15. Control & Co-ordination Qs

Question 1

Outline the roles of sensory receptor cells in the mammalian nervous system. [3m]

Answer 1

• detect/respond to change in stimulus
• eg. light, sound, touch, pressure, chemicals
• acts as transducers
• produce receptor POTENTIAL
• pass impulse to SENSORY neurone

Question 2

2 importance of refractory period in the transmission of action potentials

Answer 2

• limits maximum frequency of action potentials

- action potentials travel in 1 direction

Question 3

Eugenol affects the movement of sodium ions through the CSMs of sensory neurones.
Suggest and explain how the action of eugenol may reduce pain. [5m]

Answer 3

• reduced entry of Na+ into sensory neurone
• eugenol prevents opening of Na+ channels {b/c}
• reduced depolarisation of sensory neurone MEMBRANE
• receptor potential does not exceed threshold potential
• fewer action potentials/impulses
• impulses do not reach brain

Question 4

Suggest and explain how an inhibitor of acetylcholinesterase could work. [3m]

Answer 4

• Ach cannot bind to active site
• no enzyme-substrate complexes form
  in competitive inhibition,
• inhibitor complementary to active site
• binds to a.s. and blocks a.s.
  in non-competitive inhibition,
• inhibitor binds to allosteric site
• causes change to tertiary structure / active site

Question 5

Describe and explain the changes to the uterus during the menstrual cycle. [6m]

Answer 5

• fall in conc. of progesterone {due to degeneration of corpus luteum}
• endometrium breaks down
• menstruation occurs
• follicular cells secrete oestrogen
• oestrogen conc. increases
• oestrogen stimulates thickening & increase in blood vessels of endometrium
• corpus luteum secretes progesterone
• progesterone conc. increases
• progesterone maintains endometrium

Question 6

Name the cells of a human female that carry

i) FSH receptors
ii) LH receptors

Answer 6

i) Follicle cells

ii) Corpus luteal cells

Question 7

FSH and LH bind to different receptors in the CSM of their target cells. This binding leads to steroid synthesis by the target cells.

Describe what happens when FSH binds to its receptors on its target cells. [3m]

Answer 7

• (binding to a receptor) acts as a signal to the cells
• to start SYNTHESIS of hormone
• OESTROGEN secreted
• stimulates thickening of endometrium / inhibits FSH production

Question 8

A muscle can contract with force, but it cannot pull itself back to its original relaxed length.
With reference to the mechanism of muscle contraction, explain why. [2m]

Suggest how a contracted muscle can return to a relaxed state. [2m]

Answer 8

• myosin heads can only tilt in 1 direction
• myosin heads cannot pull actin the other way
• most skeletal muscles are arranged in antagonistic pairs
• contraction of an antagonist pulls on the muscle so sarcomeres lengthen
• actin slides past myosin to give a wider I band

Question 9

Venom, which contains bungarotoxin, acts at the neuromuscular junction, causing muscle paralysis (loss of muscle function).
Suggest how bungarotoxin may cause muscle paralysis. [4m]

Answer 9

• lower release of Ach by presynaptic neurone
• bind to receptors on sarcolemma
• prevent binding of Ach
• inhibit depolarisation of sarcolemma

Question 10

2 ways of reducing the effects of acetylcholinesterase inhibitors

Answer 10

1. add compound to degrade the inhibitor (and prevent it binding to the active site of acetylcholinesterase)
2. (use compound to) stimulate production of acetylcholinesterase