Coordination

Question 1

What are the two main forms of coordination in mammals?

Answer 1

The nervous system and the hormonal system.

Question 2

Describe the coordination of the nervous system.

Answer 2

Uses nerve cells to pass electrical impulses along their length. They stimulate their target cells by secreting neurotransmitters directly onto them. -> rapid communication + responses produced are often short-lived and restricted to a localised region of the body

Question 3

Describe the coordination of the hormonal system.

Answer 3

Produces hormones that are transported in the blood plasma to their target cells, which they then stimulate. Results are slower, less specific form of communication between parts of an organism. Responses are often long-lasting and widespread.

Question 4

What are two examples of chemical mediators?

Answer 4

Histamine and prostaglandins

Question 5

Histamine

Answer 5

Stored in certain white blood cells and released following injury or in response to an allergen. Causes dilation of small arteries and arterioles and increased permeability of capillaries, leading to localised swelling, redness and itching.

Question 6

Prostaglandins

Answer 6

Found in cell membranes also cause dilation of small arteries and arterioles. Released following injury increases the permeability of capillaries. They also affect blood pressure and neurotransmitters -> pain sensation

Question 7

Features of plant growth factors

Answer 7

1. Exert their influence by affecting growth
2. Made by cells located throughout the plant
3. Some plant growth factors affect the tissues that release them rather than acting on a distant target organ

Question 8

What is an example of a plant growth factor?

Answer 8

Indoleacetic acid (IAA)

Question 9

Outline the control of tropisms by IAA in a plant shoot

Answer 9

1. Cells in the tip of the shoot produce IAA, which is then transported down the shoot
2. The IAA is initially transported to all sides as it begins to move down the shoot
3. Light causes the movement of IAA from the light side to the shaded side of the shoot
4. A greater conc. of IAA builds up on the shaded side of the shoot
5. As IAA causes elongation of cells and there is a greater conc. on shaded sides, cells on this side elongate more
6. The shaded side of the shoot grows faster, causing the shoot to bend towards the light

Question 10

Neurones

Answer 10

Specialised cells adapted to rapidly carrying nerve impulses from one part of the body to another

Question 11

What is a mammalian neurone made of?

Answer 11

A cell body, dendrons, an axon, Schwann cells, myelin sheath, nodes of Ranvier

Question 12

Cell body of a neurone

Answer 12

contains a nucleus and a large amounts of RER prod. neurotransmitters + proteins

Question 13

Dendrons

Answer 13

Small extensions of the cell body which subdivide into dendrites, carry nerve impulses towards cell body

Question 14

Axon

Answer 14

Single long fibre that carries nerve impulses away from cell body

Question 15

Schwann cells

Answer 15

Surround the axon, protecting it and providing insulation. Carry out phagocytosis + play a part in nerve regeneration. Wrap themselves around the axon many times, so that layers of their membranes build up around it.

Question 16

Myelin Sheath

Answer 16

Forms a covering to the axon and is made up of the membranes of the Schwann cells. Membranes are rich in a the lipid, myelin.

Question 17

Nodes of Ranvier

Answer 17

Gaps between adjacent Schwann cells were there is no myelin sheath.

Question 18

Sensory neurone

Answer 18

One dendron that carries the impulse towards the cell body and one axon that carries it away from cell body

Question 19

Motor neurone

Answer 19

Long axon and many short dendrites

Question 20

Intermediate neurones

Answer 20

Numerous short processes

Question 21

Outline the transition from a resting potential to an action potential

Answer 21

1. Resting potential some K+ voltage-gated channels are open but Na voltage gated channels are closed
2. Energy of stimulus causes some Na voltage-gated channels in axon membrane to open and => Na+ diffuses into the axon along electrochem. gradient. This triggers a reversal in p.d. across membrane
3. As Na+ diffuses into the axon, more sodium channels open causing an even greater influx of Na+ by diffusion
4. Once action potential of around +40mV is reached, voltage gates on Na+ channels close and voltage gates on K+ channels begin to open
5. With some K+ voltage-gated channels open, the electrical gradient that was preventing further outward movement of K+ ions is now reversed, causing more K+ channels to open. , repolarising the axon
6. The outward diffusion of K+ causes a temp. overshoot of the electrical gradient, with the inside of the axon being more negative than usual (hyperpolarisation). Gates on K+ channels now close and the activities of the Na-K pumps once again cause Na+ to be pumped out and K+ in. Axon is repolarised.

Question 22

Passage of an action potential along a myelinated axon

Answer 22

In myelinated axons, the fatty sheath of myelin around the axon acts as an electrical insulator, preventing action potential from forming. Action potentials occur at nodes of Ranvier. -> localised circuits arise between adjacent nodes of Ranvier -> saltatory conduction.

Question 23

Nerve impulse

Answer 23

transmission of the action potential along the axon of a neurone

Question 24

How does the diameter of the axon affect the speed at which an a.p. travels?

Answer 24

The greater the diameter of an axon, the faster the speed of conductance. This is due to less leakage of ions from a large axon, leakage makes membrane potentials harder to maintain.

Question 25

How does temperature affect the speed at which an a.p. travels?

Answer 25

rate of diffusion, respiration -> atp, atp-> enzymes in Na+ K+ pump and active transport

Question 26

What is the refractory period?

Answer 26

When it is impossible for a further action potential to be generated due to shut Na voltage-gated channels

Question 27

What 3 purposes does the refractory period serve?

Answer 27

1. Ensures that an a.p. is propagated in one direction only
2. It produces discrete impulses
3. It limits the number of action potentials

Question 28

What is the all or nothing principle?

Answer 28

Any stimulus, whatever strength, below the threshold value will fail to generate an a.p. and any above the threshold value will succeed in generating an a.p. no matter how much above the threshold value it will still only generate 1 a.p.

Question 29

How can an organism perceive the size of a stimulus?

Answer 29

1. the number of impulses passing in a given time

2. by having different neurones with different threshold values

Question 30

What is the importance of reflex actions?

Answer 30

1. Involuntary
2. Protect from harmful stimulus
3. Role in homeostasis
4. Posture/balance
5. Finding food

Question 31

Why are there more hormones than neurotransmitters?

Answer 31

Hormones reach all cells, NT’s are direct to target cell. Different hormones are specific to different target cells.

Question 32

Differences between a cholinergic synapse and neuromuscular junciton

Answer 32

1. Neurone to neurone and neurone to muscle
2. Action potential in neurone and no action potential in muscle/ sarcolemma
3. No summation in muscle
4. muscle response always excitatory (never inhibitory);
5. some neuromuscular junctions have different neurotransmitters

Question 33

Why is the rate of conduction of nerve impulse in myelinated neurones in mammals faster than in reptiles?

Answer 33

Higher body temperature so faster diffusion of ions