The nervous system is one of the vital organ systems in the body.
It controls the whole body’s physiology, movements, and also behavior.
Anatomically, it is subdivided into two parts the central nervous system and the peripheral nervous system.
The central nervous system comprises the brain and spinal cord.
While the peripheral system has neurons coming out from the brain and spinal cord.
The peripheral nervous system is again of two subdivisions a visceral and autonomic nervous system. The autonomic system has involuntary control over many organs of the body like the heart, lungs, digestive tract, etc.
While the visceral system is under voluntary control by which we could do tasks such as walking, running, handling things, etc.
The autonomic system is differentiated into the sympathetic and parasympathetic systems based on function and effects in the body.
The sympathetic system is always favorable to the body while the 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 total body mass. It is a very smallest yet very complex system in the body. The brain and spinal cord are the only organs that are completely sealed and protected by a bone case called the skull and vertebral column respectively.
2. Brain in the skull has 100 billion neurons. This brain is divided into many regions with distinct functions. Like Hippocampus is concerned with memory, the hypothalamus regulates stress, the amygdala is concerned with fear and anxiety, while the cortex is involved in judgment, learning and memory.
3. There are 12 pairs of cranial nerves and 31 pairs of spinal nerves.
4. There is no blood flow into the brain and spinal cord. So other words, there is no blood in the head. The blood flows to the upper layers of the brain called the arachnoid mater. There the glucose, water, oxygen, and other essential nutrients get into the brain as cerebrospinal fluid. This cerebrospinal fluid flows through the 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 the nervous system. While the neuroglia acts as supporting tissue to safeguard neurons and nourish them.
6. Brain has a blood-brain barrier and an intense protective system wherein the wall of blood capillaries which end to supply blood to the brain are modified in such a way that no harmful toxin or bacteria can pass through. Thus any toxins or foreign agents in the blood will be restricted to the remaining body and does not enter the brain.
7. Nerve cells unlike other body cells do not divide and multiply. Once formed, they stay such throughout life. In general, all the body cells undergo mitosis to produce new cells and old cells are worn out and discarded as waste.
Even when there is an injury, the normal cells divide and multiply and repair the wound.
Whereas this is not so with neurons, they never divide or multiply. Only new cell organelles within them have 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 up to 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 nerve potential and helps in conducting the signal till the entire length of the neuron. At the end of the neuron, the nerve impulse is transmitted to the next neuron by the release of different types of neurotransmitters.
10. Structurally, neuronal cells are of three types unipolar, 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 eyebrows when something suddenly comes towards the eye.
12. All the important centers which control involuntary functions like heartbeat, respiration, and intestinal motility are present in the hindbrain called the medulla oblongata. Any injury to the back of the head can drastically affect the function of these organs of the body.
13. Brain and spinal cord regulate the whole body’s physiology by nerve signals and also the release of hormones. The hypothalamus of the brain releases hormones like prolactin, oxytocin, thyroid-stimulating hormone, vasopressin, etc.
14. Disorders of the nervous system are few but can be complicated and even deadly. Examples include sunstroke, paralysis, Parkinsonism, Alzheimer’s disease, etc.