Organization of nervous system
ion channel receptor
- either open or closed
- a closed channel prevents ions from flowing along a concentration gradient
- an open channel allows ions to flow along a concentration gradient
Example: voltage gated Na+ channel
G Protein Coupled Receptor
Works in 1 of 2 ways:
- Opens/closes ion channel (Ex: Musc. 2 receptor in SA node)
- Activates or inhibits an enzyme inside a cell (A1 receptor in vascular smooth muscle- picture)
Enzyme-linked receptor
- receptor is also an enzyme
- at rest, catalytic domain inactive
- signal binds, catalytic domain activated
Ex: insulin receptor in skeletal muscle (linked to enzyme tyrosine kinase)
Intracellular receptor
- located in cytoplasm or nucleoplasm
- signal diffuses through cell membrane and binds to receptor inside cell
Ex: steroid binds to receptor in cystoplasm; thyroid hormone binds to receptor in nucleus
GPCR Signal Transduction
Receptors:
* A1
* M1, 3, 5
* V1
* H1
- Signal transduction: Gq
- Effector: stimulates Phospholipase C
- 2nd mess: increase IP3, DAG, Ca+
Receptors:
* A2
* M2, 4
* D2
- Signal transduction: Gi
- Effector: inhibit adenylate cycle
- 2nd mess: decrease cAMP
Receptors:
* B1, B2, B3
* D1
* V2
* H2
- Signal transduction: Gs
- Effector: stimulates adenylate cyclase
- 2nd mess: increase cAMP
B1 (sympathetic)
Effects:
Heart
* + inoptropy
* + chronotropy
* + dromotropy
B2 (sympathethetic)
Effects:
Lung
*Bronchodilation
Urinary tract
* Bladder sphincter contraction
* Increase renin secretion
Skeletal muscle
* Vasodilation
A1 (sympathetic)
GI tract:
*Vasoconstriction sphincter contraction
Glands:
* Sweating
* Decrease pancreatic activity
Urinary Tract
* Bladder sphincter contraction
* Increase renin secretion
Skin
* Vasoconstriction
Pupils
* Dilation (mydriasis)
M1 (Parasympathetic)
Glands-
Increased:
* Salivation
* Lacrimation
* Pancreatic activity
M2 (Parasympathetic)
Heart
* - inotropy
* - chronotropy
* - dromotropy
M3 (Parasympathetic)
Lungs
* Bronchoconstriction
* Increased gland secretions
GI
* Increase motility
* Sphincter relaxation
* Increase gland secretion
Glands
Increased:
* Salivation
* Lacrimation
* Pancreatic activity
Urinary Tract
* Bladder sphincter relaxation
Pupils
* Constriction (miosis)
ANS influence on eye
- SNS > A1 stimulation > radial (dilator pupillae) muscle contraction > mydriasis (pupil dilation)
- PSNS > Muscarinic stimulation > sphincter pupillae muscle contraction > miosis (pipil constriction)
Stimulation of alpha-2 receptors reduces: (select 2)
A. sympathetic tone
B. shivering
C. serum glucose
D. platelet aggregation
A. sympathetic tone
B. shivering
Also produces sedation, hypnosis, analgesia, depresses LOC, inhibits insulin release > hyperglycemia, promotes platelet aggregation
Name three A2 receptor locations
- Presynaptic: NE releasing neurons in CNS & PNS
- Postsynaptic: smooth muscle & other tissues/organs
- Nonsynaptic: Platelets
A2 receptor location and effects
A2 receptor stimulation & transient HTN
Rapid administration of precedex can produce biphasic BP pressure response:
- stimulation of postsynaptic A2 receptors in PERIPHERAL aterial & venous circulation > acute vasoconstriction 7 HTN
- CNS effects lag behind; once kick in, CENTRAL A2 effect over powers peripheral A2 effects: sedation, MAC reduction, bradycardia, vasodilation (hypotension)
