Physio - Automatic Nervous System

Question 1

How does the ANS act as Regulator of Homeostasis?

Answer 1

• Sympathetic (Fight or Flight)
  
  • pupil dilation
  • fast heart rate
  • decrease GI motility
• Parasympathetic (Rest / Digest)
  
  • pupil contraction
  • slow heart rate
  • increase GI motility

Notes:

• Often antagonistic (opposite) systems
• Evolutionary old system since homeostasis = prerequisite for survival
• Some body functions are under dual control of both systems

Question 2

Examples of Dual Anatgonistic Regulation

Answer 2

• Pupillary dialtion physiology
  
  • Sympathetic activity = physiologic stressors
    
    • ex: hypoglycemia, physical activation, orgasm, emotions
  • Inhibition of parasympathetic
    
    • ex: drinking decaffeinated espresso by habit
• Mydriasis
  
  • Extreme sympathetic activity = medical issue
    
    • ex: hemorrhage, brain tumor, sympathomimetic drugs (bronchodilator)
  • Parasympatholytic drugs
    
    • ex: atropine (dilates pupils)

Question 3

Examples of Complementary or Cooperative interplay between

Para & Sympathetic Systems

Answer 3

• Complementary effects:
  
  • Parasympathetic stimulates secretion of watery saliva
  • Sympathetic constricts blood vessels –> secretion becomes thicker
• Cooperative effects:
  
  • Sexual arousal
    
    • Parasympathetic = vasodilation & erection
    • Sympathetic = ejaculation
  • Urination
    
    • Parasympathetic = urinary bladder contraction
    • Sympathetic = helps w/ bladder muscle tone/control of urination

Question 4

Examples (7) organs that are NOT dually innervated

Answer 4

1. Sweat gland
   
   • sweat production
2. Kidney
   
   • renin secretion
3. Liver
   
   • gluconeogenesis/glycolysis
4. Adipose tissue
   
   • Lipolysis
5. Arrector pili muscles in skin
   
   • goose bumps
6. Adrenal medulla
   
   • E & NE release
7. (Most) blood vessels
   
   • increase = vasoconstriction
   • decrease = vasodilation

Question 5

Characteristics ANS vs Somatic NS

Answer 5

• Autonomic Motor Neurons
  
  • Can stimulate or inhibit depending on the organ & receptors
  • Effect does NOT depend on type of transmitter
  • Effect DEPENDS on type & signaling of receptors
  • Pre-ganglionic = weakly myelinated
  • Post-ganglionic = no myelin
    
    • Slow fiber communication
  • Involuntary
    
    • cant usually be trained
      
      • except: GI (enteric NS)
• Example: Epinephrine
  
  • stimulates heart
  • inhibits bronchioles in lungs
• Somatic Nervous System
  
  • Excitatory ONLY
  • Pre & Post Ganglion = myelinated
    
    • Fast fiber communication
  • Voluntary
    
    • can be trained (generally)
      
      • except for reflexes

Question 6

How does the Sympathetic Nervous System operate?

Answer 6

Basics:

• Central ANS regulates the Peripheral ANS
• Sympathetic NS uses:
  
  • Ach & nACh receptors btw pre/post ganglionic nerves
    
    • nicotine & muscarinic receptors
  • NE & Adrenergic receptors btw post ganglionic & end organs
    
    • Catecholamine receptors
• Exception:
• Sympathetic postganglionic neurons that innervate sweat glands & some skeletal muscles blood vessels release Ach

Sympathetic Activation:

• activates most postganglionic fibers as a bulk
  
  • aka: Mass Activation
• Causing: Sympathetic Tone
  
  • Divergence: 1 preganglionic fiber sends input –> up to 100 postganglionic fibers
  • Convergence: 1 postganglionic fiber receives input –> many preganglionic fibers

Question 7

How does the sympathetic nervous system respond to stress?

Answer 7

Basics:

• activates hormonal stress response in Adrenal Medulla
  
  • releases epinephrine & norepinephrine
• adrenal medulla = modified ganglion
  
  • innervated by preganglion sympathetic neurons

Process:

• Stress –> Amygdala –> Hypothalamus –> Sympathetic Nerves

Sustained Stress:

• hypothalamic - pituitary - adrenal cortex helps the body survive
  
  • Coritsol is released
    
    • biomarker for chronic stress
  • Increased heart rate
    
    • biomarker for acute stress

Question 8

What are NANC transmitters?

Answer 8

• Non-adrenergic (NE,E) & Non-cholinergic (Ach)

Examples:

• ATP
• Calcitonin
• Dopamine
  
  • enteric NS, kidney
• GABA
  
  • enteric NS, gut relaxation
• Serotonin
  
  • enteric NS
• Substance P
  
  • Sensory neurons

Question 9

How does the parasympathetic nervous system function?

Answer 9

Basics:

• Activated by “rest & digest” during recovery from stress
  
  • Uses ACh & nACh receptors btw pre/post ganglion nerves
  • Uses Ach & mACh btw post ganglionic/end organs
• Causes more DIRECT actions in the end organs compared to SNS
  
  • Faster than sympathetic effects due to fast AChEsterase
  • Fast body responses rely on activation & deactivation
    
    • Respiratory Sinus Arrythmia
      
      • heart rate increases = inspiration
      • decreases = expiration

Nicotinic AChR

• fast EPSP
• opening of ion channels
• blocked by curare, hexamethonium

Muscarinic AChR

• slow long-lasting EPSP
• G-protein coupled
• blocked by atropine

Question 10

What is the Enteric Nervous System?

Answer 10

Basics:

• located in wall of GI tract
• includes postganglionic parasympathetic neurons
• regulated by postganglionic sympathetic & parasympathetic fibers

Brain-Gut Connection:

• enteric & CNS connection explain many medical symptoms
  
  • anxiety, stress, depression –> IBS
  • drug side effects –> nausea, vomiting, constipation, dry mouth