Drugs acting on the parasymapathetic and somatic nervous systems Flashcards
how do stimulations travel from the CNS to the effector in the ANS
travels from the CNS as part of cranial or spinal nerve to the ganglia
Then travels along post ganglionic neurons to C- fibre synapses on the visceral effector
what type of outflow is the para sympathetoc nervous system
Craniosacral
what type of pre and post ganglionic fibres does the parasympathetic nervous system have (long or short)
pre long , post short
what nerve carries many parasympathetic fibres
the vagus nerve
how any post ganglionic neurons do the post ganglionic fibres synapse to
4-5
what is pseudo colouring
adding colour to imaging techniques after the black and white version is obtained
what is dual innervation
when an organ has both parasympathetic and sympathetic innervation - controlled by both
can the 2 divisions of the ANS work together, give an example
- the parasympathetic promotes erection
- the sympathetic produces ejaculation
what is the role of the parasympathetic nervous system
rest & digest / feed & breed
what is the PSNS outflow
cranial and sacral
is the PSNS’s ganglia close or far from the effector
close
what is the neurotransmitter at the ganglia in the PSNS
ACh
what types of receptors are found at the ganglia
nicotinic
what type of receptors are found at the effector in the PSNS
nuscarinic
what is Muscarine
an Alkaloid
isolated from Amanita
muscaria (Fly Agaric)
what is the role of muscarine
to
selectively stimulate the
receptors present at
parasympathetic nerve
terminals
what type of channel links nicotinic receptors
ion linked
what type of channel is muscarinic receptors linked to
G protein
why are there different types of muscarinic receptors
have different couplings
and different tissue distributions – provides range
of pharmacological targets:
where do we find these different types of mAChR? (muscarinic ACh receptors )
M1 (‘neural’) Brain, stomach
* M2 (‘cardiac’) Heart
* M3 (‘smooth muscle’) Eye, GI
tract, bladder, lung
Types and
examples of
muscarinic
agonists
Choline esters
- acetyl choline
- methacholine
Alkaloids
-muscarine
- pilocarpine
Why not use Acetylcholine
itself as a drug?
it gets broken down quickly by
acetylcholinesterase so has Short-lived effects
So it is not used therapeutically
what are choline esters
Range of compounds structurally
similar to acetylcholine
Varying levels of action at
muscarinic receptors, nicotinic
receptors
Different levels of susceptibility to
cholinesterase, so differing
durations of action
Clinical uses of muscarinic agonists?
pilocarpine is used in the treatment of glaucoma
- bethanechol to stimulate the emptying of the bladder
why is pilocarpine used to treat glaucoma
Lipid soluble - penetrates cornea
what is glaucoma
Raised intraocular pressure
* Due to reduced drainage of aqueous humour
* Folding of the iris tissue blocks drainage when the iris is
dilated
* Can result in damage to optic nerve
* Impairment ranges from loss of peripheral vision to
blindness
what are the symptoms of glaucoma
early cupping of the occular disk
- vision shrinks
how does pilocarpine treat glaucoma
it contracts the constrictor pupillae muscle
- this then constricts the pupil and restores drainage
How are muscarinic antagonists used clinically?
treatment of brady chardia (slow heart rate)
- during general anesthesia - to block vagal slowing of the heart and inhibit bronchial secretion
But Muscarinic Antagonists exhibit side-effects because muscarinic receptors mediate other effects such as
- Dry mouth
- Constipation
- Urinary retention
- Sedation
- High doses -> restlessness, agitation,
disorientation - Tachycardia (mild- 80-90 bpm)
what is used instead of Non-selective Muscarinic Antagonists to prevent other areas being effected
Subtype-selective Muscarinic Antagonists
Newer muscarinic antagonists have been
developed that are more selective for one
particular subtype (‘subtype selective’).
However, none are completely free from side
effects due to some action at the other subtypes
whats an example of a subtype selective muscarinic antagonist
pirenzepine which selectively blocks M1 receptors involved in gastric acid secretion
its also used as an anti ulcer agent
what is the role of the somatic nervous system
consciously controlled
what is the function of the SNS
Control of skeletal muscle nerve
stimulation => muscle contraction
what is the structure of the SNS
Structure: Single neurone - no ganglia
what neurotransmitter is used in the SNS
Neurotransmitter: Ach
what type of receptor is present at the effector
Nicotinic (Neuromuscular)
how does a NMJ work
Cholinergic neuron
* AChdepolarises
muscle fibre
(excitation
contraction
coupling)
* AChbroken down
by
acetylcholinesterase
how is ACh produced and broken down
The synthesis of acetylcholine
from choline and acetyl CoA
requires choline acetyltransferase.
Acetyl CoA is derived from
pyruvate generated by glycolysis,
while choline is transported into
the terminals via a Na+-dependent
transporter. After release,
acetylcholine is rapidly
metabolized by
acetylcholinesterase and choline
is transported back into the
terminal
