The brain is an amazing one-kilo organ that controls all the functions of the body, interprets information from the outside world and embodies the essence of the mind and soul. Intelligence, creativity, emotion and memory are some of the many things the brain governs. Protected within the skull, the cerebrum is composed of the cerebrum, cerebellum and brainstem.
The cerebrum receives information through our five senses: sight, smell, touch, taste and hearing, often many at once. It assembles the messages so that they have meaning for us and can store that information in our memory. It controls our thoughts, memory and speech, the movement of our arms and legs, and the functioning of many organs in our body.
The central nervous system (CNS) is composed of the brain and spinal cord. The peripheral nervous system (PNS) is composed of the spinal nerves that branch from the spinal cord and the cranial nerves that branch from the brain.
What parts is the brain divided into?
We can divide the brain into three main parts: the encephalon, the cerebellum and the brain stem.
Encephalon: this is the largest part of the brain and is composed of the right and left hemispheres. It performs higher functions such as interpretation of touch, vision and hearing, as well as speech, reasoning, emotions, learning and fine control of movement.
Cerebellum: located below the cerebrum. Its function is to coordinate muscle movements, maintain posture and balance.
Brainstem: acts as a relay center connecting the cerebrum and cerebellum to the spinal cord. It performs many automatic functions such as breathing, heart rate, body temperature, wake/sleep cycles, digestion, sneezing, coughing, vomiting and swallowing.
The cerebral hemispheres
The brain is divided into two halves: the right and left hemispheres. They are linked by a bundle of fibers called the corpus callosum that transmits messages from one side to the other. Each hemisphere controls the opposite side of the body. If the stroke occurs on the right side of the brain, the left arm or leg may be weak or paralyzed.
Not all functions of the hemispheres are shared. In general, the left hemisphere controls speech, comprehension, arithmetic and writing
The right hemisphere controls creativity, spatial ability, and artistic and musical abilities. The left hemisphere is dominant in the use of hands and language in approximately 92% of people.
Cerebral lobes
The cerebral hemispheres have distinct fissures that divide the brain into lobes. Each hemisphere has 4 lobes frontal, temporal, parietal y occipital . Each lobe can be divided, once again, into areas that serve very specific functions. It is important to understand that each lobe of the brain does not function alone. There are very complex relationships between the lobes of the brain and between the right and left hemispheres.
Below we briefly describe the main functions of each of the lobes. You can find a detailed article on each of them in our blog.
Frontal lobe
- Personality, behavior, emotions
- Judgment, planning, problem solving
- Language: speaking and writing (Broca’s area)
- Body movement (motor strip)
- Intelligence, concentration, self-awareness
Parietal lobe
- Interprets language, words
- Sense of touch, pain, temperature (sensory band)
- Interprets signals from vision, hearing, motor, senses, and memory
- Spatial and visual perception
Occipital lobe
- Interprets vision (color, light, movement)
Temporal lobe
- Understands language (Wernicke’s area)
- Memory
- Hearing
- Sequencing and organization
The cerebral cortex
The surface of the brain is called the cortex. It has a folded appearance with hills and valleys. The cortex contains 16 billion neurons (cerebellum has 70 billion = 86 billion total) that are arranged in specific layers. The nerve cell bodies color the cortex gray-brown, which gives it its name: gray matter
The cortex contains neurons (gray matter), which are interconnected with other brain areas by axons (white matter). The cortex has a folded appearance. A fold is called a gyrus and the valley in between is a sulcus.
The folding of the cortex increases the surface area of the brain, which allows more neurons to fit inside the skull and enables higher functions. The folds and sulci have names that help define specific brain regions.
Deep brain structures
Pathways called white matter tracts connect areas of the cortex to other areas. Messages can travel from one gyrus to another, from one lobe to another, from one side of the brain to another, and to structures deep in the brain.
Hypothalamus: the right lobe of the brain: is located in the floor of the third ventricle and is the main control of the autonomic system. It is involved in the control of behaviors such as hunger, thirst, sleep and sexual response. It also regulates body temperature, blood pressure, emotions and hormone secretion.
Pituitary gland: located in a small pocket of bone at the base of the skull called the sella turcica. The pituitary gland is connected to the hypothalamus of the brain by the pituitary stalk. Known as the “master gland,” it controls other endocrine glands in the body. It secretes hormones that control sexual development, promote bone and muscle growth, and respond to stress.
Pineal gland: located behind the third ventricle. Helps regulate the body’s internal clock and circadian rhythms by secreting melatonin. It has some role in sexual development.
Thalamus: the cortex: serves as a relay station for almost all information going to and from the cortex. It is involved in pain sensation, attention, alertness and memory.
Basal ganglia: includes the caudate, putamen and globus pallidus. These nuclei work with the cerebellum to coordinate fine movements, such as fingertip movements.
Limbic system: is the center of our emotions, learning and memory. This system includes the cingulate gyrus, hypothalamus, amygdala (emotional reactions) and hippocampus (memory).
Language-related structures
In general, the left hemisphere of the brain is responsible for language and speech and is referred to as the “dominant” hemisphere. The right hemisphere plays an important role in the interpretation of visual information and spatial processing
In about one-third of left-handed people, speech function may be located on the right side of the brain. Left-handed people may need special tests to determine whether their speech center is on the left or right side prior to any surgical intervention in that area.
Aphasia is a language impairment affecting speech production, comprehension, reading or writing due to brain injury, most often from stroke or trauma. The type of aphasia depends on the damaged brain area.
Broca’s area: located in the left frontal lobe. If this area is damaged, the person may have difficulty moving the tongue or facial muscles to produce speech sounds. The person can still read and understand spoken language, but has difficulty speaking and writing (i.e., forming letters and words, not writing inside the lines), which is called Broca’s aphasia.
Wernicke’s area: located in the left temporal lobe . Damage to this area causes Wernicke’s aphasia. The individual may speak in long meaningless sentences, add unnecessary words and even create new words. He can emit speech sounds, but has difficulty understanding speech and is therefore unaware of his errors.
Memory-related structures
Memory is a complex process involving three phases: encoding (deciding what information is important), storage and recall. Different types of memory involve different areas of the brain. The brain has to pay attention and rehearse in order for an event to move from short-term to long-term memory, which is called encoding.
The prefrontal cortex briefly stores recent events in short-term memory. The hippocampus is responsible for encoding long-term memory.
Short-term memory, also called working memory, is produced in the prefrontal cortex. It stores information for about one minute and its capacity is limited to about 7 items. For example, it allows you to dial a phone number that someone has just told you. It also intervenes during reading, to memorize the sentence you have just read, so that the next one makes sense.
Long-term memory is processed in the hippocampus of the temporal lobe and is activated when you want to memorize something for a longer time. This memory has unlimited content and capacity for unlimited duration. It contains personal memories as well as facts and figures.
Procedural memory is processed in the cerebellum, which transmits the information to the basal ganglia. It stores automatic learned memories, such as tying a shoe, playing an instrument or riding a bicycle.
The cerebral ventricles
The brain has hollow, fluid-filled cavities called ventricles. Inside the ventricles is a ribbon-like structure called the choroid plexus that produces colorless cerebrospinal fluid (CSF). CSF flows in and around the brain and spinal cord to help cushion injuries. This circulating fluid is constantly being absorbed and replenished.
Illustration, side view of the brain showing the ventricles deep within the brain and the flow of CSF
CSF is produced within the deep ventricles of the brain. Cerebrospinal fluid circulates within the brain and spinal cord and then exits into the subarachnoid space. Common sites of obstruction: 1) foramen of Monro, 2) aqueduct of Sylvius and 3) obex.
There are two ventricles deep in the cerebral hemispheres called lateral ventricles . Both connect to the third ventricle through a separate opening called the foramen of Monro
The third ventricle connects to the fourth ventricle through a long, narrow tube called the aqueduct of Sylvius. From the fourth ventricle, CSF flows into the subarachnoid space, where it bathes and cushions the brain. CSF is recycled (or absorbed) by special structures in the superior sagittal sinus called the arachnoid villi.
A balance is maintained between the amount of CSF that is absorbed and the amount that is produced. A disruption or obstruction of the system can lead to an accumulation of CSF, which may cause enlargement of the ventricles (hydrocephalus) or cause a buildup of fluid in the spinal cord (syringomyelia).
The meninges
The brain and spinal cord are covered and protected by three layers of tissue called the meninges. From the outermost layer inward they are: the dura mater, arachnoid and pia mater.
Dura mater: is a strong, thick membrane that closely lines the inside of the skull; its two layers, dura and meningeal, are fused together and separate only to form venous sinuses. The dura creates small folds or compartments. There are two special dural folds, the falx and the tentorium. The falx separates the right and left hemispheres of the brain and the tentorium separates the cerebrum from the cerebellum.
Arachnoid: is a thin web-like membrane that covers the entire brain. The arachnoid is formed by elastic tissue. The space between the dura and arachnoid membranes is called the subdural space.
Pia mater: it hugs the surface of the brain following its folds and grooves. The pia mater has many blood vessels that run deep into the brain. The space between the arachnoid and the pia mater is called the subarachnoid space. This is where cerebrospinal fluid bathes and cushions the brain.
Circulatory system and brain
Blood is carried to the brain by two paired arteries, the internal carotid arteries and the vertebral arteries. The internal carotid arteries supply most of the brain.
The vertebral arteries supply the cerebellum, the brain stem and the lower part of the cerebrum. After passing through the skull, the right and left vertebral arteries join to form the basilar artery. The basilar artery and the internal carotid arteries “communicate” with each other at the base of the brain called the Circle of Willis
Communication between the internal carotid and vertebral-basilar systems is an important safety feature of the brain. If one of the major vessels becomes blocked, it is possible for collateral blood flow to cross the Polygon of Willis and prevent brain damage.
The venous circulation of the brain is very different from that of the rest of the body. Usually, arteries and veins run together as they supply and drain specific areas of the body. So one would think that there would be a pair of vertebral veins and internal carotid veins. However, this is not the case in the brain
The main venous collectors are integrated into the dura mater to form the venous sinuses, not to be confused with the air sinuses of the face and nasal region. The venous sinuses collect blood from the brain and pass it to the internal jugular veins. The superior and inferior sagittal sinuses drain the brain, the cavernous sinuses drain the anterior skull base
All the sinuses end up draining into the sigmoid sinuses, which leave the skull and form the jugular veins. These two jugular veins are essentially the only drainage of the brain.
what types of cells are in the brain?
The brain is made up of two types of cells: nerve cells (neurons) and glia or glial cells.
Nerve cells
There are many sizes and shapes of neurons, but all consist of a cell body, dendrites and an axon
The neuron transmits information through electrical and chemical signals. Try to imagine the electrical wiring in your home. An electrical circuit is made up of numerous wires connected in such a way that when a switch is turned on, a light bulb lights up. An excited neuron will transmit its energy to the neurons around it.
Neurons transmit their energy, or “talk”, to each other through a small space called a synapse
A neuron has many arms called dendrites, which act as antennae that pick up messages from other nerve cells. These messages are transmitted to the cell body, which determines whether the message should be transmitted
Important messages are transmitted to the end of the axon, where sacs containing neurotransmitters open at the synapse. The neurotransmitter molecules cross the synapse and fit into special receptors on the receiving nerve cell, which stimulates that cell to transmit the message.
Glia cells
Glia (Greek for glue) are the cells in the brain that provide neurons with food, protection and structural support. There are 10 to 50 times more glia than nerve cells and they are the most common cell type in brain tumors.
Astroglia or astrocytes are the caretakers: they regulate the blood-brain barrier, allowing nutrients and molecules to interact with neurons. They control homeostasis, neuronal defense and repair, scar formation and also affect electrical impulses.
Oligodendroglia cells create a fatty substance called myelin that insulates axons, allowing electrical messages to travel faster.
Ependymal cells line the ventricles and secrete cerebrospinal fluid (CSF).
Microglia are the brain’s immune cells, protecting the brain from invaders and clearing debris. They also prune synapses.
