Neurons

Question 1

The nervous system

Answer 1

1. Neurons are cells in neuronal tissues where they form interconnected neural networks
2. CNS - central nervous system
3. PNS - peripheral nervous system

Question 2

Neurone structure

Answer 2

1. each neuron has similar organelles as any other cell
2. nucleus containing dna
3. mitochondria
4. cytoplasm
5. cell membrane is special

Question 3

natures electric potential

Answer 3

1. 1780 - bioelectricity discovered by physicians in frog muscles
2. scientific controversy - theory was contested by physicist arguing only metal produces electricity

Question 4

electrophysiology

Answer 4

1. electrodes make contact with non metallic parts of an electric circuit in living specimen or cells
2. recording electrode is placed inside or outside the neuron, or further away on the body surface
3. ground electrode is placed in or on tissues at a further distance

Question 5

Giant squid axons

Answer 5

Large neurones from giant squid put into water or any liquid and measure with electrodes the difference in voltage

Question 6

Resting potential

Answer 6

1. zero potential difference when two electrodes are in water bath
2. when the electrode enters the axon it records a negative potential

Question 7

action potential

Answer 7

1. current pulses flowing inward across the membrane capacitance hyperpolarise the membrane
2. small pulses of outward current elicit depolarisations that are nearly the mirror image of the corresponding hyperpolarisations
3. but as a critical voltage threshold is reached the depolarisation triggers an action potential
4. a larger pulse of depolarising current produces an identical action potential to that produced by a smaller pulse but a prolonged suprathreshold current elicits a train of action potentials

Question 8

all or nothing response

Answer 8

1. the stronger the above-threshold excitation, the higher the frequency of action potentials
2. higher frequency , not more energy

Question 9

polarised cell membrane

Answer 9

movement of sodium, potassium, chlorine and calcium ions through ion channels

Question 10

three classes of ion channels

Answer 10

1. ion channels differ in their selectivity for certain types of ions
2. leak channels allow a specific ion type to freely diffuse
3. ion channels remain closed until activation for a brief period of time either by electrical signals, drugs and neurotransmitters or mechanical signal
4. ion pumps actively transport ions from one side of the membrane to the other

Question 11

chemical concentration gradients

Answer 11

1. particles move from areas of high concentration to areas of low concentration
2. down the concentration gradient 3. neural membrane is semi-permeable, brief opening of membrane lets some ions through

Question 12

electrochemical forces

Answer 12

1. ions are in constant motion
2. closed channels - ions accumulate near the membrane due to the electrostatic forces
3. open channels - ions cross the membrane at a rate and in a direction that depends on both forces (diffusion and electrostatic)

Question 13

when the neuron generates a signal

Answer 13

1. ion channels in the membrane briefly open
2. depending on the type of channel that opens, the respective ions are pushed into the cell or leave the cell

Question 14

hodgkin-huxley model

Answer 14

1. resting potential - voltage gated Na+ and K= channels are closed, below -55mV threshold, both depolarisation and hyperpolarisation can take place
2. depolarisation - changes in ligand-gated or mechanical gated ion channels, action potential crosses the -55mV threshold, depolarisation caused by the opening of the voltage gated Na+ ion channels
3. Overshoot - the membrane potential becomes positive as more and more Na+ flow into the cell
4. Repolarisation - Na+ ion channels become inactivated and close, while K+ channels open leading to a reduction of positive charge insife the cell
5. undershoot - K+ ions flow out of the cell through the open K+ channels - hyperpolarisation
6. recovery - refractory period during which all channels are closed and membrane potential returns to resting value

Question 15

unidirectional transmission of the action potential

Answer 15

1. due to the refractory period, the voltage gated Na+ channels can open only on one side
2. the action potential travels along the axon away towards the output zone