Nerves, homeostasis and communication notes

Notes on chapters one and two of the ocr A2 biology course. Includes the different types of neurones, synapses, myelination, positive and negative feedback and endotherms and ectotherms. Enjoy!

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Communication and Homeostasis

Homeostasis ­The ability to control internal conditions and maintain a stable internal environment.

Homeostasis controls:

Temperature ­ low temperatures will slow metabolic reactions, whereas higher
temperatures may denature proteins, harming enzymes and membranes
Water volume ­ Can cause crenated or lysed cells if the amount of water…

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Ectotherms ­ Animals that obtain most of their heat from outside their bodies. Eg. Reptiles. They
cannot generate large amounts of heat within their bodies. Endotherms tend to be inactive in cold
environments, as their cells are too cold and metabolic reactions therefore take place slowly.

Nerves

Motor Neurone:




Sensory…

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Schwann cells wrap themselves around some neurones, called a myelin sheath. Every 1-3mm there is
a Node of Ranvier. About one in three motor and sensory neurones are myelinated. Myelin Sheath
means faster conduction of nerve impulses.

Axons of neurones are always found in bundles. These are protected by a…

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Synapses

A synapse is a junction between neurones, or between a neurone and an effector cell.

1. An action potential arrives at the synaptic knob of the presynaptic neurone. It stimulates
voltage-gated Calcium ion channels to open.
2. Calcium ions diffuse into the synaptic knob.
3. The influx of Calcium…

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