ANS

Question 1

Functions of the ANS:

Answer 1

1. maintain homeostasis
2. emergency responses
3. facilitate reproduction function

• modality: visceral motor

Question 2

Target Organs Innervated by the ANS:

Answer 2

1. cardiac muscle
2. smooth muscle
3. glands

Question 3

Divisions of the ANS:

Answer 3

1. sympathetic
2. parasympathetic
3. enteric

Question 4

What are the neurotransmitters for the ANS?

Answer 4

1. Sympathetic
   
   1. **Preganglionic​: **Ach
   2. **Postganglionic: **
      
      • Most target organs: NE
      • Sweat glands & vasodilator fibers: ACh
   3. **Divergence: **1 : 10
2. ​Parasympathetic
   
   1. Preganglionic​:
      Ach
   2. Postganglionic: Ach
   3. Divergence: 1 : 3

Question 5

Where do the sympathetic and parasympathetic systems originate?

Answer 5

1. Sympathetic Division:
   
   • Thoraco-lumbar origin (T1-L2)
2. Parasympathetic Division:
   
   • Cranio-sacral origin (CN’s III, VII, IX, X; S2-S4)

Question 6

Four courses of a sympathetic preganglionic axon:

Answer 6

1. Establish synaptic contact with postganglionic neuron in sympathetic trunk (paravertebral chain) ganglion at same level
2. Pass up or down sympathetic trunk to contact postganglionic neuron in ganglion at a different level
3. Pass through paravertebral ganglion to contact postganglionic neuron within a prevertebral ganglion (3 sites)
4. Pass through paravertebral ganglion en route to adrenal medulla

Question 7

What are the 4 parasympathetic pathways orginating from the brainstem?

Answer 7

1. Edinger-Westphal (CN III) ⇒ Ciliary ganglion ⇒ Sphincter pupillae m.
2. Superior Salivatory (CN VII) ⇒ Pterygopalatine & Submandibular ganglia ⇒ Lacrimal gland, Sublingual and Submandibular glands
3. Inferior Salivatory (CN IX) ⇒ Otic ganglion ⇒ Parotid gland
4. Dorsal Motor Nuclues of X ⇒ Myenteric & Submucosal (terminal) ganglia ⇒ Smooth muscle; glands of GI tract

Question 8

Vasovagal Syncope:

1. Symptoms
2. Explanation

Answer 8

1. Symptoms:
   
   • muscle weakness
   • warm sensation
   • nausea
   • sweating
2. Explanation:
   
   • Peripheral venous pooling ⇒
   • Splanchnic pooling activates low-pressure mechanoreceptors (brain interprets this as increased venous pressure) ⇒
   • Withdrawal of sympathetic activity and increase in vagal activity ⇒
   • Inappropriate peripheral vasodilation and bradycardia ⇒ hypotension and syncope

Question 9

ANS components of baroreceptor reflex:

1. Receptor:
2. Afferent Limb:
3. CNS Processing:
4. Efferent Limb:

Answer 9

1. Receptor:
   
   • stretch receptors in carotid sinus (IX) and aortic arch (X)
2. Afferent Limb:
   
   • glossopharyngeal n. (IX) and vagus n. (X)
3. CNS Processing:
   
   • nucleus solitarius
4. Efferent Limb:
   
   1. Parasympathetic: axons of vagus nerve (X) from neurons in nucleus ambiguus and dorsal motor nucleus
   2. Sympathetic: interomediolateral cell column of spinal cord; sympathetic neurons inhibited

Question 10

Horner’s Syndrome:

Answer 10

1. ptosis (loss of innervation of superior tarsal muscle (of Mueller)
2. miosis (loss of innervation of dilator pupillae muscle)
3. anhidrosis (loss of innervation of sweat glands)

Question 11

Lateral Medullary Syndrome (of Wallenberg):

Answer 11

1. Dysarthria
2. Dysphagia
3. Contralateral loss of pain and temperature
4. Ipsilateral loss of facial sensation
5. Horner’s syndrome

Question 12

Autonomic Dysreflexia following Spinal Cord Injury:

Answer 12

• Disordered autonomic response in persons with SCI at T6 and above
• Caused following noxious stimulus ⇒ pain fibers cannot ascend through damaged zone
  
  • results in activation of local reflexive sympathetic outflow ⇒ widespread vasoconstriction and elevated BP
• Can become life threatening
• parasympathetic response (vagal outflow) alone is unable to compensate for this
• Symptoms: headache, hypertension, bradycardia, piloerection, pallor

Question 13

Urinary Bladder Control:

1. Micturition
2. Storage

Answer 13

• Micturition:
  
  • S2-S4 ⇒ preganglionic fibers run as pelvic splanchnic nerves ⇒ inferior hypogastric plexus and associated terminal ganglia ⇒ postganglionic fibers ⇒ detrussor m. ⇒ contraction (micturition or voiding)
• Storage:
  
  • Interomediolateral cell column (T11-L2) ⇒ lumbar splanchnic nerves ⇒ internal urethral sphincter (in males only) ⇒ contraction ⇒ **storage **
  • Somatic motor innervation (S2-S4 / pudendal n.) ⇒ external urethral sphincter ⇒ contraction ⇒ storage

Question 14

How is the ANS involved in male reproduction?

Answer 14

1. Sexual stimulation ⇒ Erection which is purely vascular and is controlled by the parasympathetic division
2. Ejaculation consists of 2 processes:
   
   • emission & ejaculation
   • these processes are under sympathetic and somatic control

Question 15

How is the ANS involved in female reproduction?

Answer 15

• External genitalia
  
  • supplied by ilioinguinal and perineal nerves (somatic)
• Internal reproductive structures
  
  • autonomic innervation
  • also are regulated by hormones

Question 16

Hirshprung’s Disease:

Answer 16

• Congenital absence of myenteric plexus
  
  • No peristalsis in denervated colon (which appears small) compared to proximal part of colon which becomes distended
  • Constipation
• Surgically attach normal colon to rectum