Neural Signalling and Communication Flashcards
When do neural impulses occur?
When a stimulus depolarises a cell membrane, prompting an action potential
How do electrical impulses travel along the axon?
Via depolarised voltage-gated ion channels in the membrane
How do electrical impulses travel along myelinated axon?
‘Jump’ (salutatory) due to Nodes of Ranvier
How do electrical impulses travel along non-myelinated axon?
Travel continuously
When does an action potential occur?
When an electrical signal disrupts the original balance of Na+ and K+ within a cell membrane (briefly depolarises the concentrations of each)
What is depolarisation?
Change within a cell, when cell undergoes a shift in electric charge distribution, resulting in a less negative charge inside the cell
How does one neurone affect another?
A neurone affects other neurones by releasing a neurotransmitter that binds to chemical receptors
What is the effect on the postsynaptic neurone determined by?
The effect upon the postsynaptic (receiving) neurone is determined by the receptor that is activated (not the presynaptic neurone or the neurotransmitter itself
What must occur for a presynaptic neurone to release a neurotransmitter?
A series of changes in electric potential
How can the potential difference (voltage difference) between inside and outside of cell be measured?
When both are in the bath solution, what is the potential difference?
Stick electrodes inside a neurone and measure the potential difference between the inside and outside of the cell
The record is of the potential difference between the 2 electrodes
Zero
What does insertion of electrode into cell reveal?
The resting potential –> negative (approx -65mV)
i.e. inside of cell is -65mV lower than outside
What does the magnitude of resting membrane potential depend on?
Type of cell involved
What is the resting potential?
Name for the electrical state when a neurone is not actively being signalled (the nearly latent membrane potential of inactive cells)
A neurone at resting potential has a membrane with established amounts of Na+ and K+ ions on either side –> inside of neurone is negatively charged relative to outside
What 4 factors contribute to resting membrane potential?
- Charged intracellular proteins
- Na+/K+ pump
- Potassium ions
- Sodium ions
How do intracellular proteins contribute to membrane potential?
Large negatively charged intracellular proteins cannot cross cell membrane to leave as to big (lack of membrane permeability). Contributes to its negativity.
How does Na+/K+ pump contribute to membrane potential?
Na+/K+ pump moves 3 Na+ ions out for every 2 K+ ions in (cell gets more negative)
N+/K+ ATPase pump is to maintain resting potential so that the cells will be keeping in a low concentration of sodium ions and high levels of potassium ions within cell
What form of transport is Na+/K+ pump?
Active transport (uses hydrolysis of ATP)
What are the gradients acting on potassium ions?
- Concentration gradient (K+ tends to leak out of cell down concentration gradient)
- Electrical gradient (K+ also wants to move back into cell down electrical gradient due to large -vely charged protein molecules trapped in cell)
Eventually becomes balanced –> equilibrium
What is the equilibrium potential for any ion determined by?
Nernst Equation
Does the cell resting membrane potential equal the potassium equilibrium potential?
No - cell resting membrane potential is close to but not equal to the potassium equilibrium potential as there is also a small leak for Na+ ions
What are the gradients acting on sodium ions?
Net inward diffusion of Na+ slightly adds to positivity of cell
Both concentration and electrical gradients operate in same direction (inward flow of ions)
Why is the effect of Na+ on the cell’s resting potential only small?
Membrane is only slightly permeable to Na+
At the resting potential, what gradients are acting on ions?
Electrical and chemical gradients
What is an action potential?
The means by which a neurone sends information down its axon, away from the cell body. The action potential (aka ‘spike’ or ‘impulse’) is an explosion of electrical activity
A short-term change in electrical potential (polarity) that travels along a cell (such as a nerve or muscle fibre) which enables nerves to communicate