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Essential Biology 06.5: Nerves, Hormones and Homeostasis

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1. Extend the organizational chart below to briefly describe the components of the central and peripheral nervous systems.

Neurons are cells which can carry rapid electrical impulses. 2. Draw a simple diagram of a motor neuron (nerve cell), including:

Cell body, nucleus, dendrites, axon, terminal branches, motor end plates, myelin sheaths, Nodes of Ranvier and the direction of the nerve impulse.

3. The diagram below shows a typical reflex arc. Name the labeled structures and state the processes taking place at 1, 2 and 3.

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4. Define resting potential.

5. Define action potential.

6. Complete the diagram below to show why the resting potential of a neuron is negative.

7. Define depolarization.

8. Define repolarisation.

9. Complete the table below to compare action potentials and resting potentials:

Resting potential Action potential

Also known as… ____-polarisation ___- polarisation

Internal potential is… (positive/ negative)

Sodium ions are…




Potassium ions are…

Membrane proteins used(voltage-gated sodium channels or sodium potassium pump?)

10. Annotate the graph below to explain what is happening in each stage of an action potential (AP). Include the movement of ions into and out of the cell and how this occurs.

11. What is the importance of the refractory period in propagation of an action potential?

12. What is the importance of these membrane proteins in nerve impulses?

Sodium-potassium pump

Sodium channel

Potassium channel

13. In a nerve impulse, what happens at the site following the highest point of the action potential?




A. Voltage-gated sodium ion channels open and Na+ is pumped in.

B. Voltage-gated sodium ion channels open and Na+ diffuses out.

C. Voltage-gated potassium ion channels open and K+ is pumped out.

D. Voltage-gated potassium ion channels open and K+ diffuses out.14. Define synapse.

When an AP reaches the terminal end of a neuron, it is converted from an electrical signal to a chemical message for synaptic transmission.

15. What form does this ‘chemical message’ take?

16. Complete the summary of synaptic transmission below:

17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.17.

Neurotrasmitters are specific to their receptors. What does this mean?




18. Some drugs act as competitive inhibitors to neurotransmitters. What would be the effect of this?

19. What are the roles of the following components of the endocrine system?

Glands

Hormones

Target tissues

20. The endocrine system is responsible for hormone-mediated communication within the body. Which endocrine glands are mostly responsible for:

Control of blood sugar

Control of body temperature

Control of water levels in blood

Initiation of puberty

Production of sex cells

21. Draw a simple flow chart to show how the endocrine system functions based on stimulus, hormone secretion and negative feedback control.

22. Define homeostasis.




23. List five factors that are maintained through homeostasis.

24. Complete the flow chart below to show how the hypothalamus controls body temperature through hormones. What are the body’s responses?

25. The sense of taste is normally caused by the stimulation of chemoreceptors in the taste buds of the tongue. There are four main 'tastes': sweet, salty, bitter and sour. The tongue also has receptors for temperature. It is known that the taste of food can vary according to whether it is cold, warm or hot. Scientists discovered that just warming or cooling parts of the tongue, even when no food was present, also caused a sensation of taste.

Scientists experimented with a group of people. They gradually cooled the tips of their tongues and measured the intensity of the taste felt by each member of the group. The experiment was repeated, this time warming the tip of the tongue. The graphs show the average values for the group.




K ey: S a lty B itte r S w ee t S o u r

C o o lin g th e to n g u e tip

D ec re ase in te m p era tu re fro m 3 5 ºC In c rease in tem p era tu re fro m 2 0 ºC

m o d era te

w e ak

ju s td e te c tab le

Tast

e in

tens

ity fe

lt/ a

rbitr

ary

units

W a rm in g th e to n g u e tip

3 5 2 5 2 0 2 5 2 0 3 0 2 0 3 5 2 0 4 03 5 2 0 3 5 1 5 3 5 1 0 3 5 5

[Source: modified from Cruz and Green, Nature (2003) 403, page 889]

(a) Identify which taste was felt most strongly when the tip of the tongue was

(i) cooled............................................................................................................

(ii) warmed..........................................................................................................(1)

(b) Compare the effects on the taste of sweetness, of warming and cooling the tip of the tongue.

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................(2)

(c) It is important that such experiments use a population sample that is representative. Suggest two biological criteria the scientists would have used to select the people to be tested.

.........................................................................................................................................

.........................................................................................................................................(1)

(d) Explain whether cooling or warming the tip of the tongue has the greater effect on the sensation of taste.




.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................(2)

Continued…

The scientists discovered that there were two types of chemoreceptor in the tongue tip. They called these A and B. They tested these chemoreceptors using solutions of sucrose to find out the type of taste and the intensity felt. The results are shown in the bar chart.

Taste in te n sity fe lt/ a rb itra ry u n its

m o d era te

w eak

ju s t d e te c tab le

sw ee t d e tec ted so u r d e tec ted

K ey: A B

(e) Compare the effects of sucrose on the A and B chemoreceptors by giving two similarities and two differences.

Similarities........................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

.........................................................................................................................................

Differences.......................................................................................................................

.........................................................................................................................................




.........................................................................................................................................

.........................................................................................................................................(4)

(Total 10 marks)

26. Blood glucose levels are maintained by hormones produced in the pancreas. Complete the table to show glucoregulation.

High Blood Sugar Low Blood Sugar

The pancreas contains… ___________________ cells… ___________________ cells…

…which secrete…

… carried in blood to…. &

… causing conversion of..

… to …

Overall effect: Glucose removed from blood Glucose released into blood

27. Diabetes mellitus is a disease in which regulation of blood glucose is difficult. There are two types of diabetes (Type I and Type II)Distinguish between them in terms of action, age of onset and risk factors.

Type I: Type II:




28. How can we tell from this table that the patient has diabetes?

29. Distinguish between nerves and hormones.

Nerves Hormones

Route Direct from coordinator to effectorThrough: From: To:

Signal type Chemical

Time to take action longer

Duration of effects

30. In which part of the brain are nerve impulses converted to hormonal signals?

31. Complete the steps below to show how the nervous and endocrine systems work together to regulate body temperature.

Stimulus:

Sensory neurons:




Relay:

Effector:

Hormone 1:

Gland:

Target cells:

Effect: release of thyroid hormone

Target cells:

Effect:



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