Nervous system.

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  • Created on: 18-01-13 08:44
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Organisation Of The Human Nervous System
The human nervous system is far more complex than a simple reflex arc, although the same stages still apply.
The organisation of the human nervous system is shown in this diagram:
It is easy to forget that much of the human nervous system is concerned with routine, involuntary jobs, such as
homeostasis, digestion, posture, breathing, etc. This is the job of the autonomic nervous system, and its motor
functions are split into two divisions, with anatomically distinct neurones. Most body organs are innervated by
two separate sets of motor neurones one from the sympathetic system and one from the parasympathetic
system. These neurones have opposite (or antagonistic) effects. In general the sympathetic system stimulates
the "fight or flight" responses to threatening situations, while the parasympathetic system relaxes the body. The
details are listed in this table:
Organ Sympathetic System Parasympathetic System
Eye Dilates pupil
Constricts pupil
Tear glands No effect
Stimulates tear secretion
Salivary glands Inhibits saliva production
Stimulates saliva production
Lungs Dilates bronchi
Constricts bronchi
Heart Speeds up heart rate Slows down heart rate
Stimulates peristalsis
Gut Inhibits peristalsis
Stimulates bile production
Liver Stimulates glucose production
Stimulates urination
Bladder Inhibits urination

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