F214 OCR Biology: Nerves

F214 OCR Biology: 

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  • Created by: Hamed
  • Created on: 15-06-11 11:24
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Nervous System Summary
Sensory receptors
All receptor cells are transducers which convert one form of energy into another form, electrical
Type of receptor Type of stimulus energy Type of stimulus
Photoreceptor Electromagnetic Light intensity & wavelength
Electroreceptor Electromagnetic Electricity
Mechanoreceptor Mechanical Sound, touch, pressure, gravity
Thermoreceptor Thermal Temperature change
Chemoreceptor Chemical Humidity, smell, taste, water
potential, ion concentration
Sensory neurones
Transmit impulses from receptors to CNS
Have a Dendron carrying impulses to the cell body
Axon carries impulses away from the cell body
Motor neurones
Transmit impulses from CNS to muscle or gland
Cell body is where the nucleus and organelles are
Dendrites carry impulses to the cell body
Axon carries impulses away from the cell body
Resting potential
1. Active transport / pumping of Na+ and K+
2. 3 Na+ pumped out for every 2 K+ pumped in;
3. Many K+ channels open;
4. Many K+ diffuse out of axon;
5. Few Na+ channels open;
6. Few Na+ ions diffuse into axon;
7. Causes an imbalance of Na+ & K+ ions
inside/outside of membrane;
8. Overall more positive charges outside;
9. Inside of axon is -70mV compared to outside;
Action potential
1. Is when the axon membrane is depolarised;
2. Sodium ion channels open;
3. Allowing rapid influx of sodium ions;
4. Positive feedback;
5. Axon becomes positive inside;
6. Depolarisation occurs
7. Na+ channels close
8. Axon becomes +40mV inside;

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Resting potential is re-established
1. Sodium ion channels close and potassium ion channels open;
2. Allowing potassium ions to move out of axon;
3. Positive feedback, more K+ ions move out of axon;
4. Axon membrane begins to re-polarise;
5. Na+ ions pumped out of axon to complete re-polarisation;
6. Membrane become hyperpolarised, below -70mV;
7. Sodium/potassium pump continues to re-establish resting potential;
Transmission of an action potential along an axon
1. Depolarisation of axon membrane causes local currents to be set up;
2.…read more

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The greater the stimulus the greater the frequency of impulses
The greater the sensation
Conduction of action potential across cholinergic synapse
In a cholinergic synapse the neurotransmitter is acetylcholine
1. Impulse arrives at pre-synaptic membrane
2. Depolarisation causes Ca2+ channels to open
3. Ca2+ ions diffuse through pre-synaptic membrane
4. Ca2+ ions cause vesicles carrying acetylcholine to
move to the pre-synaptic membrane
5. Vesicles fuse with pre-synaptic membrane and
release acetylcholine substance, by exocytosis
6. Acetylcholine diffuses across synaptic cleft
7.…read more

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P shows temporal summation. Action potentials
arrive closely after one another
Q shows spatial summation. Action potentials R shows inhibition
arrive at two synapses at the same time
An excitatory synapse causes the post-synaptic membrane to depolarise
An inhibitory synapse causes the post-synaptic membrane to hyperpolarise.…read more


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