178 



ELEMENTARY PHYSIOLOGY 



Some nerves are purely sensory, that is, consist of sensory 

 fibres only. Other nerves consist of sensory and motor fibres, 

 and can consequently convey nerve impulses in both directions, 

 only, of course, not by the same fibres. Such nerves are termed 

 mixed nerves. The nerves which enable us to see, hear, and 

 smell are purely sensory ; but most of the nerves in the body are 

 composed of mixed fibres. 



, Cerebro- 

 I spinal 



NERVOUS 



SYSTEM 



Sympathetic, 



NEEVE SUB- 

 STANCE 



NEEVE 



FIBRES 



NEBVES . 



Cellular . 



Fibrous . 



Fresh . . 

 After death 



Afferent . 



Efferent . 

 Mixed . 



SUMMARY. 

 Consists of 



Brain and its nerves. 



I Spinal cord and its nerves. 

 Fibres debuted , 



/-. . f 

 Consists of - 



Double chain of ganglia, on 

 each side of the vertebral 

 column. 



\ Various disconnected ganglia. 

 I The internal organs. 



* Fibres distributed to The walls of blood- 



^ vessels 



Greyish in nerve centres. 

 j Nerve fibres forms nerves, and enters into 

 1 the structure of nerve centres. 



A simple semitransparent filament. 

 i A tube, containing a 



- White opaque substance, surrounding 

 ^ The axis -cylinder. 



j Convey impressions to a centre only. 

 ( Also called sensory nerves. 



Convey impressions/r0/ a centre only. 



Fibres terminate in muscular fibres. 



Also called motor nerves. 



Contain both afferent and efferent fibres. 



QUESTIONS ON LESSON XXX. 



1. What do you know of the general arrangement of the parts forming the 



nervous system ? 



2. What is the cerebro-spinal system ? To what points are its nerves dis- 



tributed ' 



3. Describe the general arrangement of the sympathetic system. 



4. What is a nerve ? What does it look like in the body ? What is the 



difference between a nerve and a n*rve centre ? 



5. What is a sensory, and what a motor nerve ? Give illustrations of the use 



of each. 



6. A boy, seeing an apple on a tree, stretches out his hand to pluck it. What 



is the general nature and the order of the changes which take place in 

 the nervous and the muscular systems of the boy under these circum- 

 stances ? 



