F4 Neurotransmission

Question 1

what is meant by ‘excitability’?

Answer 1

• the ability to dynamically alter the voltage across the plasma membrane (i.e. the electrochemical gradient)

Question 2

what is the range for resting membrane potential?

Answer 2

-50 to -90 mV

Question 3

during resting potential, is the inside or outside of the cell more negative?

Answer 3

inside is more negative

Question 4

describe the distributions of sodium, chloride, calcium and potassium ions in resting potential

Answer 4

• more sodium and chloride ions outside the cell rather than inside
• more potassium ions inside cells rather than outside
• minimal calcium ions inside and outside

Question 5

what happens when an ion channel is activated?

Answer 5

• membrane becomes porous to charged molecules
• causes rapid movement along electrochemical gradient

Question 6

the concentration of what ion is strictly regulated and how do they typically move?

Answer 6

• calcium ions
• they typically flow into the cell from the exterior after calcium ion channels are activated to open

Question 7

what happens to the charge of the inside of the cell during depolarisation?

Answer 7

becomes more positive

Question 8

what does membrane depolarisation cause in regards to the ion channel protein and what does this lead to?

Answer 8

• structural rearrangements
• leads to channel opening and allowing ions to flow into cell

Question 9

in terms of charges, explain how voltage-gated channels open and close

Answer 9

• paddle of channel protein has positive residues
• when inside of cell is negative, the positive paddle is attracted to the inside of the cell so the channel stays closed
• inside of cell becoming positive causes paddle to repel and channel to open

Question 10

describe membrane DEpolarisation

Answer 10

• depolarisation open sodium ion channels fast
• sodium ions flood into cell causing further depolarisation

Question 11

describe membrane REpolarisation

Answer 11

(after sodium floods into cell)

• potassium ion channels open (slower than sodium channels)
• potassium ions flood out of cell
• sodium ion channels inactivate
• membrane is repolarised (due to lots of positive ions moving back out of cell)

Question 12

describe the process of establishing resting potential after depolarisation and repolarisation

Answer 12

• potassium channels inactivate but too many will have left so the inside of the cell is too negatively charged
• ion pumps and transporters use energy from ATP or counter-transport to reestablish membrane conditions (3 sodium ions out, 2 potassium ions in)

Question 13

what does saltatory conduction help to do?

Answer 13

increase speed and reliability of conduction

Question 14

what types of cells coat axons in insulating myelin sheaths?

Answer 14

glial cells / oligodendrocytes

Question 15

describe saltatory conduction

Answer 15

• action potentials ‘jump’ between nodes of ranvier where ion channels are clustered
• sodium ion channels open, sodium ions move into the cell, cell becomes more positive and current flows through the axon to the next node
• current gets to next node and pushes the next node to threshold potential to open the sodium ion channels here too
• action potential is generated here too and the cycle repeats

Question 16

why can action potential not back flow during saltatory conduction?

Answer 16

• sodium channels inactivate for a short period of time after opening

Question 17

what is a synapse?

Answer 17

neuron to neuron junction in the ganglion

Question 18

how is neurotransmitter made?

Answer 18

• synthetic enzymes make transmitter from inactive precursors
• they convert precursor into neurotransmitter
• vesicles will store the neurotransmitter in the active zone until their release is triggered

Question 19

where is transmitter transported into vesicles and how?

Answer 19

• in the presynaptic nerve terminal
• vesicular transporters use active transport to concentrate transmitter into vesicles

Question 20

describe how vesicles are released from the presynaptic membrane

Answer 20

• action potential depolarises the terminal
• voltage-gated calcium channels open and calcium flows into presynaptic knob
• calcium triggers vesicle fusion with presynaptic membrane are NT is released into synaptic cleft

Question 21

describe how action potential is initiated in postsynaptic knob after NT is released to synaptic cleft

Answer 21

• NT binds to nicotinic receptors on postsynaptic cell and they’re activated
• ligand-gated sodium ion channels open and action potential is initiated when sodium ions influx into postsynaptic knob

Question 22

what needs to bind to the receptor for a ligand-gated ion channel to open?

Answer 22

an agonist

Question 23

what are varicosities?

Answer 23

• swellings formed by nerve terminals of autonomic projections in almost all tissues
• often the sites of synapses
• lie close to target cells and receptors

Question 24

describe the release of NT at autonomic terminals

Answer 24

• boutons release onto smooth muscle, endocrine cells etc.
• activate GPCRs
• causes activation or inhibition of second messenger pathways

Question 25

what does noradrenaline act on?

Answer 25

alpha and beta adrenoceptors

Question 26

what does acetylcholine act on?

Answer 26

muscarinic receptors

Question 27

what are the 3 types of muscarnic receptors and what are their effects when ACh binds?

Answer 27

• M1, M2, M3
• M1 and M3 lead to smooth muscle contraction when ACh binds
• M2 leads to cardiac muscle relaxation when ACh binds