Communication and Homeostasis

A2 Biology F214

Why do multi cellular organisms need communication systems?

• Organisms need to detect changes in their external environment eg: pressure on skin, light, sounds, temperature, chemicals etc. The receptor cells need to signal these changes to the organism so it can respond and maintain its safety.

Why do multi cellular organisms need communication systems?

Organisms need to detect changes in internal environments such as temp, pH, water potential of blood , tissue fluid, level of toxins, etc as these can affect the ability of cells to function efficiently.

Enzymes, dehydration, lack of respiratory substrate, toxins inhibiting metabolism, etc.

Why do multi cellular organisms need communication systems?

• Organs work together to maintain a constant internal environment with different organs having different functions. These functions have to be co-ordinated to keep the environment constant (Homeostasis)

• Pancreas, liver, muscles, digestive system organs are all used to maintain blood glucose levels.

Why do multi cellular organisms need communication systems?

• Cell Signalling: one cell releases a chemical that is detected by another cell. The second cell may respond to the chemical signal in any of a large number of ways depending on the type of cell and the chemical stimulus recieved.

• Cells signal using hormones (the Endocrine system) that travel in the blood stream and are picked up by their target cells. The endocrine system enables long-term responses.

Why do multi cellular organisms need communication systems?

• Nerve impulses are transmitted by neurone networks across synapses using neurotransmitters. This allows fast signalling and responses to rapidly changing stimuli.

Homeostasis

•What does it mean?

•Write a definition and give some examples

Homeostasis

• A system of monitoring and adjustment to keep conditions within safe limits

Homeostasis

Monitoring Controlling Internal conditions To keep them constant (or within safe limits) Despite external changes

Egs• temperature • blood glucose levels• blood salt concentration• relative water potential of

blood, tissue fluid and cells,

• pH • Blood pressure • CO2 levels

Negative and Positive FeedbackWhat’s the difference?

Negative Feedback

Can you complete this with some real life examples?

Stretch and challenge questions

• Remember Stretch and challenge is about making synoptic links

• You need to access information from previous work and use it in your explanations in this module.

• In the questions asked you need to use information from the sections on enzymes and natural selection.

Homeostasis and Controlling Body Temperature

Learning Outcomes• Describe the physiological and

behavioural responses that maintain a constant body temperature in Ectotherms and Endotherms.

• In Endotherms refer to the role of peripheral temperature receptors, Hypothalamus and effectors in the skin and muscles

What is an Ectotherm?How does an Ectotherm

control its body temperature?

• Write down as many different ways that you can think of.

• Complete the card sort to see how different Ectotherms deal with regulation of temperature

Control of temperature

• Ectotherms• Seek sun or shade

depending on outside temperature

• Expose more or less body surface to sun

• Alter body shape to change surface area

• Increase breathing movements to evaporate more water

What is an Endotherm?How does an Endotherm

control its body temperature?

• Write down as many different ways that you can think of.

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

Diagram to show

changes to skin

surface blood

vessels in warm and

cold conditions.

What are the Advantages and Disadvantages of

Endothermy and Ectothermy?

Sensory Receptors and Stimuli

Match the stimulus, sense and receptors in the card sort activity

Sensory Receptors, Senses and Stimuli

Eye Rods and cones (light sensitive cells)

Light intensity (rods) and wavelength (cones)

Nose Olfactory cells lining inner surface of nasal cavity

Presence of volatile chemicals

TongueTaste buds in tongue, hard

palate, epiglottis and first part of oesophagus

Presence of soluble chemicals

Skin Pacinian corpuscles (pressure receptors) Pressure on skin

Ear Sound receptors in cochlea (inner ear) Vibrations in air

Muscle Proprioceptors (stretch detectors) Length of muscle fibres

Labelling Neurone DiagramsUse these terms to label the diagrams you have been given.• Axon - specialised to conduct the action potential away

from the 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 action potential

• Myelin sheath-insulating fatty layer composed of Schwann cells

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

potential towards the cell body

Structure of

neurones

Establishing the “Resting Potential”

• At rest, the inside of a neuron's membrane has a relatively negative charge.

• As the figure shows, a Na+ / K+ pump in the cell membrane pumps 3 sodium ions out of the cell and 2 potassium ions into it.

• However, because the cell membrane is a bit leakier to potassium than it is to sodium, more potassium ions leak out of the cell, increasing the positive charge outside.

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

• As a result, the inside of the membrane builds up a net negative charge relative to the outside. (-70mV is the resting potential, the cell is “polarised”

Sodium – Potassium pump online tutorial

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

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All stimuli produce generator potentials but some don’t cause a big enough change in p.d. to reach threshold potential so no action potential is generated.

You should be able to:Describe and explain how an action potential is generated.Interpret graphs of the voltage changes taking place during the generation and transmission of an action potential.

Reaching the threshold potential

• Any stimulation of a receptor cell causes some 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 the threshold potential) then voltage gated channels open

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Small stimuli don’t cause a big enough change in p.d. to generate an action potential.(P.d. doesn’t reach generator potential.)

Generating an Action Potential

• Stimulation of the receptor causes Na+ channels to open. The bigger the stimulus the more channels open.

• Na+ ions diffuse into cell lowering potential difference

• This makes even more channels open (positive feedback)

• When potential difference reaches threshold (-50mV) the voltage gated Na+ channels open

Generating an Action Potential (2)

• As more Na ions flood in the potential difference across the membrane changes to +40mV

• Voltage gated K channels open and Na channels close (2&3)

• K ions diffuse out of cell repolarising the cell (4)

• So many ions diffuse out that the cell is hyperpolarised (5)

• The Na/K pump re-establishes the resting potential (6)

Local Current

Transmission of Action Potentials in myelinated neurones (Saltatory conduction)

• AP at 1 causes Na ions to move into axon• Na ions diffuse to areas of –ve 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-

establish distribution of ions using the Na/K pump.• So the neurone cannot depolarise again immediately in that region

(refractory period)

3

Transmission of Action Potentials in myelinated neurones (Saltatory

conduction)

Extension: Animation showing the

linking of an action potential to muscle movement

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

Animation to explain a synapse

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

http://www.youtube.com/watch?v=90cj4NX87Yk&feature=PlayList&p=80C4BB58745CB30E&index=24

Use your new knowledge to create a script to describe and explain the following animation: