Neurons Flashcards
1
Q
What are the main functions of the nervous system?
A
- to monitor, regulate and coordinate inner systems and organs, release chemical messengers, change internal states, to mate and produce offspring
- to acquire and analyse information from environment and from inside body, make decisions
- to generate, coordinate and control motor patterns
2
Q
What major changes occur in the nervous system during evolution?
A
- the CNS appeared in animals that had evolved more complex body plans, elaborate movements, senses and reproductive systems
- cephalisation: formation of central ganglia and brains in 1 end of animal body
- dorsal cord in the vertebrate line of the animal kingdom
- ventral cord in the invertebrate line
3
Q
What role does the cell membrane hold?
A
- only few soluble and uncharged can pass any cell membrane, other molecules need channels and transporters to pass
- membrane is polarised and selectively permeable
- ion channels distributed along the neural membrane, movement of ions across neural membrane generates tiny localized bioelectric currents
4
Q
What are ion channels?
A
- most are made of 4 proteins that assemble themselves to produce central pore
- have selectivity filter that allow ions of particular type to pass
- each membrane contains different classes of ion channels
- nearly all channels open for brief period of time, minority of channels are always open (leak channels)
- pumps are always active to stabilise the concentrations of ions inside and outside neuron
5
Q
How do electrochemical driving forces act on the ions?
A
- ion concentration inside differs from the outside medium of the neuron
- concentration of Na+ and CI- ions are lower and K+ are higher inside cell in intracellular fluid (is the opposite in the extracellular fluid outside neuron)
- move to create equilibrium
- ions will move randomly unless strong chemical concentration gradient or electrostatic force of attraction/repulsion
- at membrane, direction of movement is mainly determined by electrochemical driving forces
6
Q
What do all neurons have?
A
- input zone: neurons collect and integrate information, from environment or other cells
- integration zone: where decision to produce neural signal is made
- conduction zone: where information can be transmitted over great distances
- ouput zone: where neuron transfers information to other cells
7
Q
What are microelectrode recordings of membrane potentials?
A
- reference electrode is placed further away in/on the body
- microelectrode is placed inside neuron and outside
- neuronal signals are measured as difference in potentials between wired electrodes by creating circuit that connects the electrodes with the intra- or extracellular fluids
8
Q
What is the resting potential?
A
- the membrane potential when no signals are transmitted (around -70mV)
- when ion channels are closed there’s always negative ions on the inside and positive ions on the outside accumulated along membrane due to electrochemical driving forces
9
Q
What are the 2 types of neural signals?
A
- graded potential
- action potential
10
Q
What are graded potentials?
A
- hyperpolarised when the membrane potential is more negative than resting potential
- stronger the stimulating current the stronger the graded potential
- is depolarised when membrane potential is more positive than resting potential
- generates in soma and dendrites
- travels towards integration zone
11
Q
What are action potentials?
A
- spike following depolarisation that crosses voltage threshold
- the stronger the above-threshold excitation is the higher the frequency of action potentials
- generated at integration zone
- travel along axon to axonal terminals
12
Q
What are the 3 classes of ion channels?
A
- gated ion channels: remain closed til activation for brief time, either by electrical signals or drugs and neurotransmitters
- ion pumps: actively transport ions from 1 side of membrane to other side against the concentration gradient (it’s costly)
- leak channels: allow specific ion type to freely diffuse
