ANS Flashcards
Where is the ANS located?
Both the CNS and PNS
Preganglionic neurons of the ANS are (myelinated/unmyelinated)
Myelinated
Postganglionic neurons of the ANS are (myelinated/unmyelinated)
Unmyelinated
The craniosacral outflow of the PSNS arises from
Cranial (Medullary CNS 3, 7, 9, 10)
Sacral (Sinal cord S2-4)
Most important function of the SNS
Maintenance of vasomotor tone
Most organs are innervated by both SNS and PSNS, except:
Only innervated by the SNS
- Sweat glands
- BVs (although muscarinic receptors are here)
Only innervated by the PSNS
- Ciliary muscles of the eye
- Bronchial smooth muscle (although B2 receptors here)
Baseline tone of HR and BVs are dominated by
HR- Vagal
BVs- SNS
Type of ACh receptor at the NMJ
Nicotinic
Type of receptor on sweat glands for SNS innervation
Muscarinic (Ach)
Type of receptor at all pre/postsynaptic junctions of the PSNS
ACh (nicotinic)
These two medications are anti-muscarinics
Atropine and glycopyrrolate
People who receive these will stop sweating and salivating
Types of nAChRs and mAChRs
nAChRs: Nn and Nm
mAChRs: M1-5
Types of Adrenergic Receptors
Alpha (1&2)
Beta (1, 2, & 3)
Amount of epi and norepi released from the adrenal medulla
Epi (80%)
Norepi (20%)
Effect of circulating ACh on BVs
Circulating ACh will bind to the muscarinic receptors on BVs, activating NO, resulting in eventual vasodilation
Muscarinics and adrenergics are examples of this type of receptor
G-protein coupled receptors
Alpha 1 receptor type and action
Alpha 1 is a G-a-q receptor. Stimulated phospholipase C, which increases IP3 and DAG, which raises intracellular calcium. This increase in calcium causes smooth muscle contraction (vasoconstriction).
Alpha 2 receptor type and action
Alpha 2 is a G-a-i receptor. This inhibits adenylyl cyclase, reducing cAMP in the cell, causing vasoconstriction and an increase in K+ conductance.
Effect of cAMP in smooth muscle and cardiac cells
Smooth muscle- relaxation
Cardiac muscle- increase in force of contraction and rate
Beta 1, 2, & 3 receptor type and action
G-a-s. Stimulates adenylyl cyclae, increasing intracellular cAMP. This relaxes smooth muscle and increases cardiac contractility and rate.
Alpha 1 Effects
1) Most vascular smooth muscle (BVs, sphincters, & bronchi)- contraction
2) Iris- contraction of radial muscle resulting in pupil dilation
3) Pilomotor smooth muscle- contraction/hair erection
4) Prostate and Uterus- Contraction
5) Heart- Increases the force of contraction (but not as much as B1. Remember this is through Ca, not cAMP)
Alpha 2 Effects
1) Platelets- aggregation
2) Presynaptic adrenergic and cholinergic nerve nerminals- inhibits NT release (decrease in BP and HR)
3) Vascular smooth muscle (can cause vasoconstriction due to effect on BV, but more often causes VASODILATION due to the effect of rapidly inhibiting NE release from the presynaptic terminal)
4) GI tract- relaxation (pre-synaptic effect)
5) CNS- sedation and analgesia due to the decrease in SNS outflow
You should think of alpha 2 as being in these three locations
1) Brain (works by decreasing SNS outflow, causing sedation and a decrease in BP and HR)
2) BVs (causing vasoconstriction)
3) Pre-synaptic to BV (nerve fiber terminating on BVs)
Negative feedback signal with alpha 2
Norepi released from the postsynaptic neuron onto the BV cycles back to that pre-synaptic membrane of the post-synaptic neuron, binds to an alpha 2 receptor, which decreases cAMP and opens K+ channels which hyperpolarize the cell. This reduces the release of norepi. This prevents the system from getting too amped up.