sept 29: autonomic nervous system

what is the sympathetic NS responsible for (3Fs)

fight, flight, fright

describe autonomic nerves

-always going to be a ganglia -motor nerves come out from front of spinal cord... -affecter organ and two nerves -pre and post gangleon neuron (pre are myelinated and post are not)

How is pain in a visceral organ experienced?

As a dull aching pain (often called visceral pain) and often not at the site of damage. The nerves that carry referred pain are visceral afferents. They are sympathetic nerves and they come in to the CNS at the level of the thoracic and lumbar spine.

What would happen if a sympathectomy were performed on the heart (i.e., all the sympathetic input was stopped)?

Because only the parasympathetic (rest and relax) branch of the ANS is still functioning after sympathectomy then the heart would slow down and and blood pressure would fall. Also, the force of contractions would decrease and blood pressure would fall.

If all autonomic input to the peripheral blood vessels were to stop what would happen?

Blood vessels would dilate and blood pressure would drop. The peripheral blood vessels only have sympathetic input so blocking autonomic input would be the same as blocking sympathetic input. The sympathetic effect on the blood vessels is constriction so blocking sympathetic input would cause the blood vessels to dilate and therefore blood pressure would fall.

how do Beta-agonists for asthma work? (adrenergic drugs)

Dilate bronchioles but speed up the heart because both ß1 and ß2 receptors are stimulated Specific ß2 -agonists mostly just dilate the bronchioles. Salbutamol (Ventolin) is a specific agonist of the ß2 receptor and provides tremendous relief for asthma sufferers.

what are Cholinergic Receptors

Found in the synapses of the sympathetic and parasympathetic ganglion the postganglionic parasympathetic target organs (two types)

what are Muscarinic receptors (type of cholinergic receptor)

Found on all parasympathetic target organs Acetylcholine (or muscarine) stimulating these receptors leads to Decreases heart rate Increases intestinal motility All parasympathetic effects!

what are Adrenergic Receptors

Found only on the sympathetic postganglionic target organs (or effectors)

describe the vagus nerve

Notice that the vagus innervates lots of viscera. You might think that increased vagus output would increase all the parasympathetic effects on the organs it innervates. That is true to a limited extent but still we can control parasympathetic function to individual organs more tightly than we can sympathetic input. The strange thing about the vagus is that it looks like a giant motor nerve but over half of the fibers are visceral afferents sending messages about mechanical and chemical changes in the heart and other organs to the CNS.

what is the parasympathetic NS responsible for? (3Rs and SLUDD)

Rest Relaxation Rumination or SLUDD Salivation, Lacrimation, Urination, Digestion and Defecation

ANS and its affect on the heart

Sympathetic input speeds up heart rate (tachycardia) and increase the force of contractions (i.e., a positive inotropic effect) This is an appropriate response for preparing for fight and flight. Parasympathetic input slows heart rate (bradycardia) and decreases the strength of contractions (i.e., causes a negative inotropic effect) This is, of course, an appropriate response for rest and relaxation . In the heart there are both branches of the autonomic nervous system but the sympathetic nervous system is dominated by the parasympathetic nervous system

ANS and the Gastrointestinal tract

Sympathetic input yields relaxation Parasympathetic increase activity In the GI tract the parasympathetic nervous system dominates for regulating gastrointestinal motility.

what is the autonomic nervous system ?

The branch of your nervous system that controls your involuntary muscles like the heart and smooth muscles. For this reason it is sometimes called the visceral motor nervous system. There is also a sensory part (made of visceral afferent nerves) of the system but it is largely ignored except in regard to referred pain and interoceptors The most important role of the ANS is to maintain homeostasis of things like blood pressure.

If all autonomic input to the heart was stopped then what would happen to heart rate and force of contraction?

The heart rate would fall and the force of contractions would fall. This is because there is more parasympathetic input than sympathetic before removal of autonomic input. Removing all autonomic input removes more parasympathetic input than sympathetic so the net effect is an increase in heart rate and force of contractions. heart rate would increase and force of contractions increases as well -ask: what are you removing more of? -answer: dominated by parasym...when you remove autoonomic input

what are the Adrenergic Receptors

The neurotransmitters are adrenalin and noradrenalin (= epinephrine and norepinephrine, respectively) Two subtypes exist α (alpha) Generally stimulate contractions β (beta) Generally inhibit contractions (except in the "heart muscle" myocardium

Atropine blocks the muscarinic cholinergic neurons (i.e., the postganglionic parasympathetic receptors). What would this drug do to the pupil size?

The parasympathetic control of the eye muscles would be blocked since atropine keeps the ACh from binding to the muscarinic cholinergic receptors. Once it is blocked you would only get the sympathetic effect and the pupils would dilate. You could also say that the iris sphincter (which is parasympathetic) would be inhibited and the radial muscle of the iris (under sympathetic control) would remain stimulated.

Nicotinic receptors (type of cholinergic receptor)

The receptor found in sympathetic and parasympathetic ganglia Stimulation of these receptors (like with nicotine) leads to both sympathetic and parasympathetic effects

what are visceral afferents

The viscera are the internal organs of the body. The visceral afferents are nerves which run from the internal organs to the brain and spinal cord (i.e., the central nervous system). So, the visceral afferents carry messages like the degree of stretch in the stomach or irritation in the bowel and other messages about the internal organs to the CNS. Just to be clear efferent nerves are motor nerves and they travel from the CNS out.

Explanation for referred pain:

The visceral sensory pain fibers synapse in the dorsal root ganglia, like other sensory nerves, but the origin of the pain is interpreted as arising from the somatic sensory nerves that synapse in the ganglia not from the viscera where the pain is produced.

what is An interoceptor

a sensory receptor that receives stimuli from within the body. We usually speak of interoceptors as being from the heart, gut and other internal organs. Normally you are not aware directly of their sensation. You cannot, for example, know what your blood pressure is by making yourself aware of pressure receptor (baroreceptor) in your blood vessels. These interoceptors are critical in regulation of autonomic activities.

effectors are what kind of muscle

always striated muscles

What happens to your pupils when an anticholinesterase like the nerve gas sarin is consumed?

anticholinesterase stops the breakdown of ACh. Without breakdown there is lots of ACh in the synapse. However, ACh is only a neurotransmitter in the postganglionic, parasympathetic nerves so parasympathetic effects are found to dominate. if given nerve gas: blocks anticholinesterase, parasym effects -pupils will constrict.... hardly see it! extreme miosis

how do Beta-blockers for tachycardia and hypertension work? (adrenergic drugs)

beta-receptors are blocked which slows the Slow heart rate and make the heart more efficient Specific ß1-receptor antagonists are better Do not block ß1-receptors so bronchioles are not constricted

what are somatic motor nerves

cell bodies (soma) in brain and spinal cord and single neuron attaches to muscle fibre to contract

The radial muscle of the iris has what ANS input?

has only sympathetic input (it dilates the pupil)

what is miosis and what causes it

miosis is the constriction of the pupil. parasympathetic stimulation causes circular muscles to contract.

what is mydriasis and what causes it

mydriasis is the relaxation of the pupil. sympathetic stimulation causes radial muscles to contract

iris sphincter has what type of ANS input?

only parasympathetic inputs (it constricts the pupil)

stimulation of the adrenergic receptors leads to:

relatively long term activation of the neurons Breakdown or removal of the neurotransmitter is slow compared to acetylcholine The long activation of the neurons combined with the large spread of the sympathetic NS stimulation means sympathetic effects last a relatively long time

visceral arterials have what form of ANS input?

sympathetic

Adrenergic Receptor Subtypes( α )

α1 Causes contractions of smooth muscle Found mostly in blood vessels of the viscera except the heart α2 Presynaptic receptors Promotes clotting (tip to remember: they look like blood vessels!)

adrenergic receptor subtypes (β )

β1"you have one heart" Heart muscle tachycardia and increased contractility β2 "you have two lungs" Relaxes the bronchioles Relaxes the uterus Almost all sympathetic target organs are relaxed β3: Increases lipolysis