L5.2 Intercellular Communication

Question 1

what are the types of extracellular messengers?

Answer 1

1. paracrines: short-range chemical messengers; exert effect only on neighbouring cells in immediate environment of secretion site
2. neurotransmitters: short-range chemical messengers; secreted by neurons in response to action potentials; act locally on neurons, muscle or glands
3. hormones: long-range messengers; secreted into the blood by endocrine glands; exert effect on target cells some distance away from release site
4. neurohormones: hormones released into the blood neurons; distributed through blood to distant target cells

Question 2

explain cellular receptors

Answer 2

• target cells detect a signal when the extracellular messenger binds to a receptor
• extracellular messengers have a complementary shape to a specific receptor : a cell can only receive the message if it has the ‘right’ receptor
• the receptor changes shapes and becomes activated when a messenger has bound
• receptors can be in the cell membrane or inside the cell

Question 3

explain cellular receptors

Answer 3

• target cells detect a signal when the extracellular messenger binds to a receptor
• extracellular messengers have a complementary shape to a specific receptor : a cell can only receive the message if it has the ‘right’ receptor
• the receptor changes shapes and becomes activated when a messenger has bound
• receptors can be in the cell membrane or inside the cell

Question 4

explain cellular receptors

Answer 4

• target cells detect a signal when the extracellular messenger binds to a receptor
• extracellular messengers have a complementary shape to a specific receptor : a cell can only receive the message if it has the ‘right’ receptor
• the receptor changes shapes and becomes activated when a messenger has bound
• receptors can be in the cell membrane or inside the cell

Question 5

explain receptors in the plasma membrane

Answer 5

• most extracellular messengers bind to receptors in the cell membrane : large or hydrophilic messengers
• these messengers cause an effect on the cell through three mechanisms:
  1. opening/closing chemically gated receptor channels
  2. activating receptor enzymes
  3. activating second messenger pathways through G-protein-coupled receptors

Question 6

explain chemically gated receptor channels

Answer 6

1. extracellular messenger binds to receptors
2. binding of messenger leads to opening of channel
3. ions enter
4. ion entry brings about desired response (through multiple differing steps)
5. cellular response

Question 7

explain signal transduction

Answer 7

• the process by which incoming signals are conveyed to the target cell’s interior
• usually a cascade of protein activation inside the cell

Question 8

explain signal transduction pathways

Answer 8

extracellular messenger binds to receptor activates intracellular signal molecules alters designated proteins creates cellular response

Question 9

see notes for receptor enzymes, g-protein-coupled receptors and intracellular receptors

Answer 9

see notes for receptor enzymes, g-protein-coupled receptors and intracellular receptors

Question 10

nervous system consists of ________ which secrete _________

Answer 10

nervous system consists of NEURONS (AND SUPPORTING CELLS) which secrete NEUROTRANSMITTERS

Question 11

endocrine system consists of ________ which secrete _________

Answer 11

endocrine system consists of ENDOCRINE GLANDS which secrete HORMONES

Question 12

compare the nervous system and endocrine system in relation to “the nervous system is ‘wired’ and the endocrine system is ‘wireless’”

Answer 12

• the nervous system is anatomically linked to the target cells
• endocrine glands are anatomically separated from the target cells

Question 13

compare the nervous system and endocrine system in relation to the type of chemical messenger

Answer 13

nervous: neurotransmitters
endocrine: hormones

Question 14

compare the nervous system and endocrine system in relation to distance of action of the chemical messenger

Answer 14

nervous: short distance (across synaptic cleft)
endocrine: long distance (into the blood)

Question 15

compare the nervous system and endocrine system in relation to the specificity of messenger

Answer 15

nervous: specificity depends on the closeness of neurons and target cells
endocrine: specificity depends on the presence of the target receptor

Question 16

compare the nervous system and endocrine system in relation to speed of response

Answer 16

nervous: rapid (milliseconds)
endocrine: slow (mins to hours)

Question 17

compare the nervous system and endocrine system in relation to duration of action

Answer 17

nervous: short (milliseconds)
endocrine: long (mins, days or hours)