Chapter 2: Neurophysiology Flashcards
What does it mean to say that neurons are polarized?
They have a different charge inside the cell versus outside the cell
What is the difference between anions and cations
Anions - negative ions
Cations - positive ions
Define Membrane potential.
Membrane potential is the difference in electrical charge between the fluid in the membrane and fluid outside the membrane. A neuron has a negative resting potential between -50 to -80 mV.
How does the neuron maintain equilibrium potential?
During rest, only positive potassium ions (k+) can flow freely through the membrane. Two opposing forces drive this movement.
- Diffusion: the movement of a substance from areas of high concentration to low concentration. There are MORE k+ inside the cell than outside so diffusion pushes k+ to move OUT of the cell.
- Electrostatic pressure: the movement of ions towards areas oppositely charged. It is more NEGATIVE inside the cell than outside so the positive K+ is pulled back into the cell.
Sodium Potassium pumps affect both the diffusion and the electrostatic pressure to create the negative equilibrium potential.
- The pump moves 3 Na+ OUT for every 2 K+ IN. This concentrates the K+ in the cell causing it to diffuse OUT but also contributes to the negative charge because every time it pumps it removes more + ions than it lets in.
What is hyperpolarization and depolarization?
Hyperpolarization i an increase in membrane potential (it becomes MORE negative)
Depolarization is a decrease in membrane potential (it becomes LESS negative)
What is a graded response?
A graded response is when a stimulus changes the membranes local potential (one small area) by depolarizing or hyperpolarizing it. Graded potentials dissipate over time.
How to Action Potentials occur?
- At rest, k+ channels are open and voltage gated Na+ channels are closed. When a stimulus depolarizes the local potential (makes it more positive) to the point of the threshold (~-40), the voltage gated Na+ channels open. This causes a rush of Na+ into the cell (electrostatic pressure) until the membrane potential reaches +40mV (Na+’s equilibrium potential. The now positive membrane potential triggers the opening of voltage gated K+ channels and the K+ rush out to restore the resting potential.
What is the all or none law?
The law that Action potentials do not vary in strength. Once the threshold is reached and an action potential is triggered, it will always look the same. This means that it is not the strength of the action potential that conveys the information but rather the frequency of the action potentials.
What is an after potential?
An after potential is the slight hyperpolarization that occurs after an action potential. It occurs as the cell attempts to restore the balance between Na+ ions and K+ ions. After potentials make it harder for another Action potential to occur right away because now it will take a larger stimulus to depolarize the cell to the point of the threshold.
What is the refractory phase and what are the different types?
When stimuli are closely spaced, only the first can trigger an action potential. In absolute refractory, no action potentials can be produced. In relative refractory, only strong stimulation can produce an action potential (due to the after potential)
How do action potentials travel down the axon?
They are propagated along the axon. Each adjacent section is depolarized by the action potential, thus triggering their own action potential.
Action potentials travel through the process of saltatory conduction: they travel down the inside of the axon, “jumping” from node to node (node of ranvier). They only occur at Node’s of ranvier because the breaks in the myelin allow for the movement of ions across the membrane.
What is Multiple Sclerosis?
WHen the body makes antibodies that attack the myelin and therefore interfere with action potential conduction.
What is the end result of an Action potential in simple terms?
When an action potential reaches the axon terminals it triggers the release of neurotransmitters. The transmitters move from the presynaptic cell to the post synaptic cell. The neurotransmitters cause brief changes in the post synaptic cell’s membrane potential and (if strong enough) can trigger an action potential)
What is a postsynaptic potential and it’s different types?
Changes in the membrane potential of the postsynaptic cell due to the neurotransmitters released by the presynaptic cell.
When the change is depolarizing, it is called an excitatory postsynaptic potential and it makes it more likely for an action potential to occur.
When the change is hyperpolarizing, it is called an inhibitory post synaptic potential. It is caused by an increase of Chloride ions (Cl-), making the cell more negative. IPSP makes it harder for an action potential to occur.
How do neurons integration information?
Spatial summation: is the sum of input (the sum of EPSP and IPSP) in a given space. i.e. the inputs are arriving from different locations on the dendrite but are arriving at the same time)
Temporal summation: is the sum of input in a given period of time. i.e. the inputs are arriving from the same location on the dendrite at different times.
