Excitable Cells

Question 1

What is ECF?

Answer 1

Extracellular fluid

Question 2

What is ICF?

Answer 2

Intracellular fluid

Question 3

What chemical is dominant in the ECF?

Answer 3

Na+ and Cl-

Question 4

What chemical is dominant in the ICF?

Answer 4

K+

Question 5

What are passive channels?

Answer 5

Channels in the cell membrane that are always open allowing ions to flow across the cell membrane freely

Question 6

How does K+ move in cells?

Answer 6

K+ constantly leaks out of the cell via passive channels down its concentration gradient

Question 7

What is the ATPase pump?

Answer 7

A pump that runs on ATP and moves three sodium ions out of the cell and two potassium ions in

Question 8

What is the net charge of cells?

Answer 8

Net negative charge inside the cell and net positive charge outside the cell

Question 9

What is membrane potential?

Answer 9

The separation of ions across a membrane causing opposite charges

Question 10

What are excitable cells?

Answer 10

Are cells that can generate and transmit signals

Question 11

What are the main types of excitable cells?

Answer 11

Neurons and muscle cells

Question 12

What is the resting membrane potential?

Answer 12

The constant state of separated charges

Question 13

What is the resting membrane potential in neurons?

Answer 13

-70mV

Question 14

What is polarisation?

Answer 14

When the membrane potential is at resting levels

Question 15

What is depolarisation?

Answer 15

When there is a decrease in potential hence becomes less negative

Question 16

What is repolarisation?

Answer 16

When it is returning to resting potential after depolarisation

Question 17

What is hyperpolarisation?

Answer 17

When the resting potential is overshot at there is an increase in potential hence becomes more negative

Question 18

What triggers a change in membrane potential in neurons?

Answer 18

Voltage gated Na+ channels which open in response to a change in voltage

Question 19

What is graded potential?

Answer 19

Temporary changes in the electrical charge of a cell membrane

Question 20

What impacts the size of graded potential?

Answer 20

The size of the trigger

Question 21

What is the threshold level in neurons?

Answer 21

-50mV - -55mV

Question 22

What happens when threshold levels are met in neurons?

Answer 22

Lots of Na+ channels open and Na+ flows into the cell until peak polarisation is reached

Question 23

What is the peak polarisation in neurons?

Answer 23

+30mV

Question 24

What happens when Na+ channels close?

Answer 24

Voltage gated K+ channels open to let K+ out of the cell

Question 25

What is hyperpolarisation in neurons?

Answer 25

-80mV

Question 26

How do neurons become polarised after overcorrection?

Answer 26

By the continuous flow of K+ through passive channels

Question 27

What are the gates of the Na+ channels?

Answer 27

An activation gate which is like a hinged door and an inactivation gate which is like a ball and chain

Question 28

What is the gate in the K+ channel?

Answer 28

One gate which opens and closes

Question 29

What is the all or nothing rule?

Answer 29

Action potentials always last for the same amount of time

Question 30

Why are action potentials unidrectional?

Answer 30

Due to the refractory period

Question 31

What is the refractory period in neurons?

Answer 31

Time after an action potential when a neuron is less likely to fire another action potential

Question 32

What happens when action potential reaches an axon terminal?

Answer 32

Causes the voltage gated calcium channels to open and calcium flows into the presynaptic cell which releases acetylcholine

Question 32

How does conduction occur in neurons?

Answer 32

The original action potential doesn't travel but rather triggers identical events down the axon

Question 33

What does acetylcholine do?

Answer 33

Diffuses across cleft and binds to receptors on membrane of postsynaptic cells which opens Na channels allowing the target cell to depolarise

Question 34

How is action potential ended?

Answer 34

The synaptic cleft releases acetylcholine esterase which stops binding and recycles ACh closing the Na channels

Question 34

What is the sarcolemma?

Answer 34

A cell membrane of a muscle fiber that conducts the stimulus throughout the muscle fiber