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Lecture 9

PSY2301 Lecture 9: PSY 2301 - Feb 09 - Action PotentialPremium

5 pages85 viewsSpring 2018

Department
Psychology
Course Code
PSY 2301
Professor
Patrick Davidson
Lecture
9

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How Do Neurons Use Electrical Signals to Transmit Information?
Part 1:
- Searching for electrical activity in the nervous system
- Electrical activity of a membrane
Early Clues that Linked Electricity and Neuronal Activity
- Electrical Stimulation Studies
- Fritsch and Hitzig (mid-nineteenth century)
- Electrical stimulation of the neocortex causes movement (arms and
legs)
- Bartholow (1874)
- First report of human brain stimulation
- Von Helmholtz (nineteenth century)
- Flow of information in the nervous system is too slow to be a flow of
electricity
- Nerve conduction: 30-40 meters/second
- Electricity: 3 x 108 meters/second
- It is not the ions themselves that travel along the axon but rather a wave of
charge (Bernstein, 1886)
Resting Potential
How the Movement of Ions Causes Electrical Charges
- Diffusion
- Movement of ions from an area of higher concentration to an area of lower
concentration through random motion
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- Concentration gradient
- Differences in concentration of a substance among regions of a container
allow the substance to diffuse from an area of higher concentration to an
area of lower concentration.
- Voltage gradient
- Difference in charge between two regions that allows a flow of current if
the two regions are connected
- Opposite charges attract
- Similar charges repel
- Ions will move down a voltage gradient from an area of higher charge to
an area of lower charge
Electrical Activity of a Membrane
- Resting potential
- Electrical charge across the cell membrane in the absence of stimulation
- A store of negative energy on the intracellular side relative to the
extracellular side
- The inside of the membrane at rest is -70 millivolts relative to the
extracellular side
- Four charged particles take part in producing the resting potential
- Na+ and Cl-
- Higher concentration outside the cell
- K+ and A-
- Higher concentration inside the cell
- Channels and pumps help to maintain the distribution of ions inside and
outside of the cell
Summary of Resting Potential
- Maintaining the resting potential
- Large A- molecules cannot leave the cell: make the inside negative
- Ungated channels allow K+ and Cl- to move into and out of the cell more
freely, but gated sodium channels keep out the Na+ ions
- Na+ - K+ pumps extrude Na+ from the intracellular fluid and inject K+
- The cell membranes semipermeability and the actions of its channels,
gates, and pumps thus produce voltage - resting potential - across the cell
membrane
Graded Potentials
- If the concentration of any of the ions across the unstimulated cell membrane
changes, the membrane voltage changes
- These graded potentials are small voltage fluctuations across the cell membrane
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