Download Lecture 1, Chapter 1 Overview: History and the neuron

Lecture 1, Chapter 1 Overview: History and the neuron
History
Galen
Nerves were tubes, brain had holes (ventricles)
__________ flowed through the tubes, much like ____________
Ramon y Cajal
Showed that nerve cells were ____________________
____________________ and not networks of tubes
Noticed __________ between units
Noticed ____________________ (cell bodies)
How does one part of the body communicate with another part?
Loewi (1921)
Stimulated the vagus nerve in one heart to __________ it down
Removed some of the fluid it was bathed in
Added that removed fluid to a different heart
The second heart ______________________________
Some ______________________________ must be working
to slow the heart
What is the nature of these chemicals?
Hodgkin and Katz (1949)
Working with giant squids can lead to problems
“The values for spike height are in good agreement with those
obtained by Hodgkin and Huxley (1945), but are considerably
smaller than those reported by Curtis and Cole (1942). The average
value for the resting potential is slightly smaller than that given by
Curtis and Cole… The average action potential was about 20mV
smaller than that given by Curtis and Cole. But a more serious
discrepancy arises from the fact that we have never observed
action potentials greater than 100mV at 18-23 degrees C, whereas
Curtis and Cole describe a spike as large as 168mV in a fibre
which gave a resting potential of 58mV. The matter is not one that
can be lightly dismissed, because the existence of a fibre capable
of giving an overshoot of 110mV has far reaching implications.
We can no longer be inclined to think that our relatively small
action potentials can be attributed to the poor condition of the
experimental animals, since a number of the squids employed were
extremely lively and in perfect condition. Nor does it seem likely
that axons were damaged in the process of isolation… the only
explanation that can be offered is that there is a real difference
between the properties of L.Peali used at Woods Hold and L
forbesi used at Plymouth.”
What did they find?
Knew that when frog muscles are put into a solution with low levels
of sodium and chloride, they were ________________________
So either sodium or chloride in needed for excitation
Replaced chloride in sea water solution with sulphate and the nerve
was ________________________________________________
Conclusion: ________________________is at the root of the action
potential
What about increasing sodium levels?
“The concentration of sodium chloride was increased… This
solution…damaged the axon by osmotic effects in 5-15 min. But
before the osmotic effects became apparent the axon gave an
increased action potential with characteristics which were the
converse of those in sodium-deficient solutions.”
The Resting Potential
A difference between the voltage of the inside and the outside of the
neuron (approx -70mV)
Occurs because ions are found in different amounts inside of the cell
compared to outside of the cell
The players:
________________________ (Na+)
________________________ (K+)
________________________ (Cl-)
Other Anions (A-)
Two forces at work in a neuron
Electrostatic gradient
Charge- ___________________________________________
Diffusion gradient
________________________________________________
Why don’t ions just move to where the forces push them?
_____________________________________________membranes
Contain ion channels which open and close to let certain ions in or
out of the cell
Two types of channels
________________________________________________channels
Opened by a chemical
________________________________________________channels
Opened by a change in voltage
The sodium potassium pump
Forces three sodium ions out of the cell for every two potassium ions
brought back in
Creates an ________________________between the inside and
the outside
The outside gets more sodium, which makes it more
________________________
Takes up to 20% of a cell’s energy to keep going
In addition
Ion channels are “________________________”
Small amounts of ions get through even when the channels are
“closed”
This further contributes to the status of the resting potential
________________________by the sodium potassium pump
The action potential
Ligand gated channels play a large role
Opened by a ________________________
The chemical is usually a neurotransmitter
Some chemicals ________________________the amount of
positive ions entering the cell
Others increase the amount of ________________________ions
entering the cell
EPSPs and IPSPs
If the inside of the cell becomes more positive, this is called an
________________________________________________ (EPSP)
If the inside of the cell becomes more negative, this is called an
________________________________________________ (IPSP)
Keys to the action potential
If enough of an EPSP leads to the surpassing of the threshold (approx
-55mV), an ______________________________________________
The increase in voltage inside the cell triggers the opening of more
and more ___________________________________sodium channels
These allow a LOT of sodium to enter the neuron and increase the
positive charge inside the cell
Keys to the action potential
Around +40 to +50mV, the sodium channels ___________________,
leaving just the potassium channels _____________________
Potassium is now repelled to exit the neuron by the positive charge
inside (electrostatic force) and by its concentration gradient
Too much potassium leaves and the cell becomes
____________________________
Refractory period
While the cell is hyperpolarizing, it cannot fire again (sodium
channels are unable to open)
________________________refractory period
Once the potassium has overshot the resting potential (too much
left), the cell can re-fire if it receives a larger than average EPSP
________________________refractory period
Getting back to rest
Due to the sodium potassium pump, the resting potential is
eventually ________________________and the cell is ready to go
again
“leaky” channels aid in this process as well
The axon terminal
The change in voltage in the axon terminal leads to the opening of
voltage gated ________________________channels
________________________________________________
Calcium leads to ________________________- the
neurotransmitter is released into the synapse
The synapse
The neurotransmitter crosses the synaptic gap and ________________
___________________________________on the postsynaptic neuron
Many different types of receptors exist
Action of NTs at synapse
Receptors can be either single step or multiple steps
________________________: single step
NT binds to channels and opens them
Can work quickly: ________________________
________________________receptors
Multiple steps
NT binds to receptor- triggers G protein to bind to ion channel
and open it
The majority of receptors in the brain are metabotropic
Slower than ionotropic receptors: ________________________