Chemical/ electrical coordination

- Are chemicals

- Are made by endocrine glands that secrete directly into the blood stream

- Travel in the blood

- Have an effect on particular target cells or organs

- When they have found the target cell, they fit into the receptor

-This biniding activates a enzyme, which in turn converts ATP in the cytoplasm into cyclic AMP ( a second messenger)

- The second messenger brigs about an effect by activating specific enzymes

- Chemical

- Amplitude modulated- determined by concentration of hormone

- Usually rather slow

- Signal often prolonged

- Often a general signal

- Cannot be modified by previous experience

- Impulses are iconic/electrical charge; chemical transmission at synapses

- Frequency modulated, dtermined by number of impulses sent along an axon, and the number of axons stimulated

- Very rapid , usually a fraction of a second

- Duration of signal is short lived

- Very precise

- Can be modified by previous experience, "learning"  

- Also known as plant growth regulators

- Auxin- The substance involved in tropism

- auxin diffuses down the stem from it's site of production. When illuminated from one side, auxin accumulates on the dark side and diffuses downwards, promoting cell elongation that bends the coleoptile towards the light  

- Young stem- coleoptile 

- A neurone is a nerve cell, specialized to carry impulse from one side of the neurone to the other

- Basic features

* A cell body that contains the nucleus and other organelles 

* Dendrites tha tae impulses towards the cell body

* An axon that takes impulses away from the cell body 

* Synapses that junction with other neurones or effectors 

- Resting potential: A state of readiness 

- Action potential: Another name for a nerve impulse 

- The resting potential results from an unequal distribution of ions, brought about by two processes  these are:

* Active transport: All animal cells contain the pump Na+K+ATPase. This uses the energy from splitting ATP to pump ions; three sodium ions pass out the cell and two potassium ions move in. It is an unequal exchange, more positive ions move in than out

* Faciliated diffusion: There are also sodium and pottasium ion channels in the membrane. These channels are normally closed, but they "leak" allowing sodium ions to diffuse in and potassium ions out, down their respective concentration gradients. 

- These two processes cause an imbalance of Na+ and K+ ions accross the membrane

- Is generated when the nerve is stimulated, brought about by a quick reversal in the permebality of the axon membrane. This has two stages:

* Depolarisation:

1) When a neurone is stimulated, the voltage accross the axon membrane changes

2) A few volotage- gated sodium channels detect thus change, opening to allow some sodium to diffuse in 

3) This causes sodium ions to rapidly diffuse in , making the inside of the cell more positive. This is an example of positive feedback

* Repolarisation

When the membrane potential reaches 0, the pottasium channels open, causing pottasium ions to rush out. Making it more negative again.  

- Absolute refractory period: This is the time during which it is impossible to create another impulse, no matter how intense the stimulus is

- Relative refractory period: This is the time during which it is possible to create another impulse, but the stimulus needs to be greater than normal

-Facts!

* An action potential is not an electric current nor is it a message

* All action potentials are the same size

*The speed of the transmission depends on:

1) Axon diameter: larger= faster

2) temperature: higher = faster

3) Whether it is myelinated or not