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CHAPTER 4: Anatomy and Research Methods Subtopic 1: Structures of vertebrate nervous system 1.1: Terminology to Describe the Nervous System The central nervous system consists of the brain and spinal cord. The peripheral nervous system is the nerves outside the brain and spinal cord Part of the PNS...
CHAPTER 4: Anatomy and Research Methods Subtopic 1: Structures of vertebrate nervous system 1.1: Terminology to Describe the Nervous System The central nervous system consists of the brain and spinal cord. The peripheral nervous system is the nerves outside the brain and spinal cord Part of the PNS is the somatic nervous system, which consists of the axons conveying messages from the sense organs to the CNS and from the CNS to the muscles. Another part of the PNS, the autonomic nervous system, controls the heart, intestines, and other organs. The autonomic nervous system has some of its cell bodies within the brain or spinal cord and some in clusters along the sides of the spinal cord. Anatomical directional terms are used to describe the location of structures or regions of the body relative to other parts. Here are the main anatomical terms: 1. Superior and Inferior Superior (cranial or cephalic): Toward the head or upper part of a structure; above. Inferior (caudal): Away from the head or toward the lower part of a structure; below. 4. Proximal and Distal Proximal: Closer to the origin of the body part or the point of attachment of a limb to the body trunk. Distal: Farther from the origin of a body part or the point of attachment of a limb to the body trunk. 2. Anterior and Posterior Anterior (ventral): Toward the front of the body; in front of. Posterior (dorsal): Toward the back of the body; behind. 5. Superficial and Deep Superficial (external): Toward or at the body surface. Deep (internal): Away from the body surface; more internal. 3. Medial, Lateral, and Intermediate Medial: Toward the midline of the body; on the inner side. Lateral: Away from the midline of the body; on the outer side. Intermediate: Between a more medial and a more lateral structure. 6. Ipsilateral and Contralateral Lumbar (L1-L5): Controls signals to the lower back, hips, and parts of the legs. Ipsilateral: On the same side of the Sacral (S1-S5): Controls signals to the body. thighs, lower legs, feet, and parts of the Contralateral: On the opposite side pelvic organs. of the body. 31 Pairs of Spinal Nerves: Each segment gives rise to a pair of spinal nerves that exit the spinal cord and innervate specific body regions. The spinal cord is the part of the CNS within the spinal column. The spinal cord communicates with all the sense organs and muscles except those of the head. It is a segmented 1. Gray Matter and White Matter: structure, and each segment has on both the left and Gray Matter: located in the center of the right sides a sensory nerve and a motor nerve. spinal cord, arranged in a “H” or butterfly The spinal cord is a vital part of the central shape, containing neural cell bodies, nervous system (CNS), acting as a dendrites, and synapses. communication highway between the brain and the White Matter: surrounds the gray matter, rest of the body. consisting of myelinated axons that carry nerve impulses to and from the brain (ascending sensory tracts and descending Anatomy of the Spinal Cord motor tracts). Location: The spinal cord is housed within the 2. Spinal Cord Tracts: vertebral column(spine), extending from the Ascending Tracts: Carry sensory brainstem (medulla oblongata) at the base of the information from the body to the brain (e.g., skull to approximately the level of the first and the spinothalamic tract for pain and second lumbar vertebra (L1 or L2) in adults. temperature, the dorsal columns for Length and Width: It is about 42-45 cm long in proprioception and fine touch). adult and has diameter of about 1-1.5 cm, tapering Descending Tracts: Carry motor commands as it descends. form the brain to the body (e.g., the corticospinal tract for voluntary movement). Structure of the Spinal Cord 1. Regions and Segments: The spinal cord is divided into four regions: Cervical (C1-C8): Controls signals to the neck, shoulders, arms, and hands. Thoracic (T1-T12): Controls signals to the chest muscles, some abdominal muscles, and parts of the back. Function of the Spinal Cord Transmission of Nerve Signals: o The spinal cord serves as a conduit for sensory signals from the peripheral nerves to the brain and for motor signals from the brain to the peripheral nerves, facilitating conscious sensation and voluntary movement. Reflex Actions: o The spinal cord is responsible for coordinating reflexes, which are involuntary and automatic responses to stimuli. Reflexes occur at the level of the spinal cord without involving the brain, allowing for quick reactions (e.g., the patellar reflex or withdrawal reflex). Integration of Motor Activity: o The spinal cord integrates and processes some neural inputs locally, modulating sensory and motor pathways to provide coordination and balance during movement. 1.3: The Autonomic Nervous System The autonomic nervous system consists of neurons that receive information from and send commands to the heart, intestines, and other organs. Its two parts are the sympathetic and parasympathetic nervous systems Sympathetic Nervous System (SNS) Often referred to as the "fight or flight" system, the sympathetic nervous system prepares the body for stressful or emergency situations. Key Functions: o Increases heart rate and force of contraction. o Dilates the bronchioles in the lungs to increase airflow. o Dilates pupils to enhance vision. o Inhibits digestive processes. o Sympathetic stimulation inhibits digestive activities, diverting energy o Stimulates the release of glucose and blood flow away from the from the liver for energy. digestive organs. o Constricts blood vessels in non- o Parasympathetic stimulation essential areas (e.g., skin and promotes digestion and absorption of digestive organs) and dilates vessels nutrients by increasing peristalsis in muscles. and secretion of digestive enzymes. Parasympathetic Nervous System (PNS) Often referred to as the "rest and digest" system, the parasympathetic nervous system conserves energy and promotes maintenance activities during restful states. Key Functions: o Decreases heart rate. o Constricts bronchioles in the lungs. o Constricts pupils. o Stimulates digestion and absorption of nutrients. o Promotes bladder contraction and defecation. 1.4: The Hindbrain o Stimulates saliva production. The hindbrain, also known as the “rhombencephalon”, is one of the three major divisions of the brain, along with the midbrain (mesencephalon) and forebrain Functions of the Autonomic Nervous System (prosencephalon). The hindbrain is located at the 1. Cardiovascular Regulation: lower back part of the brain, sitting above the spinal cord, and is responsible for regulating many o Sympathetic activation increases essential life- sustaining functions, including heart rate and breathing, heart rate, and balance. contractility, promoting blood flow to essential organs (heart, muscles). o Parasympathetic activation decreases heart rate and conserves energy during restful states. 2. Respiratory Control: o Sympathetic stimulation dilates the bronchioles to improve airflow. o Parasympathetic stimulation constricts bronchioles when resting. 3. Digestive and Metabolic Functions: Anatomy of the Hindbrain Myelencephalon (Major Structures) Medulla Oblongata: The hindbrain is divided into two main parts: The medulla oblongata is the lowest part of the metencephalon and the myelencephalon. the brainstem, continuous with the spinal cord. Functions: Metencephalon o Regulates vital autonomic functions Pons: such as heart rate, blood pressure, The pons is located above the medulla and respiration. oblongata and below the midbrain, forming o Contains centers that control reflex a bridge between different parts of the actions like coughing, sneezing nervous system, including the cerebrum and swallowing and vomiting. cerebellum. o Acts as conduit fir ascending and Functions: descending natural pathways o Serves as a relay station for between the brain and spinal cord. transmitting signals between the o Includes several cranial nerve nuclei cerebrum (forebrain) and the that contribute to sensory and motor cerebellum. functions. o Plays a role in regulating sleep, breathing, and arousal. 1.5: The Midbrain o Contains nuclei that are involved in controlling facial expressions, The midbrain, also known as the chewing, swallowing, and hearing. “mesencephalon", is the middle part of the brainstem, located between the forebrain (diencephalon) and the hindbrain (pons and medulla Cerebellum: oblongata). The midbrain is relatively small compared to other brain regions but plays a crucial The cerebellum is a large, cauliflower- role in a variety of important functions. including shaped structure located at the back of the motor control, auditory and visual processing, brain, just below the occipital lobes. arousal, and the regulation of certain autonomic Functions: functions. o Coordinates voluntary movements, such as posture, balance, and coordination. o Ensures smooth, precise movements by integrating sensory information from the spinal cord and brain. o Involved in motor learning, such as learning to ride a bicycle or play an instrument. o Plays a role in cognitive functions like attention and language. Midbrain Major Structures Tectum ("Roof"): The dorsal part of the midbrain located posteriorly. Key Components: Superior Colliculi: Involved in visual processing and reflexes, such as coordinating head and eye movements in response to visual stimuli. Inferior Colliculi: Involved in auditory processing and reflexes, such as the startle reflex in response to loud sounds. Tegmentum ("Floor"): 1.6: The Forebrain The ventral part of the midbrain located anteriorly. The forebrain, also known as the Key Components: "prosencephalon", is the largest and most complex Red Nucleus: Involved in motor part of the brain. It is responsible for a wide range coordination, particularly in controlling limb of higher cognitive functions, sensory processing, movements. voluntary movement, emotional responses, and Periaqueductal Gray (PAG): Surrounds autonomic control. The forebrain is divided into the cerebral aqueduct and is involved in pain two major regions: the diencephalon and the modulation, defensive behaviors, and the telencephalon. autonomic regulation of heart rate and blood pressure. Reticular Formation: Extends through the midbrain and plays a critical role in regulating arousal, consciousness, and the sleep-wake cycle. Substantia Nigra: gives rise to a dopamine- containing pathway that facilitates readiness for movement Divided into two parts: Pars Compacta: Contains dopaminergic neurons that project to the basal ganglia Anatomy of the Forebrain (striatum) and play a key role in regulating voluntary motor control. Degeneration of The diencephalon is located deep within the brain, these neurons is a hallmark of Parkinson's just above the midbrain and below the cerebral disease. hemispheres. It consists of the following key Pars Reticulata: Involved in regulating eye structures: movements and motor control. Two major regions of the Forebrain: Diencephalon and Telencephalon Thalamus: The thalamus is a large, dual-lobed mass of gray matter located at the center of the brain. Functions: o Acts as a major relay station for sensory information (except for smell) coming from the body and sending it to the appropriate areas of the cerebral cortex. Thalamus: Involved in the regulation of consciousness, sleep, and alertness. o Involved in the regulation of consciousness, sleep, and alertness. Hypothalamus: Involved in emotional regulation, sexual behavior, and aggression. o Plays a role in motor control by relaying signals between the cerebellum, basal ganglia, and motor Telencephalon as region of the forebrain cortex. The telencephalon, also known as the cerebrum, is Hypothalamus: the largest part of the brain. It consists of the A small but crucial structure located below cerebral cortex, the basal ganglia, and the limbic the thalamus. system. Functions: 1. Cerebral Cortex: o Maintains homeostasis by regulating The cerebral cortex is the outermost layer of the autonomic functions such as hunger, brain, composed of gray matter and characterized thirst, body temperature, and by its folds (gyri) and grooves (sulci). circadian rhythms. It is divided into two hemispheres (left and right) o Controls the release of hormones and four major lobes: from the pituitary gland, influencing Frontal Lobe: growth, metabolism, reproduction, and stress responses. Located at the front of the brain, responsible for higher cognitive functions such as o Involved in emotional regulation, reasoning, problem-solving, planning, and sexual behavior, and aggression. decision- making. Epithalamus: Contains the primary motor cortex (in the Contains the pineal gland, which secretes precentral gyrus), which controls voluntary melatonin, a hormone that regulates sleep- movements. wake cycles. Includes the prefrontal cortex, involved in Plays a role in the regulation of circadian personality, behavior, and social rhythms and reproductive functions. interactions. Parietal Lobe: Subthalamus: Located beneath the thalamus, involved in Located behind the frontal lobe, responsible regulating movements, particularly those for processing sensory information such as associated with the basal ganglia. touch, temperature, pain, and spatial orientation. Contains the primary somatosensory cortex (in the postcentral gyrus), which receives sensory input from Telencephalon as region of the forebrain the body. 2. Basal Ganglia: Temporal Lobe: A group of nuclei located deep within the Located beneath the frontal and parietal cerebral hemispheres, including the caudate lobes, responsible for processing auditory nucleus, putamen, globus pallidus, information, language comprehension, and substantia nigra, and subthalamic nucleus. memory formation. Contains the primary auditory cortex and Functions: Wernicke's area (important for language 1. Involved in regulating voluntary motor comprehension). control, procedural learning, habit formation, and Occipital Lobe: reward processing. Located at the back of the brain, primarily 2. Plays a critical role in coordinating responsible for processing visual smooth and purposeful movements by modulating information. motor commands from the cerebral cortex. Contains the primary visual cortex, which 3. Dysfunction of the basal ganglia is interprets visual stimuli. associated with movement disorders such as Parkinson's disease and Huntington's disease. Lobes of the brain 3. Limbic System: The brain's hemispheres have four lobes. A complex network of structures located on both sides of the thalamus, just beneath the cerebrum. The frontal lobes help control Key components include the hippocampus, thinking, planning, organizing, amygdala, cingulate gyrus, fornix, and parts of the problem-solving, short-term hypothalamus. memory and movement. The parietal lobes help interpret Functions: feeling, known as sensory 1. Regulates emotions, including fear, pleasure, and information. The lobes process aggression. taste, texture and temperature. The occipital lobes process images 2. Plays a vital role in the formation and retrieval of from your eyes and connect them memories, particularly spatial and declarative to the images stored in your memory. memory. This allows you to recognize images. 3. Involved in motivation, learning, and olfactory The temporal lobes help process processing (sense of smell). information from your senses of Thalamus: Involved in the regulation of smell, taste and sound. They also consciousness, sleep, and alertness. play a role in memory storage. Hypothalamus: Involved in emotional regulation, sexual behavior, and aggression. Hippocampus: sends memories to be stored in areas of the cerebrum. It then recalls the memories later. Amygdala: part of the circuit that is most central for evaluating emotional information, especially fear. 1.7: The Ventricles The brain's cerebral cortex is divided into four major lobes, each with distinct functions The ventricles are a set of interconnected, fluid- related to sensory processing, movement, cognition, filled cavities within the brain. They are an essential and emotion. These lobes are the frontal lobe, part of the central nervous system (CNS) and play a parietal lobe, temporal lobe, and occipital lobe. crucial role in producing, circulating, and storing cerebrospinal fluid (CSF), which provides cushioning and support to the brain and spinal cord, as well as helping to maintain 1. Frontal Lobe homeostasis within the brain. It is also responsible Location: The frontal lobe is located at the for removing waste and delivering nutrients to your front of the brain, behind the forehead. brain. Functions: Motor Control: Contains the primary motor cortex (located in the precentral gyrus), which is responsible for the voluntary movement of muscles. It sends signals to the muscles of the body to produce movement. Executive Functions: Involves the prefrontal cortex, which is responsible for higher cognitive functions such as decision- Why is CSF important? making, planning, problem-solving, reasoning, and impulse control. It is crucial Cerebrospinal fluid is made by tissue that lines the for personality, behavior, and social ventricles (hollow spaces) in the brain. It flows in interactions. and around the brain and spinal cord to help cushion them from injury and provide nutrients. Speech Production: Houses Broca's area (typically in the left hemisphere), which is essential for speech production and language Subtopic 2: The Cerebral Cortex processing. Damage to Broca's area can result in Broca's aphasia, characterized by The brain's cerebral cortex is divided into four difficulty speaking but with preserved major lobes, each with distinct functions related to comprehension. sensory processing, movement, cognition, and emotion. These lobes are the frontal lobe, parietal Emotional Regulation: Involved in lobe, temporal lobe, and occipital lobe. regulating emotions and social behavior, including the expression of personality traits. Working Memory: Plays a key role in maintaining and manipulating information over short periods (short-term memory). Clinical Relevance: Damage to the frontal lobe can lead to changes in personality, impaired judgment, loss of motor skills, difficulty in planning and organizing, and problems with speech and language. 2. Parietal Lobe 3. Temporal Lobe Location: The parietal lobe is located Location: The temporal lobe is located on behind the frontal lobe, at the the sides of the brain, near the temples, upper middle part of the brain. beneath the lateral fissure. Functions: Functions: o Sensory Processing: Contains the o Auditory Processing: Contains the primary somatosensory cortex primary auditory cortex, which is (located in the postcentral gyrus), responsible for processing sound which receives and processes information. It helps with the sensory information from the body, perception and interpretation of such as touch, temperature, sounds, including language. pain, and proprioception (the sense of body position). o Language Comprehension: Houses Wernicke's area (typically in the left o Spatial Awareness: Involved in hemisphere), which is critical for the spatial orientation and navigation. comprehension of spoken and The parietal lobe helps us understand written language. Damage to where objects are in relation to our Wernicke's area can result in body and enables coordination of Wernicke's aphasia, characterized by movements in response to sensory fluent but nonsensical speech and input. poor understanding of language. o Integration of Sensory o Memory Formation: The temporal Information: Integrates sensory lobe includes the hippocampus, information from various parts of the which is crucial for the formation body to create a unified perception of and retrieval of long-term memories, the world. It plays a role in the particularly episodic and declarative recognition of objects, shapes, and memories. faces. o Emotional Regulation: Contains the o Mathematical and Analytical amygdala, which is involved in the Abilities: Contributes to numerical processing of emotions, particularly processing, calculation, and fear and pleasure responses. It plays reasoning. a key role in emotional memory and social behavior. Clinical Relevance: Damage to the parietal lobe can cause issues such as loss of o Recognition of Objects and sensation, difficulty with spatial orientation, Faces: Involved in the recognition of problems with coordination and balance, and objects, faces, and complex visual disorders like hemianopia (loss of vision in stimuli (this function is also partly half of the visual field), Gerstmann shared with the occipital lobe). syndrome, and neglect syndrome (where a person ignores one side of their body or Clinical Relevance: Damage to the visual field). temporal lobe can lead to problems with memory, language comprehension, auditory processing, and emotional regulation. It can also cause visual and auditory hallucinations and is often implicated in conditions like epilepsy, especially temporal lobe epilepsy. 4. Occipital Lobe o Example: When you see an apple, the occipital lobe processes the shape Location: The occipital lobe is located at and color, while the temporal lobe the back of the brain, behind the parietal and identifies it as an apple, and the temporal lobes. parietal lobe helps determine where Functions: it is in space relative to you. o Visual Processing: Contains the primary visual cortex (V1), which is Auditory Information: Sound signals responsible for processing visual detected by the ears are processed in the information received from the eyes. primary auditory cortex in the temporal lobe. It interprets aspects like color, light, This region interprets sound frequency, movement, and depth. pitch, and intensity and sends the o Visual Perception: Involved in the information to other brain areas for further higher-level processing of visual processing (e.g., linking sounds with information, such as recognizing memory or speech). shapes, patterns, and objects. o Example: When you hear a friend o Visual Association: The occipital calling your name, the temporal lobe lobe also sends processed visual processes the sound, and the frontal information to other parts of the lobe helps decide whether to turn brain (like the parietal and temporal toward the sound and respond. lobes) for further interpretation, including recognizing faces (temporal lobe) and spatial location Movement and Motor Control (parietal lobe). Motor Planning and Execution: The Clinical Relevance: Damage to the occipital frontal lobe, particularly the primary motor lobe can lead to various visual disturbances, cortex, initiates voluntary movements by such as cortical blindness (total or partial sending signals to the muscles. The frontal loss of vision despite healthy eyes), visual lobe works closely with other areas, such as agnosia (inability to recognize objects or the basal ganglia and cerebellum, to fine- faces), and hemianopia (loss of vision in one tune and coordinate movements. half of the visual field). o Example: When you decide to pick up a pen, the frontal lobe plans the movement, the motor cortex sends Subtopic 2.5: How dop the parts work together? signals to your arm and hand Intergeneration of function across the brain’s muscles, and the cerebellum ensures lobes the movement is smooth and coordinated. Sensory Processing and Perception Integration of Sensory Feedback: During Visual Information: Visual signals detected movement, sensory feedback from the by the eyes are sent to the occipital lobe, parietal lobe (regarding position and where the primary movement of the limbs) is continuously visual cortex processes basic visual integrated with motor commands from the information, such as edges, color, and frontal lobe to adjust and refine movements movement. This processed information is in real time. then sent to the parietal lobe to help understand spatial orientation and to the o Example: When catching a ball, temporal lobe to recognize objects and faces. sensory input about the ball's position, speed, and your hand's position is integrated to adjust the Attention and Multitasking: The parietal movement for a successful catch. lobe and frontal lobe work together to focus attention and switch Language and Communication between tasks. The parietal lobe helps filter Speech Production and sensory information to maintain focus, while Comprehension: Broca's area in the frontal the frontal lobe lobe is involved in speech production, while directs attention to the task at hand. Wernicke's area in the temporal lobe is o Example: While driving, the parietal crucial for understanding language. These lobe processes visual and spatial areas communicate through neural information (like the location of pathways to enable coherent speechand other cars), while the frontal lobe language comprehension. helps decide when to change lanes or o Example: When you hear someone apply the brakes. speak, Wernicke's area helps you o understand the words, while Broca's area helps you form a response. The Emotional Regulation and Social Behavior frontal and temporal lobes coordinate to ensure appropriate language use. Emotion and Social Behavior: The frontal lobe (prefrontal cortex) interacts with the Memory and Learning temporal lobe (amygdala) to regulate emotions and guide social behavior. The Formation and Retrieval of frontal lobe modulates emotional responses Memories: The temporal lobe (especially and ensures that behavior is socially the hippocampus) plays a critical role in appropriate. forming new memories and retrieving them when needed. The frontal lobe is involved in o Example: When feeling angry working memory (holding and manipulating during a disagreement, the amygdala information over short periods) and planning may trigger an immediate emotional based on past experiences. reaction, but the prefrontal cortex helps regulate the response, o Example: When trying to recall a promoting a calm and rational fact for an exam, the frontal lobe discussion. helps you focus and retrieve the information stored in the temporal lobe. Subtopic 3: Research Methods Cognitive Functions and Decision-Making Subtopic 3.1: Effects of Executive Functions: The frontal lobe is Brain Damage responsible for complex cognitive functions, such as decision- making, problem-solving, Brain damage can produce an inability to planning, and impulse control. It uses input recognize faces, an inability to perceive from all other lobes to make informed motion, a shift of attention to the right side of the decisions. world, changes in motivation and emotion, memory impairments, and a host of o Example: When planning a trip, the other specialized effects. The implications are deep: frontal lobe integrates sensory If you lose part of your brain, you lose part of your information (such as weather mind. conditions), past experiences (memories stored in the temporal Brain Damage lobe), and spatial understanding Frontal Lobe Damage (parietal lobe) to make decisions. Motor Control Issues: Difficulty with Visual Processing Issues: Problems with voluntary movements; paralysis or weakness interpreting visual information, such as on one side of the body. color, movement, and depth perception. Cognitive Impairments: Problems with planning, decision-making, problem-solving, and impulse control. Subtopic 3.2: Effects of Brain Stimulation Personality Changes: Altered personality, social behavior issues, and difficulties with emotional regulation. Brain stimulation therapies can play an Speech Problems: Difficulty in speaking or important role in treating mental disorders. forming coherent sentences (if Broca’s area These therapies work by activating or inhibiting the is affected). brain with electricity. The electricity can be given directly through Parietal Lobe Damage electrodes implanted in the brain or indirectly through electrodes placed on the scalp. Sensory Deficits: Loss of sensation, difficulty perceiving touch, temperature, and If brain damage impairs some behavior, pain on the opposite side of the body. stimulation should increase it. A popular approach today is optogenetics, using light Spatial Awareness Issues: Problems with to control a limited population of neurons. understanding spatial relationships and navigating through space. Optogenetics is a biological technique to control the activity of neurons or other cell Coordination Problems: Difficulty in types with light. This is achieved by coordinating movements, and challenges expression of light-sensitive ion channels, with tasks requiring precise motor skills. pumps or enzymes specifically in the target cells. Temporal Lobe Damage Auditory Issues: Difficulty in processing and understanding sounds; potential hearing loss. Language Comprehension: Problems understanding spoken and written language (if Wernicke’s area is affected). Memory Problems: Difficulty forming new memories or retrieving past memories (if the hippocampus is affected). Emotional Problems: Changes in emotional responses and behavior. Occipital Lobe Damage Visual Impairments: Loss of vision or visual field deficits, difficulty recognizing objects Subtopic 3.3: Recording and faces. brain Activity Recording brain activity involves several techniques, each with its own strengths and applications. Here’s a summary of the main methods used to capture and study brain activity: Electroencephalography (EEG) How It Works: EEG measures electrical activity in the brain through electrodes placed on the scalp. It captures the voltage fluctuations resulting from neuronal activity. Temporal Resolution: Excellent (milliseconds). Spatial Resolution: Limited; better for detecting activity from cortical regions. Applications: Used for diagnosing epilepsy, Functional Magnetic Resonance Imaging (fMRI) sleep studies, and monitoring brain activity in various cognitive tasks. How It Works: fMRI measures changes in blood flow and oxygenation levels in the brain, which are related to neuronal activity. It uses magnetic fields and radio waves to create images. Temporal Resolution: Moderate (seconds). Spatial Resolution: Excellent (millimeters). Applications: Mapping brain activity related to cognitive tasks, emotions, and various brain functions; research and clinical diagnostics. Magnetoencephalography (MEG) How It Works: MEG detects the magnetic fields generated by neuronal electrical activity. Sensors are placed around the head to capture these fields. Temporal Resolution: Excellent (milliseconds). Spatial Resolution: Good, particularly for cortical activity. Applications: Research on sensory Positron Emission Tomography (PET) processing, motor control, and language; How It Works: PET scans measure pre-surgical brain mapping. metabolic activity in the brain by detecting radioactive tracers injected into the bloodstream. These tracers highlight areas of high brain activity. Temporal Resolution: Moderate (minutes). Spatial Resolution: Good (millimeters). Applications: Evaluating brain metabolism, diagnosing neurodegenerative diseases, and assessing brain function in various conditions. Chapter 5: Genetics, Evolution, Development, and Plasticity Subtopic 1: Genetics And Evolution of Behavior Near-Infrared Spectroscopy (NIRS) How It Works: NIRS uses near-infrared light MENDELIAN GENETICS to measure changes in blood oxygenation in Mendelian genetics refers to the set of principles the that Gregor Mendel formulated based on his brain. Sensors are placed on the scalp to experiments in the mid-19th century. Mendel is detect light absorption. often called the "Father of Modern Genetics" Temporal Resolution: Moderate (seconds). because his work laid the foundation for understanding how traits are inherited through Spatial Resolution: Limited; primarily used generations. The key concepts of Mendelian for cortical regions. genetics are what are known as Mendel's Laws of Applications: Monitoring brain oxygenation Inheritance. during cognitive tasks, in infants, and in Mendel demonstrated that inheritance occurs clinical settings. through GENES, units of heredity that maintain their structural identity from one generation to another. As a rule, genes come in pairs because they are aligned along CHROMOSOMES (strands of genes) that also come in pairs. Genes Genes are segments of DNA that carry the instructions for the synthesis of proteins, which are essential for the functioning, growth, and development of all living organisms. Each gene contains specific sequences of nucleotides that code for a particular trait or function. Genes are the fundamental units of heredity, meaning they are passed down from parents to offspring, determining various characteristics such as eye color, blood type, and susceptibility to certain diseases. A gene is made up of a sequence of nucleotides in DNA. Each nucleotide consists of three components: Phosphate group Deoxyribose sugar (in DNA) Nitrogenous base (Adenine, Thymine, Guanine, Cytosine) Summary of mendelian Principles 1. Inheritance of biological traits is determined by genes, which are passed from parents to offspring. 2. Principle of Dominance - Where two or more forms (alleles) of the gene for a single trait exist, some alleles may be Where do our genes live? dominant, and others may be recessive. Genes are segments of DNA located on structures Dominant refers to a relationship between two called chromosomes. versions of a gene. If one is dominant, the other one Chromosomes are long, thread-like structures made must be not dominant. In that case, we call up of DNA and proteins. They carry many genes it recessive. A dominant gene, or a dominant and are found inside the nucleus of our cells. version of a gene, is a particular variant of a gene, which for a variety of reasons, expresses itself more Humans typically have 46 chromosomes, which strongly all by itself than any other version of the come in pairs, with 23 inherited from each parent. gene which the person is carrying, and, in this case, the recessive. Chromosomes have proteins called histones that bind to DNA. DNA has two strands that twist into 3. Principle of Segregation- In most the shape of a spiral ladder called a helix. DNA is sexually reproducing organisms, each made up of four building blocks called nucleotides: adult has two alleles of each gene—one adenine (A), thymine (T), guanine (G), from each parent. These alleles segregate and cytosine (C). The nucleotides attach to each from each other randomly and other (A with T, and G with C) to form chemical independently when gametes are formed. bonds called base pairs, which connect the two DNA strands. Genes are short pieces of DNA that An allele is simply a different version of the same carry specific genetic information. gene. For example, genes control traits like eye color, and different alleles of the eye color gene might give you blue or brown eyes. You inherit two alleles for each gene—one from each parent. If both alleles are the same, you're homozygous for that trait, and if they're different, you're heterozygous. Sometimes, one How Does it Happen? allele is dominant and will show up more strongly (like brown eyes), while the other might be The principle of independent assortment happens recessive and only appear if both alleles are the during a process called meiosis, which is how sex recessive type (like blue eyes). any other version of cells (sperm and eggs) are made. the gene which the person is carrying, and, in this case, the recessive. Here's how it works: What is Homozygous and Heterozygous? 1. Chromosomes separate: You have pairs of chromosomes, one from your mom and one Homozygous: You inherit the same version from your dad. During meiosis, these pairs of the gene from each parent, so you have are randomly separated into different sperm two matching genes. or egg cells. Heterozygous: You inherit a different 2. Shuffling of genes: The genes located on version of a gene from each parent. different chromosomes are separated independently. This means that each gamete 4. Principle of independent (sperm or egg) gets a random mix of genes assortment states that genes for different from both parents. traits can segregate independently during 3. Random assortment: Because the formation of gametes chromosomes line up in random order during meiosis, each gamete ends up with a It states that genes for different traits are passed to different combination of traits. offspring independently of each other. This means that the inheritance of one trait (like eye color) This is why siblings can inherit different doesn't affect the inheritance of another trait (like combinations of traits—genes for different traits hair color), as long as the genes for these traits are aren't tied together and are mixed in a random way. located on different chromosomes. During the formation of gametes (sperm or eggs), chromosomes are randomly shuffled. As a result, What is DNA? each gamete gets a different combination of alleles (gene variants), allowing for a wide variety of DNA is a molecule that carries genetic information genetic combinations in offspring. This principle in living organisms. It looks like a twisted ladder increases genetic diversity, as it ensures that the (double helix) and is found inside the nucleus of our traits inherited from parents are assorted in many cells. DNA stores the genetic blueprint for an possible combinations. organism, containing instructions for building proteins and controlling cell activities. It is passed For example, just because you inherit a gene for from parents to offspring, ensuring heredity. brown eyes doesn’t mean you’ll automatically inherit a gene for tall height —they are inherited DNA stands for deoxyribonucleic acid. independently from each other. This random assortment happens during the creation of egg and sperm cells, which is why siblings can look different even though they have the same parents. How DNA controls development of the organism? Sex-Linked and Sex-Limited Genes Deoxyribonucleic Acid controls the development of Sex-linked genes are genes located on the an organism through two main processes: sex chromosomes (X and Y chromosomes in humans). These genes can affect traits that A. Genetic Instructions for Proteins: DNA are expressed differently in males and females. For contains the instructions for making proteins, which example, many genetic disorders, like hemophilia are the building blocks of all cells and tissues. and color blindness, are X- linked, meaning they are These proteins control almost every function in an carried on the X chromosome and typically manifest organism, from building muscles to making in males who have only one X chromosome. enzymes that digest food. Each gene in the DNA carries the code to make a specific protein, and The genes on the sex chromosomes (designated X these proteins work together to guide the and Y in mammals) are known as sex-linked development of the organism. genes. A female mammal has two X chromosomes, whereas a male has an X and a Y. During B. Regulation of Gene Expression: Not all genes reproduction, the female necessarily contributes an are active at the same time. DNA also controls X chromosome, and the male contributes either an when and where certain genes are turned on or off X or a Y. If he contributes an X, the offspring is during the organism's development. This ensures female; if he contributes a Y, the offspring is male. that the right proteins are made at the right time, (Exceptions to this rule are possible, but very helping the organism grow and develop in an uncommon.) organized way. This regulation is essential for processes like the development of different organs SEX-LINKED GENES or tissues. Sex-linked genes are genes found on the X or Y -In summary, DNA controls development by chromosomes. They can affect traits differently in encoding proteins and regulating when genes are males and females. For example, color blindness is expressed, shaping the entire structure and function more common in males because it’s often linked to of an organism. the X chromosome Men: They have one X and one Y chromosome. If a man has the gene for red- What is RNA? green color blindness on his X chromosome, he will be color blind because he has no RNA is usually single-stranded. It is a molecule in second X chromosome to possibly have a cells that helps make proteins. It works by copying normal gene. information from DNA and carrying it to other parts Women: They have two X chromosomes. A of the cell, where proteins are made. Unlike DNA, woman needs to have the color blindness which stays in the nucleus, RNA moves around the gene on both X chromosomes to be color cell to do its job. blind. If she has one normal gene on one X, it will prevent her from being color blind. RNA acts as a messenger, taking the instructions from DNA and helping the cell build the proteins In short, color blindness is much more common in that are essential for life. men because they only have one X chromosome. RNA stands for ribonucleic acid. SEX-LIMITED GENES What IS EPIGENETICs? Sex-limited genes, on the other hand, are genes that Epigenetics deals with changes in gene expression can be present in both sexes but are expressed only or cellular phenotype that do not involve alterations in one sex due to hormonal or developmental to the underlying DNA sequence. These changes factors. A classic example is the gene for milk can affect how genes are turned on or off, production in mammals, which is typically influencing how cells function without changing the expressed only in females. Though both males and genetic code itself. females may carry the gene, only females produce milk. Other examples include the genes that control Every cell in your body has the same DNA as every the amount of chest hair in men, breast size in other cell (except your red blood cells, which have women.. Both sexes have the genes, but sex no DNA). However, the activity of a gene can hormones activate them in one sex and not the vary. The genes that are most active in your other, or one sex much more than the other. Many brain are not the same as those active in your sex-limited genes show their effects at puberty lungs or kidneys, and those most active in one part of your brain are not the most active in another part. Many genes that are essential to a developing fetus become less active after birth, GENETIC CHANGES and others that did little for the fetus become important after birth (Hannon et al., 2016; Jaffe et Genes change in several ways. One way is al., 2016). At puberty, certain genes that had by mutation, a heritable change in a DNA been almost silent become much more molecule. Changing just one base in DNA to any of active (Lomniczi et al., 2013). A gene may be the other three types means that the mutant gene active in one person and not another. After all, will code for a protein with a different amino acid at monozygotic (“identical”) twins sometimes differ in one location in the molecule. handedness, mental health, or other aspects. Various experiences can turn a gene on or off. Even forming Mutation refers to a change in the DNA sequence of a new memory or habit increases the activity of a gene. Mutations can occur naturally during DNA certain genes in particular neurons (Feng, Fouse, & replication or as a result of environmental factors, Fan, 2007). like radiation or chemicals. It is a permanent change in the genes Key concepts in epigenetics include: Another kind of mutation is a duplication or DNA Methylation: The addition of a methyl group deletion. to DNA, which can suppress gene expression. When DNA is heavily methylated, the gene may be Deletions: Loss of a chromosome segment. "turned off." Duplications: Extra copies of a chromosome segment. Histone Modification: Proteins called histones help package DNA into a compact structure. During the process of reproduction, part of a Modifications to these proteins can affect how chromosome that ordinarily appears once might tightly or loosely DNA is wrapped around them, instead appear twice or not at all. When this process influencing gene accessibility and expression. happens to just a tiny portion of a chromosome, we call it a microduplication or microdeletion. Non-coding RNAs: These are RNA molecules that Microduplications and microdeletions of brain do not translate into proteins but play roles in relevant genes are responsible for several regulating gene expression. They can influence how psychological or neurological disorders, probably genes are expressed and can be involved in including some cases of schizophrenia silencing specific genes. Subtopic 1.2: Heredity and Environment Brain Chemistry: Genes can affect the production of neurotransmitters (chemicals Heredity and environment are two key factors that transmit signals in the brain) like that influence an individual's traits, behaviors, serotonin and dopamine. Variations in these and overall development: genes can influence mood, emotions, and behavior. For instance, some genetic Heredity (Genetics): This refers to the genetic variations are linked to a higher risk of information passed down from parents to their depression or addiction. offspring through genes. Heredity determines many physical traits (like eye color and height) and can Developmental Processes: Genes play a also influence certain behaviors and predispositions crucial role in brain development. Genetic to diseases. Each person inherits a unique factors can influence how the brain forms combination of genes from their parents. and functions, which in turn can affect behavior. For example, genes can impact Heredity and environment are two key factors how quickly a child learns to walk or talk, that influence an individual's traits, behaviors, which can shape social interactions and and overall development: behaviors. Environment: This encompasses all external Interaction with Environment: Genes can factors that can influence an individual, including interact with environmental factors to shape lifestyle, nutrition, education, social interactions, behavior. For instance, a person with a and cultural context. The environment plays a genetic predisposition for anxiety may only crucial role in shaping behaviors, personality, and develop anxiety disorders in stressful or even physical health. For example, a person's traumatic environments. upbringing, experiences, and surroundings can significantly impact their development and Epigenetics: Environmental factors can lead opportunities. to changes in gene expression through epigenetic mechanisms. This means that Example: A person may inherit a genetic experiences can influence how genes are predisposition for a certain height (heredity), but turned on or off, which can impact behavior. their actual height can be influenced by factors like Examples are: the experience of feeling nutrition and health during childhood socially isolated or rejected alters the (environment). activity of hundreds of genes (Slavich & Cole, 2013). How well one of your grandparents was nourished or malnourished in childhood correlates with your chances HOW GENES INFLUENCES BEHAVIOR? for a long, healthy life, apparently because of changes in your father’s sperm cells Genes can influence behavior in roundabout ways. (Pembrey et al., 2006). although it's important to note that behavior is also shaped by environmental factors. Here are some key Evolutionary Factors: Certain behaviors points about how genes affect or influences may have been favored by natural selection. behavior: For example, behaviors that promote survival and reproduction (like cooperation Genetic Predispositions: Certain genes can or competition) may be influenced by predispose individuals to specific behaviors genetic factors that have been passed down or traits. For example, some genes may through generations. influence personality traits like aggression, sociability, or anxiety levels. Subtopic 1.3: EVOLUTIONARY PSYCHOLOGY Altruism: Helping kin for increased inclusive fitness. Evolutionary psychology Fears of Heights: Fear as a protective mechanism against falls. Evolutionary psychology concerns how behaviors evolved. The emphasis is on evolutionary and functional explanations— that is, how our genes Subtopic 2: Development of the brain reflect those of our ancestors and why natural selection might have favored the genes that promote 2.1: Maturation of the Vertebrate Brain certain behaviors. The assumption is that any behavior characteristic of a species arose through When animals, plants, and even fungi are just natural selection and presumably provided some starting to develop, their early growth looks advantage, at least in ancestral times. surprisingly similar. This is because they all use a special group of genes called homeobox genes. is a field of psychology that seeks to understand These genes act like a set of instructions, telling the how evolutionary processes shape human behavior cells how to grow and where to place important and mental processes. It is based on the idea that body parts, like deciding what will become the front many psychological traits and behaviors have and what will become the back. These homeobox developed as adaptations to help our ancestors genes are found in many different living things, survive and reproduce in their environments. including humans, insects, plants, and even tiny organisms like yeast. Even though these organisms are very different, their homeobox genes have a lot of the same DNA, showing that this system of development has been around for a long time and is shared across many types of life. A mutation in a homeobox gene can lead to dramatic changes in an insect's body plan. For example, if there's a mutation in the gene that controls where the antennae should grow, legs might form in that spot instead of antennae. Similarly, a mutation in another homeobox gene could cause an insect to develop an extra set of wings. This happens because homeobox genes act as "master switches," guiding the development of the body parts. When these genes don't work correctly due to a mutation, the instructions for Common evolutionary psychology examples where certain parts should grow can get mixed up, include: leading to unusual or extra features in the insect's anatomy. Mate Selection: Preferring traits indicating genetic fitness, like facial attractiveness. In Humans, mutations in homeobox genes have Parental Investment: Varied parenting been linked to many brain disorders including strategies based on reproductive investment. mental retardation, as well as physical deformities Fear of Snakes: Ancestral fear due to historical danger, leading to quick fear The human central nervous system begins to form responses. when the embryo is about 2 weeks old Sexual Jealousy: Emotions to prevent mate desertion. The dorsal surface thickens and then long Food Preferences: Cravings for scarce thin lips rise, curl, and merge, forming a energy sources like fatty, sugary foods. neural tube that surrounds a fluid-filled cavity. prefrontal cortex and other cortical areas responsible for attention, working memory, and decision making In short, the infant brain is set up to see, hear, and so forth, but limited in its ability to interpret that information or to decide what to do about it. The human prefrontal cortex continues slowly maturing through the teenage years and beyond. In general, the brain areas that are slowest to develop, such as the prefrontal cortex, are the ones most likely to As the tube sinks under the surface of the deteriorate in conditions such as Alzheimer’s skin, the forward end enlarges and disease differentiates into the hindbrain, midbrain, and forebrain Growth and Development of Neurons 1. Proliferation 2. Migration The rest becomes the spinal cord. The fluid-filled cavity within the neural tube becomes the central canal of the spinal cord and the four ventricles of the brain, containing the cerebrospinal fluid (CSF). At birth, the average human brain weighs about 350 grams. By the end of the first year, it weighs 1,000 g, close to the adult weight of 1,200 to 1,400 g. In early infancy, the primary sensory areas of the cortex—responsible for registering vision, hearing, and other senses—are more mature than the rest of the cortex. Their gyri and sulci are mostly formed, and their connections with the thalamus are fairly well established. They continue to develop, of course, but the greatest changes over the first couple of years happen in the 3. Differentiation accepting certain combinations of axons and rejecting others. This kind of competition among axons continues throughout life. 2.3: Determinants of Neuronal Survival When the nervous system is developing, it creates more neurons (brain cells) than are needed. Later on, there’s a period where many of these extra neurons die off. This is completely normal and helps the brain mature. In fact, loss of cells in a 4. Myelination particular brain area often indicates maturation As the brain develops, it keeps the neurons that work well and get rid of the ones that aren’t needed. So, the death of some cells is a natural part of the process, helping the remaining neurons to grow stronger and work more efficiently. The brain essentially "trims" itself to become more organized and effective. Nerve growth factor is a neurotrophin, meaning a chemical that promotes the survival and activity of 5. Synaptogenesis neurons. Neurotrophins are essential for growth of axons and dendrites, formation of new synapses, and learning. Although neurotrophins are essential to the survival of motor neurons in the periphery, they do not control survival of neurons within the brain. When cortical neurons reach a certain age in early development, a certain percentage of them die 2.4: The Vulnerable Developing Brain During early development, the brain is highly vulnerable to malnutrition, toxic chemicals, and 2.2: Pathfinding by Axons infections that would produce milder problems at later ages. The infant brain is highly vulnerable 1. Axons must travel great distances across the to damage by alcohol. Children of mothers who brain to form the correct connections. drink heavily during pregnancy are born with fetal 2. Growing axons find their way close to the alcohol syndrome, a condition marked right locations and then arrange themselves by hyperactivity, impulsiveness, difficulty over a target area by following chemical maintaining attention, varying degrees of mental gradients. retardation, motor problems, heart defects, and 3. After axons reach their targets based on facial abnormalities. Drinking during pregnancy chemical gradients, the postsynaptic cell leads to thinning of the cerebral cortex that persists adjusts the connections based on experience, to adulthood (Zhou et al., 2011). More drinking causes greater deficits, but even moderate drinking produces a measurable effect (Eckstrand et al., 2.6: FINE TUNING BY EXPERIENCE 2012). refers to how the brain adjusts and refines its neural Exposure to alcohol damages the brain in several connections and functions based on real-world ways. At the earliest stage of pregnancy, it experiences and interactions. While the brain forms interferes with neuron proliferation. A little later, it general structures and networks during early impairs neuron migration and differentiation. Still development, experience helps shape, strengthen, or later, it impairs synaptic transmission (Kleiber, eliminate certain pathways to optimize performance Mantha, Stringer, & Singh, 2013). Alcohol kills and learning. neurons partly by apoptosis. For example, if you practice a musical instrument regularly, the brain areas involved in motor skills and auditory Apoptosis is a natural process of programmed processing will become more efficient cell death that occurs in the body. It’s like the through fine-tuning. body's way of safely removing cells that are no longer needed, damaged, or potentially harmful. For instance, children exposed to multiple Unlike accidental cell death (such as from languages early on have a stronger ability to injury), apoptosis is a controlled and organized distinguish sounds from those languages process. compared to adults learning later. The developing brain is vulnerable to chemical Repeated physical movements (like learning insult. Many chemicals that produce only mild, to ride a bike) help the brain fine-tune motor temporary problems for adults can impair early pathways, making movements smoother and brain development. more automatic. The developing brain is highly responsive to many For example, someone who plays chess influences from the mother. For example, children regularly will refine their brain’s decision- of impoverished and abused women have on making and strategy-planning areas. average, increased problems in both their academic and social lives. Stress to the mother changes her behavior in ways that change her offspring’s behavior. FINE TUNING BY EXPERIENCE The brain has some limited ability to reorganize itself in response to experience 2.5: Differentiation of the Cortex Axons and dendrites continue to modify their structure and connections throughout the lifetime Dendrites continually grow new spines The gain and loss of spines indicates new connections, which relates to learning Measurable expansion of neurons has also been shown in humans as a function of physical activity The thickness of the cerebral cortex declines in old age, but much less in those that are physically active Neurons also become more finely tuned and responsive to experiences that have been important in the past. Extensive practice of a skill changes the Compared to adults, adolescents tend to be brain in a way that improves the ability for impulsive and centered more on present pleasures that skill. than future prospects. In most cases, risky behaviors People who learned to read as adults in adolescents probably reflect increased drive for compared to those who never learned how to excitement, more than lack of ability to inhibit read show more gray matter and greater impulses. The prefrontal cortex, responsible for thickness in part of the corpus callosum. decision-making and impulse control, is still MRI studies reveal that: The temporal lobe maturing during adolescence. In contrast, the limbic of professional musicians in the right system, which drives emotions and rewards, hemisphere is 30% larger than non- develops earlier, leading to heightened sensitivity to musicians. Thicker gray matter in the part of rewards. the brain responsible for hand control and vision of professional keyboard players. As people age, many experience declines in Some professions may require skills that are memory and reasoning skills, along with shrinkage known to form in brain areas before birth in certain areas of the brain. However, these (e.g., phoneticians). changes vary widely among individuals. Generally, Practicing a skill reorganizes the brain to those who maintain physical fitness tend to preserve maximize performance of that skill. their cognitive abilities better. Additionally, many Certain types of training may also exert a older adults adapt to cognitive changes by engaging bigger effect if they begins early in life. different brain areas to compensate for any Example: musicians who began before age 7 inefficiencies in their usual brain functions. This showed advantages over those who started adaptability can help them continue to perform well later in life in various cognitive tasks despite age-related Specialized experiences can alter brain changes. development, especially early in life. For example, in people who are born blind, Aging can lead to the shrinkage of specific representation of touch and hearing expands brain regions, particularly those involved in in the brain areas usually reserved for vision. memory and executive functions, such as the Extensive practice of a skill expands the hippocampus and prefrontal cortex. brain’s representation of sensory and motor Levels of certain neurotransmitters (e.g., information relevant to that skill. For dopamine, serotonin) may decrease with example, the representation of fingers age, impacting communication between expands in people who regularly practice neurons and affecting cognitive musical instruments. processes. Poor cardiovascular health can reduce blood 2.7: Brain Development and Behavioral flow to the brain, contributing to cognitive Development decline. Conditions like hypertension and diabetes can exacerbate this issue. As people grow older, their behavior changes. How much of that change has to do with the brain? Let’s consider adolescence and old age. SUBTOPIC 3: PLASTICITY AFTER BRAIN Adolescents tend to have weaker responses DAMAGE in the part of the brain called the prefrontal cortex, which is responsible for controlling 3.1: Brain Damage and Short-Term Recovery behavior and making decisions. This area is not as fully developed as in adults, which Possible causes of brain damage include: means teenagers may find it harder to resist impulses. The more developed the prefrontal Tumors cortex and its connections, the better a Infections person is at controlling their impulses. Exposure to toxic substances Degenerative diseases Closed head injuries - a sharp The overstimulation of neurons leads to sodium and blow to the head that does not puncture the other ions entering the neuron in excessive amounts. brain (temporary loss of consciousness, Excess positive ions in the neuron block metabolism confusion, headache, dizziness) in the mitochondria and kill the neuron After a severe injury, recovery can be slow and Immediate Treatments incomplete. A drug called tissue plasminogen activator (tPA) A common cause of brain damage, breaks up blood clots and can reduce the effects of especially in older people, is temporary an ischemic strokes. interruption of normal blood flow to a brain area during a stroke, also known as Research has begun to attempt to save neurons from a cerebrovascular accident death by: Types of strokes include: 1. Blocking glutamate synapses 2. Blocking calcium entry A. Ischemia: the most common type of stroke, resulting from a blood clot or obstruction of an Cooling the brain after a stroke is a method known artery as therapeutic hypothermia. This approach has shown promise in minimizing brain damage, Neurons lose their oxygen and glucose particularly within the first few days post-stroke. At supply the clinical level, current practices suggest lowering body and/or brain temperature for 12–24 h to 32– B. Hemorrhage: a less frequent type of stroke 34°C. resulting from a ruptured artery 3.2: LATER MECHANISM OF RECOVERY Neurons are flooded with excess blood, calcium, oxygen, and other chemicals After brain damage, such as from a stroke, the areas of the brain that survive the injury often adapt by Ischemia and hemorrhage also cause: increasing or reorganizing their activity. This process can help compensate for the lost functions Edema: the accumulation of fluid in the of the damaged regions. brain resulting in increased pressure on the brain and increasing the probability of Diaschisis: decreased activity of surviving further strokes neurons after damage to other neurons. Disruption of the sodium-potassium pump Because activity in one area stimulates other leading to the accumulation of potassium areas, damage to the brain disrupts patterns ions inside neurons of normal stimulation. Use of drugs (stimulants) to stimulate The combination of edema and excess sodium activity in healthy regions of the brain after provokes excess release of the transmitter a stroke may be a mechanism of later glutamate, which overstimulates neuron, damaging recovery both neurons and synapses. Destroyed cell bodies cannot be replaced, chronic pain, where the person feels pain even but damaged axons do grow back under certain without typical triggers. circumstances. If an axon in the peripheral nervous system is crushed, it follows its myelin sheath back Phantom limb sensations happen when people to the target and grows back toward the periphery at who have had a limb amputated still feel sensations a rate of about 1 mm per day. as if the limb were still there. Damaged axons only regenerate one to two After losing a limb, some people feel things millimeters in mature mammals. like warmth, itching, or pain in the missing limb, even though it's gone. Paralysis caused by spinal cord damage After amputation, the brain reorganizes is relatively permanent itself. The area that used to control the missing limb starts responding to other parts Scar tissue that forms after a brain or spinal cord of the body, like the face. injury can create a physical barrier to axon The original axons from the amputated limb growth. degenerate, leaving vacant synapses. Nearby axons from other body parts can sprout and When the central nervous system (CNS) is connect to these vacant synapses, damaged, glial cells—such as astrocytes and contributing to the reorganization of sensory oligodendrocytes—react by releasing various processing. chemicals that can inhibit axon growth. This response is part of the injury response but can also Phantom limb can lead to the feeling of sensations create challenges for recovery. in the amputated part of the body when other parts of the body are stimulated, e.g., a touch on the face can bring about the experience of a phantom arm. Use of an artificial limb can reduce the likelihood of AXON GROWTH experiencing phantom limb. Axon growth is crucial for several reasons, Therapy for a person with brain damage begins particularly in the context of nervous system with careful development and recovery from injury. evaluation of a patient’s abilities and disabilities. Collateral sprouts are new branches that grow For example, someone who has trouble carrying out from healthy axons after some nearby axons have spoken instructions might be impaired in hearing, been damaged. These new branches can connect to memory, language, muscle control, or alertness. empty receptors left by the damaged axons, helping After identifying the problem, a physical therapist to restore communication. If the new connections or occupational therapist helps the patient practice work well, they can help regain lost functions. the impaired skills. Behavior recovered after brain damage is effortful, and its recovery is precarious. When postsynaptic cells lose their usual synaptic inputs (like after an axon is damaged), they often A person with brain damage may seem to function become more sensitive to the neurotransmitters they normally, but they are often putting in extra effort to receive. This process is known as denervation manage tasks. This increased effort can lead to supersensitivity. This means that even a normal significant difficulties when they face challenges amount of neurotransmitter can have a stronger like alcohol consumption, physical exhaustion, or effect. stress, which might only slightly impact
