S1: Physiology of the Sympathetic Nervous System Flashcards
The sympathetic nervous system prepares the body for ‘fear, fight and flight’
List some changes of the body that occur with ‘fear, fight and flight’
- Increase in heart rate and contractility meaning increased cardiac output resulting in more blood to the muscles
- Diversion of blood to skeletal muscle to provide more energy for movement
- Maintains blood pressure as a result of diverting blood
- Increase air to lungs by bronchodilation, resulting in increased O2 Uptake and CO2 removal
- The dilation is pupils, allow more light into the eye for better vision
- There is increased fuel for muscles to get ready for physical activity
- Sweating is increased to regulate temperature
- There is a decrease in non- essential functions such as GI Tract to limit amount of energy being used
What is the role of the hypothalamus in the sympathetic system?
The hypothalamus releases a ‘danger’ signal which sends information to the rostral ventral lateral medulla (RVLM)
It is the higher sensors that perceive danger etc. and modulate
What fibres travel down to the spinal cord (T1-L2/3)?
Excitatory bulbospinal fibres
Where does the excitatory bulbospinal fibres synapse with preganglionic fibres?
The inter medio lateral point
Compare the length of the sympathetic pre and post ganglionic fibres
The pre-ganglionic fibres are short
The post-ganglionic fibres are long
Where are a2 receptors found?
They are primarily on the blood vessels
However, also found in: Eye Certain sphincters Genitalia GI
Where are B1 receptors found?
They are found primarily in the heart and kidney
Also in GI
Where are B2 receptors found?
Vascular smooth muscle of coronary arteries Cerebral vessels Skeletal muscles Airways GI tract Smooth muscle of bladder
Where in the heart are the B1 receptors found?
They are located on the sino atrial node (SAN)
Muscle cells
What happens when noradrenaline acts in the B1- adrenoreceptors in the SAN?
NA causes an increase in the frequency of the pacemaker potentials which produces an increase in heart rate at the SAN
The increase in the rate of impulses through atria to ventricles helps to maintain balance between heart rate and contractions
What happens when noradrenaline acts in the B1- adrenoreceptors in muscle cells?
NA binding to B1 will result in increased force of contraction of atria and ventricles resulting in increased stroke volume (SV) and they relax faster
Sympathetic nerve stimulation increases cardiac output (CO)
What is the CO equation?
CO = SV x HR
Cardiac output= stroke volume x heart rate
SV is measured in (vol/best)
HR is measured in (beat/min)
What happens when NA/A act at a1 adrenoreceptors on blood vessels?
When they bind, they cause contraction of arterioles (vasoconstriction) which increases total peripheral resistance.
It will also cause the construction of veins (Venoconstriction). This increases cardiac output as it brings more blood back to heart —> starlings law
Why do we get blood flow?
Pressure difference- the pressure of blood leaving the heart is greater than that of blood entering the heart
What happens when adrenaline (releases by sympathetic nerve activity on adrenal gland) acts on B2 adrenoreceptors on coronary arteries and skeletal muscle arteries?
It causes vessels to dilate increases blood flow through coronary arteries and skeletal muscle
Name the key function of the kidney
It controls blood pressure
It also filters the blood and produces urine
What organ secretes renin?
Kidney
How does the sympathetic nervous system cause the release of renin?
The sympathetic nerves synapsing at granular cells which have B1 receptors which when stimulates release renin
What receptors are found in the kidney (that are sympathetic)?
B1 adrenoreceptors
Renin links the sympathetic system to a chemical called angiotensin II
Why is angiotensin important?
Angiotensin causes increased blood pressure and cardiac output
It causes vasoconstriction of arterioles increasing total peripheral resistance
What happens when angiotensin stimulates the adrenal cortex?
It causes the adrenal gland to release aldosterone which results in increased Na+ and H2O retention from the kidney (more sodium and water is taken back into the blood).
This leads to increase blood volume
Short summary on how sympathetic NS increases blood pressure
Sympathetic system - B1 receptor on granular cells in kidneys - renin - angiotensin II - vasoconstriction - aldosterone from adrenal glands - increased Na+ and H2O retention - increased blood volume = increased blood pressure
Why is B1 blockers successful at reducing blood pressure?
They prevent the sympathetic nervous system from releasing renin and so angiotensin II production is stopped
What happens when a/b receptors are stimulated by sympathetic NS in liver and skeletal muscle?
- breaks down glycogen into glucose (glycogenolysis)
- promotes glucose synthesis (gluconeogenesis)
Both of these help increase levels of glucose so more ATP is formed for fight or flight
What happens when a adrenoreceptors are stimulated by sympathetic NS in pancreas?
Decrease of insulin from beta cells and it prevents global uptake (we want to use the glucose not store it)
This also stops insulin from inhibiting glycogenolysis, glucagenogenesis and lipolysis
What happens when B adrenoreceptors are stimulated by sympathetic NS in adipose tissue (fat)?
- increased lipolysis (where triglycerides are broken down into free fatty acids + glycerol)
- free fatty acids go under beta oxidation into acetylcholine coA and enter the kerbs cycle
- glycerol is recycled into glycolysis pathway
Both of these increase ATP yields
What happen when a1/a2 and B2 adrenoreceptors are stimulated by sympathetic NS in GI motility?
It induces inhibition of GI motility
Activation of a1 adrenoreceptors evokes construction of the internal bladder sphincter
B2 adrenoreceptors induces relaxation of smooth muscle allowing filling of the bladder and prevents urination
The bowel/bladder function is non essential during ‘fear,fight and flight’
Do the lungs receive sympathetic innervation?
No
What activates the B2 adrenoreceptors in the lungs?
The bronchioles contain B2 adrenoreceptors which are activated by circulating adrenaline in the blood. This produces bronchodilation which helps facilitate breathing
What happen when a1 adrenoreceptors are stimulated by sympathetic NS in dilator papillae?
This causes dilation of pupil allowing more light into retina for more acutely sight
It does this by constricting the dilator muscle
How does the sympathetic NS act on sweat glands?
Acetylcholine act at muscarinic receptors
