L4 The Excitable Cell Flashcards
What does the nervous system do ?
System of communication that allows an organism to react rapidly and modifiably to changes in its environment
What are the roles of neurones?
Collect
Integrate
Output
What evolved properties do neurons have that allow them travel long distances quickly and transmit electrical signals?
Excitable membranes
Explain the reflex arc
1) Receptor detects a stimulus
2) Sensory neuron: Neuron transmits sensory information from receptor towards CNS
3) Integration centre: A point of connection between the sensory and motor neurons
4) Motor neuron: A neuron that carries the response signal from integration centre to the effector
5) Effector: A muscle or gland carries out response
What provides more flexibility for inhibition within the cells of the nervous system?
Chemical messengers and receptors between cells
What are the electrical signals divided into?
- Action potentials: fixed size, all-or-nothing signals that travel along (propagate) the axon
- Graded potentials: Variable size, local signals not propagated over long distances
What is the difference in terms of direction between the action and graded potential?
Action potentials can pass either way along an axon, but tend to go one way
Graded potentials pass both ways along the neuronal membrane
Is positive or a negative Vm a requirement for the nervous system?
A negative Vm is an absolute requirement for a functioning nervous system
When is a neuron said to be at rest?
When a neuron is not generating any types of impulse like action potential and graded potential.
What is the charge of a ‘resting’ neuron?
Between -65 and 90mV
Why do neurons have a resting potential?
The resting potential is essential for neurons to function properly.
It allows them to be excitable, generate electrical signals, and communicate with other cells
How are graded potentials coded?
They are coded by size and vary according to the strength of the stimulus
How is the membrane selective and unequal concentration of ions?
Channels confer selectivity
Pumps assist unequal charge distribution
What is the functioning of the nervous system critically dependent on?
The functioning of the nervous system is critically dependent on the flow of ions across neuronal membranes
What is the role of the lipid bilayer?
The lipid bilayer provides a barrier to diffusion, so that we can end up with different concentrations of ions on either side of the membrane….ie. We have a ‘CONCENTRATION GRADIENT.
What two forces control the movement of ions in aqueous solution ?
Diffusion and electrical field
How does an electrical field control the movement of ions in aqueous solution ?
Opposite charges attract and similar charges repel
Give me two examples of important ion pumps
- Na+/K+ ATPase
- Ca2+ pumps
Why are ion pumps important?
Ion pumps are important because without them, the resting membrane potential would not exist and the brain would not function due to no unequal concentration of ions
What is the equilibrium potential of potassium?
-80mV
What is nernst equation used for in a excitatory cell?
Used to calculate the equillibrium potential for an ion.
What is the equillibrium potential of Na+, Ca2+ and Cl-?
Na+ = 62mV
Ca2+ = 123mV
Cl- = -65 mV
What is the Nernst equation?
E(ion) = 2.303 ((RT/zF) . Log ([ion]o/[ ion]i))
What does increasing extracellular K+ cause to the membrane potetial?
Causes depolarization.
What’s the difference between the Nernst equation and the Goldman equation?
Nernst equation- Calculates the equilibrium potential for a single ion across a membrane
Goldman equation: Calculates the membrane potential considering the contributions of multiple ions
What does Vm stans for?
Membrane velocity
How are action potentials coded?
APs Are coded by frequency as they are of a unit size
At rest, is the membrane highly permeable to K+ or Na+? And why?
At rest, the membrane is highly permeable to K+ because the cell membrane has more potassium leak channels which means these channels are always open allowing potassium to flow out of cell making inside of cell more negative
