lecture 21

Question 1

define membrane potential

Answer 1

 The measurement of the difference in the charge across the membrane; is electrical and very important for neuron communication

Question 2

leakage channels

Answer 2

– the non-gated channels that are always open

Question 3

the types of gated channels

Answer 3

o Chemical (ligand) channels – open in response to a chemical signal
o Voltage-gated channels – opens in response to a change in membrane potential or voltage
o Mechanically gated channels – opens form a mechanical stimulus, from pressure, vibration, etc.

Question 4

electrochemical gradient

Answer 4

 This determines the direction that ions will flow through an open ion channel. Is a combination of concentration and electrical field gradients.

Question 5

resting membrane potential

Answer 5

 Resting membrane potential is maintained mostly through the process of the Sodium-Potassium pump

Question 6

depolarization

Answer 6

is a decrease in membrane potential inside the cell when sodium goes in and the inside of the membrane becomes less negative

Question 7

repolarization

Answer 7

– when the membrane potential turns back to being more negative because Potassium flows back in.

Question 8

hyperpolarization

Answer 8

is an increase in membrane potential, and is when the inside of the cell membrane becomes more negative than where it started

Question 9

graded potential

Answer 9

is a short-range signal that is like local depolarization. Is mostly with the dendrites and cell bodies
 The current is decremental, and the stronger the stimulus the more voltage charge.as the signal travels away is gets weaker and weaker. If the cell receives signals from multiple sources that can all add up together

Question 10

action potential

Answer 10

is a long distance signal that can travel across the entire cell. Is mostly dealing with the axon.

Question 11

define threshold

Answer 11

o This is the max a action potential or growth can be. If depolarization reaches threshold, then an action potential is initiated.
 No matter how much stronger it gets, after reaching threshold, it will give the same action potential each time

Question 12

• Discuss the sequence of events that initiate and propagate an action potential

Answer 12

o An action potential is initiated when a stimulus depolarizes the neuron membrane to reach the threshold potential, causing voltage-gated sodium channels to open, leading to a rapid influx of sodium ions which further depolarizes the membrane; this depolarization then spreads along the axon, triggering the opening of sodium channels in the adjacent region, propagating the action potential down the axon until it reaches the axon terminal, where neurotransmitters are released; the process then concludes with the closing of sodium channels and the opening of potassium channels, allowing potassium ions to flow out and repolarize the membrane, returning it to its resting potential.

Question 13

absolute refractory periods

Answer 13

– the time right when the action potential happens, and immediately after during repolarization. No matter what stimulus it receives, it cannot initiate another neuron to fire again, because the sodium-channels have not reset.
 The cell is unable to respond to additional stimuli

Question 14

relative refractory period

Answer 14

is the time after an action potential where the neuron can gradually become excitable again. Occurs during repolarization and hyperpolarization (if it occurs)

Question 15

electrical synapse

Answer 15

 These are very rare, and is a gap junction where electrical signals can travel directly through the gap junction to the next cell
 Benefit: allows for a very quick response
 Disadvantage: does not allow for any complex communication
* Is in the heart and muscles of the eyes

Question 16

chemical synapse

Answer 16

 Uses chemical signals to communicate, all signals have to be converted to chemical for the postsynaptic cell to then pick it up

Question 17

the steps of chemical synapse in order

Answer 17

 The action potential travels down the presynaptic axon and reaches the axon terminal
 Voltage-gated calcium channels open, and calcium diffuses into the axon terminal
 Then calcium binds to a protein called synaptotagmin, which then allows SNARE to initiate exocytosis
 Which allows for the neurotransmitters to diffuse across the synaptic cleft and bind to the receptors on the postsynaptic cell membrane
 Then ion channels open, which creates graded potentials (localized change at the site of the receptors)
 Lastly, neurotransmitters are removed to end the signal
* Diffusion
* Uptake
* Degradation

Question 18

what is EPSP

Answer 18

 EPSP – excitatory because it is more likely that the postsynaptic cell will initiate its own action potential. This causes depolarization

Question 19

what is IPSP

Answer 19

 IPSP – you inhibit the postsynaptic cell and make it less likely to be able to respond and create its own action potential. This causes hyperpolarization.

Question 20

what is summation

Answer 20

o Summation – where the EPSPs and IPSPs are tabulated at the axon hillock. The summation is the process of adding up all of the signal

Question 21

the three types of summation

Answer 21

 Cancelation – you have a excitatory and inhibitory coming from opposite directions so that nothing happens and they cancel each other out.
 Spatial – signals are being sent form multiple sources at the same time. Multiple presynaptic sending them at the same time. The excitatory potential from many of the neurons will trigger threshold points.
 Temporal – many excitatory potentials are released from one neuron that triggers a threshold point.