ANS Flashcards
What are some of the major functions of the ANS?
- maintain homeostasis
- coordinate response to external stimuli (fight or flight)
- specific regulatory functions
what are some of the specific functions of the ANS?
- contraction and relaxation of the vascular and visceral smooth muscle
- CVS reflexes
- all exocrine and endocrine secretions
- energy metabolism, particularly in liver and skeletal muscle
What are the divisions of the ANS? what do they do?
SNS
- dominates during stress and emergency situations
- expenditure of energy
- increase in BGL, heart activity and BP
PNS
- conserve energy
- reduce HR
- increase GI and secretions
Enteric
- comprises the intrinsic nerve plexuses of GI tract
What are some of the responses of the SNS?
- increased HR
- vasoconstriction and increased BP
- skeletal muscle vasodilation and tremor
- pupil dilation, adjusting for far vision
- bronchodilation
- glycogenolysis, gluconeogenesi, lipolysis, thermogenesis
- sweating
- release of adrenaline
What are some responses of the PNS?
- decrease HR to resting
- digestion and secretion of waste products, increased Gi motility, gastric acid secretion, defecation, urination
- pupil constriction, accommodation for near vision, lacrimation
What are autonomic efferent pathways made of?
- Preganglionic neurons
- autonomic ganglia (contains nerve endings of preganglionioc and cell bodies of postganglionic)
- post ganglionic neurons
What are the main neurotransmitters in the ANS?
Acetylcholine and noradrenaline
How do cholinergic nerves function?
Using Acetycholine on:
ALL preganglioninc nerves
ALL post ganglionic nerves in the PNS
ACTS on nicotininc and muscurain
How do noradrenergic nerves function?
Use noradrenaline on:
most post ganglionic nerves in the SNS
Describe the neurons and their actions in the PNS
Preganglionic neurons release Ach which acts on nicotinic receptors in the cell body of the postganglionic neuron
Postganglionic neurons release AcH which acts on the muscarinic receptors on the effector tissue
What is cholinergic transmission?
Nerve transmission mediated by acetylcholine
What are the functions of acetylcholine in the CNS and PNS?
CNS: arousal, learning, memory and motor control
PNS:
- ANS: involuntary control of many structures
- enteric: involuntary control of the GIS
- somatic: voluntary control of skeletal muscles
Describe the steps in cholinergic transmission
- Uptake of choline
- Synthesis of AcH
- Uptake of transmitter into synaptic vesicles
- degradation of surplus AcH
- depolarisation by propagated action potential
- opening of voltage gated Ca2+ channels
- release of transmitter by exocytosis
- diffusion to postsynaptic membrane
- binding to postsynaptic receptors
- inactivation of ACh by ACHE
- reuptake of transmitter or degradation products by nerve terminal
- uptake of ACh by non-neuronal cells
- Binding with presynaptic receptors
What is the nicotinic receptor?
a cholinergic receptor activated by acetycholine.
Ligand gated ion channel with two Ach binding sites.
What happens when ach binds to a nicotinic receptor?
the channel opens and Na+ enters, causing membrane depolarisation
Where are nicotinic receptors located and what do they do?
Skeletal muscle: cause contraction
Autonomic ganglia: allow transmission between pre and post ganglionic neurons
adrenal medulla: cause release of adrenaline
CNS: excitation
What is the muscarinic receptor?
A GPCR activated by acetylcholine. It passes on a message within the cell that generates a cellular response
What are the types of muscarinic receptors and their general functions?
M1: neural
M2: cardiac
M3: glandular/smooth muscle
M4/M5: mostly CNS
What is the role of M1 receptors and where are they located?
Found mainly on CNS and peripehral neurons and gastric parietal cells, M1 receptor activation has excitatory effects
What is the role of M2 receptors and where are they located?
Found mainly on the heart, M2 receptor activation has inhibitory effects
What is the role of M3 receptors and where are they located?
Located mainly on smooth muscle and glands, receptor activation has excitatory effects
What is the role of M4/M5 receptors and where are they located?
Mainly in the CNS. Function is not well understood
What is the mechanism of the M1 receptor? What is the result?
Gq: activates phospolipase C
= increased IP3 and DAG
= increased Ca2+
RESULT: neuronal excitation
What is the mechanism of the M2 receptor? What is the result?
Gi: inhibitis adenylate cyclase
= decreased cAMP
= decreases PKA
= decreased opening of Ca2+ channels
RESULT: reduce HR and contractility
What is the mechanism of the M3 receptor? What is the result?
Gq: activates phospholipase C
= increased IP3 and DAG
=increased Ca2+
RESULT: contraction of visceral smooth muscle. secretion of exocrine glands.
CAN cause relaxation of some smooth muscles, mainly vascular, via the release of nitric oxide from neighbouring endothelial cells (not innveravted by PNS but respond to circulating muscarinic agonists)
What are the PNS effects of M2 on the heart?
decreased rate and force of contraction
What are the PNS effects of M3 on the blood vessels?
generally none as there is no PNS innervation.
exception: erectile tissue which has mediated vasodilation via nitric oxide. dilated by exogenous muscarinic agonsts
PNS effects of M3 on smooth muscle (incl. bronchi, GI and bladder)?
contraction
PNS effects of M3 on the eye?
Contraction of the pupil = miosis
contraction of the ciliary muscle = near vision
PNS effects of M3 on the exocrine sweat glands
No PNS innervation, but muscarinic receptors respond to sympathetic innervation
PNS effects of M3 on the exocrine lacrimal, salivary and bronchial glands?
secretion
What does the SNS do?
control the fight or flight response
What do preganglionic neurons in the SNS relase?
Ach which acts on nicotinic receptors in cell bodies of the postganglionic neuron
What do most postganglionic neurons release in the SNS?
noradrenaline, which acts on alpha or beta receptors of the effector tissue
How are sweat glands innervated?
By SNS Ach acting on muscarinic receptors
How is the adrenal medulla innervated?
by SNS Ach acting on nicotinic receptors
What is the transmitter used in noradrenergic transmission?
noradrenaline
What are the functions of NA in the CNS and periphery?
CNS: arousal, mood and BP regulation
Peripheral: functions associated with the SNS
What are the receptors that are activated by noradrenaline and adrenaline?
alpha and beta
What are the steps in noradrenergic transmission?
- uptake of precursor (tyrosine)
- synthesis of NA
- uptake of NA into synaptic vesicles via vesicular monoamine transporter (VMAT)
- degradation of surplus NA via monoamine oxidase (MAO)
- depolarisation by propagated action potential
- opening of voltage gated ca2+ channels
- release of transmitter by exocytosis
- diffusion to postsynaptic membrane
- binding to postsynaptic receptors
- inactivation of transmitter (most is recycled)
- reuptake of transmitter by nerve terminal via norepinephrine transporter (NET)
- uptake of transmitter by non-neuronal cells via extra neuronal transporter (ENT)
- binding with presynaptic receptors (alpha 2 autoinhibitory receptors)
What are the 3 actions of noradrenaline?
- stimulate post synaptic noradrenergic receptors on effector organs
- stimulate pre synaptic auto-inhibitory receptors
- undergo re-uptake back into the nerve for re-storage in vesicles or metabolism to inactive metabolites by monoamine oxidase
Describe a noradrenergic receptor
GPCR that is activated by adrenaline and noradrenaline. Passes on a message within the cell, generating a cellular response
What are the four types of noradrenergic receptors? What are their functions?
Alpha-1
- smooth muscle
- excitation
Alpha-2
- presynaptic autonomic nerves
- inhibition
Beta-1
- cardiac muscle
- excitation
Beta-2
- smooth muscle
- inhibition
Describe the receptor mechanism of alpha-1
Gq: activates phospholpiase C
- increased IP3 and DAG
- increased intracellular calcium
- causes contraction of smooth muscle
describe the receptor mechanism of alpha-2
Gi: inhibits adenylate cyclase
- decreased cAMP
- decreased PKA
- decreased opening of ca2+channels
- acts on autonomic nerves to inhibit and cause a decrease in NA release
Describe the mechanism of beta-1 receptors
Gs: activates adenylate cyclase
- increased cAMP
- increased PKA
- opening of ca2+ channels
- increases HR and contractility of cardiac muscle
Describe the mechanism of beta 2 receptors
Gs: activates adenylate cyclase
- increased cAMP
- increased PKA
- inhibition of contractile enzymes leading to contraction
What is the effect of B1 on the heart
increased rate, increased force of contraction
What is the effect of A1 on the blood vessels of the viscera, skin, brain and large coronary
constriction
What is the effect of B2 on the blood vessels of the skeletal muscle and small coronary
dilation
What is the effect of B2 on the bronchial smooth muscle
relaxation
What is the effect of B2 on the GI muscle
relaxation
What is the effect of B2 on the smooth muscle of the bladder
relaxation
What is the effect of A1 on the pupil
dilation (control of radial muscles)
What is the effect of B2 on the ciliary muscle of the eye
relaxation (far vision)
What is the effect of A1 and B2 on the liver
Increased glycogenolysis
increased gluconeogenesis
What is the effect of A2 on the pancreas
decreased insulin secretion via adrenaline
What is the effect of B2 on the skeletal muscle
tremor
Summarise the drug targets in the ANS
Receptors
- Muscarinic
- nicotinic
- alpha
- beta
Enzymes
- ACHE
- MAO
Transporters
- NET
- VMAT
