Autonomic Nervous System Flashcards
What is the autonomic nervous system?
Maintains homeostasis of internal and external environment. Through involuntary control of the viscera and glands.
What is the autonomic nervous system split into?
Sympathetic and parasympathetic nervous systems.
What do the sympathetic and parasympathetic nervous systems prepare you for?
Fight or flight AND rest and digest respectively.
What does the parasympathetic nervous system do to the body?
PSBHPBB - Pervy sheep bhahh. Herders praise (the) bhahh bhahh. REALLY IMPORTANT! Constricts pupils Stimulates flow of saliva Constricts bronchi Slows heartbeat Stimulates peristalsis (involuntary constriction and relaxation) and secretion in the stomach Stimulates bile release in the liver and gall bladder Contracts bladder. Stimulates an erection. PSBHPBB - Pervy sheep bhahh. Herders praise (the) bhahh bhahh everytime.
What does the sympathetic nervous system do to the body? Identify the differences? (x5)
PSBHPGABOSCP – Pervy sheep bhahh. Herders praise (the) gleeful ahhh bhahhh. Oliver, speak courteously, please! REALLY IMPORTANT! Dilates pupils inhibits salivation Relaxes bronchi Accelerates heartbeat Inhibits peristalsis and secretion Stimulates GLUCOSE PRODUCTION and release in the liver so that you CAN fight or flight without exhausting straight away. Secretion of ADRENALINE and NORADRENALINE by the kidneys Inhibits bladder contraction STIMULATES ORGASM/EJACTULATION. STIMULATES SWEATING CONSTRICTS BLOOD VESSELS (e.g. in the skin). ERECTOR PILLI MUSCLES in the skin. PSBHPGABOSCP – Pervy sheep bhahh. Herders praise (the) gleeful ahhh bhahhh. Oliver, speak courteously, please!
What anatomical regions of the central nervous system concern the sympathetic nervous system? Two names?
Between T1 and L2/3 = called the sympathetic chain. The overall area of emergence is known as thoracolumbar flow.
What anatomical regions of the central nervous system concern the parasympathetic nervous system?
The cranial nerves and the sacral splanchnic nerves (S2-4). No spinal cord!
What are the cranial nerves involved in the parasympathetic nervous system? (x4)
III Oculomotor VII Facial nerve IX Glossopharyngeal X Vagus
What are each of the cranial nerves involved in the parasympathetic nervous system responsible for? (x4) Nature of the vagus nerve?
III Oculomotor – pupil constriction. VII Facial nerve – salivation. IX Glossopharyngeal – salivation (yes, again). X Vagus – bradycardia, gastric motility, digestion, bile release. The vagus nerve is the biggest component of the PNS – this can also be denoted by the picture.
What are ganglia?
Structures outside the CNS containing a collection of neural cell bodies (somas).
What is the structure of the sympathetic nervous system? (in relation to synapses)
Pre-sympathetic neurones run down the length of the spinal cord and terminate (and SYNAPSE) at the area of the spinal cord where the relevant pre-ganglionic efferents are located. Preganglionic sympathetic neurones emerge efferently from the relevant region of the spinal cord. A synapse occurs at the paravertebral ganglia, or some synapse at smaller regions called prevertebral (also called collateral) ganglia. From these ganglia, impulses are synapsed onto new neurones: postganglionic sympathetic efferents – to the target organ. THERE ARE GANGLIA ON EACH SIDE OF THE SPINAL COLUMN. (so there are two ganglia).
What are paravertebral ganglia?
Ganglia that extend the length of the sympathetic trunks.
What are prevertebral ganglia? eg. Coeliac ganglion or Superior Mesenteric Ganglion
Also called collateral ganglia. Ganglia found between the paravertebral ganglia and target organ. Pre-ganglionic neurones still pass through the paravertebral ganglia; they don’t synapse there. They only synapse at the prevertebral (collateral) ganglia.
What neurotransmitters are found along each region of the SYMPATHETIC nervous system? i) Pre-sympathetic –> preganglionic. ii) Preganglionic –> postganglionic. iii) Post-ganglionic –> target organ (x3). Exception?
i) Glutamate always.
ii) Acetylcholine always. EXCEPT in the sympathetic pathway that controls the adrenals – there are NO GANGLIA for neurotransmission (as shown in the photo).
iii) Heart, kidney, blood vessels: Noradrenaline. Sweat glands: Acetylcholine. Renal vessels: Dopaine.
Exception: neurone goes from the CNS and stimulates the adrenal glands to produce adrenaline (80%) and noradrenaline (20%), which THEN go on to affect the target organs e.g. heart and blood vessels. Here, the neurotransmitter acetylcholine stimulates the adrenal glands.
NOTE: drugs that block the SNS pathways may not affect adrenaline or noradrenaline, because it is secreted into the circulation, and not associated with pre-ganglionic and post-ganglionic synapses!
What are noradrenaline and adrenaline also called?
Norepinephrine and epinephrine, respectively.
What is the structure of the parasympathetic nervous system? (in relation to synapses)
Cranial (or sacral) nerves emerge from the CNS. They are inside (or LIE VERY CLOSELY) to the target organ. As a result, the pre-ganglionic neurone is very long, while the post-ganglionic neurone is extremely small (and inside the target organ only (if the ganglia are inside the target organ)).
What neurotransmitters are found along each region of the PARASYMPATHETIC nervous system?
The cranial nerves emerge straight from the brain, so there’s no synapse in the spinal cord. The first synapse is in the ganglia close to or inside the target organ – between the long parasympathetic preganglionic neurone and the parasympathetic postganglionic neurone. Acetylcholine is released into this synapse. Acetylcholine is also released into the synapse between the postganglionic neurone and the effector organ e.g. heart. View the top of the picture. (presumably, there is some kind of pre-parasympathetic neurone that extend down to S1-4 for the sacral parasympathetic nerves!)
For comparison, how is the somatic nervous system structured in relation to its synapses?
There is a long neurone that extends down to the relevant section of the spinal cord. Synapse occurs where this neurone terminates – using Glutamate. Motor neurone goes straight to effector = skeletal muscle! Here, the neuromuscular junction uses ACETYLCHOLINE – this is important later when we look at drugs affecting the nervous system!
Why does the anatomy of the sympathetic and parasympathetic nervous differ?
Sympathetic NS wants to cause a mass response so that the whole body is mobilised, ready for increased activity. Fight/flight is a whole-body response. Parasympathetic NS is discrete or localised, as it looks to conserve body energy – this requires cutting down on specific areas that are not needed.
What are the principle stages of biosynthesis for noradrenaline (and the sites of biosynthesis (x2))?
Note that dopamine is synthesised in the pathway. Noradrenaline is synthesised in the PRESYNAPTIC vesicles from dopamine.
What are the principle stages of biosynthesis and metabolism of acetylcholine? And the enzymes? (x2)
Choline acetyltransferase catalyses the forward reaction (in the glial cells and pre-synaptic neurones). Acetylcholinesterase catalyses the backwards reaction (in the synaptic cleft).
Why is acetylcholinesterase a clinically important enzyme to target in pharmacology?
Acetylcholinesterase can be targeted in pharmacology to increase stimulation of the post-synaptic neurone.
What is the name of the structure labelled? (could be x2 things that differ SLIGHTLY)
INTERMEDIOATERAL CELL COLUMN – where the sympathetic preganglionic neurons emanate from. LATERAL HORN OF THE SPINAL CORD – contains cell bodies of preganglionic neurons, found not just in T1 – L2-3 (as is the intermediolateral cell column), but also found in the PNS for S2-S4.
What is the structure of the paravertebral ganglia at each ‘swelling’?
The white ramus communicans carries preganglionic axons of the sympathetic nervous system into the paravertebral ganglia. The grey ramus communicans takes postganglionic neurons away from the ganglia, towards the target organs. Preganglionic neurones that do NOT terminate here, leave the ganglia in a different direction and are carried separately to the prevertebral (collateral) ganglia via splanchnic nerves. You need to recognise what they look like anatomically, relative to each other.
What are the three pathways for motor neurons in the sympathetic nervous system?
Synapse in the paravertebral ganglia and leave via the grey ramus. Pass through the paravertebral ganglia and out to the collateral ganglia via the splanchnic nerve. Reach the paravertebral ganglia, transverse up or down the ganglia to a new level, and synapse there – then moving efferently via the grey ramus on their new layer.
What type of receptors are baroreceptors?
Mechanoreceptors.
What do baroreceptors detect?
Changes in pressure.
Where are baroreceptors located in the heart? How do they communicate with the CNS?
Aortic baroreceptors – communicate via the AFFERENT vagus nerve. Also found in the carotid arteries – communication via the AFFERENT glossopharyngeal nerve.
What happens to the baroreceptors in the heart when there is an increase in blood pressure? HOW is a response delivered to the heart?
Receptors become activated at a threshold. They send impulses to the brain. How the brain responds is covered later. NB: it’s not just the heart that responds. A response is delivered down the EFFERENT vagus nerve (parasympathetic nervous system).
How does baroreceptor firing change according to a change in blood pressure – baroreflex?
When there is increased blood pressure, there is increased baroreceptor firing. From the set-point, a small change in BP = large change in baroreceptor firing – so system is VERY sensitive.
How does the baroreflex change in hypertensive patients?
In hypertensive patients, their baroreceptor reflex is set higher, so their set point is HIGHER. Sensitivity hasn’t changed, but the brain will defend the high blood pressure.
What does the cephalic response describe? What is it caused by? (x3)
The cephalic phase of digestion is the GASTRIC SECRETION that occurs even before food enters the stomach, especially while it is being eaten. It results from the sight, smell, thought, or taste of food.
What is secreted in the cephalic response?
Small increase in insulin from the pancreas to prepare for glucose influx. Enzymes and gastric juices in the STOMACH for digestion.
What is the cephalic response stimulated by?
Vagus nerve – PNS. Kind of already covered.
How does the autonomic nervous system detect that you have ingested food and initiate a feeling of fullness? (x2 pathways).
Mechanoreceptors in the stomach measure the degree of distension in the stomach caused by the ingestion of food. In the small intestine, certain hormones are released by the small intestines when you are digesting food. These hormones are detected by chemoreceptors and proportional to amount of food ingested. More distension / more hormones mean that these receptors increase their firing down the VAGUS nerve to the BRAINSTEM – which then goes on to initiate your feeling of fullness.
For obese people, what can be said about the receptors that bring about a feeling of fullness after eating? (x2 points of focus)
In obese people, the vagus nerve has a lower firing rate for the same sized stimulus (whether it be chemical or mechanical). So, more food required to initiate feeling of fullness. The vagus nerve is plastic so can change its expression of receptors. In the obese state, the chemoreceptors that respond to hormones that make us feel full are removed, so the feeling of fullness no longer occurs through the chemoreceptors.
How is respiration coordinated by the brainstem in the autonomic nervous system?
The brain stem contains many centres which work with each other to regulate breathing. The dorsal group actually physically makes breathing happen – the other centres coordinate the rhythm and rate of breathing.
What sensory information is used to regulate breathing in the autonomic nervous system? (x3) Does each pathway work to increase or decrease breathing rate?
[Lots to remember here, but it’s really important.] Chemoreceptors in the heart – detect low O2, low pH, and high CO2 and input this information via the vagus and glossopharyngeal nerves. THESE DRIVE AN INCREASE IN BREATHING. You also have chemoreceptors in the brain stem – central chemoreceptors – detect low pH, and high CO2 (but not O2) (associated with INCREASED respiration). THESE DRIVE AN INCREASE IN BREATHING RATE. Lung mechanoreceptors – measure distension in the lungs and send sensory information via the vagus nerve. THESE DRIVE A DECREASE IN BREATHING RATE. All feedback directly to the dorsal centre!!!
What is the basic structure of the bladder? (x3)
Detrusor muscle is the outer muscular wall. You have two sphincters – an internal and external one.
What parts of the autonomic and somatic nervous systems are linked to each area of the bladders anatomy? (x3 + x1)
Parasympathetic NS (S2-S4) innervates the detrusor muscle of the bladder. Sympathetic NS (T10-12) innervates the INTERNAL sphincter. Motor neurones in the somatic NS (voluntary control from S2-S4) innervates the external sphincter.
Afferent mechanoreceptors send sensory information to the brain from the detrusor muscle to tell brain how full the bladder is.
What happens in the autonomic nervous system when the bladder is full?
When the mechanoreceptors are activated (only when the bladder is full), the PNS is stimulated (=detrusor muscle contraction), and the SNS is inhibited (= internal sphincter relaxation). Control over urination is now solely controlled by voluntary control of the external sphincter.
How is the entire autonomic nervous system regulated?
Central regulation of autonomic function is regulated by the hypothalamus.
What does the Nucleus Tractus Solitarius do?
Nucleus Tractus Solitarius (NTS) – innervated by the CNX and CNIX. NTS sends sensory information to the hypothalamus, which integrates the sensory information, and sends corresponding information back into the brainstem.
Where does the hypothalamus send information, in relation to the autonomic nervous system? (x2)
Into the dorsal motor nucleus of the vagus (DMNX) = found in the brainstem and is the outflow for the vagus nerve. You also have information that goes straight down to the intermediolateral cell column (spinal cord) from the hypothalamus.
What are the inputs to the hypothalamus? (x2)
NTS Higher regions of the brain – e.g. cerebellum. This is where voluntary information can affect the hypothalamus e.g. voluntary breathing can break the autonomic regulation of breathing which is coordinated by the hypothalamus.
What are the two MAIN types of receptor in the ANS?
Adrenoreceptors – SNS. i.e. predominantly uses adrenoreceptors as its post-synaptic receptor because most SNS responses are mediated by adrenaline. Cholinoceptors – PNS.
What are types and subtypes of adrenoreceptor? (x2 (x2 (x3 and x3) and x2))
Alpha and Beta.
What are the two types of cholinoceptor?
Nicotinic and Muscarinic
What is the difference between nicotinic and muscarinic receptor?
Both use acetylcholine as their neurotransmitter. But nicotinic are ionotropic receptors. Muscarinic are G-protein receptors.
What are the two different mechanisms that receptors use?
Ion channels – ionotropic. G-protein coupled receptors (GPCR).
How do ion channels work?
Ligand (Ach) binds to receptor. Results in conformational change which results in ion flow through the channel = action potential or hyperpolarisation.
How do GCPR work?
Binding of ligand to outer membrane. Activates downstream signalling components.
What’s the difference between the effects of ion channel and GCPR receptor?
Ion channels are on/off – rapid response to ligand. GCPR effects can last for a LONG time.
What are the two types of receptor location? And their function in each case?
POSTSYNPATIC RECEPTOR (neurotransmitter receptor found on post-synaptic knob) = responds to neurotransmitters from pre-synaptic neuron to deliver a response in the post synaptic cell. PRESYNAPTIC RECEPTOR (neurotransmitter receptor found on pre-synaptic knob) = responds to neurotransmitters release from the pre-synaptic neurone to regulate how much is released.
What loci in the autonomic nervous system (SNS and PNS) are cholinoceptors found?
Nicotinic also found at NMJ in somatic NS. Cholinreceptors are the MAIN receptor found in the PNS, that doesn’t mean you can’t find them anywhere else. They ARE found in the SNS – as can be seen in the photo – but this isn’t the MAIN receptor in the SNS. Adrenoreceptors are the spla receptor because MOST of the SNS actions are mediated by adrenaline (although it doesn’t follow the usual pre- and post- ganglionic pathway).
What two drugs target the cholinoceptors?
Atropine targets the muscarinic cholinoceptors. The drug is a competitive muscarinic receptor antagonist. Tubocurarine targets the nicotinic cholinoceptors. The drug is a nicotinic receptor antagonist.
Why is tubocurarine rarely used?
It targets nicotinic receptors which are also present in NMJs. So the drug would inhibit all muscular movement also = PARALYSIS = death!
What does atropine do to heart rate and why?
Increase. Because actions of PNS would be blocked. PNS slows down the heart rate.
!!! What does atropine do to sweat production and why?
Decrease. TRICKY – remember, there are some muscarinic receptors in the SNS – found in sweat glands!!!
What does tubocurarine do to respiration rate and why?
Decrease. Trick question - because involved in NMJs too which would put patient in respiratory arrest.
!!! What does tubocurarine do to heart rate and why? Increase.
It removes SNS and PNS control, so all autonomic control is lost. TRICKY: Because nicotinic receptors found in both SNS and PNS control of heart rate!!!
What type of mechanism does nicotinic and muscarinic receptor have?
Nicotinic – ionotropic. Muscarinic – GPCRs.
What loci in the autonomic nervous system (SNS and PNS) are adrenoreceptors found?
Not found in the PNS at all! Alpha 1 promotes contraction in the effecter organ! Alpha 2 is a pre-synaptic receptor = regulates and inhibits release of more NA. Blue squares are the nicotinic receptors – but these are cholinoceptors.
What type of mechanism do adrenoreceptors use?
GPCRs.
What four drugs target the adrenoreceptors? Effect on body for each?
Medetomidine – alpha 2 receptor antagonists – so inhibit NA release!!! Doxazosin – alpha 1 receptor antagonist – so inhibit smooth muscle contraction. There is dilation instead! Atenolol – beta 1 receptor antagonist – heart specific. Salbutamol – beta 2 receptor agonist (meaning it ACTIVATES) – relaxes the smooth muscle. This is what NA is supposed to do anyway.
REVISE AND RECITE: The Baroreceptor reflex (an autonomic reflex arc).
Baroreceptors – blood pressure.
Affected by Cardiac Output and Total Peripheral Resistance (determined by radius) [BP = CO/R].
Cardiac Output = Heart Rate x Force of contraction.
Intrinsic heart rate = 100-110bpm (meaning NO autonomic control). Resting heart rate is 72bpm though! Autonomic nervous system is responsible for this – the parasympathetic system is dominant!
What is the pathway of the reflex arc?
Afferent nerve from baroreceptors in heart go to CNS. CNS determines level of stimulation in nerves that control HEART and BLOOD VESSELS (PNS innervates JUST the heart). Parasympathetic nerves ARE excitatory nerves, and synapse onto INHIBITORY nerves in a ganglion – this is how they bring about a parasympathetic/slower response. Sympathetic nerves ARE ASSOCIATED with inhibitory nerves (notice that this is in the CNS completely, while excitatory nerves in PNS extend FROM the CNS). (Refer to photo!).
Baroreceptor firing is PROPORTIONAL to size of the excitatory and inhibitory signals sent down the parasympathetic and sympathetic nervous systems, respectively.
NORMAL BLOOD PRESSURE: normal baroreceptor firing. Parasympathetic nerve is excited, and inhibitory nerve excited. = inhibition of sympathetic nerve! AND parasympathetic response in the heart. This PNS dominance explains LOWER THAN INTRINSIC RATE heart rate.
If BP increases, baroreceptor firing rate increases. = more powerful stimulation of parasympathetic nerve. This results in significant excitation of the PNS inhibitory nerve = lower heart rate = lower Cardiac Output = lower BP ^^^. AND = more powerful stimulation of SNS inhibitory nerve. This results in smaller excitation of the (excitatory pre-ganglionic and) sympathetic nerve = no increase in heart rate or vasoconstriction/venous tone.
If BP falls, baroreceptor firing rate decrease. = less powerful stimulation of the parasympathetic nerve and inhibitory nerve in SNS. Results in larger than normal impulse in the (preganglionic and) sympathetic nerve = sympathetic nervous system exerts dominance over the PNS = increased HR, venous tone and vasoconstriction (increases total peripheral resistance AS WELL. Increased TPR has opposite effect on BP, but its effect is not significant).
How can the Baroreceptor reflex be put into context of standing from a supine position?
BP is greater the more inferior you go in the body because of gravity.
When you go from a laying to supine position, HYDROSTATIC PRESSURE INCREASES in the blood vessels of the legs, which increases distension in those vessels. = more blood POOLED in veins of the lower limbs.
Hydrostatic pressure increase also increases the amount of protein-free plasma that filters OUT of the capillaries into the interstitial fluid = BULK FLOW (increased H pressure and same osmotic pressure means more movement out).
Increased venous distension AND capillary fluid loss = DECREASED VENOUS RETURN! So, stroke volume decreases! This is sensed by the autonomic nervous system by baroreceptors = sympathetic nervous system.
In the baroreceptor reflex, what are the relative sizes of the effects of changes in heart rate and changes in arterioles and veins? Increased venous tone and arteriole vasoconstriction is LESS effective at increasing blood pressure than increasing heart rate.
What does the SNS do to veins in the baroreceptor reflex?
Increased venous tone –> less flexible walls –> less distension –> increased venous pressure –> increased venous return.
What happens when the SNS autonomic response to decreased blood pressure is impaired?
Arterial pressure is not maintained. Cerebral hypo-perfusion. FAINT.
REVISE AND RECITE: The Pupillary light reflex (an autonomic reflex arc) – what are the structures in the arc?
Iris muscle controlled by PNS and SNS. The nerves and how they are innervated are shown in the photo.
REVISE AND RECITE: The Pupillary light reflex (an autonomic reflex arc) – how does it work?
PNS is the main controller in this reflex!
Parasympathetic nerve activation results in marked pupil constriction – pupil gets really small. If the parasympathetic nervous system is blocked e.g. with drug called Tropicamide, then you get MASSIVE dilation.
So, the parasympathetic nervous system keeps the iris MILDLY CONSTRICTED.
How does the PNS do this?
Light comes in, activating the optic (afferent) nerve. This information is received in the brain by the Pretectal nucleus. The pretectal nucleus kickstarts the efferent response. Action potential, via the Edinger-Westphal nucleus, travels down the pre-ganglionic parasympathetic neurone to the ciliary ganglion, and then down the post-ganglionic to the iris for contraction.
When it is dark, less light hits the retina, the optic nerve stimulation is reduced, so parasympathetic nerve also less stimulated, so pupil dilates, so retina receives more light.
Nature of response means that if ONE eye is affected, BOTH will react in the same way – both eyes will have the same papillary response. This is used clinically to assess whether there’s damage to efferent nerves if one does not respond, OR damage to the afferent nerve on the side you are testing (or both efferent nerves) if both eyes do not respond.
Why do the ganglia communicate?
It permits mass activation of the sympathetic nervous system in conditions of stress.
What does the splanchnic bed describe?
Describes organs in the abdominal cavity.
What is autonomic neuropathy?
Refers to conditions that involve damage to or dysfunction of the autonomic nervous system.
What parts of the autonomic nervous system are affected by localised and generalised autonomic failure?
Localised affects a SPECIFIC part of the autonomic nervous system. Generalised affects the WHOLE autonomic nervous system.
What part of the nervous system does the ANS concern?
REMEMBER, the autonomic nervous system is considered to be JUST the peripheral nervous system.
What are the main abnormalities in generalised autonomic failure? Example of a condition.
Can affect everything that is controlled partly/wholly by the ANS. Weakness, blurred vision, dizziness, chronic fatigue, low blood pressure, orthostatic hypotension (BP falls suddenly when standing from a supine position), fainting, tachycardia, urinary incontinence. e.g. Parkinson’s disease.
What are the main abnormalities in localised autonomic failure?
Can affect very specific areas of the ANS depending on what is affected. My best guess is that it is mainly caused by trauma as this has the ability to target specific areas, rather than have a general affect.
