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F214 Module 1: Communication and Homeostasis
4.1.2 Nerves

(a) outline the roles of sensory receptors in mammals in converting different forms of energy into nerve
Sensory receptors ­ specialised cells that can detect changes in our surroundings. They are energy transducers
that convert one form of energy to another…

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F214 Module 1: Communication and Homeostasis
Difference Carries the action Carries the action
s potential from a potential from the central
sensory receptor the nervous system to the
central nervous effector .
system . Long axon carrying the
Short axon carrying action potential to the
the action potential effector.

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F214 Module 1: Communication and Homeostasis
4. This all results in a potential difference of 60mV between the inside and outside of the cell. The
difference is called the resting potential . The axon membrane is said to be polarised when it is in this

(d) describe and explain…

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F214 Module 1: Communication and Homeostasis
4. This is called a local current the movements of ions along the neurone. The flow of ions is caused by an
increase in concentration at one point, which causes diffusion away from the region of higher concentration.

The Myelin Sheath:
The myelin sheath…

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F214 Module 1: Communication and Homeostasis
When a stimulus is at a higher intensity the sensory receptor will produce more generator potentials . This will
cause more frequent action potentials in the sensory neurone. When these arrive at the synapse they will cause
more vesicles to be released. Therefore this…

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F214 Module 1: Communication and Homeostasis

(j) outline the role of neurotransmitters in the transmission of action potentials
1. An action potential arrives at the presynaptic neurone. The voltagegated calcium ion channels open and Ca+
ions diffuse into the synaptic knob.

2. The Ca+ ions causes the vesicles containing acetylcholine…

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F214 Module 1: Communication and Homeostasis
Acclimatisation after repeated stimulation a synapse may run out of vesicles containing the transmitter
substance. The synapse is said to be fatigued , which explains why we soon get used to a smell or a
background noise . It may also help to avoid…


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