8. The Sympathetic Nervous System Flashcards Preview

Year 1 - Term 2: Carriage of Oxygen > 8. The Sympathetic Nervous System > Flashcards

Flashcards in 8. The Sympathetic Nervous System Deck (22)
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Where are the pre- and post- ganglionic neurones in the sympathetic trunk?

What supplies vasoconstrictor nerves to arterioles?

Preganglionic - in lateral horn of grey matter, driven from reticulospinal tract

Postganglionic - cell bodies in sympathetic ganglia and project out to skin and BVs


Thoraco-lumbar sympathetic ganglia


What are the 3 main cervical ganglia that supply the head (e.g. iris, skin, salivary glands)?

1. Superior cervical ganglion (largest)  2. Middle cervical ganglion  3. Inferior cervical ganglion


Label A-E

A: superior cervical sympathetic ganglion

B: Cervical sympathetic trunk

C: Vertebral artery

D: Middle cervical ganglion

E: Inferior cervical ganglion


Describe how the sympathetic postganglionic faibres enter the skull.

Describe the parasympathetic and sympathetic paths of the pupil reflex.

They form nerve plexi around the carotid arteries and enter the skull with the carotids

Dilator pathway: sympthetic, from superior cervical ganglion -> carotid plexus -> opthalmic nerve

Constrictor pathway: parasympathetic from CNIII, from optic tract -> pretectal nucleus -> edinger westphal nucleus -> oculomotor nucleus -> oculomotor nerve -> ciliary ganglion -> short ciliary nerve


What does this patient have and why? What are the triad of main sysmptoms?

Horner's Syndrome - sympathetic fibres stretched/damaged along course to head/neck. If unilaterally disturbed, get triad of main symptoms:

1. Partial ptosis (paralysis of superior tarsal muscle)

2. Miosis (constriction of pupil die to paralysis of dilator pupillae)

3. Anhydrosis (decreased sweating affecting same side of face as leision due to loss of facial sweat gland innovation)


Describe the sympathetic efferent system to muscle, compared to the somatic nervous system to skeletal muscle

Sympathetic efferent system has 2 neurons between spinal cord and muscle, and single neuron in somatic.

NB: sympathetic pregaglionic is myelinated -> ACh -> postganglioninc unmyelinated -> NA onto arterial SM to make it contract via alpha-1 adrenoreceptors.


Smoking a cigarette releases nicotine into the blood stream. Does this stimulate the sympathetic or parasympathetic NS, or both, and why?

Both because all autonomic ganglionic receptors are of the cholinergic nicotinic type.


What innervates the a) heart and b) lungs, and where is it found.

Cardiac plexus around aorta and atria, from upper thoracic sympathetic chain

Pulmonary plexus around large bronchioles


Label A-C

A: cardiac plexus 

B: pulmonary plexus

C: eosophageal plexus


What is a common characteristic of sympathetic ganglia below the diaphragm? Give examples.

What is the one exception?

Long preganglionic axons. E.g. coeliac ganglion and plexus, superior and inferior mesenteric ganglia and plexi

Adrenal gland: preganglionic neurone directly to AG -> sits atop kidneys and secretes adrenaline from its inner medulla into gland capillaries. (Outer cortex secretes cortisol).


Label A and B. What do they secrete?

A: adrenal cortex, secretes cortisol

B: adrenal medulla, secretes adrenaline


Give the pathway to adrenaline formation.

Tyrosine -> (tyrosine hydroxylase) DOPA -> (dopamine decarboxylase) DA -> (dopamine beta-hydroxylase) NA -> adrenaline


NB: DA, NA, adrenaline are catecholamines


All sympathetic postganglionic fibres are noradrenergic EXCEPT which one?

Sweat glands - use ACh instead


Give an example of a drug that blocks the resting level of sympathetic nerveous output, and explain what condition it causes.

What vascular beds do not have this resting tone?

Alpha blockers e.g. prazosin, block resting tone, can cause postural hypotension - body unable to increase vasoconstrictor tone in leg muscles when you stand -> BP drops -> faint.

Heart and brain


What do muscles release during exercise, and how does the sympathetic NS compensate for this?

Muscles release chemical local vasodilators which decrease total peripheral resistance. Sympathetic NS maintains BP in normal range and increases HR which increases C.O. to compensate.


What 3 things does the sympathetic NS do in preparation for a fight or flight response?

1) vasoconstriction via NA release

2) Adrenaline releases glucose into blood from liver and muscle cells

3) Airways dilate


NB: Also pupil dilation, Ejaculation (Point and shoot), and gut peristalsis inhibition


What acts mainly on alpha-adrenoreceptors?

What are the 2 types and where are the found? 

What drugs work on them?



Alpha-1: on vascular SM, vasoconstriction. Also contract uterus, vas deferens, hair. Antagonists e.g. prazosin decrease BP

Alpha-2: on presynaptic sympathetic nerve terminals, decreases NA release by -ve feedack. Also inhibit insulin release and induce glucagon release in pancreas, contract sphincters in GI tract, increase thrombocyte aggregation. Agonists e.g. clonidine decrease BP



What acts mainly on beta-adrenoreceptors?

What are the 2 types and where are the found? 

What drugs work on them?


Where is beta-3 found and what does it do?


Beta-1: in heart, increase force and rate of myocardial contraction. Also increases renin from kidney and ghrelin from stomach. B-blockers e.g. propanolol (but bronchoconstriction) and atenolol decrease HR and force.

Beta-2: relax bronchial smooth muscle. Also decrease GI motility, lipolysis, insulin secretion. Agonists e.g. salbutamol relax SM in asthmatics.


Beta-3: adipose tissue cells, stimulates lipolysis


How do the alpha and beta adrenoreceptors work together during exercise?

Alpha receptors constrict vessels in gut and redistribute blood to exercising muscles.

Beta-1 receptors increase cardiac output

Beta-2 receptors relax bronchial SM to increase ventilation and O2 uptake

Beta-2 and 3 also increase glucose release from liver and increase glucose uptake into active muscle. Also increase lipolysis.


How does the sympathetic NS react following injury/haemorrhage? (5 ways)

Immediate reaction. Stim. and contraction of SM in veins will decrease venous reservoir of blood and maintain venous return to heart (makes up for blood lost through hemorrhage). 

If blood loss severe, atrial vasoconstriction in non-essential organs like gut/skin help maintain BP.

Kidney releases renin to maintain BP.

ADH release reduces urine flow and thus fluid loss.

Alpha receptors sensitise vascular SM so it constricts quickly after injury and increase clotting speed by sesntitising platelets to exposed collagen and making endothelium more sticky.


Fear/excitement are stressors which activate the sympathetic NS. What else do they also activate?

hypothalamo-pituitary-adrenal axis (HPA) which releases adrencoricotrophic hormone (ACTH) which stimulates cortisol release from adrenal outer cortex, which has 2 important actions:

1) release glucose to supply muscles with energy

2) stimulate adrenaline and NA synthesis


What happens if cortisol production is lowered?

Sympathetic NS becomes progressivly weaker and less able to secrete catecholamines.

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