Autonomic reflexes Flashcards
Autonomic Nervous System - Control of Cardiac Output
The ANS affects both ………… …………. AND ……….. ……………. ……………..
CO = ….. x ……..
Sympathetic stimulation of the heart causes:
………………… Effect (increased SV)
…………………. Effect (increased HR)
Therefore, cardiac output increases
Release of noradrenaline which then binds to the adrenergic receptors in the cardiac muscle causes an ………….. in the force of contraction of the cardiac muscle
Sympathetic nerves also innervated the SAN and release ……………….. to the adrenergic receptors in the SAN which causes an ………………. in heart rate
Autonomic Nervous System - Control of Cardiac Output
The ANS affects both cardiac output AND total peripheral resistance
CO = SV x HR
Sympathetic stimulation of the heart causes:
Inotropic Effect (increased SV)
Chronotropic Effect (increased HR)
Therefore, cardiac output increases
Release of noradrenaline which then binds to the adrenergic receptors in the cardiac muscle causes an increase in the force of contraction of the cardiac muscle
Sympathetic nerves also innervated the SAN and release noradrenaline to the adrenergic receptors in the SAN which causes an increase in heart rate
How does the sympathetic nervous system cause an increase in TPR?
Total Peripheral Resistance
The sympathetic nervous system tends to cause mass vasoconstriction
Increased sympathetic activity leads to vasoconstriction
This causes an increase in total peripheral resistance
Baroreceptor Reflex
What happens when there is an decrease in blood pressure?
Where are baroreceptors found?
What other type of receptors do you have?
The more pressure and volume there is, the …………… the neurons from the baroreceptors and volume receptors fire
The frequency of the signals being sent to the brain …………………. with greater volume and pressure
The Baroreceptor Reflex
The baroreceptor reflex makes the sympathetic increase its firing rate
There are baroreceptors in the carotid sinus and aortic arch
You also have cardiopulmonary volume receptors which respond to changes in volume and pressure in the system
The more pressure and volume there is, the faster the neurons from the baroreceptors and volume receptors fire
The frequency of the signals being sent to the brain increases with greater volume and pressure
If there is a DECREASE in blood pressure:
Firing rate from the baroreceptors ………………
There is ………………stimulus to the brain
You get a ……………… in the INHIBITION of the SNS
Sympathetic activity ………………
Normally, the baroreceptors and volume receptors act on the brain and stimulate the brain to switch ……………… the sympathetic nervous system
If there is a normal rate of firing - this tells the brain that the blood pressure is FINE and this tends to ……………… activation of the sympathetic nervous system
A fall in pressure brings about reflex activation of the sympathetic nervous system to bring the blood pressure back up
If there is a DECREASE in blood pressure:
Firing rate from the baroreceptors decreases
There is less stimulus to the brain
You get a decrease in the INHIBITION of the SNS
Sympathetic activity increases
Normally, the baroreceptors and volume receptors act on the brain and stimulate the brain to switch OFF the sympathetic nervous system
If there is a normal rate of firing - this tells the brain that the blood pressure is FINE and this tends to decrease activation of the sympathetic nervous system
A fall in pressure brings about reflex activation of the sympathetic nervous system to bring the blood pressure back up
Draw a diagram showing the barorreceptor reflex when you have low BP.
include in the diagram an Aterial baroreceptor, Afferent nerve, Parasympathetic nerve, heart, inhibitory neuron, sympathetic nerve, heart, arterioles and veins and nerve signals
Draw a diagram showing the barorreceptor reflex when you have high BP.
include in the diagram an Aterial baroreceptor, Afferent nerve, Parasympathetic nerve, heart, inhibitory neuron, sympathetic nerve, heart, arterioles and veins and nerve signals
Draw a flow diagram, of the baroreceptor, when there is a increase in arterial blood pressure.
Lable the diagram below
Lable the diagram below
Postural Hypotension
The baroreceptor reflex is a normal response to gaining an upright posture
When you stand up you are bringing GRAVITY into play - gravity tries to push the blood down to your feet
As the veins are distensible, you can get blood pooling in the lower limbs
If you have more blood pooling in the veins, then there is reduced venous return meaning that there is a lower blood pressure
Decreased cardiac output therefore decreased arterial blood pressure (STARLING’S LAW)
This decrease in blood pressure causes activation of the baroreceptor reflex
Decreases stimulation of the baroreceptors means that less stimulus is delivered to the brain to switch off the sympathetic nervous system so there is an increase in activity of the sympathetic nervous system and so blood pressure increases (due to an increase in SV, HR and vasoconstriction)
Why does standing up cause a decrease in arterial pressure?
What does a normal person’s body do to conteract this decrease in arterial pressure?
How does this differ with people with postural hypotension?
Most people suffer with transient postural hypotension at some point in their lives (more likely if you’re tall)
Some people suffer a more clinical postural hypotension
You can get autonomic failure where the autonomic nervous system doesn’t act the way it should - so people struggle to maintain blood pressure when they stand up
When you stand up, there will be a pooling of blood in the lower limbs –> reduced venous return –> decreased cardiac output –> decreased arterial blood pressure
This will cause decreased stimulation of the baroreceptors and (in people with clinical postural hypotension) there is an impaired sympathetic nerve response
This means that the baroreceptor reflex has little effect on the heart and particularly on the TPR and, therefore, your ability to maintain arterial blood flow is diminished
This will lead to less blood flow to the brain resulting in fainting
Fainting is a way of getting you on the floor so that the blood flow to your brain can return to normal and you remove the effect of gravity in causing pooling of blood in the veins of the lower limbs
SUMMARY of Postural Hypotension:
Autonomic (sympathetic) impairment:
Acute reduced sympathetic response
Postural Hypotension
Blood flow to the brain is impaired resulting in loss of consciousness
Once body is supine:
Blood flow to the brain is restored
Consciousness is (usually) regained
What is the name of the parasympathetic nerve which is involved with the autonomic control of the eye?
What is the name of the ganglion on which this nerve goes to?
What effect does Parasympathetic activity and sympathetic activity have on the eye?
The parasympathetic nerve that we’re looking at is the oculomotor nerve (CN III)
This nerve goes to the ciliary ganglion and there is a short post-ganglionic nerve fibre going to the ciliary muscle
Parasympathetic and sympathetic act in opposition
The iris muscle is under BOTH CONTROLS of the ANS
Parasympathetic will cause pupil constriction
Sympathetic will cause pupil dilation
What does pilocarpine do to the eye?
What Molecule does it mimic?
What type of receptors are activated by this drug?
Pilocarpine is an acetylcholine drug
If you insert pilocarpine into the eye, you get miosis (pupillary constriction)
By inserting pilocarpine into the eye, you activate the muscarinic acetylcholine receptors in the iris and make the iris contract inwards thus narrowing the pupil
Sympathetic would have the opposite effect
What does tropicamide do?
If you block the parasympathetic with tropicamide, the only thing that’s left is the sympathetic control of the iris so you get massive pupil dilation
This is called MYDRIASIS (pupil dilation)
Block muscarinic receptor
This is the machinery controlling the pupil’s response to light
Light comes through the pupil, reaches the retina and information is relayed to the brain via the ……….. …………..
The efferent control of pupil diameter originates in the ……….. ………….. which is relayed to the ……….. ………….. ……….. - from here, the parasympathetic neurons originate
Remember there is a LINK between the ……….. ………….. and the ……….. ………….. ………..
There parasympathetic neurons DO NOT start from where the optic nerve ends
The short post-ganglionic parasympathetic neuron innervates the ……….. and causes pupil constriction and decreases the amount of light coming to the eye
So pupil constriction is mediated by a parasympathetic reflex
This is the machinery controlling the pupil’s response to light
Light comes through the pupil, reaches the retina and information is relayed to the brain via the optic nerve
The efferent control of pupil diameter originates in the Pretectal nucleus which is relayed to the Edinger-Westphal nucleus - from here, the parasympathetic neurons originate
Remember there is a LINK between the pretectal nucleus and the Edinger-Westphal nucleus
There parasympathetic neurons DO NOT start from where the optic nerve ends
The short post-ganglionic parasympathetic neuron innervates the iris and causes pupil constriction and decreases the amount of light coming to the eye
So pupil constriction is mediated by a parasympathetic reflex
What is the consensual reflex?
Why does this happen?
Consensual Reflex - if you shine light in one eye, both pupils will contract
This happens because the afferent information CONVERGES on the pretectal nucleus
If you shine light in the right eye, the information is relayed to the pretectal nucleus which activates BOTH parasympathetic nerves to the right and left eye
Even though the stimulus only comes through one eye, you get activation of both efferent nerves
If you achieve a direct response in the right pupil without a consensual response in the left pupil, where is the lesion?
The information is going in and the effect isn’t coming out
As there is no response in the left eye but there is a response in the right eye, there must be a problem with the parasympathetic nerves of the left eye
If you shine the light in the right eye and don’t get a response in either pupil then there is a problem with the optic nerve
If you shine the light in the right eye and there is no response in the right eye but you get a response in the left then the optic nerve is fine but the parasympathetic nerve in the right eye has a problem but the parasympathetic nerves on the left side are fine
