The Sympahtetic Nervous System Flashcards
ventral root is the
motor root
the dorsal root is the
sensory root
what does visceral mean
preganglionic motor neurones
describe how visceral motor neurones travel
In the thoracic segments of the spinal cord preganglionic (visceral) motor neurons are present in the lateral horn
These visceral motor neurons send axons out of the ventral roots and across white rami nerve to end on postganglionic neurons in the paravertebral sympathetic ganglia. Theses ganglia are connected together by the sympathetic trunk.
Preganglionic neurones may not synapse in the ganglion that they enter but may travel to rostral or caudal ganglia before they synapse.
where do the axons of the postganglionic sympathetic neurones project on to
- smooth muscle of the surrounding blood vessels mainly
What is the sympathetic chain
The sympathetic ganglia together with the sympathetic trunk are often called the sympathetic chain.
what spinal level does the sympathetic chain travel to and from
T1-L2
what does the thoracic sympathetic ganglia supply
The thoracic sympathetic ganglia supply vasoconstrictor nerves to arterioles these are blood vessels that supply oxygen to skeletal muscles in the chest, upper limbs and neck.
how many pairs of ganglia are there
25 pairs joined by nerve trunks
what is divergence
pre-ganglionic fibres branch out to postganglionic fibres at different levels of the chain
what is convergence
a postganglionic neuron can receive information from many pre-ganglioinic fibres
What are the three cervical ganglia
superior cervical ganglion
middle cervical ganglion
inferior cervical ganglion
what is the largest cervical ganglia
superior cervical ganglia
what do the cervical ganglia supply
supply sympathetic nerves to the head;
- innervation of the iris of the eye - main job is dilating the eye
- skin of the face
- the salivary glands.
where do the sympathetic post ganglionic fibres form nerve plexus around
Carotid arteries
- they enter the skull together with the carotids
what is the main job of the sympathetic plexus
dilating the eye
what does the sympathetic plexus trigger
Triggers
- blushing
- reduces the production of the salvia by the salivary gland and makes it more thicker and viscous
the sympathetic efferent system has a…
2 neurone chain between a spinal cord and smooth muscle
describe the preganglionic neurones and postganglionic neurones
- preganglionic neurones have small myelinated axons which re type alpha and beta axons
- postganglionic neurones have unmyelinated type C axons
what neurotransmitter does the pre-ganglionic neurone release
acetylcholine in the ganglion which activates the postganglionic neurone
what neurotransmitter does the post ganglionic neurone release
noradrenaline on to the arterials smooth muscle to make it contract via alpha 1 adrenoreceptors
what type of receptor are all autonomic ganglia (parasympathetic and sympathetic)
- they are cholinergic nicotinic type
what does smoking do to the sympathetic and parasympathetic system
- it releases nicotine into the bloodstream
- this stimulates both the sympathetic and parasympathetic nervous system via the ganglionic nicotinic receptors
what do the postganglionic sympathetic neurones project on to
- project onto smooth muscle in arterioles producing vasoconstriction
what receptor causes smooth muscle contraction
alpha 1 adrenoreceptor
- this is a G protein coupled receptor
where is the sympathetic innervation of the heart
- via branches from the upper thoracic sympathetic chain which form a plexus around the aorta and atria
- the plexus is called the cardiac plexus
what is the sympathetic innervation of the lungs
- via a plexus around the large pulmonary arteries
- pulmonary plexus
describe the sympathetic nervous system below the diaphragm
- pre ganglionic neurones are long they now have prevertebral ganglia, these are away from the spinal cord
- forms the celiac ganglion, superior mesenteric ganglion and inferior mesenteric ganglion
- the long preganglionic axons to the celiac and mesenteric ganglia are called the greater and lesser splanchnic nerves
what are the prevertebral ganglia
- pre-vertebral ganglia - are what the sympathetic chain forms, they consist of one of one large or several closely adjacent small ganglia and mesh of pre and post ganglionic neurone
what are the 3 ganglion below the diaphragm
the celiac ganglion, T5-9 greater splanchnic
superior mesenteric ganglion T10-T12
lesser splanchnic
inferior mesenteric ganglion L1-L2
lumbar splanchnic
what does the coeliac plexus supply
- sympathetic vascosocnstrictor nerve fibres to the stomach and initial parts of the small intestine
what does the superior mesenteric plexus supply
innervates rest of the gut
what does the inferior plexus supply
- bladder and reproductive organs
what is the hypogastric plexus
it is a parasympathetic plexus supplying the reproductive organs
describe innervation to the adrenal gland
- some preganglionic neurones travel to the adrenal glands
- adrenal gland is a post ganglionic neurone that did not grow an axon
- adrenal gland secretes adrenaline into the capillaries of the gland, blood carries to all the parts of the body
where are the adrenal glands
sit on top of the kidneys
describe the structure of the adrenal glands
- has an outer part called the cortex
- has an inner part called the medulla
what part of the adrenal gland is adrenaline secreted from
medulla
how is adrenaline made
Tryosine – L dopa – dopamine – Noradrenaline – adrenaline
Dopamine, noradrenaline and adrenaline are….
catecholamines as they work on G protein receptors
what is the difference between noradrenaline and dopamine
Noradrenaline has an extra hydroxyl group than dopamine
what is the difference between noradrenaline and adrenaline
adrenaline has an extra methyl group on it
describe the sweat glands
- sympathetic innervation triggers it but post ganglionic do not produce noradrenaline they use acetylcholine not noradrenaline as their transmitter as the receptor is a muscarnic ACh receptor
what is the function of sympathetic nervous system
- regulates the distribution of blood around the body
what does the sympathetic is….
tonically active at all times
- but it works at a low level when you are resting
describe how postural hypotension works
- sympathetic nervous system keeps the arterioles of the vascular beds in the body slightly constricted therefore there is resting level of sympathetic nervous output in a healthy resting person
- the body increases the vasoconstrictor tone in the leg muscles when you stand up
- all vascular beds in the body are subjected to the resting tone except the brain and heart as you never want to restrict blood flow there
what happens when you have drugs that block the sympathetic effect of postural hypotension
they block this resting tone.
- produce the side effect postural hypotension
therefore the body is unable to increase vasoconstrictor tone in leg muscles when you stand up.
therefore when you stand up blood pressure drops and you faint
how is the sympathetic system activated during exercise
- local chemical vasodilators are released by the exercising muscle
- this increases muscle blood flow and oxygen needed by muscles
- this vasodilation reduces total peripheral resistance and if not compensated for causes a drop in blood pressure
- but at the start of exercise the sympathetic outflow increases producing a global vasoconstriction in the tissues of the body particularly in the non-exercising muscles
- the result is that the decrease in the vascular resistance in the exercising muscle is compensated by an increase in the vascular resistance in the nonactive muscles and a total peripheral resistance is maintained
- The increased sympathetic activity also increases heart rate. This increases cardiac output. The increased cardiac output supplies more blood & oxygen to the exercising muscles.
what does adrenaline do
- release glucose into the blood from the liver and muscle cells for extra energy this is called glycogenolysis
- increases cardiac output and respiration
- dilates airways increasing oxygen intake
what is never reduced by the sympathetic nervous system
The blood flow to the heart is never reduced by the sympathetic nervous system. During exercise the heart needs more blood There are no alpha adrenoreceptors in the heart, only beta adrenoreceptors
The blood flow to the brain is never reduced by the sympathetic nervous system. The brain needs a more or less constant supply at all times, during rest, exercise, and even when we are asleep. There are no a adrenoreceptors on the arterioles in the brain
what are the other actions of the sympathetic nervous system
Dilation of pupil (via sup cervical ganglion)
Inhibition of peristalsis in gut (via coeliac ganglion)
Ejaculation (via hypogastric ganglion; but only after a period of erection mediated by parasympathetic activity
what are the receptors for the adnrelaine and noradrenaline called
adrenoreceptors
what are the type types of adrenoreceptors
alpha and beta
name and describe the types of alpha receptors
Alpha 1 is the main receptor on vascular smooth muscle
Acts to increase contraction.
Alpha 2 receptors are found on presynaptic sympathetic nerve terminals
Act to reduce noradrenaline release by negative feedback
Alpha 1 -antagonists- eg prazosin -are given to reduce blood pressure.
Alpha 2 agonists-eg clonidine- are also given to lower blood pressure as they inhibit noramdrenaline release.
what are the two types of alpha receptors
a1 and a2
what are the other actions of alpha 1 receptor
contraction of non-vascular smooth muscle such as
ureter vas deferens hair (arrector pili muscles) uterus (when pregnant) urethral sphincter blood vessels of ciliary body (stimulation causes mydriasis)
what are the other actions of the alpha 2 receptor
inhibition of insulin release in the pancreas.
induction of glucagon release from the pancreas.
contraction of sphincters of the gastrointestinal tract
increased thrombocyte aggregation
what are the two main types of beta receptor
beta1 and beta 2.
A third type of less importance is beta 3.
what is the main neurotransmitter acting on beta receptors
adrenaline
describe the beta receptors and what they do
Beta 1 receptors found mainly in heart (and kidneys)
Act to increase force & rate of contraction of myocardium
Beta 2 found mainly in bronchial smooth muscle (but also in smooth muscle of gastrointestinal tract, liver, uterus)
Act to relax the muscle
Beta 3 receptors increase lipolysis and gluconeogenesis in adipose tissue, thus providing energy-rich substrates for the actively metabolising muscles.
name a beta blocker
- propanol
- atenolol - newer more selective for beta 1
what do beta blockers do
are given to reduce heart rate & force in stressed or hypertensive patients.
- used to manage abnormal heart rhythms
- protect heart from a second heart attack after a first heart attack
- reduce the work and oxygen demand of the heart therefore enable a damage heart to continue working even if oxygen supply is reduced by a blocked coronary artery
- used to treat high blood pressure - reduce renin release from the kidney but they are no longer the first choice for treatment as they are not as effective as diuretics, ACE inhibitors or calcium channel blockers
-
what are the benefits of atenolol
eg Atenolol – lack of side effects
Prevent overexersion of the heart
what is a side effect of beta blockers such as propanol
- Side effects are bronchoconstriction
- propranolol is dangerous to an asthmatic as it would cause bronchoconstriction
- cause fatigue and dizziness due to reduced cardiac output
- cause depression and loss of libido
- blocking beta 2 and 3 receptors this may trigger or exacerbate diabetes
what happens during exercise to alpha and beta receptors
- they become active during sympathetic stimulation
- increases the energy supply to exercising muscle s
- alpha receptors - constrict vessels in the gut and redistribute the blood to exercising muscle
- beta 1 receptors - increase cardiac output while beta 2 receptors relax bronchial smooth muscle to increase ventilation and oxygen uptake
- beta 2 and 3 receptors increase glucose release from the liver and increase glucose uptake into the active muscle, they also increase lipolysis from adipose tissue to provide extra substrates like free fatty acids for the working muscles
what does the sympathetic system don once you have had an injury or haemorrhage
- reacts immediately
- contraction of smooth muscle in veins decrease the venous reservoir of blood therefore maintains the venous return to the heart and makes up for blood loss in the haemorrhage this maintains cardiac output and blood pressure
- if blood loss is severe then arterial vasoconstriction of vessels in non essential organs like gut and skin help maintain blood pressure and perfusion of vital organs like heart brain and kidney
- renin released from the kidney Maintains blood pressure
- ADH release reduces urine flow and therefore reduces fluid loss
- alpha receptors sensitise vascular smooth muscle so it contracts quickly after blood loss to reduce injury
- also increases the clothing speed of the blood by sensitising platelets to exposed collagen and making the endothelium sticky
what does the sympathetic nervous system do after stress
- fear and excitement activate the sympathetic envois system
- also activate HPA
- HPA releases ACTH which stimulates cortisol release from the adrenal cortex
what part of the adrenals does cortisol release from
cortex
what is the action of cortisol
- stimulates the production of adrenaline and noradrenaline
- if cortisol production lowers then the sympathetic nervous system becomes weaker and less able to secrete catecholamines, - decreases ability to cope with stress and can leads to depression
