Neuropsychology Notes

The Nervous System

• The nervous system has three main functions:

  • Detecting changes in the internal and external environment through sensory receptors, which convert various stimuli into electrical signals.

  • Processing information by integrating sensory inputs and coordinating appropriate responses within the central nervous system.

  • Coordinating a suitable response by initiating motor commands to muscles or glands to maintain homeostasis or react to external stimuli.

• Sensation vs. Perception:

  • Sensation: Detecting changes in the environment through the five senses, involving sensory receptors and neural pathways.

  • Perception: Interpreting these changes, determining responses and interaction with the environment, influenced by memory, context, and emotional state.

• Key functions of the nervous system:

  • Detects changes in the environment using specialized receptor cells to monitor internal and external conditions.

  • Processes information through neural networks, integrating sensory data to formulate appropriate responses.

  • Coordinates appropriate responses, including heart rate adjustments via the autonomic nervous system and cognitive reactions mediated by the brain.

• Receptor cells:

  • Detect stimuli like visual (photoreceptors), auditory (hair cells), and tactile inputs (mechanoreceptors), initiating neural signals.

Divisions of the Nervous System

• Central Nervous System (CNS):

  • Brain: Receives and processes sensory information, initiates responses, stores memories, and generates thoughts and emotions; includes regions like the cerebral cortex, basal ganglia, and limbic system.

  • Spinal cord: Conducts signals to and from the brain and controls reflex activities, enabling quick responses to stimuli without brain involvement.

• Peripheral Nervous System (PNS):

  • Motor Neurons: Transmit signals from the CNS to muscles and glands, controlling movement and secretion.

    • Somatic Nervous System: Controls voluntary movements via skeletal muscles.

    • Autonomic Nervous System: Controls involuntary responses, maintaining homeostasis.

      • Sympathetic Division: 'Fight or Flight' response, preparing the body for stress.

      • Parasympathetic Division: 'Rest or Digest' response, conserving energy and promoting relaxation.

  • Sensory Neurons: Transmit signals from sensory organs to the CNS, providing information about the external and internal environment.

Central Nervous System (CNS)

• Composition: Brain and spinal cord, the body's primary control center.

• Protection: Encased by the skull and vertebral column, with additional protection from meninges and cerebrospinal fluid.

• Functionality:

  • Control center for physiological processes, from reflexes to advanced cognitive activities, including memory, learning, and decision-making.

  • Reflex Actions: Spinal cord enables quick responses without brain input, such as withdrawing from a hot surface.

  • Communication: Spinal cord conveys messages between the brain and the body, coordinating sensory and motor functions.

Peripheral Nervous System (PNS)

• Connects the brain and spinal cord to the rest of the body, facilitating communication between the CNS and limbs/organs.

• Somatic Nervous System:

  • Controls voluntary movements via skeletal muscles, allowing conscious control over body actions.

  • Sensory receptors send information to the brain to determine necessary body movements, integrating sensory feedback for precise motor control.

• Autonomic Nervous System:

  • Manages involuntary functions (heart rate, digestion, respiratory rate), maintaining internal homeostasis without conscious control.

  • Divided into the Sympathetic and Parasympathetic Systems, which act antagonistically to balance bodily functions.

Autonomic Nervous System

• Sympathetic System:

  • Activates the 'fight or flight' response, preparing the body for high-energy activities.

  • Prepares the body for rapid action by increasing heart rate, lung activity, muscle readiness, and blood vessel activity, ensuring adequate oxygen and nutrient supply to vital organs.

  • Uses neurotransmitters like adrenaline (epinephrine) to stimulate these responses.

• Parasympathetic System:

  • Promotes the 'rest and digest' state, conserving energy and supporting long-term health.

  • Conserves energy and enhances metabolic processes, such as digestion, to replenish energy stores.

  • Maintains homeostasis by regulating body functions like digestion, salivation, and heart rate, ensuring balanced physiological functioning.

Fight or Flight Response

• Managed by the sympathetic nervous system, triggered by perceived threats or stressful situations.

• When faced with stress or danger, the body prioritizes survival, diverting resources to immediate response mechanisms.

• Energy is diverted from normal functions to respond rapidly to threats, enhancing alertness, focus, and physical capabilities.

• Cardiovascular Adjustments:

  • Increases heart rate and blood pressure to enhance blood flow to vital organs and muscles, providing more oxygen and nutrients.

• Blood Sugar Regulation:

  • Increases glucose levels to provide quick energy for muscles and brain functions.

• Respiratory Changes:

  • Expands air passages to increase oxygen intake, ensuring efficient gas exchange.

• Energy Regulation:

  • Rapidly mobilizes energy from stored reserves, such as glycogen and fat, to fuel immediate energy needs.

• Water Elimination:

  • May initiate processes to clear potential distractions or decrease additional metabolic demands, such as bladder emptying.

• The parasympathetic nervous system restores calm, ensuring long-term health and stability by reversing the effects of the sympathetic response.

Reflex Actions

• Rapid and automatic responses involving direct pathways through the spinal cord, bypassing the brain for quick reaction times.

• Sensory neurons detect stimuli and send signals to the spinal cord, initiating a reflex arc.

• Interneurons initiate an immediate response through motor neurons, causing muscles to contract or relax.

• The brain is informed of the action after the reflex has occurred, allowing for later processing and learning.

Neurons

Structure of a Neuron

• Cell body (Soma): Contains the cell nucleus and other organelles, supporting the cell's metabolic functions.

• Dendrite: Receives signals from other neuron cells, branching extensively to increase surface area for synaptic connections.

• Axon: Conducts electrical impulses along the neuron cell, transmitting signals to other neurons or target cells.

• Nucleus: Contains the genetic material of the neuron cell, directing protein synthesis and cell growth.

• Myelin Sheath: Insulates the axon to speed up transmission of electrical impulses, formed by glial cells.

• Axon Terminal: Transmits electrical and chemical signals to other neuron cells, releasing neurotransmitters into the synapse.

• Axon Hillock: Generates impulse in the neuron, initiating the action potential.

Types of Neurons

• Sensory Neuron:

  • Carries information from sensory receptors (skin, eyes, ears) to the brain and spinal cord, enabling perception of the environment.

  • Responds to physical stimuli (sound, touch, heat, light) and chemical stimuli (smell, taste), converting them into electrical signals.

• Interneuron:

  • Facilitates communication between sensory and motor neurons within the brain and spinal cord, integrating sensory information.

  • Refines and relays signals from sensory neurons to motor neurons, modulating responses.

• Motor Neuron:

  • Controls voluntary and involuntary movements, innervating muscles and glands.

  • Transmits signals from the brain and spinal cord to the body's muscles and glands, initiating movement or secretion.

  • Lower Motor Neurons: Transmit signals from the spinal cord to muscles, directly causing muscle contraction.

  • Upper Motor Neurons: Relay commands from the brain to the spinal cord, influencing lower motor neuron activity.

Chemical Messaging in Neurons

• Action Potential:

  • Electrical impulse that travels along the axon of a neuron, enabling rapid communication.

  • At rest, the neuron is inactive until triggered by a stimulus, maintaining a resting membrane potential.

  • The action potential propagates down the axon, insulated by the myelin sheath, which speeds up signal transmission.

• The Synapse:

  • The synaptic gap prevents direct electrical contact between neurons, ensuring regulated communication.

  • It is the critical site for chemical communication between neurons, where neurotransmitters are released and received.

Release and Action of Neurotransmitters

• Storage: Neurotransmitters are stored in vesicles within axon terminals, ready for release upon stimulation.

• Release: Neural signals trigger the release of neurotransmitters into the synapse, initiating communication between neurons.

• Binding: Neurotransmitters bind to specific receptors on the post-synaptic neuron, triggering a response in the receiving cell.

• Lock and Key Mechanism: Ensures precise signal transmission, with specific neurotransmitters binding to specific receptors.

• Recycling: Neurotransmitters are reabsorbed by the pre-synaptic neuron for reuse or broken down, regulating neurotransmitter levels in the synapse.

Excitatory and Inhibitory Neurotransmitters

• Excitatory Neurotransmitters:

  • Glutamate: Enhances neural signal transmission; vital for learning, memory, and cognitive functions, promoting neuron excitability.

• Inhibitory Neurotransmitters:

  • GABA: Inhibits neural signal transmission; regulates neural activity and prevents over-excitation, maintaining neural stability.

• Glutamate Imbalances:

  • Can lead to neurological disorders like Alzheimer’s disease and seizures due to excitotoxicity and neuronal damage.

• Low Levels of GABA:

  • Associated with conditions like anxiety and depression, as inhibitory control over neural activity is reduced.

Dendrite Growth

• Dendrites expand as we learn, reflecting the brain's dynamic nature and ability to adapt.

• This growth continues throughout life, allowing for ongoing learning and adaptation.

• Each dendrite develops receptors and protein molecules for synaptic communication, enhancing connectivity between neurons.

Key Neurotransmitters

• Dopamine: Feelings of pleasure, addiction, movement, and motivation; influences reward-seeking behaviors.

• Serotonin: Contributes to well-being and happiness, helps regulate sleep cycle and digestion; modulates mood and emotional balance.

• Oxytocin: Hormone and neurotransmitter crucial in reproduction and social bonding; promotes trust and attachment.

The Brain

Basics About The Brain

• The average brain weight is 1.4 kgs or around 2% of total body weight, reflecting its high energy demands.

• 1/3 of the body's blood supply goes to the brain, ensuring adequate oxygen and nutrients for its intense metabolic activity.

• There is a small gap between the brain and the skull to protect from any damage, cushioning it against impacts.

• The brain has three main regions – the hindbrain, midbrain, and the forebrain, each responsible for distinct functions.

• Controls our thoughts, emotions, and behavior, orchestrating complex cognitive and emotional processes.

• Protected by the skull and cerebrospinal fluid, providing physical and chemical protection.

Protecting the Brain

• The brain is protected by the skull, providing a rigid barrier against external impacts.

• Three layers of protective tissue called meninges surround the brain:

  • Dura Mater: The thick, outermost layer closest to the skull, providing a tough protective barrier.

  • Arachnoid: The middle layer, containing blood vessels and cerebrospinal fluid, cushioning the brain.

  • Pia Mater: The thin, delicate layer directly covering the brain, adhering closely to its surface.

• Cerebrospinal Fluid (CSF):

  • Located between the arachnoid and pia mater, cushioning and protecting the brain.

  • Acts as a cushion to protect against injury, absorbing shocks and impacts.

• Blood-Brain Barrier:

  • Prevents harmful toxins from entering the brain, maintaining a stable internal environment.

  • Allows only water, oxygen, carbon dioxide, small lipid-soluble molecules, and small electrolytes to pass through, regulating the passage of substances into the brain.

The Hindbrain

• Located at the base of the brain, connecting the brain to the spinal cord.

• Controls vital functions: breathing, heart rate, movement, sleep, ensuring basic survival.

• Includes medulla oblongata, pons, cerebellum, each playing a crucial role in these functions.

Components of the Hindbrain

• Medulla Oblongata:

  • Controls autonomic functions: breathing, heart rate, blood pressure, maintaining essential physiological processes.

  • Coordinates reflexes like sneezing and vomiting, protecting the body from harmful stimuli.

• Pons:

  • Connects spinal cord to the brain, facilitating communication between the two.

  • Transfers sensory and motor information, enabling coordinated movements.

  • Involved in sleep, eye and facial movements, balance, contributing to overall physical coordination.

• Cerebellum:

  • Coordinates posture, balance, and movement, ensuring smooth and accurate motor control.

  • Adjusts body position automatically, maintaining equilibrium and coordination.

  • Involved in language and emotional perception, contributing to cognitive and emotional processing.

The Midbrain

• Located above the medulla, serving as a relay center for sensory and motor information.

• Associated with vision, hearing, motor movement, integrating sensory inputs to coordinate motor outputs.

• Regulates sleep/wake cycles, temperature, and alertness, influencing overall arousal and attention.

• Believed to be involved with suppression of pain, modulating pain signals.

• Substantia Nigra: Produces dopamine, which is crucial for motor control and reward.

The Forebrain

• Largest and most complex part of the brain, responsible for higher-order functions.

• Controls reproduction, sleeping, eating, emotions, and body temperature, maintaining homeostasis and regulating behavior.

• Responsible for higher-order thinking like reasoning, decision-making, and information processing, enabling complex cognitive abilities.

External Structures of the Forebrain

• Cerebrum:

  • Largest part of the brain, divided into two hemispheres connected by the corpus callosum, allowing for coordinated function.

  • Responsible for voluntary actions, conscious thought, and sensory processing, facilitating complex cognitive and motor control.

  • Grey Matter: Outer layers, process information, containing neuron cell bodies and synapses.

  • White Matter: Deeper layers, transmit information, consisting of myelinated axons.

• Cerebral Cortex:

  • Wrinkled outer layer (gyri and sulci), increasing surface area for neural processing.

  • Sensory Cortex: Processes sensory information from various parts of the body, enabling perception.

  • Motor Cortex: Controls voluntary muscle movements, coordinating motor commands.

  • Basal Ganglia: Filters movement signals, ensuring smooth and coordinated movements.

Internal Structures of the Forebrain

• Thalamus: Relays sensory information (except smell) to the cortex, acting as a sensory relay station.

• Hypothalamus: Controls hunger, thirst, temperature, and sleep; links the nervous system to the endocrine system, maintaining homeostasis.

• Pineal Gland: Produces melatonin to regulate the sleep–wake cycle, influencing circadian rhythms.

• Limbic System: Controls emotion, memory, and motivation; includes the amygdala and hippocampus, modulating emotional responses and memory formation.

Brain Lobes

• Frontal Lobe:

  • Motor control, problem solving, executive functions, and higher-order thinking.

• Temporal Lobe:

  • Hearing, language, and memory, processing auditory information and forming memories.

• Occipital Lobe:

  • Vision, processing visual information.

• Parietal Lobe:

  • Spatial navigation and touch, integrating sensory information for spatial awareness.

• Cerebellum:

  • Balance and Coordination, ensuring smooth motor control.

• Brain Stem:

  • Involuntary responses, regulating essential life functions.

Temporal Lobe

• Located behind the ears; essential for creating long-term memories and auditory processing.

  • Creating long-term memories (with the hippocampus and amygdala), encoding and storing information for later retrieval.

  • Auditory processing (understanding language and remembering verbal information), enabling comprehension of spoken words and sounds.

• Left temporal lobe:

  • Dominant in most people, specializing in language processing.

  • Focuses on language comprehension, understanding word meaning and sentence structure.

• Right temporal lobe:

  • Involved in learning and remembering non-verbal information (e.g., visual-spatial cues, music), processing patterns and sounds.

Parts of Temporal Lobe

• Auditory Cortex:

  • Processes auditory information (pitch, volume, and sound location), enabling perception of sound.

  • Converts sound signals into meaningful language and environmental sounds, facilitating comprehension.

• Hippocampus:

  • Deep within the temporal lobe, essential for memory formation.

  • Key role in forming and retrieving long-term memories, consolidating new information.

  • Supports spatial memory (e.g., navigation), enabling orientation and spatial awareness.

  • Part of the limbic system, contributing to emotional processing.

• Amygdala:

  • Located near the hippocampus; helps process emotions.

  • Regulates emotional responses, especially fear and aggression, influencing emotional behavior.

  • Triggers the fight-or-flight response, preparing the body for danger.

  • Helps recognize emotions in facial expressions, contributing to social perception.

• Hypothalamus:

  • Located in the temporal lobe; part of the limbic system, regulating homeostasis and behavior.

  • Involved in survival behaviors: feeding, reproduction, fight or flight, ensuring basic needs are met.

  • Acts as a control center for maintaining homeostasis (internal balance), controlling body temperature, hunger, and thirst.

  • Produces:

    • Dopamine: Provides pleasure and reward, influencing motivation.

    • Oxytocin: Involved in bonding and emotional regulation, promoting social attachment.

• Pituitary Gland:

  • Located beneath the hypothalamus in the temporal lobe, producing hormones.

  • Produces many essential hormones such as ones that control sperm production and egg release, regulating reproductive functions.

  • Stimulates the adrenal glands to produce cortisol - a key hormone in the fight or fight response, preparing the body for stress.

• Thalamus:

  • Located in the temporal lobe, just above the hypothalamus at the top of the brainstem, serving as a relay station.

  • Acts as a relay station for sensory and motor signals, transmitting information to the cerebral cortex.

  • Regulates:

    • Sleep and wakefulness, influencing circadian rhythms.

    • Learning and memory, consolidating new information.

    • Attention and motor coordination, facilitating cognitive and motor control.

  • Contributing to emotional regulation, modulating emotional responses.

• Pineal Gland:

  • A small gland in the center of the brain; its primary role is to regulate the sleep-wake cycle through the secretion of a hormone called melatonin.

  • Plays a role in bone metabolism, influencing bone density.

  • Natural decline in function with age:

    • May lead to lower bone density, increasing risk of fractures.

    • Increased risk of osteoporosis, especially in women, due to reduced melatonin production.

Occipital Lobe

• Located at the back of the brain; processes vision.

• Dedicated to vision and visual processing, enabling visual perception.

• Contains the visual cortex, which receives information from the retina, translating visual inputs into meaningful information.

• Key functions: mapping the visual world, spatial reasoning, recognizing color, distance, size, and depth, enabling visual interpretation of the environment.

Parietal Lobe

• Located at the top rear of the cerebrum; helps interpret touch.

• Primary role: Interprets sensations of touch (temperature, pressure, pain, vibration, body position), providing awareness of physical sensations.

• Informs the brain about movement and position of body parts, contributing to proprioception and motor control.

Frontal Lobe

• Located behind the forehead; important for cognitive functions and voluntary movement.

• Contains the motor cortex, responsible for planning and executing voluntary movement.

  • Works alongside the somatosensory cortex, organized by a motor homunculus, representing the body's motor and sensory functions.

• Controls voluntary movement, expressive language, personality and emotional expression, impulse control, memory, and social behavior, influencing complex behavior.

• Contains many dopamine neurons to regulate input from the thalamus, modulating motor control and reward-seeking behaviors.

Prefrontal Cortex

• Region responsible for executive functions, including:

  • Flexible thinking, problem-solving, and decision-making, enabling adaptability.

  • Working memory, holding information in mind for short-term use.

  • Task prioritization, organizing and planning activities efficiently.

  • Risk assessment and impulse control, evaluating potential consequences.

• Plays a role in moral and ethical decision-making, influencing social behavior.

• In teenagers, immaturity of this area may lead to increased risk-taking behavior, due to underdeveloped executive functions.

Broca's Area

• Broca's area is located in the frontal lobe; controls speech.

• Responsible for:

  • Language production, generating spoken and written language.

  • Sentence formation, constructing grammatically correct sentences.

  • Articulate, logical speech, enabling clear and coherent communication.

Brain Hemispheres

• Left Hemisphere:

  • Controls the right side of the body; language, speech, reading, writing, enabling verbal and analytical abilities.

• Right Hemisphere:

  • Controls the left side of the body; shape recognition, musical and artistic perception, visual data processing, facilitating spatial and creative abilities.

Neurotransmitters

What are Neurotransmitters

• Chemicals used by the nervous system to transmit signals between neurons.

• Influence our thoughts, behaviors, and emotions, modulating mood and behavior.

• Examples include:

  • Serotonin, regulating mood and sleep.

  • Dopamine, associated with pleasure and motivation.

  • Oxytocin, promoting bonding and trust.

  • Cortisol, released in response to stress.

  • Noradrenaline, involved in the fight-or-flight response.

Serotonin

• Function: Regulates mood, sleep, appetite, learning, and memory, influencing various physiological processes.

• Low levels are linked to depression and anxiety, contributing to mood disorders.

• SSRIs increase serotonin availability in the brain, improving mood and alleviating depression symptoms.

Dopamine

• Associated with pleasure, motivation, satisfaction, influencing reward-seeking behaviors.

• Released in the brain’s reward system, reinforcing positive behaviors.

• Plays a key role in learning and reinforcement, associating actions with rewards.

• Addiction and risk-taking behaviors are often linked to dopamine dysregulation, influencing impulsive behavior.

Oxytocin

• Released during childbirth, breastfeeding, and bonding, fostering social connections.

• Promotes trust, empathy, social bonding, strengthening relationships.

• Helps reduce stress and anxiety, promoting relaxation.

Cortisol

• Released in response to stress, mobilizing energy and increasing alertness.

• Helps regulate blood pressure, immunity, inflammation, influencing various bodily functions.

• Impacts brain structure (e.g., enlarges amygdala), altering brain circuitry.

• Chronic high levels are linked to depression, anxiety, weakened immune system, heart disease, and memory issues, impairing mental and physical health.

Instant Gratification and the Brain

• Social media provides instant rewards that change how the brain seeks pleasure, influencing reward expectations.

• Boredom becomes less