12 ANS&Limbic

The Autonomic Nervous System and Limbic System

Overview

• Health Sciences & iBioMed Course: Anatomy and Physiology I (HTHSCI 2F03, HTHSCI 2L03, HTHSCI 1D06).

Outline of Key Topics

• Limbic System

• Autonomic Nervous System (ANS)

• Emotional Response

• Referred Pain

Limbic System

• Definition: A collection of grey-matter nuclei connected via white matter tracts, essential for emotional and behavioral responses, as well as memory functions.

Anatomical Components

• Deep Nuclei: Includes Basal Ganglia and Limbic System.

• Coronal and Transverse Views: Red areas denote the limbic system; green denotes basal ganglia.

Fiber Tracts

• The limbic system is connected by arcs of fiber tracts contributing to its functionality.

Memory Formation

• Hippocampal Formation:

  • Afferent Pathway: Dentate Gyrus

  • Efferent Pathways: Subiculum and Hippocampus

• Anterior Thalamus and Hypothalamus: Includes Mammillary Bodies, crucial for memory and emotional/behavioral responses.

Grey Matter Structures

• Cingulate Lobe: Comprised of the Cingulate Gyrus and Parahippocampal Gyrus.

Major Structures of the Limbic System

• Amygdala:

  • Analyses emotions such as anger and fear.

  • Elicits fear responses and assesses danger.

  • Works closely with memory alongside the hippocampus.

• Hippocampus:

  • Critical for long-term memory formation—who, what, where, when—via the fornix.

• Mammillary Bodies:

  • Function as thalamic relay and are involved in recollective memory.

Types of Memory

• Location:

  • Medial Temporal Lobe (thalamus, amygdala, hippocampus): Event Memory.

  • Neocortex: Factual Memory.

  • Cerebellum and Basal Nuclei: Muscle Memory.

Sensory Processing

• Cingulate Cortex: Connects sensory—smell, touch, vision—with emotional responses via various brain structures, including the anterior thalamic nuclei and prefrontal cortex.

Autonomic Nervous System (ANS)

• Function: Controls glands and involuntary muscles; maintains homeostasis (blood pressure, etc.).

• Sensory Part: Largely neglected except in contexts of referred pain and interoception.

ANS at Work: Sample Scenario

• Identifying Responses: Blood pressure increases involuntarily when standing up due to detection by visceral receptors.

• Control Centers: Processes are integrated in the brainstem with afferent and efferent pathways adjusting sympathetic and parasympathetic responses.

Divisions of the Nervous System

• Somatic and Autonomic Divisions: Functions include voluntary control (somatic) versus involuntary (autonomic).

• Sub-Divisions: Sympathetic (fight, flight) vs. Parasympathetic (rest, relaxation).

Sympathetic vs. Parasympathetic Responses

• Cardiac Functionality: Sympathetic input increases heart rate; parasympathetic input decreases it.

• Gastrointestinal Activity: Sympathetic yields relaxation, while parasympathetic increases activity.

Autonomic Input Dominance

• Each organ receives input predominately from one branch of the ANS (e.g., heart mainly from parasympathetic).

• Exceptions: Sweat glands and certain blood vessels receive sympathetic only input.

Pupil Control

• Physiological Terms: Miosis (constriction) and mydriasis (dilation) are controlled by the parasympathetic and sympathetic systems, respectively.

Neurotransmission in the ANS

• Cholinergic Receptors: Involved in both sympathetic and parasympathetic ganglia and effectors.

• Adrenergic Receptors: Specific to sympathetic postganglionic targets.

Adrenergic Drugs

• Beta-blockers and Agonists: Used to manage conditions like hypertension and asthma by influencing receptor activity.

Limbic Regulation of Stress Response

• The limbic system communicates stressful signals to the ANS, particularly through connections between the amygdala and hypothalamus, leading to a rapid physiological response during stress.

HPA Axis and Hormone Signals

• Components: Hypothalamus, Pituitary Gland, and Adrenal Glands coordinate stress responses and hormone release.

Referred Pain Mechanism

• Definition: Visceral pain often felt as dull and located away from the actual site of damage due to the sympathetic nerves conveying signals to the CNS.

Summary of Control Systems

• The ANS operates involuntarily to maintain necessary regulative functions. Control is primarily exerted by the connections from the limbic system.