8. The Sympathetic Nervous System Flashcards
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)?
- 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:
- Partial ptosis (paralysis of superior tarsal muscle)
- Miosis (constriction of pupil die to paralysis of dilator pupillae)
- 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.
