Neuroanatomy of the Brain and its functionalities: 1, #172

By Stephen K. Marchant

The human brain is truly a masterpiece of creation!

The human brain is one-of-a-kind: our extraordinary cognitive ability has enabled us to invent the wheel, build the pyramids and land on the moon. Indeed, scientists have referred to the human brain as the "crowning achievement of evolution."

But what exactly is it about our brains that makes them so unique? Some of the most persuasive arguments have been that our brains have more neurons and expend more energy than would be expected for our size. Asides from this, our cerebral cortex, which is responsible for higher cognition, is disproportionately large—accounting for more than 80% of our total brain mass.

SuzanaHerculano-Houzel, a neuroscientist at Rio de Janeiro's Institute of Biomedical Science, disproved these long-held beliefs in recent years when she discovered a novel method of counting neurons—dissolving brains into a homogeneous mixture, or "brain soup." Using this technique, she found that the number of neurons relative to brain size is consistent with other primates and that the cerebral cortex, the region responsible for higher cognition, only contains about 20% of all neurons in our brain, a proportion similar to that found in other mammals. In light of these findings, she contends that the human brain is simply a linearly scaled-up primate brain that grows in size as we began to consume more calories due to the introduction of cooked food.

Other researchers have discovered that traits once thought to be unique to humans can also be found in other members of the animal kingdom. For instance, monkeys have a strong sense of justice, chimps are known for battle, while rats are altruistic and empathic. In a study published last week in Nature Communications, neuroscientist Christopher Petkov and his colleagues at Newcastle University discovered that macaques and humans share brain areas responsible for processing basic linguistic structures. [1]

Although some of the previously proposed reasons for our brain's uniqueness have been debunked, there are still numerous ways in which we differ. They have encoded in our genes as well as our ability to adapt to our surroundings. Two other studies, both recently published, add to the debate.

 

• Language: English
• Publisher: Stephen K. Marchant
• Release date: Aug 21, 2021
• ISBN: 9781915018021

Book preview

Introduction

The human brain is truly a masterpiece of creation!

The human brain is one-of-a-kind: our extraordinary cognitive ability has enabled us to invent the wheel, build the pyramids and land on the moon. Indeed, scientists have referred to the human brain as the crowning achievement of evolution.

But what exactly is it about our brains that makes them so unique? Some of the most persuasive arguments have been that our brains have more neurons and expend more energy than would be expected for our size. Asides this, our cerebral cortex, which is responsible for higher cognition, is disproportionately large—accounting for more than 80% of our total brain mass.

SuzanaHerculano-Houzel, a neuroscientist at Rio de Janeiro’s Institute of Biomedical Science, disproved these long-held beliefs in recent years when she discovered a novel method of counting neurons—dissolving brains into a homogeneous mixture, or brain soup. Using this technique, she found that the number of neurons relative to brain size is consistent with other primates and that the cerebral cortex, the region responsible for higher cognition, only contains about 20% of all neurons in our brain, a proportion similar to that found in other mammals. In light of these findings, she contends that the human brain is simply a linearly scaled-up primate brain that grow in size as we began to consume more calories due to the introduction of cooked food.

Other researchers have discovered that traits once thought to be unique to humans can also be found in other members of the animal kingdom. For instance, monkeys have a strong sense of justice, chimps are known for battle, while rats are altruistic and empathic. In a study published last week in Nature Communications, neuroscientist Christopher Petkov and his colleagues at Newcastle University discovered that macaques and humans share brain areas responsible for processing basic linguistic structures. [1]

Although some of the previously proposed reasons for our brain’s uniqueness have been debunked, there are still numerous ways in which we differ. They are encoded in our genes as well as our ability to adapt to our surroundings. Two other studies, both recently published, add to the debate.

Humans are genetically similar to other animals. We share more than 90% of our DNA with our closest relatives which include chimps, bonobos, and gorillas. Because mice and humans share many of the same genes, scientists use them as a model to study many human diseases. Recent research, however, has revealed that the way genes and the segments of DNA that code for specific proteins, are expressed in humans and other animals can differ significantly.

The rise of more robust data collection techniques is one reason scientists can now unravel these more nuanced differences between the human brain and those of other species. Scientists at the Allen Institute for Brain Science, for example, have created detailed atlases of the expression patterns of thousands of genes in various species including adult mouse and human brains. Researchers used these massive data sets in a study published last week in Nature Neuroscience to look for patterns of gene expression that are shared across the human population. They were able to find 32 distinct signatures among 20,000 genes that appear to be shared across 132 brain regions in six people (see a map here). This one-of-a-kind genetic code may help explain what gives rise to our distinctly human characteristics.

When the researchers compared humans to mice, they discovered that while genes associated with neurons were well preserved across species, those associated with glial cells (non-neuronal cells with a wide range of functions) were not. They also discovered that the gene patterns associated with glial overlap are those, associated with brain disorders such as Alzheimer’s disease. This research adds to the growing body of evidence that glial cells previously thought to be merely support cells for the brain, play an important role in both development and disease. It confirms the importance of these glial patterns in brain disease, says Michael Hawrylycz, the study’s first author and a computational biologist at the Allen Institute.

This discovery may have another significant implication: the capacity for plasticity; researchers have discovered that glia plays an important role in brain shaping. One interesting thing in the context [of the uniqueness of the human brain] is that you could imagine that one way to enhance the system would be, to make it more plastic—I’m speculating here, but [glia] could potentially be one route to do that, says senior author and Allen neuroscientist Ed Lein. However, we still need to conduct the analysis to determine whether this is unique to humans or widespread among primates.

Plasticity may be at the root of the specific differences in our brains that result in our unique cognitive abilities. According to a study published last week in the Proceedings of the National Academy of Sciences, human brains may be less genetically inheritable and thus more plastic than those of our closest ancestors, chimps.

Aida Gomez-Robles, an anthropologist at The George Washington University and her colleagues examined the impact of genes on brain size and organization in 218 human and 206 chimp brains. Although brain size was highly heritable in both species, they discovered that the organization of the cerebral cortex, particularly in areas involved in higher-order cognition functions, was much less genetically controlled in humans than in chimps. According to the researchers, one possible explanation for this difference is that because our brains are less developed than those of our primate cousins at birth, we have a longer period during which we can be shaped by our surroundings.

More research is needed, however, to pinpoint exactly where those differences exist. We still don’t know a lot about what humans have in common with great apes and other mammals, Gomez-Robles says. Understanding where we are and are not unique, will not only shed light on how we became the dominant species on the planet, but it will also help us better understand ourselves. Understanding the similarities and differences between humans and other species can also help scientists develop more effective therapies and treatments for disorders and diseases.

This book is designed to act as a primer to give you a fundamental understanding of how your brain works, how it develops and hep you understand just what makes it so special!

So, without further delays, let’s jump into the first chapter, shall we?

Part 1: Understanding the Anatomy of Your Brain

Chapter 1: What Is Your Brain?

What Is the Brain?

Brain Human Anatomy - Free vector graphic on Pixabay

The brain is a complex organ that regulates our body’s thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger, and every other process. The central nervous system or CNS comprises the brain and the spinal cord that extends from it.

What Is the Brain Made Of?

The average adult’s brain weighs about 3 pounds and is 60 percent fat. The remaining 40% is made up of water, protein, carbohydrates, and salts. The brain is not a muscle in and of itself. It is made up of blood vessels and nerves as well as neurons and glial cells.

What Is Gray and White Matter?

Gray matter and white matter are two distinct areas of the central nervous system. Gray matter refers to the darker, outer portion of the brain, whereas white matter refers to the lighter, inner section. This order is reversed in the spinal cord, with the white matter on the outside and gray matter on the inside.

Gray matter is mostly made up of neuron somas (round central cell bodies), whereas white matter is mostly made up of axons (long stems that connect neurons) wrapped in myelin (a protective coating). The two appear as separate shades on certain scans due to the different compositions of neuron parts.

Each region performs a distinct function. Gray matter is primarily in charge of processing and interpreting information, whereas white matter is in charge of transmitting that information to other parts of the nervous system.

How Does the Brain Function?

Throughout the body, the brain sends and receives chemical and electrical signals. Different signals control various processes and your brain interprets them all. Some, for example, make you tired while others make you feel pain.

Some messages are stored in the brain while others are transmitted to distant extremities via the spine and the body’s vast network of nerves. The central nervous system relies on billions of neurons to accomplish this (nerve cells).

The Brain’s Major Components and Their Functions

The brain is primarily divided into three parts: the cerebrum, the brainstem, and the Cerebellum.

Cerebrum

The cerebrum (front of the brain) is made up of gray matter (the cerebral cortex) and white matter at its center. The cerebrum, the largest part of the brain, initiates and coordinates movement and regulates temperature. Other parts of the cerebrum are responsible for speech, judgment, thinking and reasoning, problem-solving, emotions and learning. Other functions are associated with vision, hearing, touch and other senses.

Cerebral Cortex

Cortex is Latin for bark which refers to the cerebrum’s outer gray matter covering. Because of its folds, the cortex has a large surface area and accounts for roughly half of the brain’s weight.

The cerebral cortex is divided into two halves, which are known as hemispheres. It has ridges (gyri) and folds on it (sulci). The two halves come together at a large, deep sulcus (the interhemispheric fissure, also known as the medial longitudinal fissure) that runs from the front to the back of the head. The left half of the brain controls the left side of the body, while the right half controls the right side. The two halves communicate via the corpus callosum, a large C-shaped structure of white matter and nerve pathways. The corpus callosum is located in the cerebrum’s center.

Brainstem

The cerebrum is linked to the spinal cord by the brainstem (middle of the brain). The midbrain, pons and medulla are all part of the brainstem.

Midbrain.

The midbrain (or mesencephalon) is a highly complex structure that contains a variety of neuron clusters (nuclei and colliculi), neural pathways and other structures. These features aid in various functions, ranging from hearing and movement to calculating responses and detecting environmental changes. The substantia nigra, an area affected by Parkinson’s disease rich in dopamine neurons and part of the basal ganglia, which allows movement and coordination, is also located in the midbrain.

Pons

Four of the 12 cranial nerves originate in the pons, allowing for various activities such as tear production, chewing, blinking, focusing vision, balance, hearing and facial expression. The pons, named after the Latin word for bridge connects the midbrain and the medulla.

Medulla

The medulla is located at the bottom of the brainstem and connects the brain to the spinal cord. The medulla is critical for survival. Many bodily activities including heart rhythm, breathing, blood flow, oxygen and carbon dioxide levels are regulated by medulla functions. The medulla is responsible for reflexive actions such as sneezing, vomiting, coughing and swallowing.

The spinal cord runs from the bottom of the medulla to the bottom of the skull through a large opening. The spinal cord, supported by the vertebrae, transports messages to and from the brain and the rest of the body.

Cerebellum

The Cerebellum, also known as the little brain is a fist-sized portion of the brain located at the back of the head, below the temporal and occipital lobes, and above the brainstem. It, like the cerebral cortex, is divided into two halves. The outer portion is made up of neurons while the inner portion communicates with the cerebral cortex. Its purpose is to coordinate voluntary muscle movements and to keep posture, balance and equilibrium. New research is being conducted to investigate the Cerebellum’s roles in thought, emotions and social behavior, and its potential involvement in addiction, autism, and schizophrenia.

Meninges are the brain coverings

The brain and spinal cord are surrounded by three layers of protective covering called meninges.

The dura mater, the outermost layer, is thick and tough. It consists of two layers: The dura mater’s periosteal layer lines the inner dome of the skull (cranium) and the meningeal layer lies beneath it. The spaces between the layers allow veins and arteries to pass through, supplying blood flow to the brain.

The arachnoid mater is a thin layer of connective tissue that lacks nerves and blood vessels. The cerebrospinal fluid or CSF is found beneath the arachnoid mater. This fluid cushions the entire central nervous system (brain and spinal cord) and circulates around these structures continuously to remove impurities.

The pia mater is a thin membrane that hugs and contours the surface of the brain. The pia mater is densely packed with veins and arteries.

The Brain’s Lobes and What They Control

Each hemisphere (part of the cerebrum) of the brain is divided into four sections called lobes: frontal, parietal, temporal and occipital. Each lobe is in charge of a different set of functions.

The frontal lobe: The frontal lobe is the largest lobe of the brain, located in the front of the head and is involved in personality traits, decision-making and movement. Parts of the frontal lobe are usually involved in smell recognition. Broca’s area, which is associated with speech ability, is located in the frontal lobe.

The parietal lobe: The parietal lobe, located in the middle of the brain assists a person in identifying objects and understanding spatial relationships (where one’s body is compared to objects around the person). The parietal lobe is also involved in pain and touch perception in the body. Wernicke’s area is located in the parietal lobe and aids the brain in understanding spoken language.

The occipital lobe: The occipital lobe is the part of the brain in the back that is responsible for vision.

The temporal lobe: The temporal lobe is a part of the brain. The brain’s temporal lobes are involved in short-term memory, speech, musical rhythm and some degree of smell recognition. Structures with greater depth within the Mind Pituitary Gland is a type of pituitary gland.

The pituitary gland, also known as the master gland is a pea-sized structure located deep within the brain behind the bridge of the nose. The pituitary gland regulates the flow of hormones from the thyroid, adrenals, ovaries, testicles and the functions of other glands in the body. Through its stalk and blood supply, it receives chemical signals from the hypothalamus.

Hypothalamus

The hypothalamus, which is located above the pituitary gland, sends chemical messages to control its function. It controls hunger and thirst, regulates body temperature and plays a role in some aspects of memory and emotion.

Amygdala

Amygdala is a small, almond-shaped structure located beneath each half (hemisphere) of the brain. The amygdalae, which are part of the limbic system, regulate emotion and memory and are linked to the brain’s reward system, stress and the fight or flight response when someone perceives a threat.

The hippocampus is a curved seahorse-shaped organ located on the underside of each temporal lobe part of a larger structure known as the hippocampal formation. It aids memory, learning, navigation and spatial perception. It receives information from the cerebral cortex and is thought to be involved in Alzheimer’s disease.

The Pineal Gland

The pineal gland is located deep within the brain and is connected to the top of the third ventricle by a stalk. The pineal gland reacts to light and darkness by secreting melatonin, which regulates circadian rhythms and the sleep-wake cycle.

Cerebrospinal Fluid and Ventricles

There are four open areas in the brain with passageways connecting them. They also allow access to the central spinal canal and the area beneath the meninge’s arachnoid layer.

The ventricles produce cerebrospinal fluid (CSF), a watery fluid circulating in and around the ventricles, spinal cord and meninges. CSF envelops and cushions the spinal cord and brain, washes away waste and impurities, and transports nutrients.

The Brain’s Blood Supply

The vertebral arteries and the carotid arteries are two blood vessels that supply blood and oxygen to the brain.When you touch the area with your fingertips, you can feel your pulse in the external carotid arteries, which run up the sides of your neck. The internal carotid arteries branch into the skull and supply blood to the frontal lobes of the brain.

The vertebral arteries run from the spinal column into the skull, where they join at the brainstem to form the basilar artery, which supplies blood to the brain’s back half. The circle of Willis, a loop of blood vessels near the brain’s bottom that connects major arteries, circulates blood from the front to the back of the brain and allows the arterial systems to communicate with one another.

Cranial Nerves are the nerves that run through the skull.

The cranium (the dome of the skull) contains 12 nerves known as cranial