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2 primary cell types in nervous system
neurons – 10 to 100 billion neurons Role: 2. glial cells – provide support, nutrients, myelin, cleanup, etc. for neurons
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2 primary cell types in nervous system
neurons – 10 to 100 billion neurons can vary tremendously in size and shape but all have 3 components cell body or soma contains genetic material, provides nutrients,
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2 primary cell types in nervous system
1. neurons – 10 to 100 billion neurons Role: can vary tremendously in size and shape but all have 3 components cell body or soma contains genetic material, provides nutrients, dendrites axon
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How do neurons communicate?
within neurons – electrically between neurons - chemically
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Neuron receiving info Information traveling down neuron
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Ramon Y Cajal developed Golgi Stain
first determined space between neurons “synapse”
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A brief discussion about communication within a neuron
changes in electrical potential
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Neurons can exist in one of 3 states
the “resting” state the “active” state or action potential neuron is firing conveying info to other neurons or organs the recovery or “refractory” state
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How do we know about what is happening in the neuron?
giant squid axon why was work done with the giant squid axon?
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At rest: inside of the axon has a slightly negative charge relative to outside the axon called the membrane or resting potential (~ -60 mV) why?
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Neuron stimulated see depolarization (change from negative inside neuron to more positive) “threshold” – if a great enough depolarization occurs, an action potential will occur action potential – very quick - milliseconds
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When the action potential occurs…..
see depolarization (change from negative (~ -60mV) inside neuron to more positive (~ +30 mV))
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threshold resting potential
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hyperpolarization after action potential – return to negative (actually a more negative state than to begin with)
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What causes these changes in electrical potential?
All axons and cells have a membrane thin bilayer that surrounds cell allowing some chemicals and ions in but keeping others out axons also have a large number of protein channels that when open allow ions (charged molecules) to flow in or out
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What causes these changes in electrical potential?
Ions flowing across the membrane causes the changes in the potential Ions are molecules that contain a positive or negative charge anion – negative charge cation – positive charge
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Some important ions for neuronal communication
Na+ sodium HIGHER CONCENTRATION OUTSIDE THE AXON Cl- chloride HIGHER CONCENTRATION OUTSIDE AXON K+ potassium higher concentration inside the axon A- anions -large (-) molecules with a negative charge (stuck inside the axon)
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Neuron at Rest Na+ and Cl- are in higher concentration
OUTSIDE AXON (EXTRACELLULAR FLUID) INSIDE AXON (intracellular) Na+ Cl- Na+ A- Cl- Cl- A- Cl- Cl- Na+ Na+ Cl- Cl- A- Na+ Na+ A- Na+ Na+ Cl- A- Na+ Na+ Cl- Na+ Cl- Cl- Na+ A- Na+ Cl- Cl- Cl- Cl- Na+ and Cl- are in higher concentration in the extracellular fluid Neuron at Rest
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Neuron at Rest K+ and negative anions are in higher concentration
INSIDE AXON OUTSIDE AXON (EXTRACELLULAR FLUID) Cl- K+ K+ K+ Cl- A- Na+ Cl- A- Na+ K+ Na+ A- Cl- Na+ K+ A- Na+ Cl- Na+ K+ K+ K+ and negative anions are in higher concentration in the intracellular or inside the axon Neuron at Rest
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Some forces that play a role in maintaining membrane potential
concentration gradient – ions diffuse from higher concentration to lower concentration
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What would each ion do if the ion channel opened based on the concentration gradient?
Na+ K+ Cl-
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Some forces that play a role in maintaining membrane potential
concentration gradient – ions diffuse from higher concentration to lower concentration electrical gradient - opposite charges attract so ions are attracted to an environment that has a charge that is opposite of the charge they carry!
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example of electrostatic forces
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What would each ion do if the ion channel opened based on electrostatic forces ?
Na+ K+ Cl-
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What drives the action potential?
opening of Na+ channels and influx of Na+ ions
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What happens if sodium channels are blocked?
lidocaine, novocaine, cocaine TTX – tetrototoxin Sagitoxin- red tides
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What about communication between neurons?
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Communication between neurons
most psychoactive drugs work via this mechanism chemical transmission via the synapse neurotransmitters
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label some things presynaptic ending – axon – releases chemical if the neuron generated an action potential
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presynaptic ending (axon)
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label some things presynaptic ending – axon – releases chemical if the neuron generated an acton potential postsynaptic ending – can be dendrite, cell body, or axon receives chemical signal from neuron – synapse – tiny gap between neurons
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Other things to notice in presynaptic ending
Ca+ channels - synaptic vesicles contain neurotransmitter
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What happens at level of synapse when an action potential occurs?
Ca+2 enters presynaptic ending via Ca+ channels synaptic vesicles bind to presynaptic ending and release their neurotransmitter Neurotransmitter crosses synapse and binds to receptor on postsynaptic side
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postsynaptic receptors
protein embedded in membrane mechanism for neurotransmitter to influence postsynaptic activity by binding to receptor
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What happens when neurotransmitter binds to the postsynaptic receptor?
can cause the opening of localized ion channels in the postsynaptic ending Na+ or K+ or Cl-
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What happens when neurotransmitter binds to the postsynaptic receptor?
can cause the opening of localized ion channels in the postsynaptic ending IF: Na+ channels open - Na+ enters local excitation (or depolarization) K+ or Cl-
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What happens when neurotransmitter binds to the postsynaptic receptor?
can cause the opening of localized ion channels in the postsynaptic ending IF: Na+ K+ channels open – K+ leaves the cell causes local inhibition or hyperpolarization Cl-
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What happens when neurotransmitter binds to the postsynaptic receptor?
can cause the opening of localized ion channels in the postsynaptic ending IF: Na+ K+ or Cl- channels open – influx of Cl- causes local inhibition or hyperpolarization
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Graded Potentials- these local changes in ion flow are called graded potentials has impact in limited region increases or decreases the likelihood of the neuron receiving info to generate an action potential.
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How do graded potentials contribute to the likelihood of an action potential?
graded potentials are summed at axon hillock – if great enough depolarization to reach “threshold” – axon generates an action potential
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What happens when neurotransmitter binds to the postsynaptic receptor?
if Na+ channels open - increases likelihood of generating an action potential if K+ channels open - - decreases the likelihood of an action potential if Cl- channels open - decreases the likelihood of an action potential
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Ways that graded potentials differ from action potentials
action potentials are “all or none” while graded potentials decrease over space and time localized – has impact in limited region action potentials always excitatory while graded potentials can be excitatory or inhibitory
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Two types of graded potentials
excitatory - EPSPs – excitatory postsynaptic potentials Na+ ion channels IPSPs inhibitory postsynaptic potentials K+ or Cl- ion channels
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2 ways that neurotransmitter exert these effects
ionotrophic - directly opening the ion channel occurs and terminates very quickly
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2 ways that neurotransmitter exert these effects
ionotrophic - directly opening the ion channel occurs and terminates very quickly metabotropic - more indirect ultimately opens ion channel via stimulating a chemical reaction through a "second messenger system" takes longer but lasts longer
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How do we get rid of the transmitter from the synapse?
2 main ways 1. reuptake - most common transporter on presynaptic ending a means of recycling a common way for drugs to alter normal communication
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transporter
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enzyme degradation enzyme - speeds up a reaction
ex. acetylcholine (ACh) is broken down by acetylcholinesterase (AChE)
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NT binding to postsynaptic receptor
“lock and key analogy”
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Neurotransmitter represents a key
Receptor represents the lock Other keys can represent drugs
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What are possibilities?
agonist – mimics the neurotransmitter antagonist – blocks the neurotransmitter partial agonists/ partial antagonists –
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