The nervous system is one of the vital organ systems in the body.
It controls the whole of the body physiology, movements and also behavior.
Anatomically, it is sub-divided into two parts as central nervous system and peripheral nervous system.
Central nervous system comprises of the brain and spinal cord.
While the peripheral system has neurons coming out from the brain and spinal cord.
Peripheral nervous system is again of two subdivisions like visceral and autonomic nervous system. Autonomic system has involuntary control over many organs of the body like heart, lungs, digestive tract etc.
While visceral system is under voluntary control by which we could do tasks such as walking, running, handling things etc.
The autonomic system is differentiated as the sympathetic and parasympathetic system based on function and effects in the body.
The sympathetic system is always favorable to the body while parasympathetic reverses the actions of the sympathetic system.
Both in homeostatic equilibrium contributes to health.
Nervous system facts
1. It has a mass of 2kg i.e it comprises just 3% of of total body mass. It is very smallest yet very complex system in the body. Brain and spinal cord are the only organs which are completely sealed and protected by a bone case called skull and vertebral column respectively.
2. Brain in the skull has 100 billion neurons. This brain is divided in many regions with distinct functions. Like Hippocampus is concerned with memory, hypothalamus regulates stress, amygdala is concerned with fear and anxiety, while cortex is involved in judgement, learning and memory.
3. There are 12 pairs of cranial nerves and 31 pairs of spinal nerves.
4.There is no blood flow in to the brain and spinal cord. So other words, there is no blood in the head. The blood flows to the upper layers of brain called arachinoid mater. There the glucose, water, oxygen and other essential nutrients get into the brain as cerebrospinal fluid. This cerebrospinal fluid flows through brain and spinal cord.
5. Entire tissue is made of only two types of cells viz. neurons and glial cells. Neurons perform the function of nervous system. While the neuroglia acts as supporting tissue to safe guard neurons and nourish them.
6. Brain has blood brain barrier and intense protective system where in the wall of blood capillaries which end to supply blood to brain are modified in a such a way that no harmful toxin or bacteria can pass through. Thus any toxins or foreign agents in blood will be restricted to the remaining body and does not enter brain.
7. Nerve cells unlike other body cells do not divide and multiply. Once formed, they stay such through out life. In general all the body cell undergo mitosis to produce new cells and old cells are worn out an discarded as waste.
Even when there is an injury, the normal cells divide and multiply and repair the wound.
Where as this is not so with neurons, they never divide or multiply. Only new cell organelles within them are formed again while old and worn out organelles are destroyed.
However in case of damage to the neurons, the damage is partially repaired by a process called nerve plasticity.
8. Neurons are some of the longest cells in the body similar to striated muscles. Their length ranges upto meters in length.
9. Nervous system has intense electrical flow in the form of membrane potential. This electric current is due to ion exchange into and outside the neuronal membrane. This is called as nerve potential and helps in conducting the signal till the entire length of neuron. At the end of neuron, the nerve impulse is transmitted to the next neuron by release of different types of neurotransmitters.
10. Structurally, neuronal cells are of three types like uni-polar, bipolar and multi-polar cells.
11. Nervous system has a reflex action which is a protective response without the voluntary control of the person. Ex: Closing of eye brows when something suddenly comes towards the eye.
12. All the important centers which control involuntary functions like heart beat, respiration, intestinal motility are present in the hind brain called medulla oblongata. Any injury to the back of heat can drastically affect the function of these organs of the body.
13. Brain and spinal cord regulate whole of body physiology by nerve signals and also release of hormones. The hypothalamus of brain releases hormones like prolaction, oxytocin, thyroid stimulating hormone, vasopressin etc.
14. Disorders of nervous system are few but can be complicated and even deadly. Examples include sunstroke, paralysis, Parkinsonism, Alzheimer disease etc.