1.4 b) Generation of a Nerve Impulse and the Vertebrate Eye Flashcards
What is a nerve impulse?
A signal transmitted across a nerve fibre
A membrane potential is created when there is a difference in ___ ___ across the two sides of a ___.
electrical potential, membrane
The resting membrane potential is a state where there is no ___ ___ of ___ across the ___.
net flow, ions, membrane
What is responsible for maintaining the resting membrane potential?
The sodium-potassium pump
The transmission of a nerve impulse requires changes in the ___ ___ of the neuron’s ___ ___.
membrane potential, plasma membrane
What is an action potential?
a wave of electrical excitation along a neuron’s plasma membrane
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.
negative inside, positive outside.
positively.
How do neurotransmitters initiate a response?
They bind to their receptors at a synapse
What type of membrane protein are neurotransmitter receptors?
What do they do after binding a neurotransmitter?
ligand-gated ion channels.
they open
(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?
positively, ions, membrane.
depolarisation is a change in the membrane potential to a less negative value inside the nerve fibre
(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 ___ ___.
ion, threshold, voltage, sodium, down, electrochemical.
large, fast, membrane potential
(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 ___ ___ ___.
sodium channels, inactive/closed
voltage, potassium, potassium, (out of), resting membrane potential
(4/5)
Depolarisation of a patch of membrane causes ___ ___ of membrane to ___, and go through the same ___.
This happens as adjacent ___ ___ are opened.
neighbouring regions, depolarise, cycle.
sodium channels
(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.
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.
What are nerve transmissions?
a wave of depolarisation of the resting potential along a neuron
The original sodium and potassium concentration gradients in the nerve fibre are __-___ by the…
re-established by the Na/K pump of course! (send help)
What is the retina?
What does it contain?
the light sensitive region of the eye.
it contains two types of photoreceptor cells: rod and cones.
Describe rods and cones.
Rod cells function in dim light and cannot detect colour.
Cone cells function in high light levels and are capable of detecting colour.
In animals the light sensitive molecule ___, combines with the membrane protein ___, to form the ___ of the eye.
retinal, opsin, photoreceptors
(Generation of a Nerve Impulse in Rods)
What is the name of the retinal-opsin complex in rod cells?
rhodopsin
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 ___.
absorbs, photon, photoexcited rhodopsin.
cascade, amplifies.
closure, ion-channels, nerve impulse, retina
Full detail:
Each photoexcited rhodopsin molecule activates ___ of molecules of a _-___ called ____.
hundreds, G-protein, transducin
Each transducin molecule activates ___ molecule of ___.
one, PDE (phosphodiesterase)
Phosphodiesterase is an enzyme
Each activated PDE molecule catalyses the ___ of ___ of molecules of ____ per second.
hydrolysis, thousands, cGMP (cyclic-GMP)
The ___ in cGMP c___ causes closure of ___ ___, which triggers…
decrease, concentration, ion channels, a nerve impulse in neurons in the retina
What allows rod cells to respond to low light levels?
a high degree of amplification in the protein pathway
In cone cells, ___ forms of ___ combine with ___ to form different ___ proteins with maximal sensitivities to ___ ___ of light.
different, opsin, retinal. photoreceptors, different wavelengths
Which wavelengths (colours) of light can cone photoreceptors have a maximal sensitivity to?
red, blue, green or UV
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 ___.
- colour
- amplification
- rhodopsin
- absorbs
- cascade
- hundreds
- transducin
- thousands
- close
- retina
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.
- colour
- opsin
- wavelength
