Unit 1 Part 4d (Nerve Impulse Transmission) Flashcards
(I) What is the resting membrane potential?
A state where there is no net flow of ions across the membrane
(I) What does transmission of a nerve impulse require?
Changes in the membrane potential of the neuron’s plasma membrane
(I) What is action potential?
Wave of electrical excitation along a neuron’s plasma membrane
(I) How do neurotransmitters initiate a response?
By binding to their receptors - which are ligand-gated ion channels - at a synapse
(I) What is depolarisation?
Change in the membrane potential to a less negative value inside
(I) Explain the depolarisation of the plasma membrane
Depolarisation of the plasma membrane as a result of the entry of positive ions triggers the opening of voltage-gated sodium channels, and further depolarisation occurs
(I) Explain the process by which the inactivation of sodium channels and the opening of potassium channels restores the resting membrane potential
1) Binding of a neurotransmitter triggers the opening of ligand-gated ion channels at a synapse.
2) Ion movement occurs and there is depolarisation of the plasma membrane. If sufficient ion movement occurs, and the membrane is depolarised beyond a threshold value, the opening of voltage-gated sodium channels is triggered and sodium ions enter the cell down their electrochemical gradient
3) This leads to a rapid and large change in the membrane potential
4) A short time after opening, the sodium channels become inactivated.
5) Voltage-gated potassium channels then open to allow potassium ions to move out of the cell to restore the resting membrane potential.
(I) What does depolarisation of a patch of membrane cause?
Neighbouring regions of membrane to depolarise and go through the same cycle, as adjacent voltage-gated sodium channels are opened
(I) What happens when the action potential reaches the end of the neuron?
It causes vesicles containing neurotransmitter to fuse with the membrane.
This releases neurotransmitter which stimulates a response in a connecting cell.
(I) What does restoration of the resting membrane potential allow?
The inactive voltage-gated sodium channels to return to a conformation that allows them to open again in response to depolarisation of the membrane
(I) What happens to sodium and potassium ion concentration gradients following repolarisation?
They are reduced. The sodium potassium pump restores the sodium and potassium ions back to resting potential levels.
(II) What is the retina?
An area within the eye that detects light and contains two types of photoreceptor cells: rods and cones
(II) Describe rods
Function in low light but do not allow colour perception
(II) Describe cones
Responsible for colour vision and only function in bright lights
(II) How do cones work?
Different forms of opsin combine with retinal to give different photoreceptor proteins, each with a maxima, sensitivity to specific wavelengths: red, green, blue or UV.
(II) Describe the combination of opsin and retinal
In animals, the light sensitive molecule retina, is combined with a membrane protein - opsin - to form the photoreceptors of the eye, primarily rhodopsin
(II) Describe the action of rhodopsin
- Retinal absorbs a photon of light and rhodopsin changes conformation to photo excited rhodopsin
- A single photo excited rhodopsin activates hundreds of molecules of G protein called transduction
- Each activated transducin activates one molecule of the enzyme PDE.
- Each active PDE catalyses the breakdown of a molecule called cyclic GMP from many ligand-gated Na channels and they close.
- Na channels close halting inward leakage of the ions. Membrane potential increases and a nerve impulse is generated in neurons in the retina.
(II) What allows rods to respond to low intensities of light?
A very high degree of amplification
