Biopsychology: Structure of Neurons PDF

BIOPSYCHOLOGY: Generating Action Potentials: Intracellular Fluid (ICF): STRUCTURE OF NEURONS: The major ions in the ICF include Potassium (K...

BIOPSYCHOLOGY: Generating Action Potentials: Intracellular Fluid (ICF): STRUCTURE OF NEURONS: The major ions in the ICF include Potassium (K+), Phosphate (HPO4^2-), Proteins, and A neuron is a special type of cell in the body Sodium (Na+). that is responsible for sending and receiving messages, which allows different parts of the Extracellular Fluid (ECF): body to communicate with each other. The major ions in the ECF include Sodium (Na+), Chloride (Cl-), Calcium (Ca2+), and The cell body is the neuron's control center, Potassium (K+). processing incoming signals and maintaining the neuron's health. Electrochemical gradient is a combination of a chemical gradient and an electrical gradient Components of Cell body: that drives the movement of ions across Nucleus contains the cell's genetic membranes. material (DNA). Cytoplasm includes various Chemical gradient is formed due to organelles, such as mitochondria for energy differences in the concentration of ions production and ribosomes for protein across the membrane, driving ions from synthesis. higher to lower concentration. The dendrites receive signals from other Electrical gradient is formed due to neurons and conduct electrical messages to differences in electrical charge across the the cell body. membrane, attracting ions to areas of opposite charge. The axon carries electrical impulses away from the cell body to other neurons, muscles, Diffusion and Ion Movement: or glands. Diffusion is the movement of particles from Components of Axon: an area of higher concentration to an area of Axon hillock is the cone-shaped lower concentration, particularly involving region where the axon joins the cell body and ions across the cell membrane. is the site where action potentials are initiated. Ion channels are proteins that create specific Myelin sheath acts as an insulator, pathways for charged ions to pass through increasing the speed of signal transmission the cell membrane. along the axon. Nodes of Ranvier are gaps in the Ion pumps is an active transport mechanisms myelin sheath where ion channels are that move ions against their concentration concentrated, allowing the action potential to gradients using ATP. jump from node to node. The Sodium-Potassium pump (Na+/K+ The axon terminals are the end points of the ATPase) moves 3 Na+ ions out of the cell and axon where the neuron makes contact with 2 K+ ions into the cell, maintaining the other cells and releases neurotransmitters concentration gradients of these ions. into the synaptic cleft. Component of Axon Terminal: Synaptic vesicles contain neurotransmitters that are released into the synapse. The Resting Potential: The all-or-nothing principle states that an action potential either occurs fully or not at The resting potential is the electrical all once the threshold is reached. potential difference across the cell membrane when the cell is not actively The refractory period is a time-based sending signals. It is typically around -70 mV, property following an action potential, while with the inside of the cell being negative propagation describes the movement of the relative to the outside. action potential along the axon. Permeability refers to the ability of the cell EXCITATORY AND INHIBITORY membrane to allow certain substances to pass through while blocking others. NEURONS: The Action Potenial: Two main categories of Neurons: An action potential is a rapid, temporary 1. Excitatory Neurons - they promote the change in the membrane potential that firing of an action potential in the receiving travels along the axon of a neuron. neuron. During depolarization, the membrane Glutamate - most common excitatory potential becomes less negative (more neurotransmitter in the central nervous positive) as Na+ ions rush into the neuron. system. The threshold for triggering an action 2. Inhibitory Neurons - decrease the potential is around -55 mV. likelihood of postsynaptic neuron firing an action potential. During Na+ influx, the influx of Na+ ions makes the inside of the neuron less negative GABA (gamma-aminobutyric acid) - primary (more positive), moving the membrane inhibitory neurotransmitter in the brain. potential towards zero and even beyond. Key types of Excitatory Neurons: Repolarization restores the negative resting membrane potential by the efflux of K+ ions  Pyramidal Neurons: Found in cerebral out of the cell. cortex, hippocampus, and amygdala; involved in cognition, memory, and Hyperpolarization is the process by which the motor control. membrane potential becomes more negative  Granule Cells: Located in dentate gyrus than the resting potential. of hippocampus and cerebellum; involved in memory formation and Refractory Periods: motor coordination.  Spiny Stellate Cells: Found in visual The absolute refractory period is the time cortex; involved in processing visual immediately following an action potential information. during which no stimulus can trigger another action potential. Mechanism of action for Excitatory Neurons: The relative refractory period is the phase 1. Release glutamate into the synaptic cleft. following the absolute refractory period 2. Glutamate binds to AMPA and NMDA during which a neuron can fire another receptors on the postsynaptic neuron. action potential only in response to a 3. Ion channels open, allowing sodium (Na⁺) stronger-than-usual stimulus. and calcium (Ca²⁺) ions to flow in. 4. This depolarizes the cell membrane, moving it closer to the action potential threshold. Types of Glutamate Receptors: Mechanism of action for Inhibitory Neurons: 1. AMPA Receptor (a-amino-3-hydroxy-5- 1. Release GABA into the synaptic cleft. methyl-4-isoxazolepropionic acid) - mediate 2. GABA binds to GABA_A receptors on the fast synaptic transmission and allow sodium postsynaptic neuron. ions to enter the neuron, leading to 3. Ion channels open, allowing chloride ions depolarization. (Cl⁻) to enter the cell. 4. This hyperpolarizes the membrane, moving AMPA is essential for synaptic plasticity, it further from the action potential threshold. learning, and memory. They are usually responsible for the immediate response of a GABA_A Receptors - these are ion channels neuron to glutamate release. that allow chloride ions to enter the neuron, leading to hyperpolarization and inhibition of 2. NMDA Receptor (N-methyl-D-aspartate) - neuronal activity. require both glutamate binding and a depolarized membrane to activate. GABA_A Receptors regulate neuronal excitability, which helps reduce anxiety and NMPA is crucial for synaptic plasticity and promote sleep. long-term potentiation, which are important for learning and memory. Some disorders associated with disruptions in the balance between Excitation and Key differences between AMPA and NMDA Inhibition: receptors: Epilepsy: Excessive neural activity due to Activation: AMPA receptors are activated failure in inhibitory mechanisms. solely by glutamate; NMDA receptors require Schizophrenia: Imbalances in excitatory and glutamate and depolarization. inhibitory signaling affecting thought Ion Permeability: AMPA receptors are processes. primarily permeable to sodium (Na⁺); NMDA Anxiety Disorders: Deficits in inhibitory receptors allow calcium (Ca²⁺) and sodium signaling contributing to heightened anxiety. (Na⁺). Role in Plasticity: NMDA receptors are more How do Excitatory and Inhibitory Neurons significant for synaptic plasticity and long- work together in the brain? term changes. Timing: Excitatory neurons fire quickly; Key types of Inhibitory Neurons: inhibitory neurons calm down later. Different Targets: They hit different parts of  GABAergic Neurons: Release GABA, neurons, shaping overall activity. leading to hyperpolarization of Strength of Signals: Strong excitatory signals postsynaptic neurons. can still make a neuron fire despite inhibitory  Basket Cells: Control output of input. excitatory pyramidal neurons. Learning and Adaptation: Balance can  Parvalbumin-Positive Neurons: Provide change over time based on experience. rapid inhibitory signals for timing control. Network Control: Create patterns of activity  Chandelier Cells: Target axon initial important for brain functions. segment of pyramidal neurons to inhibit action potential initiation. SYNAPTIC TRANSMISSION:  Purkinje Cells: Found in cerebellum; modulate motor movements through Synapse - point where two cells, like neurons GABA release. or a neuron and a muscle cell, communicate with each other. Communication at synapse is important Types of Synapses based on location: because it is key to everything the nervous system does, from moving muscles to 1. Axodendritic - between an axon and a thinking. dendrite. Most common, usually exitatory. 2. Axosomatic - between an axon and a cell 2 Main Types of Synapses: body, often inhibitory. 3. Axoaxonic - between two axons, often 1. Electrical synapses - allow direct fast modulate neurotransmitter release. communication between cells through gap 4. Axospinous - involves a dendritic spine, junctions. important for learning and memory. 5. Dendrodendritic - between two dendrites. Gap junctions - allow electrical signals to pass 6. Neuromuscular junction - specialized directly from one cell to another. synapse between a motor neuron and a muscle cell, built for fast communication to Electrical synapses are useful for reflex ensure precise control of muscle contractions. actions because they provide extremely fast communication. Enzymatic degradation - breakdown of complex molecules into simpler ones through The key feature of electrical synapses the action of enzymes in the synaptic cleft. regarding signal direction, they are both bidirectional, allowing signals to travel both If there are issues with neurotransmitter ways. release, it can lead to disorders, emphasizing the importance of synapses in health and 2. Chemical synapses - more complex and disease. versatile than electrical synapses. NEUROTRANSMITTER SYSTEMS: Chemical synapses involve communication using chemicals called neurotransmitters. Neurotransmitter systems are crucial for brain function. After neurotransmitters bind to receptors on the next neuron, they can either excite or Immunocytochemistry - a technique used to calm the receiving neuron. visualize the location of specific proteins or antigens in cell. Neurotransmitter recycling - allows neurotransmitters to be broken down or In Situ Hybridization - method used to detect taken back into the first neuron for reuse. specific mRNA responsible for synthesizing neurotransmitters. Binding of neurotransmitters affect the receiving neuron by leading to a new Studying Neurotransmitter release: electrical signal in the receiving neuron, continuing the communication chain.  Vitro method - a method commonly used by stimulating brain slices. Action potentials trigger the release of  Optogenetics - a recent advancements neurotransmitters at chemical synapses. to activate specific synapses with light. Synaptic plasticity - process where repeated Synaptic mimicry - methods to replicate use of certain synapses strengthens them, synaptic transmission in a controlled making it easier to trigger an action potential environment. in the future and essential for learning and memory. Microiontophoresis - technique used to test if neurotransmitter candidate evokes a postsynaptic response. Studying Receptors:  Endocannabinoids - a class of lipid molecules that are produced on demand  Neuropharmacological Analysis - and act in a retrograde manner from examining how drugs affect postsynaptic to presynaptic neurons. neurotransmitter receptors. Gaseous Neurotransmitters:  Ligand-Binding Methods- techniques to Nitric Oxide (NO) - regulates blood study the binding of neurotransmitters flow and acts as a retrograde messenger in to their receptors. the brain. Carbon Monoxide (CO) Three categories of neurotransmitters based Hydrogen Sulfide (H2S) on their chemical structures: Cholinergic Neurons: 1. Amino Acids Uses acetylcholine (ACh) as their a) Glutamate - excitatory neurotransmitter that facilitates b) GABA - inhibitory communication between motor neurons and 2. Amines muscle cells. a) Dopamine b) Norepinephrine Choline Acetyltransferase (CHAT) is the c) Serotonin enzyme synthesizes acetylcholine. 3. Peptides a) Endorphins Catecholaminergic Neurons: b) Oxytocin Catecholamines are derived from the amino acid tyrosine release dopamine (DA), Amine neurotransmitters regulate mood, norepinephrine (NE) and epinephrine movement, and attention. (adrenaline), involved in mood regulation, attention and the fight or fight response. G-Protein Coupled Receptors (GPCRs) - initiate slower but more sustained cellular Serotonergic Neurons: responses through second messenger Neurons that releases serotonin, play cascades. a role in mood, appetite and sleep. Evolutionary significance of Selective Serotonin Reuptake Inhibitors neurotransmitters: (SSRIs) - prevent serotonin from being reabsorbed into the presynaptic neuron,  Tied to basic building blocks of life prolonging its action. (amino acids)  Used for multiple functions, including Amino Acidergic Neurons: neurotransmission Glutamate  Most neurotransmitters are amino acids, GABA derivatives (amines), or peptides Glycine  Acetylcholine is synthesized from acetyl CoA and choline The significance of the balance between excitatory and inhibitory neurotransmitters Dale’s Principle - posited by Sir Henry Dale is critical for normal brain function and that each neuron releases a single type of preventing conditions like seizures. neurotransmitter. Dual Roles of Neurotransmitters: Other Neurotransmitter Candidates:  Function in neural communication.  Adenosine Triphosphate (ATP) - widely  Involved in other physiological processes recognized for its role in cellular throughout the body. metabolism