*Pharmacology 4 (6 and 7) Flashcards
Afferent?
Towards the CNS
Efferent?
Away from the CNS
4 branches of the PNS?
Somatic effent
Autonomic (ANS)
Enteric
Somatic and visceral afferent
What are the 2 division of the ANS?
Sympathetic
Parasympathetic
What is the purpose of the ANS?
To carry output from the CNS to the whole body with the exception of skeletal muscle
What allows a degree of copious control of some ANS functions?
Training e.g. urination, defecation
What does the parasympathetic ANS coordinate?
the bodies basic homeostatic functions
What does the sympathetic ANS coordinate?
The body’s response to stress, associated with fight, flight and fright reactions
What 2 neurones is a sympathetic/ parasympathetic branch made up of?
Preganglionic neurone
Postganglionic neurone
What is the transmitter in the preganglionc neurone of the sympathetic ANS?
Acetylcholine (ACh)
What is the transmitter in the preganglionic neurone in the parasympathetic ANS?
Acetylcholine (ACh)
What is the transmitter in the post-ganglionic neurone in the parasympathetic division?
Acetylcholine (ACh)
What is the transmitter in the postganglionic neurone in the sympathetic division?
Usually Noradrenaline (NA)
What is the word used to describe neurones that use ACh?
Cholinergic
What is the word used to describe neurones that use NA?
Adrenergic
Where can sympathetic signals synapse?
In the sympathetic chain
In the prevertebral ganglia
What organs sympathetic supply tends to synapse in the sympathetic chain?
signals going to the eye, heart and lungs (above diaphragm)
What organs sympathetic supply tends to synapse in pre-vertebral ganglia?
Signals going to the liver, gallbladder, stomach, pancreas, spleen, kidney, intestines and genitourinary tract (below diaphragm)
What tissues sympathetic supply doesn’t synapse?
Adrenal gland (nerve supply only consists of a preganglionic neurone - transmitter released is ACh)
What branch of the ANS has thoracolumbar outflow?
Sympathetic
What branch of the ANS has craniosacral outflow?
Parasympathetic
Where does the parasympathetic axons leave the CNS?
Via cranial nerves III, VII, IX, and X
Via sacral spinal nerves
What organs does the parasympathetic outflow supply?
Parasympathetic ganglia in head = Lacrimal gland and salivary glands
Vagus nerve = organs of the neck, chest and abdomen as far as the midgut
Sacral spinal nerves “carry” parasympathetic axons to the hind-gut, pelvis and perineum
Where are parasympathetic ganglia?
Usually in the target organs (discrete ganglia exist in the head and beck)
What does sympathetic stimulation at heart cause? (2)
Increases heart rate
Increases force of contraction
What does parasympathetic stimulation of the heart cause?(1)
Decreases heart rate
What does sympathetic stimulation of the lungs cause? (2)
Relaxes bronchi
Decreases mucus production (decreasing airway resistance)
What does parasympathetic stimulation of the lungs cause? (2)
Constricts bronchi
Stimulates mucus production
How does sympathetic nervous system cause the relaxation of bronchi?
Via release of adrenaline
Effect of sympathetic stimulation on the GI tract? (2)
Reduces motility
Constricts sphincters
Effect of parasympathetic stimulation on the GI tract? (2)
Increases motility
Relaxes sphoncters
Effect of sympathetic stimulation on the arterioles?
Constricts in most locations although relaxes at muscles
Effect of parasympathetic stimulation on arterioles?
Largely no effect
Effect of sympathetic stimulation on adrenal gland?
Release of adrenaline
Effect of parasympathetic stimulation on adrenal gland?
No effect
Effect of sympathetic stimulation on penis?
Ejaculation
Effect of parasympathetic stimulation on penis?
Erection
What are the steps of neurochemical transmission?
1) Uptake of precursor
2) Synthesis of transmitter
3) storage of transmitter
4) depolarisation by action potential
5) Ca2+ influx through voltage-activated Ca2+ channels
6) Ca2+ induced release of transmitter (exocytosis)
7) receptor activation
8) enzyme mediated inactivation of transmitter
OR
9) reuptake of transmitter
What are ligand-gated ion channels?
Ion channels that are gated by chemicals
What is the name of the ligand-gated ion channel on the post-ganglionic neurone opened by ACh?
Nicotinic ACh receptors
What happens when an action potential arising from the CNS arrives at the presynaptic terminal of the preganglionic neurone? (either sympathetic or parasympathetic)
Ca2+ entry is triggered causing the release of ACh
ACh opens nicotonic ACh receptors (a ligand gated ion channel) in the postganglionic neurone causing depolarisation and the generation of action potentials
What happens when an action potential arrives at the pre-synaptic terminal of the post-ganglionic neurone in the sympathetic division?
Ca2+ entry is triggered causing the release of noradrenaline
Noradrenaline activated G-protein-coupled adrenoceptors in the target cell membrane causing a cellular response
What type of receptor in the target cell is activated by noradrenaline?
G-protein-coupled adrenoceptors
What type of receptor on the target cell is activated by ACh?
G-protein-coupled muscarinic acetylcholine receptors
What happens when an action potential arises at the pre-synaptic terminal of the post-synaptic neurone (parasympathetic)?
ACh is always the transmitter used
Ca2+ entry is triggered causing the release of ACh
At activated G-protein-coupled muscarinic acetylcholine receptors in the target cell membrane to cause a cellular response
What are other names for ligand-gated ion channels? (2)
Transmitter-gated ion channels
Ionotropic receptors
What are ligand-gated ion channels made up from?
Separate glycoprotein subunits that form a central, ion conducting, channel
What does ligand-gated ion channels allow? (2)
Allow rapid changes in the permeability of the membrane to certain ions
Rapidly alter membrane potential
What does the binding of a transmitter to a ligand-gated ion channel cause?
The gate to be opened (stays closed for a small period of time before opening)
Increases the membrane permeability to the selected ion
What are 2 types of receptors on neurones?
Ligand-gated ion channels (on post-ganglionic neurones)
G-protein-coupled receptors (on target cell membrane)
What does the G-protein couple in G-protein-coupled receptors?
Receptor activation to effector modulation
What is the speed of signalling via G-proteins like in comparison to transmitter-gated ion channels
Relatively slow
What are the 3 separate parts of a G-protein-coupled receptor?
Receptor
G-protein
Effector (enzyme or ion channel)
What is the basic structure of the receptor in in G-protein coupled receptors? (3)
Integral membrane protein formed from a single polypeptide with extracellular NH2 and intracellular COOH termini
Contains seven transmembrane spans joined by 3 extracellular and 3 intracellular connecting loops
What is the full title for a G-protein?
Guanine nucleotide binding portein
What are the 3 polypeptide subunits of a g-protein?
Alpha
Beta
Gamma
What is the structure of a g-protein?
3 polypeptide chains (alpha, beta and gamma) with a guanine nucleotide binding site in the alpha subunit that can hold guanosine triphosphte (GTP) or guanosine diphosphate (GDP)
What can the effector in G-protein-coupled receptors be?
Enzyme or ion channel
What is the appearance of a G-protein coupled receptor that has no signalling?
The receptor is unoccupied
The G protein alpha subunit binds GDP
The effector is not modulated
What happens to a G-protein coupled receptor when signalling is turned on?
Agonist activates receptor
G-protein couples with receptor
GDP dissociated from, and GTP binds to, the alpha subunit
The G-protein dissociated into separate alpha and beta-gamma subunits
The G-protein alpha subunit combines with and modifies activity of effector
The agonist may dissociate from the receptor but the signalling can persist
How is the G-protein-coupled receptor signal turned off?
The alpha subunit acts as an enzyme (a GTPase) to hydrolyse GTP to GDP and Pi
The signal is turned off
The Gprotein alpha subunit recombined with the Geta-gamma subunit completing the G-protein cycle
Structure of Nicotinic Acetylcholine receptors?
Consist of 5 glycoprotein subunits that form a central, cation conducting, channel (Na+, K+ and Ca2+)
What are the possible subunits that nicotinic Ach receptors can be formed from?
Alpha 1-10 Beta 1-4 Gamma Delta Epsilon
What are the parts skeletal muscle (alpha 1)2 beta gamma epsilon is made up of?
2 X alpha 1
1 X gamma
1 X beta 1
1 X delta/ epsilon
What are the parts that “ganglionic” alpha3 beta4 is made up from?
2 X alpha 3
3 X beta 4
What are the parts that alpha 4 beta 2 is made up from?
2 X alpha 4
3 X beta 2
What are the parts that Alpha7 is made up from?
5 X alpha 7
What are the 2 reactant in the formation of acetylcholine?
What is the enzyme in the formation of acetylcholine?
Choline (uptake via transporter)
Acetyl CoA
Choline acetyltransferase
What type of receptors can AcH activate?
Nicotinic
Muscarinic (G-protein coupled)
What happens after AcH activates a receptor?
It is degraded to choline and acetate by acetylcholinesterasen
Reuptake and reuse of choline
What does an activated nicotinic ACh receptor (alpha3 beta4) transport into the cell?
What does this create?
Na+
A graded depolarisation (excitatory post-synaptic potential) - more likely to reach action potential
What is a clinically significant drug that affects cholinergic transmission at ganglia?
Nicotine - most drugs that affect cholinergic transmission at ganglia have little clinical significance (often used experimentally)
What is an agent that selectively blocked ganglionic transmission at cholinergic receptors?
What was this previously used for?
How does this work?
Hexamethonium
First effective antihypertensive agent (no longer used)
Open channel blocker (a form of non-competitive antagonism)
How many muscarinic ACh receptor subtypes are there?
M1-3
What is the name of the junction between a neurone and effector cell?
Neuroeffector junction
What alpha subunit of G protein is associated with M1?
what does activation of this G-protein-coupled muscarinic ACh receptor cause?
What effect does this have?
Gq
Simulation of phospholipase C
Increased acid secretion
What alpha subunit of G protein is associated with M2?
what does activation of this G-protein-coupled muscarinic ACh receptor cause?
What effect does this have?
Gi
Inhibition of adenyly cyclase; opening of K+ channels
Decreased heart rate
What alpha subunit of G protein is associated with M3?
what does activation of this G-protein-coupled muscarinic ACh receptor cause?
What effect does this have?
Gq
Stimulation of phospholipase C
Contraction of airway smooth muscle (vascular smooth muscle indirectly replaces by M3 receptor activation
What are the 2 broad categories of adernoceptors?
alpha
Beta
What is noradrenaline synthesised from?
L-Tyrosine
How is NA removed from the synapse?
Repute by transporters uptake 1 (U1 - neurone) and uptake 2 (U2 - effector/ surrounding cell) and reutilised or metabolised by monoamine oxidase (MAO - neurone) and catechol-O-methyltransferase (COMT - effector/ surrounding cell)
What alpha subunit of G protein is associated with B1?
what does activation of this G-protein-coupled adrenoceptor receptor cause?
What effect does this have?
Gs
stimulation of adenylyl cyclase
Increased rate and force of heart contraction
What alpha subunit of G protein is associated with B2?
what does activation of this G-protein-coupled adrenoceptor receptor cause?
What effect does this have?
Gs
Stimulation of adenylyl cyclase
Relaxation of bronchial and vascular smooth muscle
What alpha subunit of G protein is associated with a1?
what does activation of this G-protein-coupled adrenoceptor receptor cause?
What effect does this have?
Gq
Stimulation of phospholipase C
Contraction of vascular smooth muscle
What alpha subunit of G protein is associated with a2?
what does activation of this G-protein-coupled adrenoceptor receptor cause?
What effect does this have?
Gi
Inhibition of adenylyl cyclase
Inhibition of NA release
What is an autoreceptor?
An autoreceptor is a type of receptor located in the membranes of presynaptic nerve cells. It serves as part of a negative feedback loop in signal transduction. It is only sensitive to the neurotransmitters or hormones released by the neuron on which the autoreceptor sits.
Example of auto receptor on post-ganglionic parasympathetic neurone?
M2
Example of auto receptor on post-ganglionic sympathetic neurone?
a2
What is the purpose of auto receptors?
To mediate negative feedback inhibition of transmitter release (neurotransmitter released by the neurone binds to auto receptor which inhibits the calcium channel preventing more neurotransmitter being released)
What effect does cocaine have on the autonomic nervous system?
What symptoms does this cause?
It blocks U1 increasing the concentration of NA in the synaptic cleft resulting in increased adrenoceptor stimulation (3, 4)
Peripheral actions cause vasocontriction (alpha1 stimulation) and cardiac arrhythmias (B1 stimulation)
What effect does amphetamine have on the autonomic nervous system?
What symptoms does this called?
It is a substrate for U1 and enters the noradrenergic terminal where it inhibits MAO, enters the synaptic vehicle (where NA is stored) and displaces NA into the cytoplasm
NA exits the terminal on U1 running backwards and accumulates in the synaptic cleft causing increased adrenoceptor stimulation
Peripheral actions cause vasocontriction (alpha1 stimulation) and cardiac arrhythmias (B1 stimulation)
Do agonists of presynaptic auto receptors increase or decrease release of transmitter?
Decrease release
Do antagonists of presynaptic auto receptors increase or decrease release of transmitter?
Increase release
What does Prazosin do in the ANS?
Use?
Selective, competitive, antagonist of alpha 1
Vasodilator used an anti-hypertensive agent
What does Atenolol do in the ANS?
Use?
Selective, competitive, antagonist of B1 (beta blocker)
Does not block B2, alpha 1 or alpha 2
Used as an anti-anginas and anti-hypertensive agent
What does salbutamol do in the ANS?
Use?
Selective agonist at B2
Does not activate B1, alpha 1 or alpha 2
Used as a bronchodilator in asthma
What does atropine do in the ANS?
Use?
Competitive antagonist of muscarinic ACh receptors, does not block nicotinic ACh receptors
Blocks all muscarinic ACh receptors with equal affinity (1, 2, 3)
Exerts widespread effects by blockade of the parasympathetic division of the ANS
Used to reverse bradycardia following MI and in anti cholinesterase poisoning
