Nerve cells III

Question 1

Describe the electrical gradient movement in an axon and the structure of a neuron

Answer 1

Electrical grad moves in same direction as Na+ influx

Dendrites, Cell body, Axon, Axon terminal

Question 2

Briefly describe hyperpolarisation

Answer 2

Potential prop to stimuli

Question 3

What is an action potential?

Answer 3

Large, rapid depolarisation for communication

Question 4

How does an action potential occur?

Answer 4

Due to excitable cells with voltage gated ion channels reaching threshold

Question 5

Describe an action potential

Answer 5

In neurons - Mainly axons
Triggered by graded potentials
When initiated, AP propagated long distances along length of axon without loss of strength

Question 6

Which cells generate an action potential?

Answer 6

Only neuron and muscle cells

Question 7

What factor helps initiate an AP and how?

Answer 7

VG ion channels (Na/K)

Open due to changes in membrane potential

Question 8

What are the 3 main stages of an AP?

Answer 8

Rapid depolarisation
Repolarisation
After hyperpolarisation

Question 9

Describe rapid depolarisation

Answer 9

Threshold reached, graded potentials inc membrane potential (-70mV>-55mV)
Threshold triggers VG Na channels open, influx into cell down conc grad, via electrochemical grad, inside becomes more positive hence more VG Na channels open (positive feedback loop)

Question 10

Describe repolarisation

Answer 10

VG Na Channels inactivated, VG K+ channels open as membrane becomes more positive, K rushes out of neuron

Question 11

Describe after hyperpolarisation

Answer 11

K channel stays open (opens later, closes after Na channels), hence K+ still leaves neuron, membrane potential comes closer to equilibrium potential

Question 12

Describe the 2 gating mechanisms of VG Na+ ion channels

What is it dependent on?

Answer 12

Activation gate - closed at rest, opens quickly at depol
Inactivation gate - open at rest, closes slowly
(On voltage/time closes with depolarisation)
Closed, open, inactivation

Question 13

Describe membrane permeability for resting and action potential

Answer 13

Resting potential - K+ channels open, more permeable than Na+, resting potential close to equilibrium potential for K+
Action potential - Na+/K+ permeability VG, changes with time, membrane potential of cell close to equilibrium potential for Na+

Question 14

Describe the link between channels and potentials

Answer 14

VG contribute to AP, leak channels contribute to resting potential

Question 15

Describe graded potentials

Answer 15

Affected by strength of stimulus (not for AP due to all or nothing law)
They’re small, communicate over short distances, determine whether a cell will fire an AP
If graded potential depolarises a neuron to threshold, AP generates
Initiated by stimulus eg sensory/chemical that triggers opening/closing of ligand gated channel
Magnitude varies with strength of stimulus
Can be depolarised/hyperpolarised

Question 16

Describe 2 types of ways graded potentials add up

Answer 16

Temporal summation

Spatial summation

Question 17

What is temporal summation?

Answer 17

Same stimuli, repeated rapidly together in time

Question 18

What is spatial summation?

Answer 18

Different stimuli applied at same time

Question 19

A patient lacks voltage gated Na+ channels on neurons. How does this affect them?

Answer 19

Pain threshold non-existent, can’t feel pain as no AP will be triggered (congenital analgesia)

Question 20

If a patients resting potential was reduced instead, how would it affect them?

Answer 20

Would take longer for an AP to generate, so low sensitivity

Question 21

If a patients resting potential was increased , how would it affect them?

Answer 21

Faster AP will generate, leads to high pain sensitivity

Question 22

Name some examples of electrolytes

Answer 22

Ca/Cl/Mg/K/Na

Question 23

Describe electrolytes

Answer 23

Present in blood, bodily fluids, urine > Imbalance causes in function of the body, affects vital body systems > Can lead to seizures/coma

Question 24

Summarise nerve cells III

Answer 24

RPs are unequal distribution of ions (mainly Na and K) across membrane maintained by the electrochemical grad of ions.
GPs are electrical signals that are local, vary with intensity of the stimulus, can summate, can be stimulatory or inhibitory, have no refractory period.
APs are electrical signals that are depolarising in nature, are due to the coordinated opening and closing of VG Na/K channels