PED1003/L10 Signalling in SNS

Question 1

Why are ions unevenly distributed across membranes?

Answer 1

Chemical force (conc. gradient) is in competition with electrical force (ionic gradient)
Creates electrochemical gradient

Question 2

Describe transfer of ions during resting membrane potential. (3)

Answer 2

Membrane impermeable to Na+
Na+ pumped out by Na+/K+ ATPase
2 K+ in for 3 Na+ out

Question 3

Describe movement of Cl- across a membrane. (3)

Answer 3

Membrane partially permeable to Cl-
Move down concentration gradient into cell
Forced by ionic gradient outside of cell

Question 4

Describe concentrations of ions during resting membrane potential. (3)

Answer 4

Na+ & Cl- concentrated outside
K+ & A- concentrated inside
Inside negative to outside (-60 to -90mV)

Question 5

Describe movement of Na+ ions during depolarisation. (3)

Answer 5

VG Na+ channels open at -55mV
Na+ floods into cell
Membrane potential rises

Question 6

Describe movement of Na+ ions during the repolarisation phase.

Answer 6

VG Na+ channels inactivate
Na+ ions pumped out by Na+/K+ ATPase

Question 7

Describe movement of K+ ions during the repolarisation phase. (3)

Answer 7

Slow opening of VG K+ channels
K+ pours of out cell
Reduced membrane potential

Question 8

Describe why hyperpolarisation occurs. (3)

Answer 8

K+ channels close slowly
Permeability to K+ greater than at rest
K+ continues to leave cell

Question 9

Describe the membrane structure of the axon hillock.

Answer 9

Large number of voltage-gated Na+ channels for AP initiation

Question 10

Why does the action potential only travel in one direction?

Answer 10

Refractory period
Inactivation of VG Na+ channels

Question 11

Name 2 catecholamine neurotransmitters.

Answer 11

Noradrenaline
Dopamine

Question 12

Give 2 amino acid neurotransmitters.

Answer 12

Glutamate
GABA

Question 13

Describe the synthesis of neurotransmitters.

Answer 13

Synthesised from precursors by action of enzymes

Question 14

Describe storage of neurotransmitters. (2)

Answer 14

In vesicles ready for release
Protected from metabolic enzymes

Question 15

Describe release of neurotransmitter. (3)

Answer 15

Depolarisation of terminal causes Ca2+-dependent exocytosis
VG Ca2+ channels open
Vesicles fuse with presynaptic membrane and empty into synaptic cleft

Question 16

Describe reuptake of monoamine and amino acid neurotransmitters.

Answer 16

High affinity reuptake removes neurotransmitter from synaptic cleft

Question 17

Describe reuptake of acetylcholine.

Answer 17

Extraneuronal metabolism inactivated transmitter
Choline is recycled

Question 18

Describe the structure of ligand-gated ion channels. (2)

Answer 18

5 subunits
Receptor with binding site linked directly to ion channel