Drugs of the Peripheral Nervous System. The Nervous System Review.
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Transcript of Drugs of the Peripheral Nervous System. The Nervous System Review.
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Drugs of the Peripheral Nervous System
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The Nervous System Review
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Organization of the Nervous System
• Central nervous system (CNS)– Brain and spinal cord
• Peripheral nervous system (PNS)– Neurons outside the CNS
– Sensory division• Afferent fibers transmit impulses from receptors to CNS
– Motor division• Efferent fibers transmit impulses from CNS to effector organs
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Relationship between motor and sensory fibers of the PNS and the CNS
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Autonomic Nervous System
• Sympathetic– Fight or flight, stress– Excitatory effects elicited by norepinephrine
activating beta receptors– Inhibitory effects elicited by activation of alpha
receptors
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• Parasympathetic– Rest and digest– Digestive system activated, heart rate inhibited,
blood vessels dilated– Vagus nerve primarily responsible for
activating parasympathetic responses
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Fig. 8.39
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Autonomic Neurotransmission
• Two neurons– Presynaptic and postsynaptic
• Presynaptic from the brain to autonomic ganglia– Acetylcholine released from prenaptic neuron across
synapse to activate postsynaptic neuron
• Postsynaptic neurons release norepinephrine (sympathetic) or acetylcholine (parasympathic) at the effector organ
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Fig. 8.13The Synapse
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Neurotransmitters
--packaged in synaptic vesicles.
Nerve endings of the ANS secrete:• Acetylcholine (ACh)--Cholinergic neuron
– Parasympathetic effector
• Norepinephrine (NE)--Adrenergic neuron– Sympathetic effector
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• Neurotransmitters diffuse across the synaptic cleft and bind to receptor on the post-synaptic membrane
• This can cause membrane channels (Na+, K+, or Cl-) to open or close depending on the neurotransmitter
• If stimulatory, Na+ channels will open
• If inhibitory, K+ or Cl- channels will open– Cell becomes more negative, hyperpolarized
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Catecholamines
• Norepinephrine and epinephrine– Norepinephrine primarily neurotransmitter– Epinephrine primarily hormone
• Primarily concerned with sympathetic transmission
• Released at synaptic cleft and bind to alpha or beta receptors
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Acetylcholine
• Responsible for all parasympathetic neurotransmission– Binds to mucarinic receptors at the end organ
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Ganglionic transmission
– Transmits both parasympathetic and sympathetic preganglionic signals to nicotinic receptors (Nn)
– All ganglionic transmission is cholinergic (acetylcholine)
• Drugs that block ganglionic transmission block either parasympathetic or sympathetic depending on which is active
• This is a paradox many have a problem grasping
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Fig. 8.39
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Neuromuscular transmission
• Somatic motor neurons release acetylcholine at neuromuscular junction– Acetycholine diffuses across synapse and binds
to muscular nicotinic receptors (Nm) causing sodium influx
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The Neuromuscular Junction
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Central Neurotransmission
• Acetylcholine the primary neurotransmitter in the brain
• Works by interaction with muscarinic receptors
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Neurotransmitter degradation
• Neurotransmitters which fail to bind to a post-synaptic receptor are – degraded by enzymes (acetylcholinersterase)– Taken up into the presynapse and recycled– Diffuse out of the synapse
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Receptors2 types of cholinergic receptors:• Nicotinic
– Preganglionic sympathetic and parasympathetic (Nn)– Also neuromuscular somatic motor (Nm)
• Muscarinic– parasympathetic
2 types of adrenergic receptors:• Alpha
– Generally inhibitory
• Beta– Generally excitatory
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Neurotransmission Enhancers
• Receptor agonists– Compound which bind to the receptor and activate
• Can be cholinergic or adrenergic
• Agents which induce neurotransmitter release– Stimulate release of neurotransmitter in absence of
signal (or reduced signal)
• Inhibitors of neurotransmitter degradation– Inhibit acetylcholinersterase
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Neurotransmission Inhibitors
• Presynaptic nerve blockerss
• Receptor antagonists– Bind to receptor and prevent activation
• Ganglion blockers
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