Excitable cell

Question 1

What is an action potential?

Answer 1

a fixed size, all-or-nothing response that travels along an axon

Question 2

What is a graded response?

Answer 2

variable size,local signal, that is not propagated over long distances

Question 3

What ways do graded and action potentials pass in axon?

Answer 3

Graded potentials can go either way, action potentials tend to travel in one direction(away from cell body).

Question 4

How are action and graded potentials coded?

Answer 4

APs coded by frequency (unit of size)

GPs coded by size (according to stimulus strength)

Question 5

Why do neurons have a resting potential?

Answer 5

selectively permeable membrane, unequal distribution of ions on either side of membrane, physical forces

Question 6

What physical forces determine resting potential?

Answer 6

diffusion, electircal potential

Question 7

what is Vm of nervous systen?

Answer 7

negative (-65mV)

Question 8

What is Eion?

Answer 8

the membrane potential that would be achieved in a neuron if membrane was selectively permeable to that one ion ONLY

Question 9

What does nernst equation calculate?

Answer 9

calculate Eion for an ion

Question 10

What is nernst equation at 37 degrees?

Answer 10

Eion = 61.54mV log [ion]outside/[ion]inside

Question 11

What does increase in extracellular K+ cause?

Answer 11

membrane depolarizes (more positive )

Question 12

Why is resting membrane potential close to Eion for K?

Answer 12

At rest membrane is very permeable to K+ but slughtly permeable to other ions.

Question 13

What does goldman equation calculate?

Answer 13

membrane potential but multiple ions are taken into account

Question 14

What happens to membrane ppotential during an action potential

Answer 14

it increase - from negative to positive due to sodium permeability increase

Question 15

What happens in overshoot phase?

Answer 15

Membrane potential rises to near Eion sodium

Question 16

What factors effect conduction velocities?

Answer 16

axon diameter

Myelination

Question 17

How does axon diameter affect conduction velocity?

Answer 17

The wider the axon the greater the velocity
As resistance to current flow is inversely proportion to cross sectional area of axon. so resistance is lower the wider the axon

Question 18

Why are there so many unmyelinated small axons?

Answer 18

space constant is proportional to rm/ri so benefit of high membrane resistnace is reduced by high internal resistance

Question 19

How big was sqid giant axon?

Answer 19

1000 micro meters 25m/s

Question 20

What does TEA do?

Answer 20

block K+ channels

Question 21

What blocks Na channels?

Answer 21

Lidocaine, TTX, STX

Question 22

Where is action potential initiated?

Answer 22

Spike initiation zone in the axon hillock

Question 23

What is temporal and spatial summation?

Answer 23

Temproal- more frequent APs

Spatial - multiple inputs add up to same neuron.

Question 24

How can EPSPs be shunted?

Answer 24

By inhibitory input (excitatory post synaptic potential)

Question 25

where are electrical synapses?

Answer 25

They are rare in human. but in smooth muscle, cardiac muscle and retinal neuronal cells.

Question 26

How can electrical synapses work?

Answer 26

can work 2 ways and are gap junctions.