Autonomic physiology

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AUTONOMIC PHARMACOLOGY & PHYSIOLOGY

Peripheral
Anatomy
Clinical-Anatomic
Disorders
Pharmacology
Physiology
Central
Baroreceptor pathways

AUTONOMIC ANATOMY & PHARMACOLOGY: PERIPHERAL

Autonomic Nervous System: Anatomy

From: University of Queensland

Baroreceptor Pathways: Central

Principles

Preganglionic: Motor neurons leaving CNS release acetylcholine (ACh)
- Acts on nicotinic AChRs.
- Somatic motor neuron synapses contain AChRs
  - Blocked by: α-Bungarotoxin & Tubocurarine
- Autonomic motor neuron (preganglionic) synapses (in ganglia) contain
  - Nicotinic AChRs: Blocked by hexamethonium, but not by α-bungarotoxin
  - Some muscarinic receptors: Blocked by atropine
  - Chromaffin cels in the adrenal medulla
    - Modified sympathetic ganglion cells
    - Contain only nicotinic receptors
Postganglionic axons
- Parasympathetic terminals release ACh: Acts on muscarinic AChRs
- Sympathetic terminals
  - Usually release noradrenaline
    - Acts on α, β1, or β2 adrenoceptors
  - Eccrine sweat glands and pilierector muscles: ACh acts on muscarinic AChRs
Anatomy
- Sympathetic system arises from: Thoracic & Lumbar (L2 & above) levels
- Parasympathetic system arises from: Cranial & Sacral levels

ORGAN-SPECIFIC EFFECTS OF AUTONOMIC ACTIVITY

Sympathetic vs Parasympathetic

Organ	Sympathetic Stimulation	Parasympathetic Stimulation
General Principles Parasympathetic vs Sympathetic systems Often have antagonistic effects in each organ Sweat glands & most vascular smooth muscles: Only sympathetic innervation Ciliary muscle of the eye: Only parasympathetic innervation Bronchial smooth muscle Only parasympathetic innervation: Constriction Smooth muscle sensitive to circulating adrenaline: Dilation Salivary glands: Systems produce similar, rather than opposite, effects
Heart	↑ Rate (β₁ & β₂)	↓ Rate
	↑ Contractile force (β₁ & β₂)	↓ Contractile force
	↑ Conduction velocity	↓ Conduction velocity
Artery	Constriction (α₁)	Dilation
Artery	Dilation (β₂)	Dilation
Vein	Constriction (α₁)
Vein	Dilation (β₂)
Lung	Bronchial muscle: Relaxation (β₂)	Bronchial muscle contraction
Lung	Bronchial muscle: Relaxation (β₂)	Bronchial gland secretion
Gastrointestinal tract	↓ Motility (β₂)	↑ Motility
Gastrointestinal tract	Sphincter: Contraction (α)	Sphincter: Relaxation
Liver	Glycogenolysis (β₂ & α)	Glycogen synthesis
	Gluconeogenesis (β₂ & α)
	Lipolysis (β₂ & α)
Kidney	Renin secretion (β₂)
Bladder	Detrusor: Relaxation (β₂)	Detrusor: Contraction
Bladder	Sphincter: Contraction (α)	Sphincter: Relaxation
Uterus	Contraction: Pregnant uterus (α)
Uterus	Relaxation: Pregnant & non-pregnant uterus (β₂)
Eye	Pupil: Dilate (α)	Pupil: Constrict
Eye	Pupil: Dilate (α)	Lacrimal gland secretions
Salivary glands Submandibular Parotid	Viscous secretions (α)	Watery secretions

Disorders: Clinical-Anatomic Associations

Sympathetic
- Noradrenergic
  - Tests: Adrenergic
    - Valsalva
    - Baroreflex-Sympathoneural
    - Head-up tilting
  - Disorder: Orthostatic hypotension; POTS
- Cholinergic
  - Tests
    - Thermoregulatory sweat
    - Skin sympathetic (SSR): Sudomotor
      - Recorded over skin with abundant sweat glands: Palm or Sole
      - Latency ~ 1500 ms
      - Mediated by: Unmyelinated C-axons
    - Sudomotor (post-ganglionic) axon reflex (QSART)
  - Disorder: Anhidrosis
- Noradrenergic & Cholinergic
  - Test: Skin biopsy, Sweat gland α-synuclein
  - Disorder: Parkinsons
Parasympathetic
- Tests
  - Deep beathing-Heart rate
    - Test: Heart rate variability during cyclic deep breathing
    - Asseses: Parasympathetic cholinergic afferent & efferent function
    - Complicating factor: Heart responses to deep breathing progressively decline with age
  - Valsalva ratio
  - Baroreflex-cardiovagal gain
- Disorders: Cholinergic
  - Saliva: Decreased
  - Urinary retention
  - Sex dysfunction
Enteric
- Test: Gastric emptying
- Disorder: GI dysmotility
Adrenomedullary
Smooth muscle: Visceral

T Willis
Autonomic & Other nerves: In Cerebri Anatome

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12/26/2024