Introduction to Neurosciences

Introduction to Neurosciences

• Neurosciences are a multidisciplinary field studying the nervous system at all levels: molecules, cells, and neural networks
• The objective is to understand how the brain and the rest of the nervous system generate thoughts, emotions, actions, and consciousness
• Neuroscience seeks to explain how the brain produces individual human experience through its organization and electrochemical activity
• Cognitive Neuroscience studies the neural mechanisms underlying higher mental processes such as memory, language, attention, and decision-making
• Historically, the importance of the brain wasn't always recognized
• Currently, the brain is considered the most complex organ in the universe, and its study is a scientific priority
• Structural Neuroscience (Neuroanatomy) describes the anatomical organization of the nervous system
• Functional or Physiological Neuroscience investigates how different parts of the nervous system function

Organization of the Nervous System

• The Central Nervous System (CNS) is the processing and control center of the organism
• The encephalon is the most voluminous part of the CNS, located in the skull
• The cerebrum (telencephalon) is responsible for higher cognitive functions, sensory and motor processing, language, and emotions
• The cerebrum consists of two hemispheres (right and left), with a highly folded surface (gyri and sulci) to maximize cortical surface area
• The cerebellum (metencephalon) is located in the posterior part of the encephalon
• The cerebellum coordinates movement, balance, and motor learning -Receives sensory information from muscles and joints and adjusts planned movements for precision
• The brainstem connects the upper brain with the spinal cord
• The brainstem controls functions like respiration, heart rate, and sleep-wake cycles, and contains cranial nerve nuclei
• The brainstem comprises the medulla oblongata (myelencephalon), pons (metencephalon), and midbrain (mesencephalon)
• The spinal cord is a nerve cord extending from the brainstem to the lower vertebral column
• The spinal cord transmits sensory and motor information between the body and the encephalon
• The spinal cord also controls spinal reflexes
• The Peripheral Nervous System (SNP) is the network of nerves extending from the CNS to the rest of the body

Somatic and Autonomic Nervous Systems

• The somatic nervous system involves voluntary actions and controls skeletal muscle movement
• It transmits sensory information from the skin, muscles, and joints to the CNS
• The somatic nervous system is composed of nerves connecting the CNS with skeletal muscles
• Sensory perception and conscious movement control is permitted
• The autonomic nervous system governs involuntary functions of internal organs and glands
• The autonomic nervous system maintains homeostasis (internal equilibrium)
• The sympathetic nervous system activates during stress or emergencies, preparing the body for "fight or flight"
• Heart rate, blood pressure, and respiration increase, pupils dilate, and glucose is released
• The parasympathetic nervous system predominates in calm and restful situations, promoting "rest and digest"
• The parasympathetic nervous system decreases heart rate and blood pressure
• The parasympathetic nervous system stimulates digestion and energy-conserving functions
• The enteric nervous system is a neural network in the gastrointestinal tract walls
• The enteric nervous system can function independently to control intestinal motility, secretion, and blood flow

Cerebral Hemispheres and Lobes

• The right hemisphere specializes in visuospatial processing, facial recognition, emotional understanding, and creativity, and controls the left side of the body
• The right hemisphere is dominant in visuospatial skills, face recognition, emotional processing, intuition, creativity, and non-verbal communication
• The left hemisphere specializes in language (production and comprehension), logic, analytical reasoning, and sequential processing, and controls the right side of the body
• The left hemisphere is dominant in language, logic, analytical reasoning, mathematics, and sequential processing
• Although hemispheric specialization (lateralization) exists, most complex cognitive functions involve collaboration between both hemispheres
• Communication between hemispheres is facilitated by the corpus callosum
• The corpus callosum is a large bundle of nerve fibers connecting the two cerebral hemispheres, allowing rapid and efficient communication
• The corpus callosum is near limbic structures and participates in emotional information integration
• The frontal lobe is located in the front of the brain and is crucial for executive functions like planning, decision-making, working memory, and impulse control
• The frontal lobe contains two key areas: the primary motor cortex and Broca's area (speech production)
• The posterior part of the frontal lobe contains the motor cortex, which controls voluntary movements, and Broca's area, essential for spoken language production
• The parietal lobe is situated behind the frontal lobe and processes sensory information like touch, temperature, pain, and pressure
• The parietal lobe plays a significant role in spatial awareness, navigation, and numerical processing
• The temporal lobe is underneath the parietal lobe and is involved in auditory processing (auditory cortex), language comprehension (Wernicke's area), long-term memory (hippocampus), and emotion processing (amygdala)
• The occipital lobe is located at the back of the brain and is the primary center for visual information processing, including shape, color, and movement perception
• The limbic lobe is a network of interconnected structures that regulates emotions, memory, motivation, and related physiological responses (amygdala, hippocampus, hypothalamus, thalamus, cingulate gyrus)
• Key limbic system structures include: Amygdala: Processing emotions, Hypothalamus: Regulating basic physiological functions, Thalamus: Sensory relay station for the cerebral cortex, Hippocampus: Forming new long-term memories.

Neuroplasticity

• Neuroplasticity, also known as neuronal or synaptic plasticity, is the nervous system's ability to change its structure and function over time in response to experience, learning, injury, or environmental changes
• There are four types; Reactive, Adaptative, Reconstructive, and Evolutiva
• Neuroplasticity allows adaptation and continuous learning
• It enables the brain to adapt, learn, recover from damage, and evolve
• Reactive neuroplasticity involves short-term metabolic adjustments in neuronal function in response to immediate changes in the internal or external environment. It entails rapid, temporary changes in synaptic efficiency and neuronal function in response to immediate stimuli or internal conditions
• Adaptive neuroplasticity refers to lasting changes in synaptic strength and structure that underlie memory formation and new skill acquisition
• Adaptive neuroplasticity involves creating new synapses (synaptogenesis), strengthening existing ones (long-term potentiation - LTP), or weakening unused ones (long-term depression - LTD)
• Reconstructive neuroplasticity describes the brain's capacity to reorganize its neural circuits and assume lost functions following brain injury or damage to undamaged areas assuming functions previously performed by the injured region
• Evolutive neuroplasticity relates to changes in neural organization and connectivity during nervous system development
• It is influenced by genetics and environmental interactions
• These changes are crucial for the maturation of cognitive and behavioral functions

Studying Brain Functions

• Brain functions are studied by observing brain activity and assessing an individual's cognitive and behavioral abilities
• Neuroscientific techniques measure brain electrical and metabolic activity, providing information about which areas are involved in different functions
• Psychometric tests assess cognitive abilities (attention, memory, language, executive function, etc.) and behavior to provide indirect information about brain function
• Electroencephalography (EEG) records the brain's electrical activity via electrodes on the scalp - It measures voltage fluctuations from synchronous activity of large neuron populations
• EEG non-invasive and has excellent temporal resolution for tracking brain activity changes
• EEG is is used to study consciousness states and diagnose conditions like epilepsy
• EEG main limitation is its low spatial resolution, making it difficult to pinpoint activity location
• Computerized Tomography (CT) generates detailed cross-sectional images of brain structure using X-rays
• Useful in identifying structural abnormalities, quick, economical and useful for visualizing structures, bone structures, hemorrhages, large tumors and structural anomalies
• Magnetic Resonance Imaging (MRI) produces high-resolution images of brain anatomy using magnetic fields and radio waves
• MRI allows visualization of fine tissue details
• Functional Magnetic Resonance Imaging (fMRI) detects changes in cerebral blood flow associated with neuronal activity
• fMRI maps brain areas activated during tasks
• fMRI reveals increased blood flow in active regions and creates brain activity maps during cognitive tasks or rest
• Positron Emission Tomography (PET) measures metabolic activity in brain regions using radioactive tracers
• PET useful for studying brain function, glucose metabolism, blood flow, and neurotransmitter distribution

Etiology of Brain Damage

• Brain damage is caused by many factors, its consequences depending on damage location, extent, and nature
• Even lesions in the same area can have different effects due to brain plasticity and other individual factors
• Strokes (cerebrovascular accidents) involve interrupted blood flow to the brain due to blockage (ischemic) or bleeding (hemorrhagic)
• Oxygen and nutrient deprivation causes cell death in the affected area
• Traumatic Brain Injuries (TBI) are head injuries resulting from external forces like falls or accidents
• TBIs range from mild concussions (headache, confusion, dizziness) to severe injuries with structural cerebral tissue damage
• Degenerative Diseases are progressive conditions causing gradual deterioration of brain cells,
• Example of degenerative diseases: Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis.
• Metabolic Disorders affect the body's chemical processes and can have toxic effects on the brain
• Certain medical conditions affecting normal body chemistry can have adverse effects on the brain
• Tumors Abnormal tissue growths that can exert pressure or damage the surrounding tissue
• Tumors can be benign (non-cancerous) or malignant (cancerous)
• Infections Invasion of the brain or meninges by pathogenic microorganisms, causing inflammation and damage.

Neurotransmitters and Neurons

• Neurotransmitters are chemicals released by presynaptic neurons at synapses to transmit signals to postsynaptic neurons
• Neurotransmitters can have excitatory or inhibitory effects
• Acetylcholine: Involved in muscle contraction, memory, and attention
• Serotonin: Regulates mood, sleep, appetite, and well-being -Imbalances of serotonin relate to depression, anxiety, and eating disorders
• Dopamine: Plays a key role in movement, motivation, reward, and pleasure -Deficiency is associated with Parkinson's, excess with schizophrenia
• Norepinephrine: Participates in stress response, attention, vigilance, and mood regulation
• Glutamate: The primary excitatory neurotransmitter in the CNS, essential for learning and memory
• GABA (Gamma-Aminobutyric Acid): The main inhibitory neurotransmitter in the CNS, reducing neuronal excitability and anxiety
• Endorphins: Neuropeptides acting as natural analgesics, producing pleasure sensations
• Oxytocin: A hormone and neurotransmitter involved in social behavior, bonding, and attachment
• Neurons are the basic functional unit of the nervous system
• Each neuron consists of a soma (cell body containing the nucleus), dendrites (receiving signals), an axon (transmitting electrical signals called action potentials) covered by a myelin sheath (insulating the axon and accelerating impulse conduction), and terminal buttons (releasing neurotransmitters)
• An action potential is a wave of electrical discharge that travels along an excitable cell membrane, generated by rapid voltage increase and decrease across the cell membrane
• The myelin sheath acts as an electrical insulator around the axon, increasing membrane resistance to reduce ionic current leakage
• The myelin sheath has this effect, which prevents leakage of ionic current through the axon membrane
• Nodes of Ranvier, are non-myelinated regions concentrating voltage-gated ion channels
• There are three types of neurons; Sensitive (afferent), Motora (efferent), Intereurons
• Sensory Neurons transmit sensory information from sensory receptors to the CNS
• Motor Neurons transmit motor commands from the CNS to muscles and glands
• Interneurons connect neurons inside the CNS and facilitate communication between sensory and motor circuits

Glial Cells and Synapses

• Glial cells are non-neuronal cells that serve support functions in the nervous system
• Astrocytes provide structural and metabolic support to neurons, regulate ion and neurotransmitter concentrations in the extracellular space, and contribute to the blood-brain barrier
• Oligodendrocytes produce the myelin sheath that insulates axons and accelerates nerve impulse transmission
• Microglia act as immune cells in the brain, phagocytizing cell debris and pathogens
• Ependymal cells line the cerebral ventricles and the spinal cord's central canal, contributing to cerebrospinal fluid production and circulation
• Glial cells are crucial to nervous system function and health, modulating synaptic activity, response to injury, and immune defense
• A Synapse is a specialized region for communication between two neurons or a cells (muscular or glandular)
• Electrical Synapses are direct and allow rapid ion flow between cells through gap junctions, creating less common and mammalian nervous systems
• Chemical Synapses involves releasing neurotransmitters from the presynaptic neuron that bind to receptors on the postsynaptic neuron, generating a response, more abundant with flexibility in neuronal signaling
• Synaptic Plasticity is the ability of synapses to strengthen or weaken over time in response to neural activity
• Electrical Synapses permits fast communication important for fast reflexes and rhythmic activity
• Chemical Synapses offer larger signaling to modulate through different neurotransmitters
• Neurotransmitter release is rigorously controlled, dependent on action potential arrival and calcium ion influx Neurotransmitter binding, creates changes in the membrane that dictate if it will fire a potential to react.