As a detailed study of the nervous system is impossible without a practical dissection of the parts, we content ourselves with the barest outlines of the system. We enumerate below the functions of the several parts of the nervous system.
Brain or Cerebrum exercise three principle functions which are amplified within brackets in the following table:
- Feeling—Interpreting sensation and not merely receiving them.
- Voluntary muscular movements
- Co-ordination of muscles in acting
- Inhibition of muscular acts
- Glandular activity
In other words, we are conscious so long as our brain is active and consciousness is also dependent upon the integrity of the blood-supply of the brain. All memory works (i.e., linking up of past experiences and impressions) is the result of brain activity. Feeling is not mere receiving of sensation— that is the work of sensory nerves. For example, when we swallow lime, pain is ‘felt’ in the stomach, but is ‘interpreted’ by the brain as a gripe, a feeling of discomfort. All muscular movements are at the control of brain; we can order our hands to move or we can hold back the hands from moving (i.e., inhibit their movements). Glandular activity is also in part the result of activity; thus, when we see dainty food, our mouth waters (i.e., the salivary glands of the mouth secrete). This kind of activity is called Reflex Action. It seems that there must be a sentient surface away from the brain, which when stimulated sends up the sensation to brain, which latter in turn orders either muscular or glandular activity. It is like a needy son sending a wire to his guardian who, on receiving such message, immediately sends the necessary help. Reflex act then is such a muscular or glandular activity, as is occasioned by order of the brain, in response to some sensory surface having been stimulated. This is the reason why the watering of mouth at the sight of food is called reflex act.
Cerebellum is connected with maintenance of our equilibrium by co-ordinating muscular movements.
Medulla Oblongata or BULB contains the governing centres of the following vital functions
- Keeping blood vessels in a state of tonic contraction (vaso-contraction or of dilatation locally) (local vaso-dilation); or in other words it governs the state of muscular activity of blood-vessels (vasomotor).
- Respiratory act;
- Swallowing, voice production, salivary secretion, expression.
Spinal cord—Performs a double function (a) it contains secondary centres for certain acts; (b) it conducts impulse to and from brain. As regards its possessing centres, we find the following acts being governed by centres in the spinal cord
- Centre for maintenance of muscular tone
- Centre for controlling the action of sphincter muscles, guarding the neck of urinary bladder and the orifice of anus;
- Centre for bringing on contraction of uterus;
- Centre for calling forth the erection of penis.
The other function of the spinal cord is to send up (different) impulse or sensations, received at any of the body surface or organs, to the cortex of the brain via, medulla, pons and cerebellum, and to send down impulse calling for muscular or glandular activity from the cortex of the brain via, in succession, the cerebellum, pons, medulla, spinal cord and spinal nerves, to the muscles or glands concerned.
Sympathetic System—It governs four main functions, viz.
- Quickening action of heart (cardio-acceleration);
- Regular calibre of blood-vessels (vaso-motor action);
- Governs persistalsis of stomach, intestines, and uterus;
- Governs secretory activity of abdominal viscera.
It will thus be seen that, though each individual part of the nervous system has clear-cut function, we must at all times think of the nervous system functionally as one unit, inter-dependent upon and co-relating with each other.