Hey! I hope you're doing fine. I haven't written a blog in 2 months, 12 days. I know that it is a long period of time, especially for someone who is trying out new because you would not want your audience to lose interest (especially when you have a very small one).
Today's blog is gonna be a long one, I am writing after a long time, so I've chosen a topic of great interest. Buckle up!
The Nervous System: A Brief Introduction
The nervous system in our body carries an enormously staggering amount of functions. It is responsible for involuntary functions like breathing and digestion but on the other hand also responsible for voluntary functions like moving our muscles and legs etc. It contains nerves, which carry electrical impulses through the body, they are basically like messengers which send messages to our brain whenever we want to move our body. The brain is the great supervisor of all these functions and the whole nervous system. It is responsible for everything which happens in our body. The Spinal Cord is also a part of the nervous system, as it helps transfer messages to the brain. The Nervous System is of 2 types:
1. The Central Nervous System (CNS)
2. The Peripheral Nervous System (PNS)
The Central Nervous System consists of the brain and the spinal cord, while the Peripheral Nervous System consists of nerves, and there are different types of nerves in the body. Let's talk about the PNS first.
The PNS consists of nerves which consist of nervous tissue which contain tiny cells which transmit electrical and chemical impulses throughout the body, these cells are called neurons. They do almost all of the work in the PNS.
There are 3 types of nerves, The Motor Nerves carry signals to muscles and glands, The Sensory Nerves carry signals to brain to help sense touch, pain etc and The Mixed Nerves perform both the functions. In a sense, we can say that the motor nerves carry signals downwards to help our muscles move, the sensory nerves carry signals upwards to the brain and the mixed nerves carry signals both ways.
The PNS can be divided further into 2 divisions which are the sensory and motor divisions. The direction of the nerves of the sensory division is upwards and the direction of nerves in the motor division is downwards as I have already told you. Now, the motor division can be further divided into 2 divisions which are the Somatic or Voluntary division and the Autonomic or Involuntary division. As the name suggests, voluntary functions like moving an arm, playing and jumping are controlled by the Somatic division whereas involuntary functions such as heart beating, breathing and digestion are controlled by the Autonomic division. The Autonomic division can further be divided into 2 more division which are the Sympathetic and Parasympathetic divisions. Now, the sympathetic division is known for responding to dangerous and stressful situations like increasing your heart beat when you need it or pushing more epinephrine (adrenaline) or norepinephrine (noradrenaline) into the body. The Parasympathetic division is known for controlling the Sympathetic division like decreasing your heart beat and pushing Acetylcholine into the body.
Neurons are protected by glial cells. There are types of glial cells in our body. But first we should get to know about the parts of a neuron.
A neuron consists of a cell body, a nucleus and other cell organelles which cells have. It consists of branch-like Dendrites, which help to receive the message from the other neurons. The message then travels towards the cell body to the Axon, which transfers the message to other neurons. The neurons are covered by a protective myelin sheath which is formed by glial cells. Tiny spaces between axons are known as Nodes of Ranvier. They help speed up the process of transferring messages. The end of the neuron consists of the Axon Terminal, which transmits the message to the other neuron.
Now how it all works is basically like this, imagine there is a spider on your leg, now your sensory nerves sense that there is a spider on your leg and transfer the message to the spinal cord through neurons, the message travels upwards into the brain when you recognise that thing as a spider and after that the brain sends down a signal through the motor nerves for you to either scream or remove the spider off of your leg by shaking it. Neurons are the messengers involved in this process of receiving and transferring.
Now, let's talk about the types of glial cells and their functions in the body.
The Main glial cells in the CNS are as follows:
1.Astrocytes-Exchange of materials between neurons and capillaries.
2.Microglial cells-Immune defence against microorganisms.
3.Ependymal cells-Create, secrete and circulate cerebrospinal fluid.
4.Oligodendrocytes-Wrap around the neurons and produce an insulating barrier called the Myelin Sheath.
The Main glial cells in the PNS are as follows:
1.Satellite cells-Support and surround neuron cell bodies.
2.Schwann cells-Wrap around the axon and produce an insulating barrier called the Myelin Sheath.
It is important to remember that although the Schwann cells are similar to Oligodendrocytes, they wrap around the axon and form a myelin sheath, but the Oligodendrocytes wrap around the whole neuron and form a myelin sheath. Also, that the Satellite cells do not form a myelin sheath but protect the neuron's cell body.
Depolarization, Repolarization and Hyperpolarization.
The neuron cells carry electrical impulses throughout the body, so they must have an electric charge, right? Yes, they in fact do have an electric charge. The neurons have a positive charge outside the cell and a negative charge inside the cell. The outside and inside is separated by a cell membrane. When the neurons are sitting jobless, like they are now while you are reading this blog, they sit at about an electric charge, called their potential of about -70mV, they are known to be polarized. When you touch something hot suddenly, you flinch your hand away from it, when you do that, the ion channels sitting in between the cell membrane open and let the ions flow in and out, causing your potential to go as high as +40mV. This sudden change in potential happens when the electric charge goes at least above -55mV, if very few ions flow in and out and the potential does not exceed -55mV, nothing much happens but when it does exceed that, the potential goes in positive numbers, this is known as your action potential. The process of your action potential going above -55mV is known as Depolarization and the neurons are said to be depolarized. When your body is trying to calm down again, like "its alright, it wasn't too hot", then the potential starts going downward again, this is known as Repolarization.
The neurons might also drop their action potential below -70mV, to decrease the chances of undergoing depolarization, when then action potential exceeds -70mV, the process is known as Hyperpolarization and the neurons are said to be hyperpolarized. When a neuron sends an action potential, it hits a synapse which is in between the neuron and the other neuron, after hitting the synapse, the action potential is converted into a different type of signal by the synapse and transferred to the other neuron.
Now that you know all about the PNS, the nerves and the neurons, we can talk about the CNS, which is the Brain, mostly along with the Spinal Cord.
The Body's Great Supervisor: The Brain
The Brain handles every part of our body, and crazy to think about the fact that it named itself. The Brain is covered by our skull and our skin but after that its really covered by the meninges, which consist of 3 layers. The outermost is the Dura mater, the Arachnoid mater is the middle layer and the innermost layer is the Pia mater. Meningitis is caused because of the inflammation of the meninges. The brain is made up of white matter, this is what we call the brain tissue. It's washed up in Cerebrospinal fluid, which helps it flow inside our skull, well kind of.
It is divided into 2 hemispheres, the left and the right. The left hemisphere is thought to be the logical thinking side and the right hemisphere is thought to be the creative side. The wrinkles in the brain occur because when we were a foetus, our skull was too small and it was trying to fit in there, so it got kind of like squished up, which caused it to have wrinkles. The wrinkles are called gyri and the bigger wrinkles are called sulci. The brain has 3 main parts:
1.Cerebellum-This part of the brain helps in muscle activity.
2.Cerebrum-This part of the brain helps in thinking, learning, speech and feeling emotions.
3.Brain Stem-This part of the brain helps in relaying messages to the higher parts of the brain. It consists of the medulla which helps to send functions to lower parts of the body and is connected to the spinal cord.
Both the hemispheres of the brain do not function individually, in fact a lot of the parts of the brain function together although they are in very different regions. The hemispheres communicate through the Corpus Callosum which is in the middle.
The brain also consists of 4 lobes which have different functions.
1. Frontal Lobe- Located in the front of our brain, this lobe governs muscle control, motor skills, concentration etc. Broca's area is located in this lobe which is responsible for speech production.
2. Parietal Lobe- Located at the top of our brain, this lobe processes the sensation of pain, touch and pressure.
3. Occipital Lobe- Located in the back of our brain, this lobe helps us see moving objects, and bright colours, it is also responsible for visual perception.
4. Temporal Lobe- Located below the parietal lobe, this lobe is responsible for auditory functions (hearing) and some language involvement. It contains the Wernicke's area responsible for written and spoken language.
The brain also consists of the Thalamus which relays information inside you brain's different lobes. The Hypothalamus regulates the body's homeostasis and plays a big role in influencing our behaviour. The Amygdala is responsible for sexual and social behaviour. These all are a part of the limbic system of your brain, also called the Limbic brain and they play a crucial role in influencing our behaviour.
The Brain also consists of 12 cranial nerves, these nerves transmit messages from different parts of our body, but mostly the cranium, which is the front part of the skull. These nerves are as follows:
1. Olfactory Nerve
2. Optic Nerve
3. Oculomotor Nerve
4. Trochlear Nerve
5. Trigeminal Nerve (branches out into 3 nerves, hence the "tri")
6. Abducens
7. Facial Nerve
8. Auditory Nerve
9. Glossopharyngeal Nerve
10. Vagus Nerve
11. Spinal Accessory Nerve
12. Hypoglossal Nerve
All of these nerves have different functions but we will avoid them for now because I think I have told you enough for 1 blog, however we still need to talk about the Spinal Cord.
Spinal Cord
The Spinal Cord helps us in standing straight and sitting, it also helps us bend, it is very important for a human being. If it were not there, we would not have been able to do anything, would have been lying on a bed in weird positions. It consists of 33 small bones called the Vertebrae.
Out of these, starting from the top, 7 are called Cervical Vertebrae, 12 are called Thoracic Vertebrae, 5 are called Lumbar Vertebrae, 5 are called Sacral Vertebrae and 4 are called Coccygeal Vertebrae. All of these collectively make up the Vertebral Column. Remember, that the Spinal Cord is also covered by the meninges and Meningitis can also be caused in the Spinal Cord. The Cerebrospinal fluid is called Cerebrospinal because the Spinal Cord circulates it to the brain through the glial cells known an Ependymal cells, which I already told you about. The Coccyx is the last or the tail bone of the Spinal Cord. There is also a pair of 31 spinal nerves in our body. Sitting in bad postures can hurt our Spinal Cord so we should take care of it.
Alrighty, I think that's enough for today, don't forget about my physics blog coming up, its gonna be fantastic!
By
Deeparsh Bhanot
Comments
Post a Comment