Membrane transport pt 2

Question 1

Ion channels

Answer 1

form a pore across lipid bilayer and allow passage of charged molecules through cell membranes
-advantage: allows efficiency of transport
-no shape change and not as time consuming
-once they are open, can only allows passive transport

Question 2

Selectivity filter

Answer 2

-part of the protein that becomes narrow
1. only allows ions of specific size
2. has different side chains to allow certain charges

Question 3

voltage-gated

Answer 3

opening controlled by voltage inside cell

Question 4

Ligand-gated

Answer 4

opening controlled by binding of a molecule (ligand) to the channel

Question 5

Chloride ion concentration

Answer 5

outside cell: high concentration of sodium and chloride ions

Question 6

membrane potential

Answer 6

-charge difference right at the membrane
-resting membrane potential is negative because of Na+/K+ pump
-around -70mV

Question 7

K+ leak channels

Answer 7

-main contributor to membrane potential
-if the cells are becoming a little too negative, then K+ is allowed to flow in
-unbalanced negative charges create voltage gradient which pulls K+ back into cell
-when electrochemical gradient for K+ is zero, cell is t resting membrane potential

Question 8

cell body

Answer 8

contains nucleus and most organelles

Question 9

Dendrites

Answer 9

short extension from cell body that receives signals from other cells. “antennas”

Question 10

Axon

Answer 10

long extension that branches at the end to send electrical signals away from cell body and to target cells

Question 11

nerve terminal

Answer 11

end of axon that sends signals (neurotransmitters) to target cell

Question 12

Signaling neurons

Answer 12

-dendrites send signal to “headquarters” and then decide if the signal should be sent through an electrical signal.
-once it reaches the nerve terminal it then sends a chemical signal (neurotransmitter) to another neuron
-to transmit signal to target cells, local change must spread from cell body to axon

Question 13

Action potential

Answer 13

explosion of electrical activity at plasma membrane when signal exceeds threshold (becomes super positive)
-caused by sodium rushing into cell through voltage gated Na+ channels

Question 14

polarized

Answer 14

at resting membrane potential
-voltage gated Na+ channel closed

Question 15

depolarized

Answer 15

opens ion channel to let flow through and goes from negative to positive
-if depolarization exceeds threshold then voltage-gated Na+ channels open and action potential is initiated

Question 16

refractory period

Answer 16

-After initiating electrical pulse need to get back to polarized state to create another neural signal (impulse)
-voltage gated Na+ channel is inactivated (closed)

Question 17

Repolarization

Answer 17

neuron returns to resting membrane potential

Question 18

Voltage gated K+ channels

Answer 18

open during fall of action potential; K+ rushes out to restore resting membrane potential (decline of positive charge)

Question 19

How do action potentials work?

Answer 19

-always going forward
-depolarization makes like a chain reaction
-unidirectional
-once the signal has left, it resets itself and will not be depolarized again

Question 20

Three critical steps

Answer 20

1. neuron (with a negative resting membrane potential) receives a depolarizing stimulus
2. depolarizing stimulus exceeds threshold potential and activates voltage gated Na+ channels (action potential)
3. sodium channels open long enough to activate neighboring sodium (propagation); signal travels forwards towards nerve terminal

Question 21

what is the synaptic cleft?

Answer 21

space between cell sending message (presynaptic cell) and cell receiving message (postsynaptic cell)
-to transmit message across synaptic cleft, electrical signal must be converted into a chemical signal (happens at nerve terminal)

Question 22

What is a neurotransmitter?

Answer 22

small, secreted molecules that serve as a chemical signal at a synaptic cleft
-stored in nerve terminals in synaptic vesicles in presynaptic neuron
-released upon arrival of action potential at nerve terminal

Question 23

What are voltage gated Ca2+ channels used for?

Answer 23

-relays signal to next cell
-Calcium rushes into neuron (down gradient) and triggers membrane fusion between synaptic vesicles and nerve terminal so that neurotransmitters are released.
-lets ions in ( pos or neg)

Question 24

What is the stimulus?

Answer 24

the opening of the ligand gated channel (arrival of neurotransmitters to synaptic cleft)

Question 25

What are post synaptic cells?

Answer 25

either neuron that relays signal or different cell type that will execute action of electrical signal (ex. muscle cell)

Question 26

Neuromuscular junction

Answer 26

synapse between a motor neuron and a skeletal muscle cell
-motor neuron releases acetylcholine (neurotransmitter)
-muscle cell- has acetylcholine receptor on membrane

Question 27

What are excitatory neurotransmitters?

Answer 27

-bind to ligand gated channels and allow positive ions to enter
-influx of positive ions pushes membrane potential towards threshold for action potential
-ex: glutamate and acetylcholine

Question 28

What are inhibitory neurotransmitters?

Answer 28

-binds to a different ligand gated channel and lets in negative ions
-makes cell more neg
-induces hyperpolarization => inhibiting action potential

Question 29

steps that describe signal transmission at the neuromuscular junction

Answer 29

1. action potential arrives at nerve terminal
2. synaptic vesicles fuse to membrane of presynaptic cell
3. Acetylcholine binds to receptor
4. Na+ voltage gated ions open on postsynaptic cells