6.5 Neurons & Synapses Flashcards
What are neurons?
Neurons are specialised cells that function to transmit electrical impulses within the nervous system
What is the role of the nervous system?
The nervous system converts sensory information into electrical impulses in order to rapidly detect and respond to stimuli
Why may neurons differ?
neurons may differ according to role (sensory, relay or motor)
What are the 3 basic components of all neurones?
dendrites
axon
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 may the axon be surrounded by?
In some neurons, the axon may be surrounded by an insulating layer known as a myelin sheath
What is the role of the myelin sheath?
The myelin sheath improves the conduction speed of electrical impulses along the axon, but require additional space and energy
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 does the unequal distribution of ions cause?
The unequal distribution of ions on different sides of the membrane creates a charge difference called a membrane potential
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, which part of the neurone is more negative?
In a typical resting potential, the inside of the neuron is more negative relative to the outside (approximately –70 mV)
What type of process is the maintenance of a resting potential?
The maintenance of a resting potential is an active process (i.e. ATP dependent) that is controlled by sodium-potassium pumps
What is a sodium-potassium pump and what is its role?
The sodium-potassium pump is a transmembrane protein that actively exchanges sodium and potassium ions (antiport)
What amount of ions are exchanged in a sodium-potassium pump?
It expels 3 Na+ ions for every 2 K+ ions admitted (additionally, some K+ ions will then leak back out of the cell)
What gradient does the sodium-potassium channel create?
This creates an electrochemical gradient
What does the electrochemical gradient create in terms of cell potential?
the cell interior is relatively negative compared to the extracellular environment (as there are more positively charged ions outside of the cell and more negatively charged ions inside the cell)
What does the exchange of sodium and potassium require?
The exchange of sodium and potassium ions requires the hydrolysis of ATP (it is an energy-dependent process)
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 3 stages of action potentials?
Action potentials occur in three main stages: depolarization, repolarization and a refractory period
What is depolarisation?
Depolarisation refers to a sudden change in membrane potential – usually from a (relatively) negative to positive internal charge
- What occurs in response to a signal initiated at a dendrite?
(depolarisation)
In response to a signal initiated at a dendrite, sodium channels open within the membrane of the axon
- What does the opening of sodium channels?
As Na+ ions are more concentrated outside of the neuron, the opening of sodium channels causes a passive influx of sodium