Exam 1: Slide 3 Flashcards
Neurons
- cells that are specialized for the reception, conduction and transmission of electrochemical signals.
- convert electrical signals to chemical signals and then back to electrical signals.
Electrical Energy
-created by the flow of charged particles through the selective plasma membrane
-flows from high to low charge or “potential”. This is just like a battery with + and – ends.
Potential is expressed in volts
Cations
sodium (Na+), potassium (K+), and calcium (Ca2+)
Anions
chloride (Cl-)
LArge Proteins
(A-)
Ions High Inside the Neuron
K+ and A-
Ions Hight Outside the Neuron
Na+ , Ca2+, and Cl-
The Resting Membrane Potential
- The basis of neuronal signaling is the fact that neurons are negative charged relative to the outside of the cell by about -40 to -90mV
- occurs because of a difference in how ions are distributed between the inside and outside and when they are allowed to move
- For a neuron to communicate with another neuron, this has to become more positive
Potassium K+ and the Resting Membrane Potential
-essentially the only ion that moves in a resting neuron, thus the resting membrane potential is almost entirely due to these ions
-At rest, these ions have a net movement from inside of the neuron to outside
The inside of the neuron loses positive ions as a result, making the inside more negative relative to the outside
What channels are open and which channels are closed when a neuron is in rest
Potassium leak channels are always open, allowing for free potassium movement
Ion channels for the remaining ions are closed at rest so the other ions cannot move.
Voltage Gated Channels
– a change in the membrane potential causes the channel to open and let selective ions through
Ligand Gated Channels
– a chemical binding causes the channel to open and let semi-selective ions through
Do Voltage and Ligand Gated Channels require energy?
These require no energy; ions simply move based on two passive forces: concentration and electrical gradient
Sodium Potassium Pump
- This active movement requires energy, usually the energy is ATP
- Neurons use this to maintain resting potential.
- pumps three sodium ions (Na+) out for every two K+ ions pumped in.
- creates a specific ionic environment for the neuron at rest
- These pumps move ions against their concentration
Concentration Driving Force
Diffusion causes ions to flow from areas of high to low concentration
Electrical Driving Force
causes ions to flow towards oppositely charged areas. Think “opposites attract” or “like repels like”
Electrochemical Driving Force
-These two forces can “push” ions in the same direction or opposite directions, and what the ion does is a net summation of the forces
The Nernst Equation
- predicts the potential (i.e. electrical force) needed to counterbalance the concentration force pushing an ion across a membrane.
- Each ion has a specific potential value (in mV), called the equilibrium potential, and based on what the potential of the overall cell is, you can predict ion movement. This is stated as Ex, where x is the relevant ion.
- takes in to account the temperate, concentrations of a given ion inside and outside of the cell, the Faraday constant and the valence (i.e. charge) of the ion into account
The Neuron’s State
the sum of all the individual potentials of the ions that are moving at that moment
The Goldman Equation
allows you to predict the neuronal potential with multiple ions
Equilibrium’s of K, Na, CL
Potassium Ek=-94mV
Chloride Ecl= -70mV
Sodium Ena= +60mV
Threshold Potential
If the neuron becomes depolarized beyond a certain potential an action potential is triggered
Action Potential
a large enough change will trigger the key electrical event needed to get a neuron to signal with another neuron.
The Receptor Potential
-a way for sensory neurons to “fire” an action potential.
0Ion channels on neurons will open and depolarize/hyperpolarize the neuron in response to a sensory stimuli
-This can cause the neuron to reach a threshold potential
The Synaptic Potential
a way for all other neurons to produce an action potential in another neuron
Receptor Potential Gates
various ligand, voltage-gated and mechanically-gated channels that let in/out different ions (Na+, K+, Ca2+, and/or Cl-)
Synaptic Potential Gates
various ligand and voltage-gated channels that let in/out different ions (Na+, K+, Ca2+, and/or Cl-)
Action Potential Gates
Voltage-gated Na+ channels and voltage-gated K+ channels
EPSP
If the ion channels that open make the cell depolarized, it is called an excitatory post synaptic potential (EPSP)
IPSP
If the ion channels that open make the cell hyperpolarized, it is called an inhibitory post synaptic potential (IPSP)
How do EPSP/IPSP get to the axon?
- As these EPSPs/IPSPs occur at the dendrite, they trigger adjacent voltage gated channels to open, sending this EPSP/IPSP event down the dendrite to the axon
- With enough EPSPs summating together, they trigger voltage gated sodium channels at the axon hillocks
How are the Action Potential’s regions distinct? What mv must the membrane be around?
- This region is distinct because of the massive amount of voltage gated sodium channels, and their activation causes a large change in the membrane potential that travels down the axon
- For an action potential to occur, the depolarization must cause the membrane to become around –40 mV, which is termed the threshold potential
- All-or-none . This means the neuron fires at full amplitude or not at all
Why can action potentials only occur on the axon?
- Only the axon has clusters of voltage gated sodium and voltage gated potassium channels down its length
- This clustering allows for large membrane potential changes that are not possible anywhere else on the neuron
When do voltage gated sodium channels open?
Voltage gated sodium channels open around -40mV (i.e. depolarization) but then have a separate mechanism that blocks the channel even though the cell is depolarized
When do voltage gated potassium channels open?
Voltage gated potassium channels open around 0mV and take much longer to close
The Undershoot Phase
-Because potassium channels are slow to respond to voltage and open, they similarly are slow to close as well. -The extra time potassium channels are open more than they should be takes the membrane potential past the neuronal resting membrane
Myelin and Action Potentials
- exists because it allows the action potential to be generated at the node of Ranvier, and then passive charge transfer is enough to depolarize the next node.
- saltatory conduction
Absolute Refractory Phase
—time when no action potentials are produced because all channels are open
Relative Refractory Phase
—time when only strong stimulation can produce an action potential because the inactivation of sodium channels can be removed
Multiple Sclerosis
- a immune-mediated condition that attacks myelin, with women 2-3X more likely to develop MS compared to men
- The age of onset 20-50s, average age 34 years old
- Symptoms of MS vary widely – mild symptoms to severe disability, and there is no cure
- Common symptoms include fatigue, numbness, headache, coordination problems, bladder and bowel problems, vision problems, dizziness, sexual dysfunction, pain, cognitive dysfunction, emotional changes, and spasticity.
- Relatives of those with MS have 1-3% chance of developing MS
- Identical twins have 30% chance of developing MS
What does Multiple Sclerosis Target?
In particular, the myelin produced by oligodendrocytes in the CNS is the target.
Lack of myelin leads to abnormal action potential propagation and dysfunctional signaling
Theories of Multiple Sclerosis
- One theory as to what causes an attack on the oligodendrocytes are T cells that recognize oligodendrocytes myelin-specific antigens.
- T cells cross the blood-brain barrier and secreter pro-inflammatory cytokines, which destroy the myelin cells
Hodgkin and Huxley
Knowing the exact process of an action potential was the result of monumental studies done primarily by a pair of scientists in the 1950s
Voltage Clamping Method
- hH used this method to maintain the neuron at a specific potential (i.e. voltage) while measuring changes in ionic flow (called ‘current’).
- This method allowed them to study the properties of the ion channel at any voltage/potential they wanted in order to see what causes each channel to open/close and what their properties were
How did Hodgkins and Huxley test sodium?
1) To test this, they removed sodium from the outside of the neuron. Now, the concentration inside was higher than outside.
2) Instead of flowing inside the cell during depolarization, sodium should flow out down its concentration gradient. This is exactly what they found—sodium had a slight outward current with depolarization.
3) The outward current was _unaffected by changing external sodium, indicating another ion was responsible for that outward current.
YOU GOT THIS SHIT BITCH
HELL YEAAAAAAAHHHHH
Drug Proof for Potassium
Tetraethylammonium (TEA) blocks potassium current without blocking sodium current. When TEA is applied to during a membrane depolarization, you lose the late outward current, proving potassium is responsible.
