Neurons and that Flashcards
What are neurons?
They are specialised cells that function to transmit electrical impulses within the nervous system
How does the nervous system respond and detect stimuli?
It converts sensory information into electrical impulses in order to rapidly detect and respond to stimuli
What are the three categories of roles for neurons?
Sensory, motor and relay
What are the three basic components of neurons?
Dendrites, axon and soma
What are dendrites?
Short branched fibres that convert chemical information from other neurons or receptor cells into electrical signals
What is an axon?
An elongated fibre that transmits electrical signals to terminal regions for communication with other neurons or effectors
What is a soma?
A cell body containing the nucleus and organelles. Where essential metabolic processes occur to maintain cell survival.
What is a myelin sheath?
A fatty white substance which acts as an insulating layer surrounding the axon on some neurons
What does the myelin sheath do?
The myelin sheath improves the conduction speed of electrical impulses along the axon, but requires additional space and energy.
Where do electrical impulses travel from and to?
Electrical impulses travel from the dendrites to the axon terminal.
How do neurons generate and conduct electrical signals?
Neurons generate and conduct electrical signals by pumping positively charged ions (Na+ and K+) across their membrane.
What is a membrane potential?
A membrane potential is when the unequal distribution of ions on different sides of the membrane that creates a charge difference.
What is a resting potential?
A resting potential is the difference in charge across the membrane when a neuron is NOT firing
In a typical resting potential, what is happening on the inside of the neuron?
The inside of the neuron is more negative relative to the outside (approximately -70mV)
True or false, the maintenance of a resting potential is a passive process?
False, it is an active process
What does it mean if it is an active process?
It is ATP dependent
What is the maintenance of a resting potential controlled by
Sodium potassium pumps
What is a sodium potassium pump?
The sodium potassium pump is a transmembrane protein that actively exchanges sodium and potassium ions (antiport)
How does the sodium potassium pump work?
It expels 3 Na+ ions for every 2 K+ ions admitted. (additionally, some K+ ions will leak back out of the cell
What does the sodium potassium pump create?
The sodium potassium pump creates an electrochemical gradient whereby the cell interior is relatively negative compared to the extracellular environment.
Why is the cell interior negative compared to the extracellular environment during resting potential?
There are more positively charged ions outside of the cell and more negatively charged ions inside the cell
What is needed for the exchange of sodium and potassium ions and why?
The hydrolysis of ATP as it is an energy dependent process
What are the ionic gradients for resting potentials? (Na+, K+, Cl-, A-)
Inside
- Na+ = 15mM
- K+ = 150mM
- Cl- = 10mM
- A- = 100mM
Outside
- Na+ = 150mM
- K+ = 5mM
- Cl- = 120mM
- A- = 0mM
What are action potentials?
Action potentials are the rapid changes in charge across the membrane that occur when a neuron IS firing
What are the three stages of action potentials?
Depolarization, repolarization and a refractory period.
What is depolarisation?
Depolarisation refers to a sudden change in membrane potential from a relatively negative to positive internal charge.
How is depolarisation triggered?
It is triggered in response to a signal initiated at a dendrite which results in the sodium channels opening within the membrane of the axon.
What happens after the opening of sodium channels in depolarisation and why?
There is a passive influx of sodium when the sodium channels open due to the Na+ ions being more concentrated outside of the neuron.
What does the influx of sodium cause?
The influx of sodium causes the membrane to become more positive (depolarisation)
What is the mV before and after depolarisation
Before = -70mV
After = +30mV
What is repolarisation?
Repolarisation refers to the restoration of a membrane potential after depolarisation (i.e restoring a negative internal charge)
What does the influx of sodium result in, in repolarisation?
Following an influx of sodium, potassium channels open within the membrane of the axon.
What causes a passive efflux of potassium?
As K+ ions are more concentrated inside the neuron, opening potassium channels causes a passive efflux of potassium
What does the efflux of potassium cause?
The efflux of potassium causes the membrane potential to return to a more negative internal differential (repolarisation)
What is the mV before and after repolarisation?
Before = +30mV
After = -80mV
What is the refractory period?
The refractory period refers to the period of time following a nerve impulse before the neuron is able to fire again?
Where are sodium and potassium ions found in a normal resting state?
Sodium ions are predominantly outside of the neuron and the potassium ions are mainly inside. (Resting potential)
What happens to the ionic distribution in the refractory period?
The ionic distribution is largely reversed due to the sodium influx in depolarisation and the potassium efflux in repolarisation.
What must happen before a neuron can fire again?
Before a neuron can fire again, the resting potential must be restored via the antiport action of the sodium potassium pump.
What is the mV before and after the refractory period?
Before = -80mV
After = -70mV
What are nerve impulses?
Nerve impulses are action potentials that move along the length of an axon as a wave of depolarisation
When talking about nerve impulses, when does depolarisation occur?
Depolarisation occurs when ion channels open and cause a change in membrane potential
What is special about the ion channels that occupy the length of the axon?
They are voltage gated
How do voltage gated channels open?
They open in response to changes in membrane potential