A level Biology exam revision resources written by A level Examiners





 

The nervous system is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is made of the brain and the spinal cord, and the PNS is made from all the others nerves cells in the body.

As impulses are only transmitted in one direction through the body's nerves, the PNS can be divided into two parts. One transmits impulses to the CNS and the other transmits impulses from the CNS. This can be seen in the figures below which show the way the nervous system is organised. The figure 3 shows the basic outline, and figure 4 gives all the information you would be expected to know for A level.

Figure 3
As impulses are only transmitted in one direction through the body's nerves the PNS can be divided into two parts. One transmits impulses to the CNS and the other transmits impulses from the CNS. This can be seen in the diagrams below which show the way the nervous system is organised. The first diagram shows the basic outline and the second gives all the information you would be expected to know for A level
Figure 4
As impulses are only transmitted in one direction through the body's nerves the PNS can be divided into two parts. One transmits impulses to the CNS and the other transmits impulses from the CNS. This can be seen in the diagrams below which show the way the nervous system is organised. The first diagram shows the basic outline and the second gives all the information you would be expected to know for A level

Figure 2 above shows that the autonomic part of the nervous system is responsible for involuntary responses. These include the responses such as those of homeostasis and of digestion. The autonomic part of the nervous system is divided into two branches, the sympathetic and the parasympathetic. Lots of involuntary muscles and glands in the body have an input from both of these branches. In general the sympathetic nerves cause responses which prepare the body for action, and the parasympathetic nerves cause responses which relax the body.

The specific responses you may be asked to recall for A level are shown in table 2 below.

Table 2
Organ 	,Result of sympathetic stimulation,Result of parasympathetic stimulation,Eye,Dilates pupil,Constricts pupil,Tear glands,No effect	,Stimulates secretion of tears,Heart,Speeds up heart rate,Slows down heart rate,Bladder,Bladder walls remain relaxed,Stimulates contraction of bladder walls.


Share this knowledge

 
 



Back To Top Back To Top