Development of the Human Brain

The mental processes and behaviors studied by psychology are directly controlled by the brain, one of the most complex systems in nature.


Key Takeaways

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A human brain is one of the most complex systems on earth.The brain needs to work together in order to function properly.The brain and spinal cord make up the central nervous system, which functions alongside the peripheral nervous system in regulating all bodily functions.


There are three major parts to the nervous system: 1.the brain 2. the spinal cord.Nervous system 3.Cerebral cord


By following the interaction between mental processes and behavior on a systemic level, psychology explains the mental processes and behaviors of individuals.Therefore, psychology is closely linked with the study of the brain.

The Structure of the Brain

Many stages of development take place in the developing brain. .With the development of a fetus, the grooves and folds in the neural tube deepen, giving rise to various layers of the cerebral cortex.There are three major parts to the human brain: the hindbrain, the midbrain, and the forebrain.


The embryonic brain consists of layers.


Hindbrain

Located in the brain's center, the hindbrain is the brain's best-protected part.The cerebellum, reticular formation, and brain stem are all responsible for some of the most basic autonomic function of the body, such as breathing and moving.Located in the brain stem are the pons and the medulla oblongata.According to evolutionary theory, all vertebrates possess the ancient hindbrain, though they may appear differently from species to species.

Midbrain

Among the parts of the brain stem are the midbrain.It consists of the hindbrain and forebrain.In order for sensory and motor information to travel between forebrain and spinal cord, the midbrain acts as a relay station for the central nervous system.

Forebrain

Located in the most anterior portion of the developing vertebrate brain, the forebrain possesses the most complex networks in the nervous system.The diencephalon and telencephalon are the major divisions of the frontal lobe.This lower part of the brain is called the diencephalon, which contains both the thalamus and hypothalamus (together they are known as the limbic system); the telencephalon is on top of the diencephalon and contains the cerebrum – the part of the brain that handles cognitive activities at the highest level.It is the large, complicated forebrain of the human brain that makes it unique amongst other vertebrate brains.


Lower-Level Structures

The brain’s lower-level structures consist of the brain stem, the spinal cord, and the cerebellum.


Learning Objectives

Outline the location and functions of the lower-level structures of the brain


Key Takeaways

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Below the cerebrum, the brain stem and spinal cord make up the lower-level structures of the brain.Other than the spinal cord, these structures are mostly found in the hindbrain, diencephalon (or interbrain), and midbrain.The lower dorsal structures of the brain are the oldest parts of the brain and have been around for most of its evolutionary history.Consequently, they are geared toward the most basic bodily functions that are necessary to survive.The more recent layers of the brain (the forebrain) are responsible for the higher-level cognitive functions, such as language and reasoning, that are not necessary for the survival of the body itself.

The Hindbrain

Some of the oldest and most primitive body functions are triggered by the hindbrain, which contains the medulla oblongata, the cerebellum, and the pons.We describe each of these structures below.

Medulla Oblongata

The medulla oblongata is situated at the transition zone between the brain and the spinal cord.Unlike the spinal cord, the cerebral cortex is the first part of the brain to be formally classified as such.Among its functions are respiratory, cardiovascular, and digestive.

Pons

In addition to connecting the medulla oblongata and the midbrain, the pons relays signals from the cerebellum to the forebrain.The respiratory and inhibitory control centers are located here.There is an attachment of the cerebellum to the dorsal side of the pons.

Cerebellum

There is a separate region of the brain called the cerebellum, which is located behind the medulla oblongata and pons.By controlling skeletal muscles, it coordinates smooth, graceful motions. It is connected to the rest of the brain by three stalks (called pedunculi).The cerebellum receives information about the body's position from our eyes, ears, muscles, and joints, a process called proprioception.Furthermore, it receives input from the cerebral cortex about where these parts should be.From the brain stem, the cerebellum sends motor impulses to the skeletal muscles to allow them to move.A cerebellum's primary function is to coordinate muscle movement.Nonetheless, it is also responsible for balance and posture, and it is helpful when we learn a new motor skill, such as playing an instrument or a sport.Recent research suggests that the cerebellum plays a role in emotional sensitivity as well as motor functions.


Human and shark brains: The shark brain diverged on the evolutionary tree from the human brain, but both still have the “old” structures of the hindbrain and midbrain dedicated to autonomic bodily processes.


The Midbrain

It is actually a part of the brain stem, as it lies between the hindbrain and forebrain.The spinal cord and hindbrain display the same basic functional composition.It is the cerebral cortex that transmits motor information to the central areas.Midbrain regions participating in sensory information circuits.As a result of its high density of dopaminergic neurons, the midbrain contains the substantia nigra, a part of the brain that is involved in reward, addiction, and movement.When the substantia nigra dies in Parkinson's disease, there is a deficit of dopamine.

The Diencephalon (“interbrain”)

During embryonic vertebrate development, the diencephalon gives rise to structure in the posterior forebrain.Diencephalons are located between the cerebrum and brain stem at the upper end of brain stems.This region houses the limbic system, which is considered the seat of emotions in the brain.The diencephalon is composed of four distinct parts: the thalamus, subthalamus, hypothalamus, and epithalamus.

Thalamus

As part of the limbic system, the thalamus plays a key role.A gray lobe extends along each side of the cerebral cortex.Almost all sensory information passes through the thalamus, which then transmits it to the cerebral cortex (which is in the forebrain).An injury or stimulation of the thalamus results in a change in emotional reactivity.It is important to note, however, that this structure's impact on regulating emotional behavior is not exactly due to its own activity, but rather to the connections it forms with other limbic-system structures.


Limbic system, brain stem, and spinal cord: An image of the brain showing the limbic system in relation to the brain stem and spinal cord.


Hypothalamus

Hypothalamus is situated just below the thalamus in the brain.Hypothalamic lesions impair motivated behaviors such as sexuality, combativeness, and hunger.As mentioned previously, the hypothalamus can play a role in emotions: parts of it can induce pleasure and anger, while others can cause aversion, displeasure, and uncontrollable laughter.A stimulus triggers feelings (in this case, fear) when the hypothalamus sends signals to the limbic system in response to the stimulus (for example, a dangerous stimulus).


Hypothalamus: An image of the brain showing the location of the hypothalamus.


The Spinal Cord

An extension of the spine that resembles a tail is the spinal cord.About 30 g makes up the weight of the adult spinal cord.This structure is located on the underside of the medulla oblongata, and is organized to perform four distinct functions:


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Key Takeaways

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Cortex

A mammal's brain is covered in a gray layer of wrinkly tissue called the cerebral cortex.In spite of its thinness, the cortex is responsible for all sensation, perception, memory, association, thought, and voluntary physical actions.The cerebral cortex is known as the brain's ultimate control and information processing center. Cortex neurons have many inputs, making them function like mini microprocessors or logic gates.Glia give nutrition and myelin to neurons, and absorb ions and neurotransmitters.(The parietal, occipital, temporal, and frontal lobes) are separate parts of the cortex, each with a specific function.


Brain lobes: A diagram showing the individual lobes color-coded.


Wrinkles appear on the cortex. .It has been suggested that brain size correlates positively with intelligence; however, it has also been suggested that surface area of cortex (that is, "wrinkly" appearance of the brain) correlates most directly with intelligence.Both may be true, though their degree of correlation is not clear. "Valleys" between wrinkles are called sulci (or sometimes fissures); "peaks" between wrinkles are called gyri.The brain has been studied enough to identify patterns in sulci and gyri, although there are variations from person to person.Sulcuses are visible in many places in the brain, including the central sulcus, or the wrinkle separating the frontal lobe and the parietal lobe.


Sulci and gyri: As depicted in this diagram of brain structures, sulci are the “valleys” and gyri are the “peaks” in the folds of the brain.


Cerebrum

Underneath the cerebral cortex is the cerebrum, which is responsible for the brain's main control and thought mechanisms.Higher-level thought and decisions occur in the brain (instead of lower-level functions like balance and movement). Grey matter is found in the cerebrum, as well as white matter.


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Grey matter and white matter: A sagittal cross-section of a human brain showing the distinct layers of grey matter (the darker outer layer) and white matter (the lighter inner layer) in the cerebrum.


Key Takeaways

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Brain Lateralization

Two halves of the brain, called hemispheres, are present.There is evidence that each brain hemisphere has distinct functions, an idea known as lateralization.Speech, language comprehension, and logical reasoning seem to be primarily left-hemisphere functions, while the right hemisphere is more likely to be involved in spatial tasks like vision-independent object recognition (such as identifying objects perceptually or by touch).Despite this, it is easy to exaggerate the difference between left and right hemispheres. Both brain hemispheres are involved in the majority of processes.Neuroplasticity (the capacity of a brain to adapt to experience) enables the brain to compensate for damage to one hemisphere by taking on additional functions in the other half, especially in young brains.

Corpus Callosum

In both cerebral hemispheres, communication is facilitated by the corpus callosum. .The corpus callosum is sometimes implicated in seizures. Patients with epilepsy may undergo a corpus callostomy, or removal of the corpus callosum.

The Lobes of the Brain

The brain is separated into four lobes: the frontal, temporal, occipital, and parietal lobes.


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The brain has four lobes, and each one is associated with a particular type of mental function.


The Frontal Lobe

A frontal lobe is associated with motor skills and executive functions.Among humans' highest-level cognitive functions are executive functions.For example, It is believed that the frontal lobe is the brain's moral center, since it is responsible for advanced decision-making.A limbic system-derived memory plays a role in retaining emotional memories, and modifying those memories to fit socially acceptable norms.

The Temporal Lobe

Memory related to the temporal lobe occurs on both a short-term and long-term basis.Sensory input is processed, including auditory information, language understanding, and naming.Also, it regulates the biological functions of aggression and sexuality. Hippocampus is found in the temporal lobe.Hippocampus plays a key role in the formation of emotion-laden, long-term memories based on the amygdala's input.It houses the primary auditory cortex, which is important for processing semantic information in speech. The Wernicke's area of the temporal lobe plays a key role in speech comprehension.Broca's area, on the other hand, serves to produce (rather than understand) speech.Those with Wernicke's area damage can speak clearly, but their words are unclear, and patients with Broca's area damage will have slow speech and slurred speech.Wernicke's and Broca's aphasia are two types of aphasia; aphasia means inability to speak.


The Broca's and Wernicke's areas are situated in the brain.The Broca's area is at the back of the frontal lobe, and the Wernicke's area falls roughly between the temporal lobe and the parietal lobe.


The Occipital Lobe

Located in the occipital lobe, the visual cortex is the visual processing center of the brain.A spatial map of the retinal field can be found on the posterior side of the occipital lobe.It receives sensory data from the retina of the eyes through the optic tracts, which then go to the visual cortex.Occipital lobes are also used for other visual tasks, such as color perception and visual perception of motion.Blindness can occur when lesions on the surface of the visual cortex (located on the surface of the posterior occipital lobe) damage the visual map on the surface of the cortex.

The Parietal Lobe

Sensory abilities are facilitated by the parietal lobe.It integrates sensory information and is important for spatial perception and navigation.It is crucial to the integration of sensory information from the body, understanding of numbers and their relationships, as well as manipulating objects, that the parietal lobe plays an important role.Furthermore, it is also associated with processing information concerning touch. There is a memory center in the temporal lobe, the hippocampus.An emotional input from the amygdala plays a key role in the formation of emotion-laden long-term memories in the hippocampus.It contains the primary auditory cortex, which is responsible for interpreting the semantics of speech.


The Limbic System

The limbic system combines higher mental functions and primitive emotion into one system.


Key Takeaways

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There is a complex group of structures within the limbic system on the central underside of the cerebrum, which is composed of the inner portions of the temporal and the frontal lobes.This system combines higher mental functions with primitive emotion, which is often called the emotional nervous system.Additionally, it plays a crucial role in some higher mental functions, such as learning and memory.Due to the limbic system, physical things like eating are so pleasurable to us, and even some medical conditions, like high blood pressure, are due to mental stress.In the limbic system, there are several important structures, including the amygdala, hippocampus, thalamus, hypothalamus, basal ganglia, and cingulate gyrus.


The limbic system: All the components of the limbic system work together to regulate some of the brain’s most important processes.


The Amygdala

One amygdala is located in the left and one in the right temporal lobe.The amygdala is the emotional center of the brain, which helps individuals to evaluate the emotional significance of events (e.g., happy, sad, scary).Increasing the heart rate and breathing rate helps the brain recognize potential threats and prepares the body for fight-or-flight reactions.In addition, the amygdala is responsible for learning based on reward or punishment.


The amygdala: The figure shows the location of the amygdala from the underside (ventral view) of the human brain, with the front of the brain at the top of the image.


Located close to the hippocampus, the amygdala plays a key role in the consolidation of memory, especially emotional memories.Ultimately, the strength of one's memory is influenced by the emotional arousal a person undergoes after learning something, so greater emotional arousal after learning something enhances memory retention.The results of an experiment found that administering stress hormones to individuals immediately after they learn something improves their memory retention two weeks later.

The Hippocampus

.It is composed of two horns that curve outward from the amygdala.There is disagreement among psychologists and neuroscientists about the precise role of the hippocampus, but both agree that it plays an essential role in forming new memories about past events.The hippocampus is considered to be in charge of general declarative memory (memories that have a specific form, such as facts or episodic memories). A damaged hippocampus results in challenging memories (anterograde amnesia), but may also impair access to past memories (retrograde amnesia).In some cases, the old memories remain intact even though the retrograde effect normally takes place some years before the damage to the brain; this suggests that over time the hippocampus gains less importance in storing memories.


Hippocampus: This image shows the horned hippocampus deep within the temporal lobe.


The Thalamus and Hypothalamus

Changes in emotional reactivity are related to both the thalamus and hypothalamus.Because of its connections with other limbic-system structures, the thalamus is primarily important as a sensory gateway for the rest of the brain.On both sides of the third ventricle, the hypothalamus is a small part of the brain located just below the thalamus.Many unconscious functions (such as breathing and metabolism) and some so-called motivated behaviors, like sexual activity, combativeness, and hunger, can be altered by a hypothalamic injury.In the lateral part of the hypothalamus, it appears to represent enjoyment and rage, while in the medial part, it appears to represent displeasure, aversion, and a tendency for uncontrollable and loud laughter.

The Cingulate Gyrus

Cingulate gyrus is located next to the corpus callosum on the medial side of the brain.Despite the fact that there is much to be learned about this gyrus, its frontal part appears to be linked with past pleasant memories.Moreover, it regulates aggressive behavior and our emotional reaction to pain.

The Basal Ganglia

The basal ganglia are nuclei deep in the frontal lobes that orchestrate motor behavior.In the basal ganglia are the caudate, putamen, and globus pallidus.Physical movements are inhibited by the basal ganglia until they are fully appropriate for the environment in which they are to be performed.Basal ganglia also play a role in:


Neuroplasticity

Neuroplasticity is the brain’s ability to create new neural pathways to account for learning and acquisition of new experiences.


Key Takeaways

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Neuroplasticity

The brain is constantly adapting throughout a lifetime, though sometimes over critical, genetically determined periods of time. Neuroplasticity is the brain’s ability to create new neural pathways based on new experiences. It refers to changes in neural pathways and synapses that result from changes in behavior, environmental and neural processes, and changes resulting from bodily injury. Neuroplasticity has replaced the formerly held theory that the brain is a physiologically static organ, and explores how the brain changes throughout life.

Neuroplasticity occurs on a variety of levels, ranging from minute cellular changes resulting from learning to large-scale cortical remapping in response to injury. The role of neuroplasticity is widely recognized in healthy development, learning, memory, and recovery from brain damage. During most of the 20th century, the consensus among neuroscientists was that brain structure is relatively immutable after a critical period during early childhood. It is true that the brain is especially ” plastic ” during childhood’s critical period, with new neural connections forming constantly. However, recent findings show that many aspects of the brain remain plastic even into adulthood.

Plasticity can be demonstrated over the course of virtually any form of learning. For one to remember an experience, the circuitry of the brain must change. Learning takes place when there is either a change in the internal structure of neurons or a heightened number of synapses between neurons. Studies conducted using rats illustrate how the brain changes in response to experience: rats who lived in more enriched environments had larger neurons, more DNA and RNA, heavier cerebral cortices, and larger synapses compared to rats who lived in sparse environments.

A surprising consequence of neuroplasticity is that the brain activity associated with a given function can move to a different location; this can result from normal experience, and also occurs in the process of recovery from brain injury. In fact, neuroplasticity is the basis of goal-directed experiential therapeutic programs in rehabilitation after brain injury. For example, after a person is blinded in one eye, the part of the brain associated with processing input from that eye doesn’t simply sit idle; it takes on new functions, perhaps processing visual input from the remaining eye or doing something else entirely. This is because while certain parts of the brain have a typical function, the brain can be “rewired”—all because of plasticity.

Synaptic Pruning

“Synaptic (or neuronal or axon ) pruning” refers to neurological regulatory processes that facilitate changes in neural structure by reducing the overall number of neurons and synapses, leaving more efficient synaptic configurations. At birth, there are approximately 2,500 synapses in the cerebral cortex of a human baby. By three years old, the cerebral cortex has about 15,000 synapses. Since the infant brain has such a large capacity for growth, it must eventually be pruned down to remove unnecessary neuronal structures from the brain. This process of pruning is referred to as apoptosis, or programmed cell death. As the human brain develops, the need for more complex neuronal associations becomes much more pertinent, and simpler associations formed at childhood are replaced by more intricately interconnected structures.

Pruning removes axons from synaptic connections that are not functionally appropriate. This process strengthens important connections and eliminates weaker ones, creating more effective neural communication. Generally, the number of neurons in the cerebral cortex increases until adolescence. Apoptosis occurs during early childhood and adolescence, after which there is a decrease in the number of synapses. Approximately 50% of neurons present at birth do not survive until adulthood. The selection of the pruned neurons follows the “use it or lose it” principle, meaning that synapses that are frequently used have strong connections, while the rarely used synapses are eliminated.


Neuron growth: Neurons grow throughout adolescence and then are pruned down based on the connections that get the most use.


Synaptic pruning is distinct from the regressive events seen during older age. While developmental pruning is experience-dependent, the deteriorating connections that occur with old age are not. Synaptic pruning is like carving a statue: getting the unformed stone into its best form. Once the statue is complete, the weather will begin to erode the statue, which represents the lost connections that occur with old age.