Autonomic Nervous System Flashcards
Compare autonomic nervous system and skeletal muscle innervation.
ANS: innervated by the sympathetic and parasympathetic nervous system; two peripheral sites of chemical neurotransmission; visceral innervation (heart, smooth muscle glands); involuntary
Skeletal muscle: single peripheral site of neurotransmission; somatic innervation; voluntary
Compare/contrast the sympathetic NS and parasympathetic NS’s spinal roots of origin; ganglia position and ratios, and NT’s
SNS: thoracolumbar CNS outflow; para/prevertebral ganglia; pre-ganglionic NT is ACh, and neuroeffector NT usually NE
PNS: craniosacral CNS outflow; terminal ganglia; pre-ganglionic and neuroeffector transmitters are ACh
Describe the ANS innervation of the heart
innervated by SNS and PNS with opposite effects; activation of M2 receptors (via ACh) has negative chronotropic/dromotropic/inotropic effects; activation of Beta-1 receptors (via NE) has positive chronotropic/dromotropic/inotropic effects
Describe the ANS innervation of the bronchi
innervated by PNS almost exclusively; activation of M3 receptors (via ACh) induces constriction of airway smooth muscle and promotes secretions; activation of Beta-2 (via Epi) induces relaxation.
Describe the ANS innervation of the arterioles
innervated by SNS almost exclusively; activation of M3 receptors (via ACh) promotes EDRF/NO and thus smooth muscle relaxation; Alpha 1 (junctional) and Alpha 2 (extrajunctional) receptor activation (via NE/Epi) promotes vasoconstriction; and activation of Beta-2 receptors (via Epi) promotes smooth muscle relaxation.
Describe the ANS innervation of the pupil
innervated by both PNS/SNS with opposite effects; M3 receptor activation (via ACh) causes sphincter constriction, Alpha-1 receptor activation (via NE/Epi) causes dilator muscle contraction.
Describe the ANS innervation of the bladder
innervated by both PNS/SNS with opposite effects; M3 receptor activation (via ACh) causes smooth muscle wall contraction, and sphincter relaxation; Alpha-1 receptor activation (via NE/Epi) causes sphincter contraction; and Beta 2/3 receptor activation (via NE/Epi) causes smooth muscle wall relaxation.
Describe what types of NT’s are released at ganglionic synapses in the SNS and PNS.
All ganglionic (pre-ganglionic) neurons in the PNS and SNS release ACh which activates nicotinic receptors on post-ganglionic (neuroeffector) neurons.
Describe post-ganglionic (neuroeffector) synapse neurotransmission in the Sympathetic NS.
Post-G SNS neurons that innervate cardiac and smooth muscle, gland cells, and nerve terminals release NE which acts through Alpha/Beta adrenergic receptors.
Post-G SNS neurons that innervate renal vascular smooth muscle release Dopamine.
And post-G SNS neurons in the adrenal medulla release Epi (and some NE) into circulation; generates widespread actions quickly—hormonal component of ANS.
Describe post-ganglionic (neuroeffector) synapse neurotransmission in the Parasympathetic NS.
Post-G PNS neurons innervating cardiac smooth muscle, gland cells, and nerve terminals release ACh, which acts on Muscarinic receptors.
Describe the feedback mechanism affecting NE release from Sympathetic nerves.
NE released from post-ganglionic sympathetic neurons will bind to Alpha-2 autoreceptors on the post-ganglionic neuron which in turn inhibits the relese of NE from that neuron.
Describe the baroreflex
a reflex response to acute changes in blood pressure. Stretch receptors (baroreceptors) located in blood vessels in the carotid sinus and aortic arch respond to changes in blood pressure. They feed this info to the central sympathetic NS (tonically active) which adjusts PNS and SNS impulses accordingly.
HypOtension response—baroreceptor activity decrease, PNS impulses decrease and SNS impulses increase; leads to increased BP (due to increased heart rate and force of contraction) and increased resistance in arterioles.
HypERtension response—baroreceptor activity increases, PNS activity increases, and SNS activity decreases; leads to decreased BP, and possibly pronounced bradycardia.
Drugs like histamine can induce hypertension response and phenylephrine the hypotension response.
Describe junctional vs. extrajunctional receptors.
Junctional (synpatic) receptors are located at ganglia and neuroeffector jxns, on nerve terminals, as well as on innervated organs.
Extrajunctional (noninnervated) adrenergic receptors are accessible to circulating Epi (and other drugs), but are not activated under normal conditions.
Extrajunctional cholinergic receptors are endothelial receptors linked to production of EDRF/Nitric Oxide.
Name the signal transduction processes associated with nicotinic, muscarinic, adrenergic (alpha and beta) receptors.
Nicotinic receptor is an ion channel that mediates opening of its cation channel.
Muscarinic receptors and Adrenergic receptors are GPCR.
Muscarinic receptors contribute to inhibition of adenylate cyclase, increase in cystolic Ca2+, and opening of K+ channels.
Beta-adrenergic receptors stimulate adenylate cyclase.
Alpha-1-adrenergic receptors: increase cytosolic Ca2+.
Alpha-2-adrenergic receptors: inhibited adenylate cyclase.
Discuss termination of NT action.
ACh: action terminated by cholinesterase (enzymatic hydrolysis).
NE and EPI: re-uptake of NT into nerve terminal via norepinephrine transporter (NET) and also by diffusion. Also re-uptake by non-neuronal transporter with a lower affinity by higher capacity.
Metabolic breakdown of NE by MAO (1’ neuronal) and COMT (1’ non-neuronal).
