Autonomic Nervous System and Limbic System Overview

Executive Brain vs. Limbic System vs. Brainstem

• Executive Brain:

  • Characteristics: Rational, Decisive, Accurate, Analytical, Practical, Strategic, Realistic, Emotionally Controlled.

• Limbic System:

  • Characteristics: Emotional, Intuitive, Vivid, Passionate, Creative, Related to Love and Freedom.

• Brainstem:

  • Basic life functions regulation.

Structure of the Communication System

• Multi-Tier Communication System:

  • Tier 1: Voluntary "Executive Function"

  • Location: Cerebral cortex

  • Functions: Somatic perception, voluntary movement, cognition, analysis of perceived information, controlled responses to situations.

  • Tier 2: Limbic System

  • Components: Hypothalamus, amygdala, hippocampus

  • Functions: Processes and experiences emotions and drives (e.g., thirst, hunger, libido).

  • Tier 3: Brainstem and Autonomic Nervous System (ANS)

  • Functions: Hard-wired regulation of organ functions (e.g., breathing, heart rate, core temperature) and alertness, sleep-wake regulation through the reticular activating system.

Example Scenarios

• Scenario 1: The Executive Brain chooses to smile in a situation designed to provoke anger, thus inhibiting emotional reactions.

• Scenario 2: The Limbic System generates basic motivational states like thirst, hunger, etc.

• Role of Hypothalamus: Provides information regarding the state of the internal environment.

Autonomic Nervous System (ANS)

Tier 3: ANS Anatomy

• Components:

  • Preganglionic neurons: Note the location in sympathetic and parasympathetic pathways.

  • Postganglionic pathways: Differentiated by location and neurotransmitter release.

• Efferent Pathway:

  • A series of two neurons (Preganglionic & Postganglionic).

  • Preganglionic neuron cell body located in the spinal cord connects to an autonomic ganglion and leads to the target effector organ (e.g., cardiac muscle, smooth muscle, or gland).

Divisions of ANS

• Parasympathetic Division:

  • Also known as the Craniosacral division.

  • Location: Preganglionic neurons in cranial nuclei & sacral region of spinal cord.

  • Function: Enhances digestion and energy storage (rest & digest ).

• Sympathetic Division:

  • Also known as the Thoracolumbar division.

  • Location: Preganglionic neurons located in thoracic and lumbar regions of the spinal cord.

  • Function: Energy mobilization for “fight or flight.”

• Mutual Inhibition: Increased activity in one division leads to decreased activity in the other.

Parasympathetic Division (PNS)

• Functionality includes:

  • Activate digestive processes.

  • Promote nutrient storage (in liver and muscle).

  • Slow heart rate and lower blood pressure.

Sympathetic Division (SNS)

• Functionality includes:

  • Activated by immediate or perceived crisis.

  • Mobilizes nutrients (glucose & fat) into bloodstream.

  • Increases cardiac output and perfusion of active tissues.

  • Dilates bronchial tubes for improved ventilation.

  • Slows digestion and reduces function in non-essential organ systems.

ANS Neurotransmitters and Receptors

Preganglionic Neurotransmitter

• All preganglionic neurons are cholinergic, releasing acetylcholine (ACh) at synapses. This binds to nicotinic ACh receptors on postganglionic cell bodies, leading to Na+ ion channel activation and excitatory postsynaptic potentials (EPSPs).

Postganglionic Neurotransmitters

• Parasympathetic (PNS):

  • ACh binds to muscarinic receptors on glands and smooth muscle; these are slower acting GPCRs.

• Sympathetic (SNS):

  • Norepinephrine (NE) is released, binding adrenergic receptors (GPCRs) in glands and smooth muscle.

Special Exceptions in Sympathetic Division

• Some postganglionic sympathetic neurons release ACh onto sweat glands and bind to muscarinic receptors.

Sympathetic Hormone Release

• Adrenal Medulla Activation: Preganglionic ACh activates chromaffin cells to release epinephrine (adrenaline) as a hormone, acting system-wide for prolonged effects.

ANS Functions and Body Scenarios

1. Relaxation/Sleep

• Parasympathetic Predominance:

  • Digestive activity increases.

  • Increased secretion from salivary glands and digestive organs.

  • Reduced heart rate and blood pressure, leading to decreased mean arterial pressure (MAP).

2. Vigorous Exercise

• Sympathetic Predominance:

  • Decreased digestive activity; there may be sensations of “butterflies.”

  • Increased cardiac output and MAP.

  • Dilation of bronchi for improved ventilation.

  • Energy resources are mobilized through epinephrine release affecting muscles and fat cells.

3. Stress Response

• Sympathetic Predominance: Elevated state in anticipation of danger, involving release of hormones such as cortisol through the hypothalamic-pituitary-adrenal (HPA) axis.

Brainstem Regulation and Functions

Reticular Activating System (RAS)

• Inputs:

  • Cerebral, limbic, sensory, and hypothalamic inputs.

• Outputs:

  • Sends signals to the thalamus (for sensory arousal) and reticulospinal pathways (for motor arousal).

  • Regulates levels of arousal (sleep/wake cycle, attention, alertness).

  • Damage Consequences: Can lead to coma; anesthesia affects RAS functioning.

Neurotransmitters in RAS Regulation

• Key Neurotransmitters:

  • Serotonin: Binds throughout CNS; involved in stress responses.

  • Norepinephrine: Influences arousal states; beta receptors activated during arousal.

  • Dopamine: Affects reward processing and motor control.

Impacts of Neurotransmitter Systems

• Depression: Linked with decreases in serotonin, norepinephrine, or dopamine; many treatments, especially SSRIs (Prozac, etc.), work by increasing these neurotransmitter levels.

Dopamine Systems and Reward Behavior

Dopamine Role

• Regulates 'reward' behaviors, stimulating repetition of rewarding activities.

• Bipolar Disorder: Dysregulated dopamine levels lead to manic states (excess) or depressive states (insufficient).

• Addiction: System is activated by numerous drugs leading to craving and repeat behavior.

  • Noteworthy substances: Alcohol, nicotine, opiates, and cocaine, influencing dopamine transmission.

Sleep Importance

• Categorized into Rapid Eye Movement (REM) and Slow-wave Sleep (SWS).

  • NREM Sleep: Critical for metabolic cleansing, mood regulation, and memory formation.

  • REM Sleep: Involved in dreaming and memory consolidation; deprivation can affect learning.

Tier 2: Limbic System

Components of the Limbic System

• Areas that communicate with the hypothalamus:

  • Amygdala, Hippocampus, Cingulate Cortex.

The Hypothalamus

• Contains nuclei controlling:

  • Feeding, Drinking, Self-defense, Reproduction (the “three F's”).

  • Various nuclei include Paraventricular, Supraoptic, and Suprachiasmatic.

Motivation and Behavior

Law of Effect

• Describes how the limbic system drives behaviors through states of being.

• Reward: Stimuli leading to pleasurable sensations promote behavior repetition.

• Punishment: Stimuli leading to discomfort promote avoidance of behavior.

Neurochemistry of Law of Effect

• Endorphins: Neuropeptides linked to pleasurable sensations and pain alleviation during rewarding activities or vigorous exercise.

• Types: Enkephalins (pleasurable sensations) vs. Dynorphins (unpleasant sensations).

States of Hunger vs. Satiety

• Hypothalamic Activation: Affects caloric balance and initiates feeding behavior.

  • Hunger: Triggered by low blood sugar; results in feelings of discomfort.

  • Satiety: Triggered by normalizing energy levels and leads to positive emotional feedback and memory association.

Limbic System's Role in Learning & Memory

Bit Structure Overview

• Components: Fornix, Hippocampus, Amygdala, Cingulate Gyrus shares roles in memory consolidation and emotional processing.

Amygdala Functions

• Involved with stimuli associations and emotional responses; trigers for irrational fears trigger a sympathetic response via hypothalamus.

Hippocampus Functions

• Consolidates data from STM to LTM, significant for learning and memory retention; damage leads to amnesia.

Cingulate Gyrus

• Involved in anticipation of outcomes based on past experiences, critical for decision-making processes.