Excitable Tissues

Question 1

Excitable Tissue Definition

Answer 1

Cells and Tissues that utilise electrical signals as a form of comunication, reflecting their electrical excitablity

Question 2

Major types of Excitable Tissues:

Answer 2

Neurons & the three types of muscles (skeletal, cardiac, smooth)

Question 3

How do you record the membrane potential in a single cell

Answer 3

submerged cell in solution. attach voltmeter with one lead inside cell and one out to recprd th different between intra and extracellular compartments = represents potential difference across membrane.
The Nernst equation can be used when the membrane is selectively permeable when intracellular and extracellular concentrations are known

Question 4

Membrane Potential

Answer 4

It is the membrane potential of a cell at rest which is -80mV. At rest, the membrane potential is polarised as the intracellular charge is different to the extracellular charge.

Question 5

Depolarisation Definition

Answer 5

When membrane potential decreases from RMP (i.e. the inside of the cell becomes LESS negative and the membrane becomes LESS polarised)

Question 6

Repolarisation Defintion

Answer 6

membrane potential increases back towards RMP (i.e. the inside of the cell becomes MORE negative)

Question 7

Hyperpolarisation Definition

Answer 7

membrane potential increases from the RMP (i.e. the inside of the cell becomes MORE negative & membrane potential becomes MORE polarised)

Question 8

Polarised Definition

Answer 8

when the inside of an excitable cell is negatively charged and it is different to the oustide

Question 9

Graded Potentials

Answer 9

• observed when an excitable tissue cell is subjected to an excitatory or inhibitory stimulus.
• produces small transient changes in MP (approx 1-30mV)
• size GP is directly proportional to size of stimulus
• is localised; doesnt effect whole cell

Question 10

Depolarising Graded Potential:

Answer 10

• produced by exitatory stimulus
• causes transient depolarisation from RMP
• MP becomes less negative

Question 11

Hyperpolarising Graded Potential:

Answer 11

• produced by inhibtory stimulus
• causes transient hyperpolarisation from RMP
• MP becomes more negative

Question 12

Action Potential

Answer 12

• large, fast, complex, changes in MP caused by large excitatory stimulus
• affects whole cell
• depolarising grade potential needs to be large enough to reach threshold (-65mV ish)
• if stimulus is not big enough, no action potenital

Question 13

What is the ‘All or Nothing Principle’?

Answer 13

If threshold is not reached; there is no action potential

Question 14

purpose of action potential?

Answer 14

travels along cells to enable effective communication between disparate parts of body.

Question 15

What are the 3 Phases of an action potential:

Answer 15

1. Depolarisation: period between threshold & peak. MP becomes less negative
2. Repolarisation: period between peak & RMP. MP becomes more negative
3. Hyperpolarisation: MP becomes more negative before returning to RMP

Question 16

Typical MP value at Threshold:

Answer 16

-65mV

Question 17

Typical MP value at Peak:

Answer 17

+30mV

Question 18

Typical MP value at Rest:

Answer 18

-80mV