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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…

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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;

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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

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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. This prevents any…


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