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Autonomic Nervous System - Anatomy & Physiology

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  • Divisions of the Nervous System
    The Nervous System has 2 main divisions: Central Nervous System (CNS) and Peripheral Nervous System (PNS). The PNS further divides into the Somatic Nervous System (SNS) and Autonomic Nervous System (ANS).
  • Divisions of the Autonomic Nervous System (ANS)
    The ANS has two divisions: Sympathetic (fight or flight) and Parasympathetic (rest and digest).
  • Somatic Nervous System Control
    Motor neurons of the CNS exert direct control over skeletal muscles via Lower Motor Neurons (LMN) and Upper Motor Neurons (UMN).
  • Visceral Reflex Arc Components
    Made of 2 motor neurons: Preganglionic neurons (in brainstem/spinal cord) and Ganglionic neurons (in autonomic ganglia) that innervate cardiac muscle, glands, and fat cells.
  • Enteric Nervous System
    A nerve network in the walls of the digestive tract controlled by the ANS and visceral reflexes, containing about 1 million neurons.
  • Sympathetic Division Location and Fiber Lengths
    Also called thoracolumbar division (T1-L2). Has short preganglionic fibers and long postganglionic fibers.
  • Functions of the Sympathetic Division
    Increases tissue metabolism, mental alertness, respiratory function, heart rate, blood pressure, and activates sweat glands; decreases digestive and urinary functions.
  • Sympathetic Chain Ganglia
    Also called paravertebral ganglia; paired chains on both sides of the vertebral column controlling body walls, thoracic cavity, head, and limbs.
  • Collateral Ganglia
    Also called prevertebral ganglia; located anterior to the vertebral column, innervating tissues and organs in the abdominopelvic cavity.
  • Adrenal Medullae Role
    Specialized ganglionic neurons in adrenal glands that release neurotransmitters (norepinephrine, epinephrine) into the bloodstream affecting target cells body-wide.
  • White Ramus vs Gray Ramus
    White ramus: myelinated preganglionic fibers (T1-L2 only). Gray ramus: unmyelinated postganglionic fibers, present in all spinal nerves.
  • Horner’s Syndrome
    Damage to thoracic/cervical sympathetic pathways causing loss of sympathetic control of the face, resulting in pupil constriction and flushed face due to parasympathetic dominance.
  • Parasympathetic Division Location and Fiber Lengths
    Also called craniosacral division; has long preganglionic fibers and short postganglionic fibers. Preganglionic fibers originate in brainstem and sacral spinal cord.
  • Functions of the Parasympathetic Division
    Decreases metabolic activity, heart rate, and blood pressure; increases digestive secretions, blood flow to digestive tract, urination, defecation, and sexual arousal.
  • Parasympathetic Cranial Nerves
    Preganglionic fibers are part of cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal), and X (vagus), with the vagus providing 75% of parasympathetic innervation.
  • Neurotransmitters of the ANS
    Two main types: Cholinergic (use acetylcholine) and Adrenergic (use norepinephrine or epinephrine).
  • Cholinergic Receptors
    Two types: Nicotinic receptors (excitatory, found on ganglion cells and neuromuscular junctions) and Muscarinic receptors (excitatory or inhibitory, found on target organs).
  • Adrenergic Receptors
    Two main types: Alpha (α) receptors (α1 excitatory, α2 inhibitory) and Beta (β) receptors (β1 excitatory, β2 inhibitory, β3 stimulates lipolysis).
  • Dual Innervation and Autonomic Tone
    Most visceral organs receive input from both sympathetic and parasympathetic divisions; balance between them is called autonomic tone.
  • Visceral Reflex Example
    Pupil size is controlled by sympathetic (dilation) and parasympathetic (constriction) reflexes, modulated by the hypothalamus and higher brain centers.
  • Types of Mechanoreceptors
    Include tactile receptors (touch, pressure), baroreceptors (pressure changes in vessels), and proprioceptors (joint and muscle position).
  • Types of Tactile Receptors
    Six types: Free nerve endings, Root hair plexus, Merkel discs, Meissner's corpuscles, Pacinian corpuscles, and Ruffini corpuscles, each sensitive to different touch or pressure stimuli.
  • Alzheimer’s Disease Characteristics
    Progressive loss of higher cerebellar functions causing senile dementia; associated with plaques, neurofibrillary tangles, and reduced neurotransmitter production.
  • Effects of Aging on the Nervous System
    Includes brain size and weight reduction, neuron loss, decreased blood flow, fewer synapses, and slower motor skills.