communication and homeostasis

7/28/2019 Communication and Homeostasis

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Communication and

Homeostasis

A2 Biology F214


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Why do multi cellular organisms needcommunication systems?

Organisms need todetect changes in theirexternal environment

eg: pressure on skin,light, sounds,temperature, chemicalsetc. The receptor cellsneed to signal thesechanges to the organismso it can respond andmaintain its safety.


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Cell Signalling: one cellreleases a chemicalthat is detected by

another cell. Thesecond cell mayrespond to thechemical signal in anyof a large number ofways depending onthe type of cell and thechemical stimulusrecieved.


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Cells signal using

hormones (theEndocrine system) that

travel in the bloodstream and are pickedup by their target cells.

The endocrine system

enables long-termresponses.


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Nerve impulses aretransmitted by neurone

networks acrosssynapses usingneurotransmitters. This

allows fast signalling

and responses torapidly changing

stimuli.


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Homeostasis

What does it

mean?

Write a definition and givesome examples


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Homeostasis

MonitoringControllingInternalconditionsTo keep themconstant (orwithin safe limits)

Despite externalchanges

Egs

temperature

blood glucose levels

blood salt concentration relative water potential of

blood, tissue fluid and cells,

pH

Blood pressure

CO2 levels


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Negative and Positive Feedback

Whats the difference?


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Negative Feedback

Can you complete this with some real

life examples?


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Stretch and challenge questions

Remember Stretch and challenge is aboutmaking synoptic links

You need to access information from previouswork and use it in your explanations in thismodule.

In the questions asked you need to useinformation from the sections on enzymesand natural selection.


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Homeostasis and Controlling BodyTemperature

Learning Outcomes

Describe thephysiologicaland behaviouralresponses that maintain a constant bodytemperature in Ectotherms and Endotherms.

In Endotherms refer to the role ofperipheraltemperature receptors, Hypothalamus andeffectors in the skin and muscles


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What is an Ectotherm?How does an Ectotherm control

its body temperature?

Write down as many different ways that you canthink of.

Complete the card sort to see how differentEctotherms deal with regulation of temperature


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Control of temperature

Ectotherms

Seek sun or shadedepending on outsidetemperature

Expose more or less bodysurface to sun

Alter body shape tochange surface area

Increase breathingmovements to evaporatemore water


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What is an Endotherm?How does an Endotherm

control its body temperature?

Write down as many different ways that youcan think of.


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Control of temperature

Endotherms Sweating Panting Piloerection Vasodilation

/vasoconstriction Metabolic rate in liver

Shivering Seek sun or shade Alter orientation of body Alter activity level


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Diagram toshow changesto skin surfaceblood vessels

in warm andcold

conditions.


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What are the Advantages and

Disadvantages of Endothermy

and Ectothermy?


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Sensory Receptors and Stimuli

Match the

stimulus, sense

and receptors inthe card sortactivity


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Sensory Receptors, Senses andStimuli

EyeRods and cones (light sensitive

cells)

Light intensity (rods)

and wavelength (cones)

NoseOlfactory cells lining inner

surface of nasal cavity

Presence of volatile

chemicals

Tongue

Taste buds in tongue, hard

palate, epiglottis and first part

of oesophagus

Presence of soluble

chemicals

SkinPacinian corpuscles (pressure

receptors)Pressure on skin

EarSound receptors in cochlea

(inner ear)Vibrations in air

MuscleProprioceptors (stretch

detectors)Length of muscle fibres


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Labelling Neurone DiagramsUse these terms to label the diagrams you have been given.

Axon - specialised to conduct the action potential away fromthe cell body Axon terminals release neurotransmitter to signal to other

cells Dendrites- extend from cell body and receive

neurotransmitter from axon terminals of other neurones Cell body- contains nucleus, mitochondria, ribosomes Axon Hillock - point at which the chemical signal received

may reach the threshold needed to produce an actionpotential

Myelin sheath-insulating fatty layer composed of Schwanncells

Nodes of Ranvier - Gaps between Schwann cells Dendron branch of neurone that conduct the action

potential towards the cell body


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Structureof

neurones


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Establishing the Resting Potential

At rest, the inside of a neuron'smembrane has a relatively negativecharge.

As the figure shows, a Na+ / K+ pumpin the cell membrane pumps 3 sodiumions out of the cell and 2 potassium

ions into it. However, because the cell membrane

is a bit leakier to potassium than it isto sodium, more potassium ions leakout of the cell, increasing the positivecharge outside.

There are also many organic anions(-ve charged) in the cytoplasm

As a result, the inside of themembrane builds up a net negativecharge relative to the outside. (-70mVis the resting potential, the cell is

polarised


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Sodium

Potassiumpump online tutorial

http://www.youtube.com/watch?v=bGJIvEb6x6w&feature=PlayList&p=80C4BB58745CB30E&index=19
http://www.youtube.com/watch?v=bGJIvEb6x6w&feature=PlayList&p=80C4BB58745CB30E&index=19http://www.youtube.com/watch?v=bGJIvEb6x6w&feature=PlayList&p=80C4BB58745CB30E&index=19http://www.youtube.com/watch?v=bGJIvEb6x6w&feature=PlayList&p=80C4BB58745CB30E&index=19http://www.youtube.com/watch?v=bGJIvEb6x6w&feature=PlayList&p=80C4BB58745CB30E&index=19http://www.youtube.com/watch?v=bGJIvEb6x6w&feature=PlayList&p=80C4BB58745CB30E&index=19http://www.youtube.com/watch?v=bGJIvEb6x6w&feature=PlayList&p=80C4BB58745CB30E&index=19


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All stimuli produce generator potentialsbut some dont cause a big enoughchange in p.d. to reach threshold

potential so no action potential isgenerated.


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You should be able to:

Describe and explain how an actionpotential is generated.Interpret graphs of the voltage

changes taking place during thegeneration and transmission of an

action potential.


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Reaching the threshold potential

Any stimulation of a receptor cell causessome of the sodium channels to open.

So some Na+ions diffuse down their

concentration gradient back into the cell This reduces the potential difference across

the membrane

If the reduction is big enough (ie reaches thethreshold potential) then voltage gatedchannels open


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Small stimuli dont cause a big enoughchange in p.d. to generate an actionpotential.

(P.d. doesnt reach generator potential.)


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Generating an Action Potential

Stimulation of the receptorcauses Na+ channels toopen. The bigger thestimulus the morechannels open.

Na+ ions diffuse into celllowering potentialdifference

This makes even morechannels open (positivefeedback)

When potential differencereaches threshold (-50mV)the voltage gated Na+

channels open


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Generating an Action Potential (2) As more Na ions flood in

the potential differenceacross the membranechanges to +40mV

Voltage gated K channels

open and Na channelsclose (2&3)

K ions diffuse out of cellrepolarising the cell (4)

So many ions diffuse outthat the cell ishyperpolarised (5)

The Na/K pump re-establishes the resting

potential (6)


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Local Current


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Transmission of Action Potentialsin myelinated neurones (Saltatory conduction)

AP at 1 causes Na ions to move into axon

Na ions diffuse to areas ofve charge further down axon towards 2

Voltage gated Na channels are only present at Nodes of Ranvier So new AP starts at 3 and so on

The impulse moves in one direction only as it takes time to re-establishdistribution of ions using the Na/K pump.

So the neurone cannot depolarise again immediately in that region

(refractory period)

3


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Transmission of Action Potentialsin myelinated neurones (Saltatory conduction)


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Extension:

Animation showing the linking of anaction potential to muscle

movement

http://www.youtube.com/watch?v=70DyJ

wwFnkU&feature=PlayList&p=80C4BB58745CB30E&index=17
http://www.youtube.com/watch?v=70DyJwwFnkU&feature=PlayList&p=80C4BB58745CB30E&index=17http://www.youtube.com/watch?v=70DyJwwFnkU&feature=PlayList&p=80C4BB58745CB30E&index=17http://www.youtube.com/watch?v=70DyJwwFnkU&feature=PlayList&p=80C4BB58745CB30E&index=17http://www.youtube.com/watch?v=70DyJwwFnkU&feature=PlayList&p=80C4BB58745CB30E&index=17http://www.youtube.com/watch?v=70DyJwwFnkU&feature=PlayList&p=80C4BB58745CB30E&index=17http://www.youtube.com/watch?v=70DyJwwFnkU&feature=PlayList&p=80C4BB58745CB30E&index=17


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Animation to explain a

synapse

http://www.youtube.com/watch?v=HXx9qlJetSU&feature=PlayList&p=80C4BB58745CB30E&index=29
http://www.youtube.com/watch?v=HXx9qlJetSU&feature=PlayList&p=80C4BB58745CB30E&index=29http://www.youtube.com/watch?v=HXx9qlJetSU&feature=PlayList&p=80C4BB58745CB30E&index=29http://www.youtube.com/watch?v=HXx9qlJetSU&feature=PlayList&p=80C4BB58745CB30E&index=29http://www.youtube.com/watch?v=HXx9qlJetSU&feature=PlayList&p=80C4BB58745CB30E&index=29http://www.youtube.com/watch?v=HXx9qlJetSU&feature=PlayList&p=80C4BB58745CB30E&index=29http://www.youtube.com/watch?v=HXx9qlJetSU&feature=PlayList&p=80C4BB58745CB30E&index=29


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http://www.youtube.com/watch?v=90cj4NX87Yk&feature=PlayList&p=80C4BB58

745CB30E&index=24

Use your new knowledge to create ascript to describe and explain thefollowing animation:
http://www.youtube.com/watch?v=90cj4NX87Yk&feature=PlayList&p=80C4BB58745CB30E&index=24http://www.youtube.com/watch?v=90cj4NX87Yk&feature=PlayList&p=80C4BB58745CB30E&index=24http://www.youtube.com/watch?v=90cj4NX87Yk&feature=PlayList&p=80C4BB58745CB30E&index=24http://www.youtube.com/watch?v=90cj4NX87Yk&feature=PlayList&p=80C4BB58745CB30E&index=24http://www.youtube.com/watch?v=90cj4NX87Yk&feature=PlayList&p=80C4BB58745CB30E&index=24http://www.youtube.com/watch?v=90cj4NX87Yk&feature=PlayList&p=80C4BB58745CB30E&index=24


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communication and homeostasis

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