Lecture 4 - the excitable cell Flashcards
What does the nervous system do?
- system of communication that allows an organism to react rapidly & modifiable to changes in its environment
What must neurones do?
- collect
- integrate
- output
information
Describe how sensory information is processed
sensory nerves detect information - travels to spinal cord - some send to brain - then sent to the motor neurones
How are does information need to travel to the spinal cord and back?
2m
How does the nervous system allow fast transmission?
- electrical activity provides a rapid, reliable (& flexible) mRNAs for neurons to receive, integrate & transmit signals
- chemical messengers (& receptors) between & within cells provide much more flexibility e.g. for inhibition
What is the speed of the nervous system?
- speed is approximately 45-50 meters per second
How can electrical properties of neurons and electrical signals be divided?
- action potentials
- graded potentials
Describe the properties of an action potential
- fixed size
- all or nothing signals - that travel along (propagate) the axon
Describe the properties of an graded potential
- variable size
- local signals not propagated over long distances
Describe the direction that action potentials travel
can pass either way along an axon, but tend to go one way (with important exceptions)
Describe the direction that graded potentials travel
can pass both ways along the neuronal membrane
How are action potentials coded?
coded by FREQUENCY as they are of a unit size
How are graded potentials coded?
by size & vary according to the strength of the stimulus
What is an absolute requirement for a functioning nervous system?
a negative membrane potential
Why do neurons have a negative resting potential?
inevitable consequence of:
- selectively permeable membrane
- unequal distribution of charged molecules/ions
- physical forces
Where does the selective permeability of the membrane come from?
- the membrane contains proteins within the membrane - the proteins are ion channels
- the pores in the membrane that allow only some of the ions to travel through
(channels confer selectivity)
(pumps assist unequal charge distribution)
Do channels carry out active or passive transport?
passive transport
Do pumps carry out active or passive transport?
active transport
What does the neuronal membrane separate?
electrically charged ions
How can ions cross the membrane?
only by way of protein channels and pumps, which can be highly selective for specific ions
What does movement of any ion through its channel depend on?
the concentration gradient and the difference in electrical potential across the membrane
What sets up the ionic concentration gradients found in neurons?
Ion pumps:
- Na+/K+ ATPase
- Ca2+ pumps (not just in the plasma membrane)
What would occur without ion pumps?
the resting membrane potential wouldn’t exist and the brain wouldn’t function - but the effect of pump inhibitors take some time to work
How do ionic gradients influence membrane potential?
by determining Equilibrium Potentials Eions
What is Eion?
the membrane potential that would be achieved in a neuron, if the membrane were selectively permeable to that ion
What is the equilibrium?
electrostatic forces = diffusional forces (Vm = Ek)
At rest, what is the neuronal membrane very permeable to?
K+ (it is slightly permeable others)
At rest, the real membrane potential is close to what?
Diffusional forces (Ek)
What effect does increasing extracellular K+ have on membrane potential?
depolarise
Describe the properties of potassium channels
- 4 subunits
- only allows molecules of a certain size & charges
What equation is needed to calculate the real Vm for K+?
Goldman Equation
