Most axons of the nervous system are surrounded by a myelin sheath (myelinated axons) The presence of myelin speeds up the transmission of action potentials along the axon Myelin will get laid down in segments along the axon, leaving unmyelinated gaps known as “nodes of Ranvier” of Ranvier Neurones

D) Axon B) Cytoplasm C) Myelin Sheath A) Nucleus Of Schwann Cell

How would we describe the role of the Myelin Sheath? - Serves as an electrical insulator - Allows depolarisation to occur at the nodes - The impulse jumps from node to node - Allowing faster conduction - In a process known as saltatory conduction

Coordination in plants

Phototropism – response to light. - positive phototropism- the shoot grows towards the light. Geotropism – response to gravity. - negative geotropism – shoots tend to grow away from pull of gravity. - positive geotropism – roots tend to grow towards the pull of gravity. Response of plants to the stimulus is much slower and the usual response is growth.

Why is it important for plants to root and stem behave in this way? Which part of a shoot is sensitive to light? Which part of a shoot responds to light?

The part of a shoot sensitive to light is the tip. The part of the shoot which responds to the stimulus is the part just below the tip. These two parts of the shoot must be communicating with one another by means hormones. Plant hormones are chemical that affect the activities of particular cells. They may move in the phloem (by diffusion or active transport from cell to cell).

Auxin -Made all the time by the cells in the tip of the shoot -Diffuses downwards from the tip -Make the cells just behind the tip get longer (stimulates cell elongation).

What would you expect to see if you mounted a plant pot on a vertical disc and rotated it slowly over the course of it’s growth.