io8 



ANIMAL BEHAVIOUR 



40«. The Anatomical Conception of the Neurone. 

 Whatever it may be, a nervous structure is made up of units 

 called neurones. 



A neurone consists of a nerve-cell which has at least two 

 poles. From each pole proceeds a fibre, or axon. Each of 

 these fibres breaks up into arborizations, or branches, or dendrites. 

 One of the fibres may be long. In i a typical neurone is 

 represented as beginning in a bunch of dendrites, such as a 

 receptor organ in a muscle, and as being prolonged into the 

 nerve-fibre, or axon, which then passes into a nerve-cell. From 

 the latter issues another fibre of variable length and this breaks 

 up into another series of dendrites. In 2 there is shown a 



1 



AOCOTL 



Nerve 

 celL\ 



'dendrites 



r 



2 



Fig. 19. 



I, A typical neurone ; 2, a neurone with a unipolar cell ; 3, 4, 5, neurones in ganglionic 

 centres. 



similar structure. The beginning is a series of dendrites, which 

 may be a touch-receptor in the skin. This is prolonged into 

 an axon which is one fibre in a nerve running from, say, the tip 

 of the finger up to the brachial plexus in the armpit and then 

 into the spinal cord. Just before the fibre enters the cord it 

 passes into and then emerges from a bipolar cell and the fibre 

 leaving the cell breaks up finally, in the spinal cord, into a 

 series of dendrites. 



In 3 and 4 are represented neurones which consist pre- 

 dominantly of nerve-cells. These cells may be bipolar (as at 3), 

 each pole consisting of a bunch of dendrites, or it may be 

 multipolar (as at 4). In these latter neurones the axon may be 

 short, or hardly distinguishable. 



