HUBS 191 Lecture 18

Question 1

can neurons be both pre-synaptic and post-synaptic at the same time

Answer 1

yes

Question 2

what are the three types of gated ion channels

Answer 2

chemical, mechanical and voltage

Question 3

how do chemically gated ion channels function

Answer 3

they are opened by a chemical stimulus (neurotransmitter) which binds to the ion channel. the channel then changes shape and ion cross the membrane driven by their electrochemical gradient. the neurotransmitter unbinds, causing the channel to close

Question 4

how do voltage gated ion channels function

Answer 4

when the membrane is depolarised to threshold voltage (-60mV) the channel changes shape and the ions are driven by their electrochemical gradient

Question 5

what are the three states that voltage gated ion channels can be in

Answer 5

closed, open and inactive

Question 6

how do mechanically gated ion channels function

Answer 6

these channels are opened by a stretching or deformation of the membrane. a mechanical stimulus causes the deformation of the membrane which stimulates the channel to change shape. ions cross the membrane driven by their electrochemical gradient. when the membrane returns to the original shape the channel closes

Question 7

what types of channels are found on the dendrites and cell body

Answer 7

chemically gated Na+ and Cl- (K+ too) channels

Question 8

what types of channels are found on the axon hillock of a neuron

Answer 8

voltage gated Na+ and K+ channels

Question 9

what types of channels are found on the axon of a neuron

Answer 9

voltage gated Na+ and K+ channels

Question 10

what types of channels are found on the axon terminals of a neuron

Answer 10

voltage gated Ca2+ channels

Question 11

at rest is the intercellular space negatively or positively charged

Answer 11

negatively charged because most proteins are negatively charged

Question 12

what ions are concentrated on the outside of the cell at rest

Answer 12

chlorine and sodium

Question 13

what ion is concentrated on the inside of the cell at rest

Answer 13

potassium

Question 14

what is the resting membrane potential

Answer 14

-70mV

Question 15

what are local potentials (post synaptic potentials)

Answer 15

excitatory or inhibitory changes in voltage in a small location (localised area) somewhere on the dendritic/cell body membrane of a post-synaptic cell

Question 16

when do excitatory post-synaptic potentials (EPSPs) form

Answer 16

when a presynaptic neurotransmitter releases excitatory neurotransmitter (ACh)

Question 17

what happens during a EPSP

Answer 17

when neurotransmitter binds, it opens chemically gated Na+ channels (Na because it is an excitatory neurotransmitter). Na+ enters the post-synaptic cell, causing depolarisation (membrane becomes more positive)

Question 18

what happens when the stimulus is removed during a EPSP

Answer 18

excess sodium ions are transported out of the cytosol

Question 19

when do inhibitory post-synaptic potentials (IPSPs) form

Answer 19

when a pre-synaptic neuron releases an inhibitory neurotransmitter (i.e GABA)

Question 20

what happens during an IPSP

Answer 20

when the neurotransmitter binds, it opens chemically gated K+ or Cl- channels. K+ exits or Cl- enters the post-synaptic cell, causing hyper polarisation (membrane becomes more negative)

Question 21

why do we have inhibitory local potentials

Answer 21

because they allow us to adapt. to our environment and ignore certain sensory effects

Question 22

what is summation

Answer 22

when the axon hillock decides based of the excitatory or inhibitory local potentials what signals to send

Question 23

what are the two ways local potentials are summed

Answer 23

spatial summation - summed input from multiple pre-synaptic neurons
temporal summation - summed input from repeated firing of one pre-synaptic neuron - one neuron has more of an input

Question 24

what is the first step that occurs when firing an action potential

Answer 24

voltage gated (VG) Na+ channels open when membrane depolarises to -60mV

Question 25

what is the second step that occurs when firing an action potential

Answer 25

massive influx of Na+ causes rapid depolarisation phase of the action potential - this increases the voltage of the cell

Question 26

what is the third step that occurs when firing an action potential

Answer 26

VG Na+ channels inactivate (not close) so Na+ entry stops VG K+ channels open so K+ exits. K+ exiting causes the repolarization phase of the action potential

Question 27

what is the fourth step that occurs when firing an action potential

Answer 27

VG K+ channels begin to close, but close slowly. this permits excess K+ to exit, causing the hyper polarisation phase of the action potential. membrane potential goes as low as about -90mV

Question 28

what is the fifth (and final) step that occurs when firing an action potential

Answer 28

all the VG K+ channels close, the membrane returns to -70mV. we are ready for the next signalling event