366 ANATOMY FOR NURSES [Chap. XIX 



If the cell has but one process, that one is the axis cylinder pro- 

 cess, and the cell is spoken of as a unipolar cell. If the cell has two 

 processes, one is the axis cylinder process, and the cell is called 

 bipolar ; many processes, multipolar. 



Function of the cell-body. — The cell-body affords nutriment 

 to its processes, as is proven by the fact that if a nerve-fibre is cut, 

 the part separated from the cell-body dies. It also bears the same 

 relation to the cell that the battery does to many kinds of electrical 

 apparatus: (1) it is the centre in which the action takes place 

 which gives rise to nervous impulses ; (2) the cell-bodies are ca- 

 pable of modifying impulses brought to them by their sensory 

 processes. This modification may take the form of inhibition and 

 either partially or completely block impulses ; or it may take the 

 form of summation, i.e. collect weak impulses, and combine them 

 into one effecti^'e impulse before transmission to the motor nerves. 

 As cell-bodies are found only in the brain, spinal cord, and ganglia, 

 it is only in these parts of the nervous system that these activities 

 can take place. 



(2) The cell-processes. — The cell-processes are named as fol- 

 lows : — 



(a) Dendrites or dendrons. 



(6) Axis cylinder processes, named also neuraxones, or axones. 

 fMedullated. 

 i^on-medullated. 



(d) Collaterals. 



(e) Nerve-endings. 



(«) Dendrites. — These processes are usually short, and rather 

 thick at their attachment to the cell-body. They have a rough 

 outline, diminish in calibre as they extend further from the cell- 

 body, and branch rapidly in a tree-like manner. These branches 

 are called arborizations. The number of dendrites varies. 



Function. — The essential function of a dendrite is conduction 

 of a nerve-impulse from the periphery to the cell-body. They 

 collect nerve-impulses from the processes of other cells, and carry 

 them always in one direction, i.e. to the cell-body. 



Synapse. — In this connection it is important to emphasize 

 that there is no true anastomosis of processes from different cells. 

 The arborizations interlace and intermingle so that the nerve- 

 impulse from one cell-process is able to bridge the gap and set up 



(c) Nerve-fibres j ^7 



