Control & Coordination

Nine cool facts about the Human Brain

The human brain is the heaviest organ in the human body. It is one of the most complex and least understood parts of the human body. Here are a few cool?facts that we do know about the human brain:-

  1. What happens when you touch a hot object? You will reflexly withdraw your hands, and it takes a split second for you to do this action. But in this split second, information about the hot object is first sent to the spinal cord. The spinal cord processes this information and returns a set of instructions to the muscles in your hands. So, how fast do these impulses travel? In some conducting nerve fibres, the electrical impulses can travel at speeds as fast as 170 miles/sec. Thus, the human nervous system is as fast as a high-end luxury car! However, not all nerves carry impulses at such high speeds. The unmyelinated neurons (myelin is a thin coating over the axons) conduct impulses are very slow speeds (0.5 m/sec). These neurons predominantly conduct pain impulses.

  2. The human brain is always active. It is functioning even when we sleep. The electrical energy generated by the human brain is enough to light up a 10-watt bulb. Thus, the image of a bulb lighting up when we think is not far off the mark!

  3. The human brain is a vast storehouse of information. The estimated storage capacity of the human mind is between 3 to 1000 terabytes (nobody knows). This storage capacity is five times the information contained in the Encyclopedia Britannica. The National Archives of UK, which stores over 900 years of historical records only occupies seventy terabytes of space. Therefore, there is no such thing as overloading the human brain!

  4. The human brain is the most active organ in the human body. It receives 20% of the cardiac output, and it consumes nearly 20% of the oxygen taken in by the body. The human brain is extremely sensitive to oxygen deprivation. The neurons in the brain will start dying after four minutes of oxygen deprivation. You will now appreciate why deep breathing is so refreshing to the mind!

  5. At what time of the day is the brain most active? Most of us would say- when we are awake. But, this is not true. The human brain is more active when we sleep than when awake. We do not know the exact reason, but research has shown that short-term memory is converted to long-term memory during sleep. Also, the neurons repair themselves when we are sleeping. That is why a good night sleep is recommended for students.

  6. All people have dreams, but only a few can recollect their thoughts. There is nothing unusual about this as the average duration of a dream is about 2-3 seconds only. We can have hundreds of dreams in one night. Research has also shown that people with higher I.Q. Tend to have more dreams.

  7. For many years, we believed that neurons cannot regenerate. Recent research has shown that this may not be entirely accurate. While neurons do not regenerate like other tissues, they have the capacity to take over the function of damaged neurons. This feature is called as neural plasticity.

  8. All pain impulses converge at the brain, but the majority of the brain parenchyma does not feel pain. That is why it is possible to perform brain surgery without anaesthesia. The only pain-sensitive structures in the brain are the blood vessels and the dura (a thick fibrous sheet that covers the brain and protects it).

  9. Over 80% of the brain is composed of water. The living brain has jelly like consistency. When we do not drink enough water, the brain gets dehydrated. We can then suffer from headaches and inability to concentrate. Therefore, it is important to drink enough water.

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Neurons: The building blocks of the nervous system

Neurons are the cells of the nervous system. In the previous article, we had learned about the organization of the human nervous system. In this article, we shall learn about the basic building block of the nervous system- the neurons.

The human brain and the spinal cord themselves contain a hundred billion neurons. The neuron is a long cell with three parts- the cell body, the axon, and the nerve endings. The cell body contains the nucleus and the bulk of the cytoplasm of the neuron. The cell body is metabolically active and hence contains mitochondria and storage structures like the endoplasmic reticulum and Golgi bodies. The cell body also has multiple projections called dendrites. The nerve ending of one neuron interacts with the dendrite of another neuron the synapse.

How are messages carried through the neurons?

Neurons use a combination of chemical and electrical signals to disseminate messages. These compounds are called as neurotransmitters. The common neurotransmitters in the human brain include acetylcholine, dopamine, serotonin, GABA, and glutamate. These compounds are synthesized in the cell body and transported to the nerve endings where they get stored.

The dendrites of neurons and the neuromuscular junction contain receptors for neurotransmitters. The receptors change their shape on binding with the neurotransmitters?and many downstream reactions like the influx of sodium and efflux of potassium occur. An electrical current originates because of the ionic difference, and this current reaches the nerve ending through the axon. When this current reaches the nerve ending, the stored neurotransmitters are released.

There are two kinds of neurons- myelinated and unmyelinated.

The myelinated neurons have a layer of myelin, a lipid, over them. The myelin serves to insulate the axon. Some areas of the axon, known as nodes of Ranvier, are devoid of this coating. The myelin does not cover the nodes of Ranvier. Therefore, electrical impulses have to jump from one node to another. Therefore, the speed of transmission is high in the myelinated neurons. The motor neurons are myelinated neurons.

In contrast, the unmyelinated neurons do not have the insulating layer of myelin around them. In these cells, the electrical impulse will have to travel along the full length of the axon. Therefore, the speed of transmission of impulses is slower in the unmyelinated neurons. The neurons of the pain system are unmyelinated.

Neuromuscular junction

The nerve endings terminate either on another neuron or a neuromuscular junction. The neuromuscular junction is a highly evolved structure that translates the electrical signals from the neurons into action by the muscles. The primary neurotransmitter in the neuromuscular junction is acetylcholine. Have you heard of a disease called Myasthenia Gravis? This disease causes muscular weakness because of damage to the neuromuscular junction.

So, in this article, we have learned that neurons are the basic building blocks of the human nervous system. They interact with other neurons, ranging from simple one synapse reflex arc to multisynaptic complex networks. We shall discuss the reflex arc in the next article.

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An overview of the human nervous system

The human nervous system is an organised collection of neurons that controls and coordinates, not only movements but most other life processes. In our previous articles on the musculoskeletal system, we learnt about the muscles and bone. If the musculoskeletal system is the wheel of a car, then the human nervous system performs the function of the brakes and the accelerator.

The central nervous system (CNS), the peripheral nervous system and the enteric nervous system are the three components of the human nervous system.

The CNS consists of the brain, the cranial nerves and the spinal cord. The human brain is the most evolved amongst all living beings. It is the seat of all thinking and action. It is a highly sophisticated and organised structure with different regions of the brain subserving various functions. The brain consists of three anatomical regions- forebrain, midbrain and the hindbrain.

The forebrain, comprising of the cerebrum is the area where all higher mental functions like speech, thinking, planning, execution, comprehension, etc. are carried out. The midbrain and hindbrain are more involved with maintaining vital life processes like breathing, circulation, etc. The cerebellum is a part of the hindbrain; it serves the function of coordination of movements.

The spinal cord carries the messages from the brain to the respective muscles and organs. ?Have you ever seen a telephone or a fibre optic cable? ?Within the cable are millions of slender optical fibres that transmit signals. The spinal cord also looks similar. The axons of the neurones in the brain run through the spinal cord and exit the spinal cord at different levels.

The nerves exiting the spinal cord from the peripheral nervous system. The peripheral nervous system is the final pathway for all the impulses that originate from the brain. The nerves of the peripheral nervous system terminate on the muscles and other organs and control their function.

The enteric nervous system is that part of the human nervous system that handles the control and coordination of the gastrointestinal system. The enteric nervous system is a network of neurones within the digestive tract. The enteric nervous system senses changes within the GI tract and it also receives impulses from the CNS through the Vagus nerve.

How many of you have seen a person afflicted with Polio or someone with partial paralysis of one side of the body? In both cases, the muscles are unable to move as the nerves that control them have died due to some reason. Therefore, the movement would not be possible without the human nervous system.

So how does the human nervous system send signals to the muscles? What kind of messages are sent? We will learn more about this in the next article on the structure and function of neurones.

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How do humans move: The musculoskeletal system?

Humans have a highly developed system to perform the task of movement- the musculoskeletal system. The musculoskeletal system consists of the bones that form the skeleton and specialised connective tissue- muscles that carry out the function of movement. The muscles are attached to the bones at both their ends (some muscles like the tongue are appended to a bone at only one end). The muscles are attached to bone using ligaments. Ligaments are very sturdy structures formed of collagen and other connective tissue. The muscles are excitable, elastic, and they extend and contract by the action of their contractile units, also called as sarcomeres.

A sarcomere is the basic unit (contractile) of the muscle. Actin and myosin are the essential components of a sarcomere. The actin and myosin filaments are made up of a contractile protein called myoglobin. The two filaments interdigitate and when they slide over each other, movements of the musculoskeletal system is seen.

The musculoskeletal system is divided in skeletal muscles, smooth muscles and cardiac muscle (based on the function). The skeletal muscles are attached to the bones at both their ends. The skeletal muscles handle all visible movement of humans, and they are under voluntary control. Smooth muscles are present in the gastrointestinal tract. These muscles are not under voluntary control. Cardiac muscle is a specialised form of smooth muscle. The cardiac muscle is comprised of many different cells, that functionally behave as one cell. The cells are connected to each other through structures called as a syncytium.

The musculoskeletal system can also be classified based on the pace of contractility- red and white muscles. The red muscles effect sustained activity. Therefore, they contain many mitochondria and myoglobin. In the chapter on life processes and respiration, we learnt that mitochondria are the power plants of the cell. Mitochondria produce energy in the form of ATP. ATP is then used by the actin and myosin filaments to effect movements of the musculoskeletal system. The red muscles contain many mitochondria and hence use aerobic respiration for producing energy. In contrast, the white muscles are used for short bursts of intense activity. The white muscles contain few mitochondria. Hence, they depend on anaerobic respiration for energy. Anaerobic respiration can provide power quickly, but there is an accumulation of lactic acid, which leads to fatigue. Therefore, the white muscles are primarily developed in those areas where short; quick, intense activity is required- for example the muscles of the eye.

The musculoskeletal system by itself cannot produce movement. The different parts of the musculoskeletal system need to be coordinated. The nervous system serves the function of control and coordination of the musculoskeletal system. We shall learn more about the human nervous system in the next article.

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Movement in Plants

We have all seen trees swaying in the wind. Is it an example of movement in plants? In the strictest sense, yes. However, this action is not indicative of life. Even a dead tree or plant can sway in the wind. The movement of plants here is caused by the wind and is not intrinsic to the tree or plant. So, what movements are essential to a tree or plant?

There are two such movements in plants that are indicative of life. One is the immediate response to stimuli and the other is in response to growth.

Prof. Jagdish Chandra Bose, an Indian physician, biologist and scientist was the first to demonstrate movement in plants. He invented the crescograph, an instrument that can be used to measure movement in plants.

Have you seen or touched the ?touch-me-not? plant (Mimosa pudica)? As soon as you reach the leaves, they droop and curl up. How does this happen?

Plants do not have specialised structures like nerves or neurones to control their movement. They instead rely on electromechanical signals to control movement in plants. In the above example, when we touch the leaves, the leaves sense the pressure, and this is transmitted as electric signals to the cells adjoining the leaves. These then quickly lose water, leading to drooping of the leaves. In fact, most of the movement in plants is due to ingress and egress of water from the cells.

Another movement in plants is in response to growth. We have all eaten sprouts. Have you noted how your mother makes these? Sprouts are made from a class of plants called lentils. There are different varieties of lentils, and the seeds of these plants are soaked and allowed to germinate to produce the sprouts.

When these seeds are soaked in water and left in air, they germinate, and you can see the roots and shoots coming out. If you leave them long enough, one can see them grow in length. This movement in plants is a manifestation of growth. If we take this germinating seed and plant it in the soil, in a few days you will note that the shoot starts growing upwards, and a new plant is born.

What would happen if we suspend this germinating seed in the air? Will the root grow upwards or the shoot grow downwards? ?No, irrespective of where a seed is planted, the roots will always grow in the direction of gravity, and the shoots will grow against gravity.

Now let us set up another experiment. Take two potted plants and keep them inside a cardboard box. In one box, make a hole on one side to let in sunlight. Maintain the plants for a few days inside these boxes. What would you notice?

You would see that the plant in the box with the hole has grown in the direction of the hole. Movement is plants in influenced by the direction of sunlight. Gravity also affects movement in plants. This movement in plants is called as tropism or more accurately called heliotropism and geotropism respectively.

Plants can also move in response to chemical stimuli. In the above experiment, the plant grows in the direction of sunlight by the action of a chemical called Auxin. This chemical diffuses to the shady side of the shoot and stimulates growth on that side. Therefore, the shoots grow towards the sunlight.

Thus, we have learnt that movement in plants can be a manifestation of growth, or it can be in response to environmental changes. Even though plants do not have a nervous system, they can move using electromechanical or chemical signals.

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Movement in Living Beings

Movement is an essential feature of a living being. All living beings move. Birds fly; animals walk and run, plants grow vertically and we humans move all the time. So why does movement occur at all? Change can happen as a part of the growth process. For example, the shoots of a plant will grow up towards the direction of the sun. Movement can also be in response to the environment. What would you do if go out into the harsh sunlight from the inside? You would naturally raise your hand to shield your eyes. Here, you moved in response to environmental stimuli. Similarly, all animals move in response to environmental stimuli. A mouse will start running when it sees a cat. Birds travel thousands of kilometres for food during the winter season and whales and fish can troll huge areas of the oceans for food. Therefore, we could say that movement is essential for adapting to the environment.

So, do even single cell organisms like bacteria and protozoa move? Yes, they do move, but their movement is too slow actually to be noticed by the human eye. However, if we have sophisticated equipment, then even the action at the level of individual cells can be noted.

Amoeba is a unicellular organism that inhabits most environments. It moves by creating temporary projections of its cell membrane called as pseudopods. If an amoeba sees a food particle, it will create a pseudopod to encircle the food particle and internalise it.

Other protozoa have a tail or rudder-like structure called flagella. These organisms can move by the flipping action of the flagella. Other unicellular organisms have delicate hair-like projections over the cell membrane. These are called cilia. By co-ordinated movement of the cilia, these organisms can move in a medium. ?However, if the cilia move without co-ordination, then movement is not possible. The action is only possible when all the parts move in a controlled manner. Therefore, depending on the complexity of an organism, each plant or animal has developed its structures to control and co-ordinate movement. These structures range from simple cytoskeletal elements in unicellular organisms to an extremely complex organisation of neurones like the human nervous system. We shall discuss the human nervous system in detail later.

Movement in plants is different to that in animals. Movement in plants is either related to growth or is an adaptive response. However, unlike animals, plants do not have a nervous system to control and coordinate movement. We shall learn more about movement in plants in a later article.

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