Pharmacology 2060A/B Lecture Notes - Lecture 14: Resting Potential, Sodium Channel, Substantia Nigra
15 May 2018
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Module 14 – CNS Drugs Part I
14.1 – Introduction to Neuropharmacology
- Neuropharmacology is the study of how drugs affect the function of the central nervous system
(brain)
- There are many disorders of the central nervous system and most of them have a component
that is mediated by a biochemical imbalance of the brain (mediated by imbalance of
neurotransmitters)
- In neuropharmacology we attempt to treat this biochemical imbalance with drugs
- Unfortunately the drugs treat the symptoms of disease but not the cause
Brain
- The brain is composed of literally millions of neurons
- Neurons have a cell body, multiple dendrites and axons surrounded by myelin sheath
- Neurons are cells in the brain that act to process and transmit signals and information
- Neurons are excitable cells that transmit information by electrical and chemical signaling
- The start of information transfer begins at the dendrite, which receives a signal from another
neuron
- This causes action potentials (electrical signaling) to propagate along the axon of the neuron
- When the action potential reaches the pre-synaptic nerve terminal, it causes release of
neurotransmitters (chemical signaling) which pass the signal along to the next neuron, via a
synapse
- Neurons are electrically active – pulse travels down one axon and cross a synapse to the next
neuron
Action potentials
- Action potentials play a key role in cell-to-cell communication in neurons
- The resting membrane potential of cells is approximately -70 mV
o = This means that the inside of the cell is negative with respect to the outside
- To initiate an AP, we start with a depolarization
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- During depolarization, positively charged Na+ ions enter the cell through voltage gated Na+
channels
- The Na+ channels then close and potassium channels open allowing potassium to leave the cell
during repolarization
- The current overshoots resting membrane potential and then returns to baseline (-70 mV)
- Resting potential:
o Only a few potassium channels are open
o Potassium can move in and out of cells
o For every potassium molecule that moves into the cell, another one moves out
o Meae potetial does’t hage
- Threshold:
o If a depolarizing stimulus is received it opens a few sodium channels
o This allows sodium to enter the cell
o Sodium is positively charged so when more enters the cell, it begins to repolarize
o Membrane potential comes closer to the threshold
- Rising phase:
o If threshold is achieved, other sodium channels rushes in
o Membrane potential increases further
- Falling phase:
o Sodium channels close and potassium channels open
o Potassium rushes out of the cell and the membrane potential decreases
o As the membrane potential approaches resting potential even more potassium channels
open
- Hyperpolarization:
o Membrane potential undershoots the resting membrane potential due to excess leaving
the cell
- Steady state:
o As the cell returns to steady state, the potassium channels that were opened during the
action potential are now closed
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Synapse
- Once an action potential reaches the pre-synaptic nerve terminal, it causes influx of calcium into
the presynaptic nerve terminal
- Calcium influx causes vesicles containing neurotransmitters to fuse with the pre-synaptic
membrane and release neurotransmitter
- The vesicles release neurotransmitters into the synaptic cleft (the space between the neurons)
- The neurotransmitters bind to receptors on the post-synaptic nerve membrane and the signal
continues in the post synaptic nerve
- Neurotransmission:
o Action potential propagates down the nerve causing calcium channel to open and
calcium rushes into the cell
o Vesicle fuses with the presynaptic nerve membrane
o Neurotransmitter is released and binds to receptors on the postsynaptic neuron
o Neurotransmitter come off of the receptor on postsynaptic neuron and are taken back
into presynaptic terminal and repackaged into vesicles to be used again
Neurotransmitters in the CNS
- Neurotransmitters are chemicals that transmit a signal across a synapse
- Neurotransmitters are associated with specific CNS diseases
- Neurotransmitters can be broken down into classes as summarized below:
Monoamines
- Norepinephrine – Depression and Anxiety
- Epinephrine – Anxiety
- Dopamine – Pakiso’s ad Shizopheia
- Serotonin – Depression and Anxiety
Amino acids
- Excitatory – glutaate Alzheie’s ad aspatate Alzheie’s
- Inhibitory – GABA (Anxiety) and glycine (Anxiety)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Neuropharmacology is the study of how drugs affect the function of the central nervous system (brain) There are many disorders of the central nervous system and most of them have a component that is mediated by a biochemical imbalance of the brain (mediated by imbalance of neurotransmitters) In neuropharmacology we attempt to treat this biochemical imbalance with drugs. Unfortunately the drugs treat the symptoms of disease but not the cause. The brain is composed of literally millions of neurons. Neurons have a cell body, multiple dendrites and axons surrounded by myelin sheath. Neurons are cells in the brain that act to process and transmit signals and information. Neurons are excitable cells that transmit information by electrical and chemical signaling. The start of information transfer begins at the dendrite, which receives a signal from another neuron. This causes action potentials (electrical signaling) to propagate along the axon of the neuron.
