Why is it that the parasympathetic system activates some things and not others, where the sympathetic system is more of a systemic activation?
Pre to post-ganglionic ratio is 1:1 in parasympathetic and 1:20 in sympathetic.
What type of tissue is controlled by the autonomic nervous system?
Cardiac, smooth muscle and glands.
What effects do the parasympathetic (ACh) and sympathetic nervous systems (NE) have on heart rate, atrial/nodal automaticity, conduction velocity and contractile force?
When you are running from the police, what blood vessels contract and what ones dilate? What about when you are sleeping in jail that night?
When you are running, skeletal muscle and liver blood vessels dilate and all other constrict. When you are sleeping, the parasympathetic system kicks in and has no effect on blood vessels unless you give ACh as a drug.
Where is ACh used as the transmitter in the sympathetic nervous system?
At sweat glands to increase generalized sweat secretion. It also acts on adrenal medullary cells.
Which muscles of the eye are stimulated by ACh? NE?
ACh = sphincter muscles that constrict pupil. NE = radial muscles that dilate pupils.
Where does ACh act in the sympathetic and parasympathetic ganglia? NE?
ACh is released by all preganglionic fibers. It is also released in parasympathetic postganglionic fibers. NE is released by sympathetic post ganglionic fibers.
What two enzymes do opposite actions at the neurosynapse?
Choline acetyltransferase adds choline to acetyl CoA. Acetylcholinesterase breaks ACh into choline and acetate.
What receptors does ACh act on in muscle?
What receptors does ACh act on in the heart?
Nicotinic on the post ganglionic fiber (nAChRn) and muscarinic receptors at the effector organ (M2)
What receptors does ACh act on in the adrenal medulla?
How does the nicotinic receptor work?
5 subunits form an ion channel. ACh binding to receptor allows Na+ and Ca++ to flow in while K+ flows out of the cell. This depolarizes the cell and can initiate an action potential.
How are cholinergic receptors used to decrease ACh secretion right after a synapse?
ACh binds to a muscarinic receptor on the ganglia after activating the nicotinic receptor on the postganglionic neuron. The M2 receptor is g-coupled and hyperpolarizes the cell by allowing K+ to flow out and block Ca++ entry.
Release of ACh at an effector organ results in an increase in intracellular Ca++ and contraction. What type of muscarinic receptors are likely at this post synaptic terminal?
Odd ones (M1,M3,M5)
Release of ACh at an effector organ results in hyper polarization and inhibition of Ca++ release. What type of muscarinic receptors arel likely at this post synaptic terminal?
Even ones (M2, M4)
On what receptors does NE act on in the heart? Blood vessels? Skeletal muscle?
Heart (increase HR) = beta-1 adrenergic receptors. Blood vessels (vasoconstrict) = alpha-1 adrenergic receptors. Skeletal muscle (vasodilate) = from EPI binding to beta-2 adrenergic receptors. EPI releases as a result of NE binding to nicotinic receptors on the adrenal medulla.
Why does NE look like this?
It comes from tyrosine. Two hydroxyl groups are added and the carboxyl group is taken off tyrosine to form NE.
What mechanism prevents sympathetic post ganglionic fibers from secreting too much NE?
NE feeds back to alpha-2 receptors on the post-ganglionic fiber. This then blocks Ca++ channels and opens K+ channels, hyper polarizing the cell.
What is the main mechanism by which sympathetic transmission is terminated?
NE is taken up by NET (norepinephrine transporter)
What drugs block NET and exaggerate the effects of NE?
Cocaine, antidepressants and methylphenidate (ADHD). The euphoric effects come from dopamine, bad side effects come from NE.
Why does your body need more cocaine after using it for a while
When NET is blocked, long-term exposure of NE at the neurosynaptic terminal causes down regulation of cholinergic receptors and the effect is lessened with the same amount of drug.
Which cholinergic receptor is unaffected by NE?
Beta-2 (Epinephrine). Alpha-1, alpha-2 and beta-1 are all affected by NE.
You have a runny nose, so you get a nasal spray and stop it. What is the likely drug and what cholinergic receptor is it acting on?
Phenylephrine. It stimulates alpha-1 receptors, causing vasoconstriction and less fluid secretion.
Why do people have so much energy when they are on amphetamines?
They have massive sympathetic stimulation because amphetamines replace NE in presynaptic vesicles. They also inhibit MAO (mono amine oxidase) so NE can't be metabolized and massive amounts of NE are secreted.
How is NE metabolized?
COMT (adding a methyl group to NE) and MAO (oxidizing NE)