Coordination

Question 1

What are the 2 main forms of coordination in mammals?

Answer 1

• nervous

- hormonal

Question 2

How is coordination via the hormonal system different to that of the nervous system?

Answer 2

• response is slower, and longer lasting
• communication is by hormones
• transmission is by blood stream
• hormones travel round whole body but only target organs respond

Question 3

What are chemical mediators?

Answer 3

Chemicals released by damaged cells that have an effect on nearby cells

Question 4

What does histamine do?

Answer 4

• is released following injury or in response to allergen

- causes dilation of arterioles and increased permeability of capillaries (redness and swelling)

Question 5

What are the features of plant growth factors?

Answer 5

• are made by cells throughout plant
• only small amounts are made
• exert influence by affecting growth
• transported in transpiration stream in xylem

Question 6

Define Schwann cells

Answer 6

• cells that surround the axon, protecting it and providing insulation

Question 7

Define myelin sheath

Answer 7

Made up of membranes of Schwann cells, rich in lipid myelin

Question 8

Define nerve impulse

Answer 8

A self propagated wave of electrical energy that travels down the axon

Question 9

Describe how the inside of the axon is negative with regards to outside at resting potential

Answer 9

• 3 Na+ are actively transported out for every 2 K+ actively transported in (by sodium-potassium pump)
• some K+ gates are open, Na+ gates are closed

Question 10

What is depolarisation?

Answer 10

When a stimulus causes a temporary reversal of charges, and the negative charge of axon becomes positive (-70mV to +40mV)

Question 11

What must an action potential do in order for a response to be created?

Answer 11

Reach threshold value

Question 12

What is hyperpolarisation?

Answer 12

When outward diffusion of K+ out of axon after action potential overshoots to -90mV. Gates close and sodium-potassium pump re-establishes resting potential

Question 13

Explain why the passage of an action potential is faster in a myelinated neurone than unmyelinated

Answer 13

• myelin sheath provides electrical insulation

- action potentials can only occur at nodes of ranvier; they ‘jump’ between nodes of ranvier (saltatory conduction)

Question 14

How does an action potential ‘move’ down the axon?

Answer 14

• as 1 region of membrane becomes depolarised, this acts as a stimulus for the next region to depolarise

Question 15

How does temperature affect the speed of an action potential?

Answer 15

• higher temp, means faster rate of diffusion of Na+, faster nerve impulse
• energy for active transport is from respiration, which (like the sodium-potassium pump) is controlled by enzymes, which denature is temp increases too much

Question 16

What is the purpose of the refractory period?

Answer 16

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