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How do neurons communicate?. a. b. c. How do neurons communicate?. Need to think about this question 2 ways. How do neurons communicate?. 1. within neurons – 2. between neurons-. Neuron receiving info. Information traveling down neuron. How do neurons communicate .
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a b c
How do neurons communicate? Need to think about this question 2 ways
How do neurons communicate? 1. within neurons – 2. between neurons-
Neuron receiving info Information traveling down neuron
How do neurons communicate • within neurons – electrically • between neurons – chemically • Synapse – space between neurons
Ramon Y Cajal • developed Golgi Stain • first determined space between neurons • “synapse”
Neurons can exist in one of 3 states • the “resting” state • the “active” state • neuron is firing • action potential • the “refractory” state
How do we know about what is happening in the neuron? • giant squid axon
At rest: • inside of the axon has a slightly negative charge relative to outside the axon • called the membrane potential • usually around -70mV
At rest: • inside of the axon has a slightly negative charge relative to outside the axon • called the membrane potential • why?
action potential or spike
Neuron stimulated (either electrically or by receiving a “message” • see depolarization (change from negative inside neuron to more positive)
action potential or spike
Neuron stimulated (either electrically or by receiving a “message” • 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 • Other terms – spike, firing, generating an AP
action potential or spike
Hyperpolarization • return to negative • this is the refractory or recovery period
action potential or spike
What causes these changes in electrical potential and the action potential? • All axons and cells have a membrane • thin lipid (fat) bilayer • The membranes have channels (to allow ions in or out) • Ions – molecules with a charge • These channels can be open or shut
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
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)
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
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
Some forces that play a role in maintaining membrane potential • concentration gradient – • ions diffuse from higher concentration to lower concentration
What would each ion do if the ion channel opened based on the concentration gradient?
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!
What would each ion do if the ion channel opened based on electrostatic forces ?
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 Axon depolarizing
What drives the action potential? • opening of Na+ channels and influx of Na+ ions
What happens if sodium channels are blocked? • lidocaine, novocaine, cocaine • TTX – tetrototoxin • Sagitoxin- • red tides
Concentration Gradient Electrical Gradient after the AP (+ intracellular)
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
Sodium-potassium pump – active force that exchanges 3 Na+ inside for 2 K+ outside
INSIDE AXON OUTSIDE AXON (EXTRACELLULAR FLUID) Cl- Na+ K+ K+ Cl- A- Na+ Cl- Na+ A- Na+ K+ Na+ A- Na+ Cl- Na+ K+ A- K+ Na+ Na+ Cl- Na+ K+ K+ Na+ K+ and negative anions are in higher concentration in the intracellular or inside the axon After the action potential
conduction or propogation of the action potential • myelin sheath (80% fat and 20% protein) • produced by glia
conduction or propogation of the action potential • myelin sheath (80% fat and 20% protein) • produced by glia • nodes of ranvier
conduction or propogation of the action potential • myelin sheath (80% fat and 20% protein) • produced by glia • nodes of ranvier • saltatory conduction (200 ft/sec)