The Brain | Anatomy, Functions & Medical Conditions

Jessica Lewis
October 18, 2016

The brain is the center of the nervous system and house to more than one hundred billion neurons and glial cells which process and then transmit information throughout the entire human body. Found in all vertebrates and most of the invertebrate animals, it can easily be considered one of the body’s most essential parts, along with the heart. Physically, the brain is located in the head, close to important sensory organs such as the eyes, ears or nose. It constitutes, together with the spinal cord, the central nervous system. Neurons are its main component. Their primary function is to transmit electric impulses via specialized connections called synapses.

Psychologically, it controls the rest of the body either by triggering hormone activity or generating muscle movements. It is also responsible for the human being’s mental and emotional health.

Here are some facts in brief about the human brain you might be interested in:

  • Its approximate weight in newborn babies is of four hundred grams, while in an adult it can reach up to three pounds.
  • The brain has a similar consistency to that of tofu
  • It constitutes about two percent of the body’s total weight and has a bigger volume in men (1260 cm3 compared to the 1130 cm3 in women)
  • There is no evidence in regards to the connection between the brain’s size and mental performance; evidence shows the brain reaches full maturity around the age of twenty-five
  • There are nearly one hundred billion neurons and glial cells inside the human brain
  • About 10.000 different types of neurons are known to this day
  • The brain is almost seventy-three per cent water and uses twenty percent of the body’s oxygen intake in order to function
  • Memory and cognition can be affected if only a minimum water percentage is lost(about two percent); overall brain function can be permanently damaged if there is a lack of oxygen for more than five consecutive minutes
  • The brain is among the fattiest organs, with its dry part containing no less than sixty per cent fat
  • It is devoid of pain receptors so it cannot sense pain( that is why there are surgeries performed while the patient is fully awake)
  • Scientists suggest that a woman’s brain will understand pain differently from that of a man
  • During early pregnancy, a number of 250.000 neurons appear each minute; the human being continues producing neurons throughout life
  • The child uses mainly his subconscious mind until around the age of six because the hippocampus is not fully developed as to create memories
  • The brain produces an average of 50.000 thoughts per day of which 70% are negative; memories as well as new thoughts create additional connections
  • Nearly 100.000 chemical reactions are taking place inside it every second; brain waves are more active while people dream
  • The average IQ as well as attention span have lower values in comparison to the Victorian Age and even the last century
  • Brain development can be positively influenced by reading aloud, talking, being exposed to foreign languages, meditation or daily naps; however, it can be severely affected if one is exposed to abuse and stressful conditions, consumes alcohol on a regular basis or is an avid smoker
  • There is a strong mind-body connection; studies suggest the brain makes no difference between rejection and physical pain
  • We have a ‘second brain’ inside our intestines; there are nearly 100.000 cells similar to those in our brains that can trigger emotions
  • Half of the brain can be safely removed without any kind of impact on personality or memory
  • The myth according to which people use only 10% of their brains is not backed by scientific research; each of its constituents has a known function, although many of them are yet to be fully understood
  • The human brain is 10% smaller than ten thousand years ago, still it has a greater capacity to memorize things
  • Alcohol is a potent central nervous system stimulus and can affect it in less than six minutes; evidence indicated that alcoholic beverages do not directly affect the nerve cells but rather their endings
  • Chocolate contains certain compounds able to trigger relaxation

Brain Anatomy

The brain is a soft mass of nerve tissues protected by the skull. It is also known as the ‘encephalon’, term derived from the Greek ‘enkephalos’ which means “inside the head”. The brain is constituted of cells organized in parts and connected through neuronal networks.  It has three primary areas:

  • The forebrain: cerebrum, thalamus and hypothalamus
  • The midbrain: tectum and tegmentum
  • The hindbrain: cerebellum, pons and medulla

Of these, its primary constituents are the cerebrum, cerebellum and the brain stem which is connected to the spinal cord. The cerebrum consists of two hemispheres that control different parts of the body. The cerebellum is responsible for muscular coordination while the hypothalamus, located near the center of the brain regulates body temperature and the internal organs’ activities. The brain is protected by a liquid known as the cerebrospinal fluid and a solid membrane, the dura mater. It is linked to the spinal cord through which it sends information to various organs with the help of four types of nerve attached to it:

  • Cervical nerves: the arms
  • Thoracic nerves: the skin, chest muscles and inner organs
  • Lumbar nerves: abdominal cavity and legs
  • Sacral and coccygeal nerves: legs

All parts are equally important with every single one being responsible for a certain process. However, some of them might perform the other one’s task as in the case of the cerebrum’s two hemispheres that duplicate each other’s function to a certain extent. The following are the brain’s primary constituents and some of their individual functions.

  1. Cerebrum

Regarded as the higher control center, the cerebrum is the brain’s central part. It is responsible for memory, thought, speech, action, emotional response and senses. The cerebrum is located in the superior part of the skull, above the eyes and is composed of the cerebral cortex and nerve fibers. It is divided into two hemispheres separated from each other by a fissure called the lateral sulcus. They remain connected through a bundle of nerve tissues called the corpus callosum. The hemispheres are not entirely symmetrical, although they can strongly imitate each other’s function; each half is responsible for the opposite part of the body, with the left hemisphere controlling the right side, and vice-versa.

The human brain has the largest cerebrum, aside from whales and dolphins.

The cerebral cortex is a soft outer layer made of folds which considerably increase its surface. It contains 90% of all nerve cells, and has four distinct regions, each with a different kind of mental activity:

  • Frontal lobe: positioned at the front of each hemisphere, it is responsible for communication and the way we interact with each other. It also controls muscle activity, and is strongly related to Broca’s area, a brain region which contains most of the neurons connected to speech. It is prone to the highest risk of brain injuries of all lobes; frontal lobe damage leads to personality disorders or limited facial expressions.
  • Parietal lobe: located behind the frontal lobe, it is strongly related to the senses of touch, temperature and taste. Sensory information is the fundamental notion associated with the parietal lobe whose primary function is to process it immediately. The parietal association cortex which is part of its structure offers people the ability to solve problems and understand written language.
  • Temporal lobe: located beneath the two brain hemispheres, it is responsible for hearing and selective listening. Equally important for memory, it is strongly connected with the ability to understand and recognize speech.
  • Occipital lobe: the smallest of all lobes in the human cerebral cortex, it processes visual information through the primary visual cortex. Damage could lead to visual impairments and numerous other vision-related issues.

Each lobe regulates the activity of different senses. As a result, it is unlikely for one’s function to be affected by another one’s damage. For example, if a person suffers a stroke and can no longer speak, he still understands what those around him speak, and can even communicate with them through writing.

The corpus callosum is a cluster of nerve tissues that contains nearly 200.000 axons(nerve fibers). They allow communication between the two brain hemispheres by carrying electrical impulses. It contains the highest percentage of white matter inside the brain as well as a considerable amount of myelin, a white fatty substance that protects the axons and facilitates the change of information between neurons.

The neocortex is the upper layer that covers the cerebral hemispheres, and is associated with neural activity and response, individual reasoning, thinking process and language. Considered to be a recently evolved brain part, it is mainly found in humans, primates and dolphins.

  1. Thalamus

The thalamus is a small brain structure consisting of two egg-shaped parts, positioned between the cerebral cortex and midbrain. It connects the brain stem to the cerebral cortex through many nerve connections related to all senses, except the smell. It regulates alertness, wakefulness and sleep.

  1. Hypothalamus

Located below the thalamus, it is associated with body temperature regulation and the activity of hormones through which the brain controls the inner organs. Physiological functions such as hunger, thirst, mood, sex drive or sleep depend on the hypothalamus. The role of important glands is strongly related to it, regardless of its small size. Its primary function is to regulate homeostasis, which is the body’s ability to adapt to external circumstances. The hypothalamus releases the following hormones:

  • thyrotropin-releasing hormone
  • gonadotropin-releasing hormone
  • growth hormone
  • corticotrophin-releasing hormone
  • somatostatin
  • dopamine
  • oxytocin
  • vasopressin

It might also trigger certain emotions such as anger or fear.

  1. Tectum and tegmentum

They are the dorsal and ventral parts of the mesencephalon; both structures are responsible for the auditory and visual reflexes.

  1. Cerebellum

Known as the “little brain”, the cerebellum is related to the sense of balance. It is divided into two hemispheres, similarly to the cerebrum’s structure. The cerebellum is located in the top part of the brain stem, just above the spinal cord from which it receives sensory information in order to regulate body movement. Its small size is irrelevant when it comes to its real potential: nearly half of all brain neurons are found in the cerebellum. Movement, posture, coordination, balance and speech depend on its proper functioning. Cerebellar lesion might lead to a lack of coordination, balance problems or tremors.

  1. Pons and Medulla Oblongata

The pons and medulla oblongata constitute, together with the midbrain, the brain stem.

Approximately 2.5 centimeters in length, the pond regulates the activity of many nerves related to facial expressions and sensations, respiration, swallowing, hearing, balance, taste and eye movement. A section of it was associated with the control of sleep patterns and sleep paralysis.

The medulla oblongata on the other hand controls the involuntary body functions such as vomiting or sneezing. It contains both white and gray matter. Numerous arteries such as the anterior spinal artery or the posterior inferior cerebellar one provide it with blood. The cardiac, vomiting, respiratory and vasomotor centers are found inside this cone-shaped mass.[2][3]

Brain Functions

The brain is usually associated with the thinking process, memory, cognition, logic or concentration. However, the real mechanism of action of this highly-evolved structure might leave you amazed. Let us take the lateralization of brain function. As discussed before, there are two distinct cerebral halves separated by a median fissure.

Studies show that each human being evolves in his own manner and has his own unique lateralization. The left hemisphere is associated with action and strongly related to emotional impulses that can lead to risky behaviors or unwise decisions. The manner of speech and muscular movement seem to be more dominant in this case. The right hemisphere on the other hand is connected to logical thinking and visuospatial attention. According to a study published in 2013, left hemisphere regions tend to interact with the same hemisphere, while right-hemisphere constituents are likely to do so with both halves. Still, their functions remain largely related. For example, if a portion of it or the entire hemisphere is damaged, the other region develops connections with the affected area and can replace its role to a certain extent.

The left hemisphere is related to the right side of the body, while the right one regulates activity for the left side. Roughly 95% of people with left-hemisphere dominance are right-handed.

Language processing is another brain function that helps people interact and create bonds. Probably the most specific ability for the human being, language has hugely evolved and currently enjoys an increasing number of studies conducted by specialists from various domains of research. Two major brain parts, namely the Wernicke’s area and Broca’s area are responsible for speech perception and production.

The brain is an essential organ, and, like any other body part, it needs energy in order to function. In spite of not occupying much space, the brain requires no less than 20% of the metabolized energy, a value higher than that of any other organ. It also needs about 15% of the cardiac output and one-fifth of the oxygen absorbed in the lungs. Its primary fuel is either glucose or ketones(during low food intake).[4][5]

Medical Conditions

The brain is easily one of the most affected body parts, in spite of being so well protected by the skull and cerebrospinal fluid. Due to the fact that it regulates such a great number of activities, it is only normal for it to require more energy and oxygen than any other inner organ. Because of this, the most common brain-related medical conditions occur when the oxygen supply is suddenly interrupted. Drowning, stroke, suffocation and even birth injury might lead to the oxygenation process’ blockage. The brain is likely to suffer extreme damage in case this happens for more than six minutes. Direct damage to the brain or one induced by the harm done to other organs might cause serious problems, if not immediately spotted. Specialists are able to quickly diagnose a disorder based on how the body reacts in most cases. If, for example, the area responsible for speech is injured and the patient can no longer communicate, the doctor will first investigate the cerebrum as its frontal lobe is associated with this function. There are however situations in which an immediate diagnosis is impossible.

  1. Traumatic brain injuries occur when the brain makes direct contact with an exterior A hit, blow or jolt to the head is likely to cause them. A sharp object hitting the skull or a bullet penetrating it will lead to an even more severe damage, as the brain function is certainly to be affected by them. Sports such as football and baseball practiced in unsafe circumstances or driving at higher speeds can only increase the risk for accidents. In the case of brain injuries, one might experience nausea, speech difficulty, headaches, bleeding from the ear, pupil dilatation or high blood pressure.[6][7]
  1. Infections can occur at the central nervous system level either through the action of bacteria, germs or fungi that first cause inflammation, but which rapidly reaches deeper into the brain. Below we have listed the two brain infections with the highest degree of incidence:
  • Meningitis is an inflammation of the meninges, the membrane covering the brain and spinal cord. Some of its symptoms include headaches, fever, vomiting, seizures and a stiff neck. It can lead to brain swelling and even death if not treated in time.
  • Encephalitis is a severe brain inflammation, usually caused by a virus transmitted by mosquitos or ticks. It has symptoms similar to those of flu and might last for three weeks before becoming worse. Fever, general fatigue, vomiting, headaches or visual sensitivity to light are only a few of them.
  1. A brain tumor is represented by any abnormal growth inside the skull which usually causes pressure and pain; it can interfere with the blood supply and lead to more serious issues that differ in accordance to the affected area. Brain tumors might be a sign of cancer in other body parts. It is important to see a doctor if you notice the following symptoms: frequent headaches, dizziness, disturbance of vision, seizures, or difficult body movements. The specialist will conduct various tests in order to establish a proper treatment that fits the patient’s needs. The types of treatment for this medical condition are neurosurgery, chemotherapy or irradiation.
  1. A neurodegenerative disease leads to nerve deterioration and drastic changes in personality and behavior. Memory loss, anxiety, mood swings and irritability are associated with this disorder. Often times, the medical treatments used in patients suffering from a neurodegenerative disease present little effectiveness, as the condition usually worsens as time passes. Huntington’s disease, Parkinson’s disease, dementia or Alzheimer’s disease are some of the most harmful.
  1. Mental disorders are one of the today’s main issues, with an increasing number of patients of all ages. Depression and anxiety are some of the most common problems many adolescents currently face, either because of stress, low self-esteem or family matters. Most of them choose to take refuge in their own minds, and distance themselves from society. It is important for the parents of teenagers who show signs of social withdrawal also to consult with a psychotherapist if the patient is already taking medication.[8]

Although several layers of protection keep it safe against toxins and harmful bacteria, the brain is among the inner organs most prone to damage due to its weak endogenous antioxidant defense system. In 2015, about 700.000 people from the United States suffered from one particular brain tumor. Nearly 17.000 of them died months after receiving the diagnosis.  Moreover, one in ten American is likely to show signs of depression; the disorder’s highest rate of incidence occurs in people aged forty-five to sixty-four[9]