1.4 b) Generation of a Nerve Impulse and the Vertebrate Eye

Question 1

What is a nerve impulse?

Answer 1

A signal transmitted across a nerve fibre

Question 2

A membrane potential is created when there is a difference in ___ ___ across the two sides of a ___.

Answer 2

electrical potential, membrane

Question 3

The resting membrane potential is a state where there is no ___ ___ of ___ across the ___.

Answer 3

net flow, ions, membrane

Question 4

What is responsible for maintaining the resting membrane potential?

Answer 4

The sodium-potassium pump

Question 5

The transmission of a nerve impulse requires changes in the ___ ___ of the neuron’s ___ ___.

Answer 5

membrane potential, plasma membrane

Question 6

What is an action potential?

Answer 6

a wave of electrical excitation along a neuron’s plasma membrane

Question 7

The membrane of a nerve fibre is _ve on the inside and _ve on the outside.
This explains how the entry of _vely charged ions causes depolarisation of the membrane.

Answer 7

negative inside, positive outside.
positively.

Question 8

How do neurotransmitters initiate a response?

Answer 8

They bind to their receptors at a synapse

Question 9

What type of membrane protein are neurotransmitter receptors?
What do they do after binding a neurotransmitter?

Answer 9

ligand-gated ion channels.
they open

Question 10

(Generation of a nerve impulse 1/5)

The binding of a neurotransmitter to its receptor allows entry of ___ charged ___, therefore causing depolarisation of the ___.

What is depolarisation?

Answer 10

positively, ions, membrane.

depolarisation is a change in the membrane potential to a less negative value inside the nerve fibre

Question 11

(2/5)

If sufficient ___ movement occurs (and the membrane is depolarised beyond a ___ value), then lots of ___-gated ion channels will open, and ____ ions will enter the cell ___ their ___ gradient.

This leads to a ___ and ___ change in the ___ ___.

Answer 11

ion, threshold, voltage, sodium, down, electrochemical.

large, fast, membrane potential

Question 12

(3/5)

A short time after opening, the ___ ___ become ___.

___-gated ___ channels then open to allow ___ ions to move (out of /into) the cell, restoring the ___ ___ ___.

Answer 12

sodium channels, inactive/closed

voltage, potassium, potassium, (out of), resting membrane potential

Question 13

(4/5)

Depolarisation of a patch of membrane causes ___ ___ of membrane to ___, and go through the same ___.

This happens as adjacent ___ ___ are opened.

Answer 13

neighbouring regions, depolarise, cycle.

sodium channels

Question 14

(5/5)

What happens when the action potential reaches the end of the nerve fibre/plasma membrane?

Once the action potential has moved on, ___-___ ___ channels return to their ___ ___, in response to the ___ of the ___ membrane ___ by the ___-___ ____ channels.

Answer 14

it causes vesicles containing neurotransmitter stimulate a response in a connecting cell.

voltage-gated sodium, original conformation, restoration of the resting membrane potential, voltage gated potassium channels.

Question 15

What are nerve transmissions?

Answer 15

a wave of depolarisation of the resting potential along a neuron

Question 16

The original sodium and potassium concentration gradients in the nerve fibre are __-___ by the…

Answer 16

re-established by the Na/K pump of course! (send help)

Question 17

What is the retina?

What does it contain?

Answer 17

the light sensitive region of the eye.

it contains two types of photoreceptor cells: rod and cones.

Question 18

Describe rods and cones.

Answer 18

Rod cells function in dim light and cannot detect colour.

Cone cells function in high light levels and are capable of detecting colour.

Question 19

In animals the light sensitive molecule ___, combines with the membrane protein ___, to form the ___ of the eye.

Answer 19

retinal, opsin, photoreceptors

Question 20

(Generation of a Nerve Impulse in Rods)

What is the name of the retinal-opsin complex in rod cells?

Answer 20

rhodopsin

Question 21

This is a low-detail summary and can be used to answer low-mark questions:

Rhodopsin ___ a ___ of light, which causes it to turn into ___ ___.

A ___ of proteins then ___ this signal.

This results in the ___ of ___-___, which triggers a ___ ___ in a neuron in the ___.

Answer 21

absorbs, photon, photoexcited rhodopsin.

cascade, amplifies.

closure, ion-channels, nerve impulse, retina

Question 22

Full detail:

Each photoexcited rhodopsin molecule activates ___ of molecules of a _-___ called ____.

Answer 22

hundreds, G-protein, transducin

Question 23

Each transducin molecule activates ___ molecule of ___.

Answer 23

one, PDE (phosphodiesterase)

Phosphodiesterase is an enzyme

Question 24

Each activated PDE molecule catalyses the ___ of ___ of molecules of ____ per second.

Answer 24

hydrolysis, thousands, cGMP (cyclic-GMP)

Question 25

The ___ in cGMP c___ causes closure of ___ ___, which triggers...

Answer 25

decrease, concentration, ion channels, a nerve impulse in neurons in the retina

Question 26

What allows rod cells to respond to low light levels?

Answer 26

a high degree of amplification in the protein pathway

Question 27

In cone cells, ___ forms of ___ combine with ___ to form different ___ proteins with maximal sensitivities to ___ ___ of light.

Answer 27

different, opsin, retinal. photoreceptors, different wavelengths

Question 28

Which wavelengths (colours) of light can cone photoreceptors have a maximal sensitivity to?

Answer 28

red, blue, green or UV

Question 29

Summary: Rods 1. Rod cells function in dim light and do not allow ___ perception. 2. Rod cells are able to function in low light levels due to a high degree of ___ in the protein pathway. 3. Retinal combines with opsin to form ___. 4. Rhodopsin ___ a photon of light turning into photoexcited rhodopsin. 5. A ___ of proteins then amplifies this signal. 6. Photoexcited rhodopsin activates ___ of a G-protein called transducin. 7. Each ___ molecule activates one molecule of PDE. 8. Each PDE catalyses the hydrolysis of ___ of molecules of cGMP per second. 9. The decrease in cGMP concentration is detected by ion channels in the membrane of rod cells, which ___. 10. This triggers a nerve impulse in a neuron in the ___.

Answer 29

1. colour 2. amplification 3. rhodopsin 4. absorbs 5. cascade 6. hundreds 7. transducin 8. thousands 9. close 10. retina

Question 30

Summary: Cones 1. Cones are responsible for ___ vision and only function in bright light. 2. Different types of ___ can combine with a molecule of retinal to form different photoreceptor proteins. 3. Each different retinal-opsin complex (aka photoreceptor protein) has a maximal sensitivity to a different ___ of light.

Answer 30

1. colour 2. opsin 3. wavelength