Cell to cell communication

Question 1

Define autocrine

Answer 1

Communication within the same cell

Question 2

Define paracrine

Answer 2

Communication with neighbouring cells

Question 3

Define endocrine

Answer 3

Communication with distant cells

Question 4

Describe the electrical mechanism of communication

Answer 4

Changes in resting potential, propagated along cell, neighbour depolarisations

Question 5

Describe the chemical mechanism communication

Answer 5

Substances released act on target cells either via receptors or gap junctions

Question 6

Describe action potential phases

Answer 6

• Resting potential
• Initial depolarisation
• Main depolarisation
• Peak
• Repolarisation
• Hyperpolarisation

Question 7

Describe phase 0- resting potential

Answer 7

Negative due to fixed anions, Na+/K+ ATPase and selectively permeable membrane

Question 8

Describe phase 1 - initial depolarisation

Answer 8

• Cell bodies of neurons receive multiple signals- IPSPs and EPSPs
• Begins to reach threshold, ligand-gated channels linked to receptor opened by ligand binding
• Dendrites have synapses, charge enters, resting potential rises in small depolarisations

Question 9

Describe phase 2- main depolarisation

Answer 9

• Threshold potential, all or nothing principle (due to voltage-gated Na+ channels)
• Threshold around -55mV- when Na+ channels open- increased Na+ permeability

Question 10

Describe phase 3 -peak

Answer 10

Na+ entry continues until equilibrium potential of Na+ reached, however won’t reach 60mV- K+ efflux

Question 11

Describe phases 4 and 5- re/hyperpolarisation

Answer 11

• Driven by potassium efflux- membrane potential back to resting (Na+ channels close)
• Efflux continues to -90mV- EP of K
• No potassium gradient- channels close

Question 12

Describe refractory periods

Answer 12

• During repolarisation Na+ channels closed irrespective of stimulus- absolute refractory
• Hyperpolarisation- Na+ channels active- harder to reach threshold- relative refractory
• Refractory periods keep transmission going forward

Question 13

What affects the speed of conduction?

Answer 13

• Transmission of signal dependent on size and myelination

- Larger fibres are usually myelinated

Question 14

Describe saltatory conduction

Answer 14

• Large myelinated nerves

- Conduction jumps between node of Ranvier gaps

Question 15

Describe the general function of synapses

Answer 15

• Allow communication
• Only at end so they ensure unidirectionality
• Can have stimulatory or inhibitory neurotransmitters

Question 16

Describe how cellular communication occurs

Answer 16

• Cells receive impulses via receptors
• Neurotransmitters import their response
• Target tissue contains receptors for neurotransmitters

Question 17

Describe the ionotropic receptor type

Answer 17

• Ligand-gated ion channel, e.g. nicotinic cholinergic

Question 18

Describe the metabotropic receptor type

Answer 18

Linked to enzyme cascade (e.g. GPCR)

Question 19

Describe the intracellular receptor type

Answer 19

Control transcriptional and translational for mainly steroid hormones

Question 20

Describe affinity and efficacy

Answer 20

• Ligands have both- identification of subtypes
• Physiological antagonism
• > 2 different ligands acting at different receptors and having opposing effects

Question 21

Describe the receptor action involving acetylcholine

Answer 21

• Nicotinic receptor- ionotropic, depolarisation

- Muscarinic receptor- metabotropic, various (GPCR)

Question 22

Describe the receptor action involving GABA (gamma-aminobutyric acid)

Answer 22

• Type A receptors, inotropic chloride channels, brain

Question 23

Describe the receptor action of glutamate

Answer 23

• Various types, ionotropic Na/K channels

Question 24

Describe the receptor action involving noradrenaline

Answer 24

• Alpha/beta adrenoreceptors, metabotropic, various

Question 25

What happens when chloride ions enter a cell?

Answer 25

Membrane potential becomes more negative, action potential is less likely

Question 26

What are excitatory and inhibitory inputs?

Answer 26

- Dendrites receive info from multiple other neurons (come excitatory and some inhibitory) - Generation of AP in post-synaptic neuron depends on summation of responses

Question 27

What are EPSPs?

Answer 27

- Excitatory post-synaptic potentials - Some neurotransmitters open ion channels- depolarisation (ACh + glutamate- Na+) - Increase potential toward threshold- anything that depolarises is excitatory

Question 28

What are IPSPs?

Answer 28

- Some neurotransmitters open ion channels- hyperpolarisation- Cl channels activated by GABA - Decreased resting potential further from threshold

Question 29

What is summation?

Answer 29

- Inputs added for overall change in potential - Threshold needs more EPSPs and less IPSPs - Temporal or spatial

Question 30

Describe temporal summation

Answer 30

- Related to time, summation of multiple EPSPs from the same neuron

Question 31

Describe spatial summation

Answer 31

- Related to space, summation of 2 or more EPSPs from different neurons simultaneously

Question 32

Describe electrical signalling

Answer 32

- Nerves conduct electrically down axon (signalling still chemical) - Electrical coupling does exist between adjacent cells via gap junctions - Gap functions allow rapid ion movement by neighbouring cells - Allows spread of electrical communication and rapid movement of change in potential