, polar, orbital, and medial parts.
Other notable structures within the frontal lobe are the motor cortex, Broca’s area, and orbitofrontal cortex.
Another part of the frontal lobe is the motor cortex, which functions to facilitate voluntary movement. This area resides in the frontal lobe and is positioned anterior to the central sulcus; this region of the cerebral cortex involves higher-level operations. It produces electronic impulses and transmits signals to the relevant areas.
Broca’s area is located in the inferior frontal gyrus, the part of the brain known as the motor speech area. The area is responsible for speech production, including regulating breathing while speaking and vocalizing. It’s also linked to language processing and comprehension.
Part of the prefrontal cortex is the orbitofrontal cortex (OFC), located directly above the eye sockets in the front part of the brain. It connects to the brain’s sensory regions, memory, and emotion centers. The orbitofrontal cortex is crucial in how we interact with the world.
Behind the frontal lobe and above the temporal lobe is the parietal lobe. Much of the parietal lobe handles language processing, and damage to this area of the brain can cause communication issues. Where the frontal lobe contains the “action cortex,” the parietal lobe contains the “sensory cortex. The somatosensory cortex is responsible for receiving and processing sensory information collected across the body, which is sent through the somatosensory tracts. Going beyond processing the sensory information, the somatosensory cortex is also responsible for orchestrating the reactions to the stimuli.
The frontal lobe, parietal lobe, and temporal lobe are separated by the Lateral Sulcus or Sylvian fissure. The lateral sulcus is a deep groove on the inferior flank of each cerebral hemisphere of the brain. The depth of this cerebral cortex cleft is vast and partitions the parietal and frontal lobes entirely from and temporal lobe. This sulcus is referred to as the Sylvian fissure, named after 17th-century neuroanatomist Franciscus Sylvius.
The temporal lobe also consists of structures that play a role in language comprehension, but also declarative or long-term memory. Some of the most important structures of the temporal lobe include the:
- Auditory cortex
- Wernicke’s area
The hippocampus is a section of the brain seated deep inside the temporal lobes of each cerebral cortex. It's an essential part of the brain's limbic system, which is an area that controls learning, memory, emotions, and motivations.
This is also the part of the brain that is most likely to shrink later in life.
When sounds enter your ears, they go through quite the journey on the way to your auditory cortex. The auditory cortex functions to analyze and decode auditory information collected by the ears and relayed along the auditory nerves. Wernicke's area is included in the auditory cortex and is responsible for language comprehension. The auditory cortex is found bilaterally in the temporal lobes.
Wernicke’s area is also known as the receptive language cortex. This name speaks to Wernicke’s theory on what this part of the brain does. It’s responsible for comprehending the speech that we hear. In addition to comprehension, this area of the brain also helps to plan out what a person is going to say. It’s important to know that once the speech is planned, the message still has to go to other parts of the brain before it is vocalized.
Between the temporal and occipital lobe lies the ventral stream, an essential neurological pathway that carries information from the primary visual cortex to the inferior temporal lobe and other important structures. Information processing takes place pertaining to what the item is, its shape, and assisting in memory forming.
The temporal lobe processes auditory information, but the occipital lobe processes visual information. It is the home of the primary and secondary visual cortices.
The primary visual cortex is tasked with converting external stimuli into meaningful responses and facilitating visual input memory. The V1 responds to basic aspects of vision- orientation and direction.
The lateral geniculate bodies (LGN), lingula, and dorsomedial stream are also located in the occipital lobe.
The insula, also known as the insula cortex or the insula lobe, is often forgotten when discussing the cerebrum. It sits within the lateral sulcus, underneath the cerebral cortex. It is a part of the brain responsible for sensory processing and plays an important role in emotions and empathy. The insula also has motor functions and is associated with decision-making abilities and consciousness.
The Anterior Cingulate Cortex and Corpus Callosum
Surrounding the corpus callosum is the anterior cingulate cortex, or ACC. The ACC is involved in high-level cognitive functions like decision-making and problem-solving, and psychological functions relating to social interaction, emotion, and empathic responses.
Another significant structure within the forebrain, specifically the telencephalon, is the olfactory bulb. The olfactory bulb, found in the forebrain of vertebrates, is a part of the brain that processes information about odors sent by cells in the nasal cavity. It transfers it to the amygdala, the orbitofrontal cortex, and the hippocampus, where it plays a part in learning, memory, and emotion.
The basal ganglia is a collection of nuclei responsible for feedback from several different sources within the brain. The basal ganglia relay information to the cortex via the thalamus. It is responsible for the control of descending motor pathways and controls excessive or exaggerated movements.
The basal ganglia wouldn’t be able to function without the caudate nucleus, the major input station of the Basal Ganglia. The Caudate Nucleus is responsible for several motor and cognitive functions. This structure consists of many interneurons and dopamine neurons essential for successful functioning.
At the base of the forebrain, connected to the midbrain, is the substantia nigra. The substantia nigra forms part of the basal ganglia, but it is not classified as a ganglion but instead as a nucleus. A nucleus is a collection of cells that make up a structure with the same function or connections in the brain.
…and that was everything in the telencephalon! The other main region of the brain, the diencephalon, also contains some important structures that play into memory and other functions. The thalamus, hypothalamus, and pituitary gland all reside within the diencephalon.
There are quite a few structures in the brain that cover multiple regions and provide communication throughout the brain. The thalamus is one of these structures. The thalamus resides between the midbrain and the cerebral cortex, with a multitude of nerve connections to both. Its principal function is to relay motor and sensory information to the cerebral cortex. The thalamus also plays a vital role in consciousness, alertness, sleep, learning, and memory.
In a groove above the thalamus sits the pineal gland, a small structure that is part of the endocrine system. Not much is known about how the pineal gland works, but neuroscientists do know that this small gland plays a role in hormone regulation.
In between the thalamus and the pituitary gland is the hypothalamus. Its interconnectedness is crucial to its functioning. The hypothalamus reestablishes balance via regulating hormone release from the pituitary gland. Connecting the hypothalamus and the pituitary gland is the hypothalamic pituitary adrenal axis, which helps the body prepare for stressful situations through the distribution of hormones. The hypothalamus emits elements into the bloodstream known as releasing hormones. Other functions of the hypothalamus include regulating temperature.
The hypothalamus is attached to the hippocampus via the fornix. The fornix is a collection of nerve fibers formed in a c-shape. This serves as the primary output tract of the hippocampus and is a part of the limbic system. The hippocampus is a highly intricate and sophisticated brain structure situated deep in the temporal lobe. It’s responsible for learning and memory.
The pituitary gland is attached to the hypothalamus. The pituitary gland comprises two lobes: the anterior pituitary (front) and posterior pituitary (back).
On both sides of the thalamus, you can find the limbic system. The limbic system is truly a system, and it covers multiple parts of the forebrain. Within the limbic system are the:
- Basal ganglia
- Cingulate gyrus
The limbic system is one of the oldest systems in the animal brain. It appears in fish and reptiles as well as humans.
The midbrain (mesencephalon) is a region of the brain that sits between the forebrain and the hindbrain, or brainstem. Our brainstems are important - they connect the brain to the spinal cord and the rest of the central nervous system! But the midbrain also serves an important purpose. Various parts of the midbrain offer pathways where electrical signals reach the cerebrum and the processing of information begins
When studying the midbrain, it is important to know the functions of the colliculi, the tegmentum, and the cerebral peduncles.
Superior and Inferior Colliculi
In the back of the midbrain is a structure called the tectum. The tectum (“roof” in Latin) is the rear section of the midbrain, composed of the superior and inferior colliculi. The first takes in information from the retina and visual cortex. The latter takes in input from auditory fibers. In short: the tectum is essential for visual and auditory processing.
The superior colliculus is the visual reflex center that allows eye movement, gaze shifts, and reactive reflexes like turning the head. The inferior colliculus is responsible for hearing and reacting to auditory input with non-auditory systems.
The neurons of the ventral tegmentum help to form one of the two main dopaminergic centers in the brain. It is a tiny area of neurons that has many neural branches or axons that project out into the entire brain. These fibrous branches help to transmit various messages throughout the brain that help with both emotional and cognitive functioning.
The mesocortical pathway is a major dopaminergic pathway that connects the ventral tegmentum to the dorsolateral prefrontal cortex. It facilitates these brain regions’ primary and secondary functions, including executive function, social cognition, and dopaminergic transmission.
The cerebral peduncles are essential parts of the midbrain. Several distinct fiber bundles collect together in a cylindrical shape. These fibers act like a highway between various brain and spinal cord regions, conveying sensory and motor information and refining movement-related impulses.
The hindbrain, or rhombencephalon, is located at the back of the brain and contains most of the brainstem. There is more to this region than just the brainstem, although most parts of the hindbrain serve to connect the spinal cord to the brain. Notably, the cerebellum is part of the hindbrain. The cerebellum is crucial in managing communication between your brain and body. Over half the neurons in your body are in the cerebellum!
Other parts of the hindbrain include the medullary pyramid, the pons, and the cerebellar vermis.
The medullary pyramid consists of grouped white matter formations at the intersection between the brain and the spinal cord. It contains two motor fibers (responsible for motor functions of the body): the corticospinal and corticobulbar tracts. These two components together are the pyramidal tracts.
The pons in the brainstem connects the brain and spinal cord. This connection provides a physical route for information to travel between the brain and the body. It also controls the sleep cycle, manages pain signals, and works with other organs to maintain breathing rhythm.
The pons has many vital junctions for four of the twelve cranial nerves, each having its own functions. Any injury to the pons can result in severe disorders and ultimately poor conduction of signals from the brain to various body parts.
The vermis sits at the heart of the cerebellum, and many disorders and malformations affect patients. In addition, the cerebellum regulates movement and posture automatically, and new motor patterns are learned in this region.
Other Parts of the Nervous System
Above are the basic structures in the brain, but there is much more than the different parts. Some structures, like the anterior horn, connect different regions of the brain. There are also different systems that “fill in the gaps” or prevent certain fluids from entering the brain. Some of these systems include the ventricular system, the blood-brain barrier, and the membrane surrounding the brain.
Within the brain is a ventricular system of cavities that produce cerebrospinal fluid, or CSF. The four ventricles are located throughout all parts of the brain: the two largest ventricles are in the cerebrum, while the third largest is in the diencephalon section of the forebrain. The fourth ventricle is located in the hindbrain. The third and fourth ventricles are connected by a cerebral aqueduct.
Membrane Surrounding the Brain
The membranes surrounding the brain are crucial for supporting the brain. The three cranial meninges, the dura, arachnoid, and pia mater, extend continuously in concentric layers. A medically critical space connects each layer. These are the epidural, subdural, and subarachnoid spaces.
The meninges are essential and serve the brain and spinal in several ways. They safeguard vital organs from mechanical trauma and sustain the blood vessels that provide brain tissue with nourishing blood. They also create continuous cavities or passages in which CSF passes.
The blood-brain barrier is one of the human body’s most complex and intricate parts. Given the body’s vast vascular network, you would think everything in the blood gets transported everywhere. That is not the case with the BBB, so what can cross the blood-brain barrier?
Only selected substances can cross the blood-brain barrier without intervention, such as water, small ions, lipophilic molecules, essential polar molecules, CBD and THC in cannabis, alcohol, caffeine, barbiturates, anesthetics, insulin, glucose, Melphalan, H2O2s, and ethanol.