The nervous system is a vital organ system in the body.
It controls the whole anatomy and physiology of the body 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: the visceral and autonomic nervous systems. 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 contribute to health.
Nervous system facts
1. Size
It has a mass of 2kg, and it forms just 3% of total body mass.
It is a very smallest yet very complex system in the body.
2. Safety of location
The brain and spinal cord are the only organs that are completely sealed and well protected by a bone case, namely the skull and vertebral column, respectively.
3. Numbers:
The brain in the skull has 100 billion neurons.
There are 12 pairs of cranial nerves originating from the brain and 31 pairs of spinal nerves originating from the spinal cord.
4. Distinct functions
Most organ systems in the body have one or two functions.
However, the nervous system has many distinct functions, as multiple regions are involved.
Examples:
- Memory: Hippocampus
- Fear and Anxiety: Amygdala
- Stress: Hypothalamus.
- Temperature: Hypothalamus
- Circulation, respiration: Medulla oblongata
- Body Balance: Cerebellum.
- Cerebrum: Speech, judgment, thinking, reasoning, and problem-solving
5. Access to blood:
There is no direct blood flow into the brain and spinal cord.
Instead, the blood flows to the upper layers of the brain called the arachnoid mater.
From there, water, oxygen, and other essential nutrients enter the brain through cerebrospinal fluid.
This cerebrospinal fluid flows through the brain and spinal cord.
6. Electrical energy
The body uses food to generate energy. Of these 4 types, electrical energy is specifically generated and limited to the nervous system.
To avoid the dissipation of this energy during conduction, the long nerves are covered with a myelin sheath.
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.
However, 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. The 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 conduct the signal for 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. The 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 that 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. The brain and spinal cord regulate the whole body’s physiology by nerve signals and also the release of hormones. The brain’s hypothalamus 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.
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