Review of the Sympathetic Nervous System Flashcards
Which tract supplies the sympathetic preganglionic neurones?
Reticulospinal tract
What is the sympathetic chain?
Where the cell bodies of postganglionic sympathetic neurones lie
What is the superior cervical ganglion?
Most superior sympathetic ganglion which projects into cervical region but isn’t connected to cervical ventral roots
Describe how sympathetic postganglionic fibres travel
Form nerve plexuses around the carotid arteries and enter the skull with the carotids
How do thoracic and abdominal preganglionic sympathetic neurones differ?
Thoracic have short preganglionic neurones whereas abdominal have long ones so sympathetic ganglia is a long way from the spinal cord and have different names (e.g. coeliac ganglion)
Describe the coeliac ganglion and what is supplies
Present below diaphragm and anterior to aorta, supplies stomach and initial parts of small intestine
What is the mesenteric ganglia?
Found around the lower abdominal aorta and has superior and inferior types
What does the superior mesenteric plexus supply?
Innervates small intestine, ascending and transverse colon
What does the inferior mesenteric plexus supply?
Innervates descending colon and rectum
What is the consequence of coeliac ganglion stimulation?
Sphincter contraction, abdominal vasoconstriction, mobilisation of liver glycogen and secretion of adrenaline (adrenal medulla)
What is the consequence of superior mesenteric ganglion stimulation?
Relaxation of small intestine and colon walls
What is the consequence of inferior mesenteric ganglion stimulation?
Relaxation of small intestine and colon walls, constriction of sphincters and relaxation of urinary bladder and genital vasoconstriction
How is adrenaline produced?
Tyrosine –> DOPA –> dopamine –> noradrenaline –> adrenaline
What are catecholamines?
Dopamine, noradrenaline and adrenaline
What axon type are sympathetic preganglionic neurones?
Myelinated type B
How do sympathetic preganglionic neurones activate postganglionic neurones?
Release ACh
What type of receptor is present on all autonomic ganglia?
Cholinergic nicotinic receptor
What is the role of sympathetic postganglionic neurones?
Project to smooth muscle in arterioles –> vasoconstriction
What type of axon do sympathetic postganglionic neurones have?
Unmyelinated type C
How do sympathetic postganglionic neurones activate smooth muscle in
Noradrenaline release –> alpha 1 adrenoreceptors –> vasoconstriction
What is the main function of the sympathetic nervous system?
Regulates blood distribution around the body
What is the role of the sympathetic nervous system in preventing postural hypotension?
Normally keeps all arterioles of vascular beds slightly constricted to maintain blood pressure in the leg muscles when you stand
What happens in the fight or flight response?
Vasoconstriction in non-working muscles (e.g. digestion), adrenaline release, pupil dilation
Which sympathetic ganglion is involved in pupillary dilation and thickened salivary secretions?
Superior cervical ganglion
Which sympathetic ganglion is involved in ejaculation and voiding the bladder?
Hypogastric ganglion
Which sympathetic ganglion is involved in peristaltic inhibition of the gut?
Coeliac ganglion
What does sympathetic activation of alpha receptors achieve?
Constriction of vessels in gut –> shunt to working muscles
What does sympathetic activation of beta 1 receptors achieve?
Increase CO
What does sympathetic activation of beta 2 receptors achieve?
Relax bronchial SM and increase glycogenolysis and lipolysis
What does sympathetic activation of beta 3 receptors achieve?
Increase glycogenolysis and lipolysis
How do stressors affect the sympathetic nervous system?
Stressors activate SNS ad hypothalamo-pituitary-adrenal axis –> adrenocorticotrophic hormone –> cortisol release from adrenal cortex –> stimulates adrenaline and noradrenaline synthesis
How does the sympathetic nervous system react to injury or haemorrhage?
Constriction of veins increases (increase/maintain venous return to heart to maintain BP and CO), severe blood loss –> vasoconstriction to non-essential organs, renin and ADH release to reduce urine flow and fluid loss (increase BP), alpha receptors in vascular SM –> constriction and sensitise platelets to collagen to make endothelium ‘sticky’ –> clotting
Describe sympathetic alpha adrenoreceptors
a1 = on vascular smooth muscle --> constriction a2 = on presynaptic sympathetic nerve terminals (negative feedback for noradrenaline release)
Describe sympathetic beta adrenoreceptors
B1 = on cardiac muscle to increase HR and contraction force B2 = relaxes bronchial smooth muscle B3 = on adipose tissue --> lipolysis
What molecule do alpha adrenoreceptors mainly respond to?
Noradrenaline
What molecule do beta adrenoreceptors mainly respond to?
Adrenaline (but can respond to noradrenaline)
How do beta blockers work?
Antagonist of B1 receptors to reduce HR and contraction force in hypertensive patients
How does salbutamol work?
Agonist of B2 receptor –> bronchodilation
