cell signalling

Question 1

nerve impulse

Answer 1

• wave of altered charge across nerve cell membrane that sweeps along axon
• depolarisation/action potential

Question 2

action potential

Answer 2

• at rest, there is a difference in ion concentration between inside and outside of cell
• maintained by ion pumps in plasma membrane
• electrical potential difference across neuron plasma membrane approx -70mV

Question 3

sodium ions and potassium ions

Answer 3

when nerve cell is stimulated, action potential is generated
Na+ ions channel open: positively charged Na+ ions flow into cell
K+ ion channels open in response to the depolarisation
Na+ channels close
Positively charged K+ ions flow out of the cell
K+ channels close
Na+ channels rest
return to rest

Question 4

action potential moves along axon

Answer 4

one way travel: refractory period = time immediately following AP when new AP cannot be initiated in same area of membrane

Question 5

how does an action potential start, dendrites

Answer 5

multiple inputs from multiple dendrites
- excitatory pre-synaptic potentials (EPSPs)
- inhibitory pre-synaptic potentials (IPSPs)
- vary in magnitude

Question 6

how does an action potential start, summation

Answer 6

summation of changes in membrane potential.
- EPSP increases chance of AP initiation, IPSP decreases chance.
- if overall membrane potential reaches threshold voltage, Na+ channels open and AP initiated

Question 7

summation

Answer 7

spatial summation- summation of inputs from different areas of cell eg. from different dendrites
temporal summation- input occurs multiple times from the same are/dendrite
- repeated inputs in short time period- summation
- summation -> APs generated more or less frequently

Question 8

AP magnitude

Answer 8

• is always the same
• if total voltage at axon hillock exceeds the threshold potential, an AP is generated and sent along the axon. if not, no AP is generated
• AP frequency, not magnitude, can vary
• signal intensity is encoded by AP frequency

Question 9

signalling between nerve cells

Answer 9

• neural pathways can contain multiple nerve cells eg. reflex arc
• signals passes along axon of each nerve cell as action potential
• when AP reaches end of neuron, it must cross synapse (GAP)-> AP set up in next neuron

Question 10

neurotransmitter

Answer 10

• chemical signals: transmit signals across synapse
• released when AP reaches pre-synaptic neuron termini
• bind to receptors on dendrites of post-synaptic neuron

Question 11

neurotranmitter function

Answer 11

• different NT’s associated with different nervous system function (eg. memory, movement, emotions)
• differs locations in nervous system
• excitatory or inhibitory: promote or inhibit formation of AP in receiving neuron
• many drugs act on neurotransmitter signalling

Question 12

amino acids and derivatives

Answer 12

• glutamate: main excitatory neurotransmitter in CNS
• GABA: main inhibitory neurotransmitter in CNS

Question 13

catecholamines (monoamines)

Answer 13

• derived from Tyr
• dopamine/serotonin

Question 14

acetylcholine

Answer 14

-derived from choline
- neuromuscular junction

Question 15

peptides

Answer 15

eg substance P, endorphins

Question 16

GABA binding to GABA-A receptors

Answer 16

• GABA-A receptors is an ion channel receptor ‘ionotropic’
• binding of ligand GABA to receptor causes conformational change that opens ion channel ‘ligand-gated’
• ion moves through channel along concentration gradient

Question 17

GABA-A receptor

Answer 17

-chloride ion channel
- channel opened by GABA binding, Cl- flows into cell, hyper polarisation -> harder to reach threshold voltage for AP formation in post-synaptic cell
- benzodiazepines, ethanol, some anaesthetics, potentiate GABA activation of GABA-AR, so more inhibition of APs- sedative action

Question 18

acetylcholine at neuromuscular junction

Answer 18

NMJ = junction between motor neuron (nerve that controls muscle) and muscle cell
-similar to synapse between 2 neurons

Question 19

acetylcholine “switching off’

Answer 19

-nAChR- sodium ion channel receptor
ACh binding allows Na+ entry
Na+ influx- depolarisation of muscle cell membrane
depolarisation initiates contraction
acetylcholinesterase I cleft removes ACh “switches off”

Question 20

myasthenia gravis

Answer 20

muscle weakness
-autoimmune antibodies attack ACh receptors at neuromuscular junction
- treatment: AChE inhibitors used to enhance NMJ transmission

Question 21

electrical signalling via gap junctions

Answer 21

connexion proteins form connection with channel
- ions carry charge from one cell to another (diffusion)

Question 22

cardiac myocytes

Answer 22

• heartbeat- electrical impulse travelling across heart tissue causes contraction of cardiac muscle
• specialised cells with neutron-like properties spread throughout heart eg. purkinje fibres
• atria first, then ventricles, ion flow between adjacent muscle cells (myocytes)