Neuron Basics and Synaptic Communication

Neuron Basics

• Neuron membrane depolarizes during an action potential, changing voltage and propagating along the axon.
• At resting potential, the neuron's inside is negatively charged compared to the outside.
• Potassium (K+) is the main ion establishing resting potential.
• The sodium-potassium pump actively moves sodium ions out and potassium ions into the neuron against the concentration gradient.
• The resting potential is crucial for generating an action potential when the neuron is stimulated.
• Any change in resting potential due to stimulation is a graded potential.

Synaptic Communication

• An excitatory postsynaptic potential (EPSP) occurs when a neurotransmitter binds to receptors and depolarizes the postsynaptic membrane.
• An inhibitory postsynaptic potential (IPSP) occurs when neurotransmitter binding hyperpolarizes the postsynaptic membrane.
• The axon hillock integrates the summed potential, determining if an action potential will be generated.
• Summation is the process of adding multiple EPSPs and IPSPs to determine the overall change in membrane potential.
• A neuron is more likely to reach the threshold and fire an action potential if the sum of EPSPs exceeds the sum of IPSPs.
• EPSPs typically involve sodium (Na+) influx, while IPSPs often involve chloride (Cl-) influx.
• EPSPs are usually shorter than IPSPs.
• The axon hillock has a high density of voltage-gated Na+ channels, making it sensitive to membrane potential changes.

Brain Anatomy

• The cerebral cortex is divided into four main lobes.
• The occipital lobe primarily processes visual information.
• The frontal lobe houses the primary motor cortex.

Neuron Types And Functions

• Cortical neurons are involved in higher cognitive functions, are arranged in layers.
• Subcortical and brainstem neurons are involved in basic life functions, emotion, and movement regulation, lacking the layered organization of cortical neurons.

Neurotransmitter Deactivation

• Two ways to deactivate a neurotransmitter: reuptake and enzymatic degradation.
• Reuptake involves the presynaptic neuron reabsorbing the neurotransmitter.
• Enzymatic degradation involves specific enzymes breaking down the neurotransmitter (e.g., acetylcholinesterase breaks down acetylcholine).

Excitatory Postsynaptic Potential (EPSP)

• An EPSP is a temporary depolarization of the postsynaptic membrane.
• It is caused by the influx of positively charged ions (usually Na+).
• EPSPs make the neuron more likely to fire an action potential if the threshold is reached.

Feedback Loops

• Negative feedback loop counteracts the initial change, maintaining balance.
• Example: The HPA axis regulating cortisol levels.
• Positive feedback loop amplifies the initial stimulus.
• Example: Oxytocin release during childbirth, intensifying uterine contractions.

Cerebral Cortex vs. Subcortical Structures

• The cerebral cortex handles higher cognitive functions, while subcortical structures are involved in emotion, memory, and motor control.
• Together, they integrate cognitive functions with emotional and motor responses, allowing for coordinated behavior.

Neural Signaling

• Signaling involves five steps:
  • Resting potential: The neuron is at -70 mV.
  • Depolarization: Na+ channels open, allowing Na+ to enter the neuron, raising the membrane potential.
  • Repolarization: K+ channels open, causing K+ to leave the neuron, restoring the membrane potential.
  • Hyperpolarization: The potential dips below -70 mV briefly.
  • Return to resting potential: The Na+/K+ pump restores the resting state.

Electrical vs. Chemical Communication

• Electrical communication involves transmission of action potentials along the axon through ion movement. It is fast and allows for rapid signal propagation.
• Chemical communication occurs at the synapse, involving neurotransmitter release and binding to receptors on the postsynaptic neuron. It is slower but allows for greater modulation and complex signaling.

Negative Feedback

• Negative feedback helps regulate processes by maintaining homeostasis.
• Example: In the HPA axis, when cortisol levels rise due to stress, the hypothalamus and pituitary gland reduce CRH (Corticotropin-Releasing Hormone) and ACTH (Adrenocorticotropic Hormone) production, leading to lower cortisol production and restoring balance.

Neuron Electrophysiology

• Electrophysiology studies the electrical properties of neurons, including their membrane potential and the generation of action potentials.
• Neurons communicate through changes in electrical charge across their membranes, driven by the movement of ions.

Allostatic Load

• Allostatic load refers to the cumulative "wear and tear" on the body resulting from chronic exposure to stress and physiological responses.
• It can lead to health problems like cardiovascular disease and cognitive decline.

PANDAS

• PANDAS stands for Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections.
• It is a condition where streptococcal infections trigger an autoimmune response that affects the brain, leading to sudden-onset OCD and tics in children.

Ventricles of the Brain

• The ventricles are interconnected cavities producing and circulating cerebrospinal fluid (CSF).
• The major ventricles are:
  • Lateral ventricles (1st and 2nd): Located in each cerebral hemisphere.
  • Third ventricle: Located in the diencephalon.
  • Fourth ventricle: Located between the brainstem and cerebellum.

DSM

• The Diagnostic and Statistical Manual of Mental Disorders (DSM) is a manual used by healthcare professionals to diagnose and classify mental health conditions.
• It provides standardized criteria for diagnosing various mental disorders.

SAM Pathway

• Fast response pathway (SAM): This involves the sympathetic nervous system and the adrenal medulla, which releases epinephrine and norepinephrine. This prepares the body for immediate action (fight or flight).
• Slow response pathway (HPA): This involves the hypothalamus, pituitary gland, and adrenal cortex, which releases cortisol for long-term stress adaptation.

Atomic Theory

• Before the atomic theory, it was not possible to explain chemical reactions in terms of indivisible units (atoms).
• The atomic theory provided a foundation for understanding the composition and behavior of matter at the microscopic level.

Ventricle System

• The ventricle system consists of interconnected cavities in the brain producing and circulating cerebrospinal fluid (CSF).
• It helps cushion the brain, maintain pressure, and remove waste.

Brain Structure and Function

• The appearance of a brain region affects its function. Folds (gyri) and grooves (sulci) of the cerebral cortex increase surface area, allowing for more complex processing.
• Distinct structures, like the cerebellum, are specialized for specific tasks like motor coordination.

Action Potential

• Resting potential: -70 mV.
• Depolarization: +30 mV (due to Na+ influx).
• Repolarization: Drops back to negative values (due to K+ outflow).
• Hyperpolarization: Potential dips below -70 mV briefly.
• Return to resting potential: Na+/K+ pump restores balance.

Synapse

• A synapse is the junction between two neurons where electrical signals are converted into chemical signals through the release of neurotransmitters.
• It allows communication between neurons.

Cerebrum vs. Cerebellum

• Cerebrum: Responsible for higher cognitive functions (thinking, decision-making, voluntary movement). It consists of two hemispheres with four lobes: frontal, parietal, occipital, and temporal.
• Cerebellum: Involved in motor coordination, balance, and learning new motor skills. It is located at the back of the brain, beneath the cerebrum.

Cortical vs. Subcortical Regions

• Cortical regions: The cerebral cortex is responsible for higher-order functions. It consists of four lobes: frontal, parietal, temporal, and occipital.
• Subcortical regions: Located beneath the cortex, they are involved in more fundamental processes (emotion, memory, basic survival functions).

Action Potential Process

• Resting potential: Neuron is at -70 mV.
• Depolarization: Na+ channels open, causing Na+ to enter the neuron, raising the membrane potential to +30 mV.
• Repolarization: K+ channels open, allowing K+ to leave the neuron, restoring the membrane potential.
• Hyperpolarization: The potential dips below -70 mV briefly.
• Return to resting potential: The Na+/K+ pump restores the resting state.

Action Potential vs. Resting Potential

• Action potential: A rapid, temporary change in membrane potential due to depolarization, leading to signal transmission (+30 mV).
• Resting potential: The stable, negative charge of the neuron when not transmitting signals (-70 mV).

Hormones vs. Neurotransmitters

• Hormones: Released by glands, travel through the bloodstream, slower, affect distant organs.
• Neurotransmitters: Released by neurons at synapses, fast-acting, affect nearby cells.

Hormonal vs. Neural Signaling

• Speed: Neural signaling is much faster than hormonal signaling.
• Distance: Neural signals are localized, whereas hormones travel throughout the bloodstream.

Chemical vs. Electrical Signaling

• Electrical signaling: Action potentials, fast, involves ion movement (Na+, K+).
• Chemical signaling: Involves neurotransmitter release at synapses, slower but allows for greater modulation.

Activating the SAM Pathway

• Stress activates the hypothalamus.
• The sympathetic nervous system is stimulated.
• The adrenal medulla releases epinephrine and norepinephrine, triggering the fight-or-flight response.