ocular pharmacology Flashcards
what is the mode of action of most drugs ?
the mode of action of most drugs is to inhibit or facilitate neural processes such as action potential transmission or synaptic transmission
what are agonists ?
drugs that enhance the effectiveness of neuron
what are antagonists ?
suppress specific neuron
where do most ocular drugs work?
most ocular drugs use affect nerve/muscle synapses
what is skeletal muscle innervated by?
- innervated by the somatic nervous system
- ( single motor neuron )
- releases ACH
what is smooth muscle innervated by ?
- innervated by the autonomic nervous system
- ( 2 neuron single chain ) separated by a ganglion
- sympathetic ( close to spinal cord ) and parasympathetic ( close to the effector)
what does sympathetic system release?
- post ganglionic neuron release nor-adrenaline at the effector ( alpha or beta receptors)
what does parasympathetic release?
- post ganglionic fibre releases ACH at the effector ( muscarinic or nicotinic receptors )
explain chemical synapses ?
- depolarisation of synaptic terminal
- influx of calcium
- migration of vesicles containing neurotransmitters to migrate to presynaptic membrane
- fusion of vesicle with presynaptic membrane
- release of transmitter by exocytosis
- diffusion of transmitter across cleft down the concentration gradient
- binding of transmitter to postsynaptic receptors
- change in postsynaptic membrane permeability leading to IPSPs( open Cl or K you get hyper polarisation) or EPSPs( open Na) depending on ion channel opened
- inactivation of transmitter ( enzymatic, reuptake into presynaptic neuron)
what are some types of neurotransmitters ?
- Noradrenaline
- Ach
- Dopamine
- Histamine
- GABA
- they all have their own set of neurotransmitter receptors
what is function of neurotransmitter receptors?
neurotransmitter receptors are important because its the receptors that determine which ions channels are open and shut in the posterior synaptic membrane
what are the 2 basic types of ACH receptors ?2
- Ach can bind to
- nicotinic - occurs at neuromuscular junction - open Na channels - therefore excitatory
- muscarinic - open k and cl channels - therefore inhibitory
- same neurotransmitter but 2 different effects depending on the receptor
what are the methods of transmitter inactivation ?
- diffuse away
- break it down with enzymes
enzyme acts on Ach and splits into its components part which are re absorbed into presynaptic neuron - take it back up into presynaptic neuron
what enzyme destroys Nor-adrenaline?
monoamine oxidase- which is responsible for its reuptake in the presynaptic neuron
where can drug affect a neural and synaptic process?
drugs can affect any stage of the neural and synaptic process
1 - drug can affect synthesis of transmitters by stopping it or enhancing it
2- axonal transport -
3- storage of neurotransmitters in the vesicle
4- binding of neurotransmitter to postsynaptic membrane
5- conduction of action potential
what is the simplest drug to facilitate a synape?
- the simplest drug to facilitate a synape would be to apply the neurotransmitter itself
- this is rarely done as the body has mechanism for neutralising such transmitters
what is the first muscle that may be affected by drugs in the eye?
- iris sphincter muscle
- contraction causes pupil constriction ( miosis )
- parasympathetic innervated -( from ciliary ganglion/ IIIrd nerve)
- Muscarinic Ach receptor
what happens if you put pilocarpine in eye ?
binds to muscarinic receptors, acts as an Ach agonist activating Ach receptors and causing pupil constriction (miosis)
what happens if you put anti muscarinics in the eye ( e.g. atropine, tropicamide, cyclopentolate) ?
will block Ach receptors and result pupil dilation ( mydriasis )
what happens to pupil diameter with age?
- resting pupil diameter decreases with age due to a loss of sympathetic tone ( senile miosis )
- this makes it harder for the old to read in lower light levels
what is deadly nightshade ( atropa belladona ?
deadly night shade contains atropine which is an anti-muscarinic used by some women to dilate pupil, thus making them look younger
what is atropine?
- anti-muscarinic which binds to muscarinic receptors and stops ACH from acting on iris sphincter muscle and the pupils will dilate
what happens when you put anticholinesterases ( eserine , physostigmine ) in the eye?
will enhance Ach levels and results in sphincter activation and pupil constriction by inactivating acetylcholinesterase
what is iris dilator muscle ?
- contraction causes pupil dilation ( mydriasis )
- sympathetically innervated ( from superior cervical ganglion )
- Alpha Nor-adrenalin receptors
