PHARMACODYNAMICS
Pharmacology – NUR09100
PHARMACODYNAMICS
Learning outcomes
• Describe: o the structure of neurones, o conduction of the action potential o synaptic transmission o the principal effects of stimulation of the: sympathetic nervous system and parasympathetic nervous system
• Explain and give examples of the following types of drug action: o Receptors (agonists, antagonists and partial agonists) o Enzyme inhibition o Membrane transport systems
• Apply your knowledge to explain action and side effects of β blockers and β2 agonists.
The Action potential
• Transmission is due to movement of ions (Na+ and K+) across nerve cell membrane
• Na+ found mainly outside cells – tends to diffuse inwards
• K+ found mainly inside cells – tends to diffuse outwards
• Stimulation of neurone changes the membrane permeability to ions
• Depolarisation occurs as Na+ floods into cell through sodium channels setting up the nerve impulse (very fast)
• Impulse travel is one way from stimulus
• Then K+ flows out of cell (repolarisation) and the membrane charge returns to normal
• Correct ion balance is restored by the ‘sodium-potassium pump’ (active transport mechanism)
Events at synapse (or neuromuscular junction [NMJ])
• Impulse causes depolarisation at synaptic knobs
• Release of neurotransmitter [NT] from vesicles into synaptic cleft (> 40 known NTs)
• Diffusion of NT across synaptic cleft
• NT acts on postsynaptic receptors (motor end plates [MEPs] at NMJ) – most NTs excitatory, some inhibitory)
• Depolarisation of postsynaptic membrane
• Conduction of impulse along the next neurone or activation of effector organ
Fate of PNS neurotransmitters
• Acetylcholine (ACh): broken down in synaptic cleft by the enzyme acetylcholinesterase (AChE) o anticholinesterase inhibitors act here (see below)
• Adrenaline and noradrenaline: taken back up into axon terminals (recycled) o reuptake inhibited by tricyclic antidepressants and cocaine (CNS actions)
PHARMACODYNAMICS
Learning outcomes
• Describe: o the structure of neurones, o conduction of the action potential o synaptic transmission o the principal effects of stimulation of the: sympathetic nervous system and parasympathetic nervous system
• Explain and give examples of the following types of drug action: o Receptors (agonists, antagonists and partial agonists) o Enzyme inhibition o Membrane transport systems
• Apply your knowledge to explain action and side effects of β blockers and β2 agonists.
The Action potential
• Transmission is due to movement of ions (Na+ and K+) across nerve cell membrane
• Na+ found mainly outside cells – tends to diffuse inwards
• K+ found mainly inside cells – tends to diffuse outwards
• Stimulation of neurone changes the membrane permeability to ions
• Depolarisation occurs as Na+ floods into cell through sodium channels setting up the nerve impulse (very fast)
• Impulse travel is one way from stimulus
• Then K+ flows out of cell (repolarisation) and the membrane charge returns to normal
• Correct ion balance is restored by the ‘sodium-potassium pump’ (active transport mechanism)
Events at synapse (or neuromuscular junction [NMJ])
• Impulse causes depolarisation at synaptic knobs
• Release of neurotransmitter [NT] from vesicles into synaptic cleft (> 40 known NTs)
• Diffusion of NT across synaptic cleft
• NT acts on postsynaptic receptors (motor end plates [MEPs] at NMJ) – most NTs excitatory, some inhibitory)
• Depolarisation of postsynaptic membrane
• Conduction of impulse along the next neurone or activation of effector organ
Fate of PNS neurotransmitters
• Acetylcholine (ACh): broken down in synaptic cleft by the enzyme acetylcholinesterase (AChE) o anticholinesterase inhibitors act here (see below)
• Adrenaline and noradrenaline: taken back up into axon terminals (recycled) o reuptake inhibited by tricyclic antidepressants and cocaine (CNS actions)