psychological psychology
NA19811981
5.BBBactionrestingpotential.pptDiscussion Question
- What is the best way to keep terrorists out of the U.S., while allowing others (such as tourists, athletes, and business travelers) to enter and leave the U.S. as they need?
Blood-Brain Barrier—
- Protection from germs and harmful chemicals
- Not a membrane
- A tight arrangement of cells in the brain’s blood vessels
Blood-Brain Barrier—
What can cross the BBB?
- Small molecules (not charged ions): O2, CO2
- Molecules that can dissolve in the fatty capillary walls
Blood-Brain Barrier—
What cannot cross the BBB?
- Viruses, bacteria, toxins
- Glucose—brain food
- Amino acids—building blocks of proteins
- Takes energy to transport these across BBB.
Neuron Communication
Neurons communicate via sudden electrical and chemical events
- Within Neuron = Action Potential (electrical current)
- Between Neurons = Neurotransmitters (chemicals, gases)
Within the Neuron…
Resting Potential
Action Potential
How are these three things similar?
- A runner at the starting block
- A pot just on the verge of boiling
- A snake which is coiled to strike
Resting Potential
- Prepared state
- Neuron is not in use but ready for use
- Potential = “electrical difference”
Resting Potential
- More negative voltage inside the neuron (membrane is polarized)
- Na+ and K+ ions inside & outside of neuron
- Na+ channels in membrane are shut
- K+ channels in membrane are “leaky”
- Sodium-Potassium pump in membrane:
- 2 K+ in
- 3 Na+ out
Resting Potential
- More negative voltage inside the neuron (membrane is polarized)
- Na+ and K+ ions inside & outside of neuron
- Na+ channels in membrane are shut
- K+ channels in membrane are “leaky”
- Sodium-Potassium pump in membrane:
- 2 K+ into neuron
- 3 Na+ out of neuron
- Electrical gradient & concentration gradient
Action Potential
- Polarized neuron membrane can be depolarized
- Threshold of excitation-- rapid switch from negative to positive inside the neuron.
- http://www.sagepub.com/garrettbb2study/animations/2.8.htm
Action Potential—
- Na+ channels open (axon hillock)
- Na+ rushes into the axon and it becomes positive inside
- The positive charge flows down the axon
- Causes neurotransmitter release
Myelin Sheath
- Nodes of Ranvier: small interruptions in the myelin sheath.
- Depolarization occurs at these nodes
Myelin Sheath
- Electrical flow jumps from node to node in saltatory conduction.
- Increased speed of AP by 10 – 100 times
And after the A.P.?
- Neuron “resets” to resting potential
- Na+ channels close
- K+ channels open, close
- Refractory period—difficult or impossible to have another A.P.
- Up to 1,000 AP’s per second!
- 100 billion neurons!
- Each neuron may connect with up to 10,000 other neurons!
- At 10% capacity, that’s one quadrillion AP’s per second!
Local Neurons—
- No action potentials
- Short dendrites/axons
- Exchange info only with closest neighbors
- Graded potentials -- depolarize or hyperpolarize their neighbors somewhat.
