ELECTRICAL EXCITABILITY OF CELLS

Question 1

Are muscle fibres excitable cells and what is a property of excitable cells

Answer 1

Yes and they produce Action Potentials

Question 2

What does it mean when a cell is excitable?

Answer 2

Defined by a rapid and temporary change in membrane potential. A large increase to positive mV values followed by a quick return to negative mV values.

Question 3

What sets up an electrical gradient?

Answer 3

The seperation of charge due to Na plus and K plus concentration difference across the plasma membrane

Question 4

Channels are not always open, some have gates, what are these gates called?

Answer 4

Chemically gated, Electrically gated and mechanically gated.

Question 5

How do chemically gated channels work?

Answer 5

Gates controlled by a molecule that binds to protein receptor

Question 6

How do electrically gated channels work?

Answer 6

Gating controlled by voltage differences across the plasma membrane

Question 7

How do mechanically gated channels work?

Answer 7

Physical forces put pressure on the membrane and the channel pops open

Question 8

How do we measure the electrical potential differences across the plasma membrane

Answer 8

Measured in millivolts and is called the membrane potential. Membrane potential is different for every cell type in the human body but is alwasy negative when the cell is at rest.

Question 9

How is the membrane potential maintained?

Answer 9

Maintained by Na and K concentration differences across plasma membrane

Question 10

What is the depolarization stage?

Answer 10

membrane potential becomes less negative

Question 11

What is the repolarization stage

Answer 11

Membrane potential returns to more negative stage

Question 12

ACTING POTENTIAL ACROSS THE SARCOLEMMA: THE RESTING STAGE( What happens)

Answer 12

Before a stimulus arrives, the membrane is at resting membrane potential and voltage gated Na and K channels are closed

Question 13

What kind of channels are Na and K channels?

Answer 13

Electrically gated channels meaning they will open in response to change in voltage across the sarcolemma.

Question 14

What happens during the depolarization stage?

Answer 14

In response to a stimulus, voltage gated Na channels open and Na enters the cell making the membrane potential less negative

Question 15

What happens during the repolarization stage?

Answer 15

Na channels close while voltage gated K channels open and K leaves the cell making the membrane channel morw negative

Question 16

What needs to happen for a muscle contraction to occur

Answer 16

Needs to receive a stimulus to fire an action potential

Question 17

Where does the action potential come from?

Answer 17

Comes from a motor neuron.

Question 18

How many muscle fibers is each muscle fiber innervated by?

Answer 18

By one motor neuron

Question 19

What does a motor unit conist of

Answer 19

1 motor neuron and all the muscle fibers it innervates

Question 20

what is the connection point between the motor neuron and muscle fibre called?

Answer 20

neuromuscular junction

Question 21

What happens during the neuromuscular junction

Answer 21

where nerve impulse (action potential) is transmitted into the sarcolemma of the muscle fibre