ANS Study Questions Flashcards
What effect would an increase in the potassium conductance (flow of potassium into/out of the cell) have on the cell’s excitability. (Hint: think first of which way potassium will move, then figure out what that will do to the Vm)
An increase in potassium conductance means that more potassium is moving. The electrical gradient would tend to pull potassium into the cell (since the cell is negative and potassium is positive - opposites attract), while the concentration gradient favors potassium leaving (high inside) the cell. Since the concentration gradient is stronger than the electrical gradient, potassium tends to leave the cell given its chance. If we increase the potassium conductance, we see more potassium leaving the cell, taking the positive charge with it. The net result is that the cell becomes more negative (hyperpolarized) and farther away from threshold. This means that the cell will be less excitable than it was
Describe the pre- and post-ganglionic fibers in the sympathetic nervous system (e.g. which is long/short?)
SSL: In the sympathetic nervous system, the ganglia are located close to (or right outside of) the spinal column, so the pre-ganglionic fibers have a short trip (and therefore axon), while the post-ganglionic fibers still have a ways to travel, so they are long.
What is the purpose of having multiple receptor subtypes?
By having multiple receptors, we can use the same neurotransmitter to accomplish different things. For example, sympathetic stimulation causes vasodilation of the blood vessels in the muscles, but vasoconstriction (narrowing) of the blood vessels in the intestine. . The sympathetic nervous system accomplishes this by using the same chemical (NE or epi) but putting different receptors on the blood vessels in different places. In this example (we haven=t gotten to this in lecture yet), we’re going to put beta-adrenergic receptors on the vasculature in the muscles, but alpha in the intestines
How is it that the parasympathetic NS has no effect on the radial muscle of the iris? How does it relax?
The radial muscle of the iris is NOT innervated by the parasympathetic nervous system nor does it have muscarinic receptors on it. It relaxes (and allows the sphincter muscle to take over) when the activity in the sympathetic neurons innervating it decrease. Remember, the ANS is normally a balancing act between the two systems. This is a good example of that act.
How does stimulation of muscarinic receptors on the intestinal smooth muscle cause an increase in contraction, while stimulation of muscarinic receptors on the muscle of the sphincters (which is also smooth muscle) cause relaxation of that smooth muscle?
This is where the different subtypes of muscarinic receptors come in handy. The intestinal smooth muscle expresses one subtype of muscarinic receptor, while the smooth muscle of the sphincters expresses a different muscarinic receptor.
receptor in radial m. of iris?
alpha adrenergic
sympathetic activation of radial m. of the iris causes?
contraction of muscle= dilation of pupil
sympathetic receptor in ciliary m. of lens?
beta 2 adrenergic
sympathetic activation of cillary m. of lens causes?
relaxation of m.= flattening of lens to focus on far objects
sympathetic receptors of heart?
beta 1 and beta 2 adrenergic
sympathetic activation of heart causes?
increase HR and strength of contraction
general rule of thumb for sympathetic receptors for vascular blood flow?
alpha= smooth m. contraction= vasoconstriction beta= causes relaxation of smooth m.= vasodilation
things that have only alpha receptors?
skin/mucosa, salivary glands, brain
sympathetic receptor in bronchial smooth m.?
beta 2
activation of sympathetic receptor in bronchial smooth m?
smooth m relaxation= bronchodilation
