Localization Of ANS & Hypothalamic Disorders

Question 1

What are the consequences of a lesion in the anterior hypothalamic region?

Answer 1

“parasympathetic area”

1. hyperthermia
2. insomnia
3. DI
4. emaciation

Question 2

What are the consequences of a lesion in the lateral hypothalamic region?

Answer 2

“drinking center”

1. Adipsia
2. Emaciation
3. Apathy

Question 3

What are the consequences of a lesion in the posterior hypothalamic region?

Answer 3

“sympathetic area”

1. hypothermia
2. poikilothermia (body T° fluctuates by 2°)
3. hypersomnia
4. coma
5. narcolepsy
6. apathy
7. ipsilateral Horner syndrome

Question 4

What are the consequences of a lesion in the medial hypothalamic region?

Answer 4

1. hyperdipsia
2. DI
3. SIADH
4. obesity
5. rage
6. amnesia
7. dwarfism

Question 5

Functional Regions of the hypothalamus (4):

Answer 5

1. Anterior region
   
   • ​​preoptic, supraoptic, suprachiasmatic, anterior nucleus
2. Posterior
   
   • ​​posterior nucleus
3. Medial
   
   • ​​ventromedial, dorsomedial, paraventricular, arcuate
4. Lateral
   
   • ​​lateral tuberal nucleus, lateral hypothalamic area

Question 6

Definitions:

1. Adipsia:
2. DI:
3. SIADH:

Answer 6

1. Adipsia = reduced intake of water
2. DI = diabetes insipidus
   
   • loss of water in urine
   • serum sodium concentration rises (hypernatremia)
   • caused by lack of ADH
3. SIADH = syndrome of inappropriate antidiuretic hormone secretion
   
   • ADH causes water to be retained ⇒ serum water increases ⇒ serum sodium concentration drops (hyponatremia)

Question 7

Suprachiasmatic nucleus (anterior region):

• Function:
• ​Lesion/Loss of Function:

Answer 7

• Function: Regulates circadian rhythm
  
  • stimulated by light hitting retina
• Lesion: causes insomnia
• Loss of neurons could occur in Alzheimer’s disease
  
  • people who work at night have inadequate stimulation of this nucleus

Question 8

Anterior nucleus (anterior region):

• Function
• Lesion/Loss of Function:

Answer 8

• Function: dissipate heat
• Lesion: causes hyperthermia
• Commonly stimulated by endogenous pyrogens
  
  • including IL-1 and PGE2
  • whenever a person is ill ⇒ these pyrogens travel to hypothalamus ⇒ induces a fever
  • PGE2 synthesis can be blocked by aspirin

Question 9

Medial hypothalamus:

• Function:
• Lesion/Loss of Function:

Answer 9

• Function: Regulates feeding behavior
• Lesion: causes obesity due to overeating
• Frequently lesioned by:
  
  • craniopharyngioma
    
    • or surgery to remove this tumor
  • pituitary adenoma (pituitary tumor)
  • dysfunction of this region of brain is found in Prader-Willie syndrome

Question 10

Craniopharyngioma:

Answer 10

• Tumor within hypothalamus
• Primarily found in children
• **Tumor expands & ↑ICP **⇒ headaches, bitemporal hemianopsia, and endocrine disturbances due to compression of pituitary stalk/gland
• Surgical removal itself can cause damage to hypothalamus

Question 11

Prader-Willie Syndrome:

Answer 11

• Chromosomal deletion of 15q11-13
  
  • inherited through the father
• Hypothalamic dysfunction includes:
  
  • hyperphagia with eventual obesity
  • narcolepsy
  • short stature

Question 12

What is the general sympathetic pathway?

Answer 12

1. Hypothalamus (posterior region) & descend as the descending hypothalamic fibers (DHF) in the brainstem
   
   • DHF are located laterally in the brainstem, & is in close proximity to the spinothalamic tract
2. ​DHF synapse onto cell bodies in the intermediolateral cell column (IML)
   
   • ​​thoracic spinal cord (preganglionic neurons)
3. pre-ganglionic neuron exits cord and enters sympathetic chain & synapses onto several ganglia:
   
   • ​​including superior cervical ganglion (SCG), inferior cervical gaglion, celiac ganglion
4. Post-ganglionic neurons are housed in these ganglia & sends their axons to the target

Question 13

How will a lesion of the brainstem or spinal cord affect the sympathetic system?

Answer 13

• Brainstem stroke (eg. lateral medullary stroke) could lesion DHF
• Spinal cord injury (stroke, compression, tumor) can injure IML cell column ⇒ ↓sympathetic output to various target organs

Question 14

How do sympathetic fibers innervate the eye?

Answer 14

pre-ganglionic fiber exits IML cell column ⇒ enters sympathetic chain ⇒ ascends into SCG ⇒ synapses onto post-ganglionic neuron ⇒ post-ganglionic fiber ascends internal carotid artery (which travels through cavernous sinus) ⇒ sends axon to dilator muscle of pupil

Question 15

Klumpke’s Palsy:

Answer 15

Injury to lower trunk of brachial plexus:

• may result in disrupted sympathetic output
  
  • ipsilateral Horner’s
• ipsilateral finger paralysis (all directions of movement)
• normal proximal arm muscle strength

Question 16

Pancoast Syndrome:

Answer 16

• infiltration of SCG or lower brachial plexus by a cancer
  
  • ​such as lung cancer on the apex of either lung
• can disrupt ipsilateral sympathetic output
  
  • ipsilateral Horner’s

Question 17

What happens if the ICA is dissected?

Answer 17

dissection is a separation of the various layers of an artery

• with blood ‘dissecting’ through the layers & blood may travel through a false lumen & reconnect with true lumen more distally ⇒ expands the artery ⇒ stretches the sympathetic fibers traveling on the surface of the artery ⇒ ↓sympathetic output

Question 18

Cavernous Sinus Thrombosis:

Answer 18

• žICA takes a U turn in the cavernous sinus
• Sympathetics in the cavernous sinus ⇒ pupillary dilator muscle
• Can have thrombus (blood clot) develop b/c of inflammation
• Rupture of ICA
• Pituitary adenoma

Question 19

Horner’s syndrome: ipsilateral

Answer 19

1. Miosis = small pupil
2. Ptosis = weakness of superior tarsal muscle (Müller’s muscle)
3. Anhidrosis = decreased sweating of face

Question 20

What mediates the pupillary light reflex? What is the pathway?

Answer 20

Parasympathetic innervation

information travels to pretectal nucleus in midbrain ⇒ bilateral innervation to Edinger-Westphal nucleus ⇒ neuron travels to ciliary ganglion ⇒ parasympathetic neuron travels to ciliary constrictor muscle

Question 21

What maintains urinary continence?

Answer 21

• micturition inhibitory center (medial frontal cortex) allows you to voluntarily inhibit flow of urine

1. neuron travels from **medial frontal cortex **⇒
2. travels to & inhibits pontine micturition center ⇒
3. descends to T11-L1 to activate it & inhibits parasympathetic region ⇒
4. stops urination b/c internal
   
   • urinary sphincter is contracted & detrusor is relaxed

Question 22

What controls the external urinary sphincter?

Answer 22

Onuf’s nucleus (αmns in the S2-S4; ventral horn of spinal cord) ⇒ via pudendal nerve ⇒ mediates contraction of external urethral sphincter (skeletal muscle)

Question 23

How is the sympathetic division involved in voiding of urine?

Answer 23

Sympathetic pathway is inhibited:

• neurons from the pontine micturition center ⇒
• IML cell column in T11-L1 sympathetic region⇒
• preganglionic neuron travels out of cord to inferior mesenteric ganglion ⇒
• postganglionic neuron travels via pudendal nerve to internal urinary sphincter which is not stimulated
  
  • sphincter relaxation
  • inhibition on detrusor is lessened

Question 24

How is the parasympathetic division involved in the voiding of urine?

Answer 24

Parasympathetic pathway is stimulated:

• neurons from S2-4 ⇒ stimulates detrusor to contract & internal urethral sphincter to relax

Question 25

Describe the effects on urinary continence if the sympathetic or parasympathetic divisions are lesioned:

Answer 25

• Hyperactive “spastic” bladder or underactive sphincter
  
  • ​lesion of sympathetics
  • Treat with anti-cholinergics to relax bladder walls
• Hypoactive “flaccid” bladder & overactive sphincter (latter prevents complete emptying)
  
  • lesion of parasympathetics
  • treat with anti-adrenergic to relax sphincter or intermittent self catheterization