Flashcards in Exam #1: Physiology of the ANS III Deck (27):
What is a homotropic interaction? What is the typical effect of a homotrophic interaction?
When the neurotransmitter, by binding to presynaptic autoreceptors, affects the nerve terminals from which it is being released.
- Typically this interaction leads to an autoinhibitory effect
To achieve an inhibitory effect in the SNS, what class of receptor must the pre-synaptic autoreceptor be? What about for the PNS?
What is alpha-methyl DOPA? What is the mechanism of action?
An anti-hypertensive drug that targets alpha-2 autoreceptors in the SNS, leading to a decrease in the amount of NE released from the nerve terminal & consequently, lower blood pressure.
What is a heterotrophic interaction?
One neurotransmitter affects the release of another neurotransmitter, via stimulation of a "heteroreceptor"
Heteroreceptor= presynaptic receptors whose ligand is not the same as the neurotransmitter released by that nerve terminal
What is denervation supersensitivity?
- Also called withdrawal rebound hyperactivity & disuse hyperactivity
- If a nerve is cut & its terminal degenerate, the structure supplied by that nerve becomes super-sensitive to the neurotransmitter released by the terminals
What is the mechanism of denervation supersensitivity?
- Proliferation of receptors
- Loss of mechanism for removal of transmitter
- Increased postjunctional responsiveness
What is a clinical correlation of denervation supersensitivity?
Rebound hypertension seen following the abrupt cessation of adrenoceptor blockers
E.g. abrupt beta-blocker cessation can lead to potentially dangerous rebound hypertension
What is cotransmission?
Neurons release multiple neurotransmitters, each of which interacts with specific receptors & produces effects both pre & post-synaptically
What are the main functions of the ANS?
- Assist the body in maintaining constant internal environment i.e homeostasis
- Accommodate coordinated responses to external stimuli e.g. fight or flight
What is the ergotropphic effect?
- Flight or fight
- All the responses of the sympathetic nervous system combined
List the ergotropic effects.
- Heart rate & BP increase
- Bronchioles dilate
- Intestinal motility & secretion are inhibited
- Glucose metabolism increases
- Pupils dilate
- Hairs become erect
- Cutaneous & splanchnic (organ) BV constrict
- Skeletal muscle BV dilate
What is the Trophotropic effect?
- Rest & Digest
- All of the effects to parasympathetic activation combined
List all of the Trophotrophic effects.
- Pupil constriction
- Decrease heart rate & blood pressure
- Bronchiole constriction
- Increased GI tone, secretion, & peristalsis
- Decreased sphincter tone & increased contraction of the detrusor m.
What is the definition of blood pressure (equation)?
- BP= TPR x CO
- CO= HR x SV
Thus, BP= TPR x CO x SV
Blood pressure is the product of Total Peripheral Resistance & Cardiac Output. Cardiac Output is defined as the product of Heart Rate & Stroke Volume.
What is the definition of CO (equation)?
HR x SV
Outline the autonomic feedback loop in response to an increase in mean arterial pressure.
Draw the pathway.
How does an increase in baroreceptor discharge alter the PNS?
- Increase vagal tone
- ACh activation of M2R
- Decrease in heart rate
When there is an acute increase in TPR, what receptors are activated? What is the effect?
- reflex bradycardia
When there is a decrease in TPR, what receptors are activated? What is the effect?
- reflex tachycardia
Outline the hormonal feedback loop in response to a decreased in blood pressure.
What is the net effect of adrenergic stimulation of the muscles of the eye?
Mydriasis without cycloplegia
What is cycloplegia?
Paralysis of accommodation (focus)
What adrenergic receptors are located on the radial muscle? What is the effect of their stimulation?
- Constriction leading to mydriasis (dilation of the pupil)
What adrenergic receptors are located on the ciliary muscle of the eye? What is the effect of their stimulation?
- Relaxation leading to mydriasis
What is the net effect of adrenergic stimulation on the ciliary epithelium?
Increased production of aqueous humor
What adrenergic receptors are present on the ciliary epithelium?
Beta 1 & 2