Have you ever wondered how your heart pumps blood without you doing any work?
Or why you feel instant pain when someone pinches you? Or how your hands move just at a thought?
These functions and sensations are due to the workings of the nervous system.
The nervous system is responsible for transmitting signals from one part of the body to the other. It controls voluntary as well as involuntary movements.
For involuntary movements, it sends out impulses for a movement like peristalsis (when food moves down the food tube) or to make your heart pump.
For voluntary movements, it controls every single movement or reflex action in a person’s body.
A neurological disease is a condition in which the nervous system becomes dysfunctional or faulty due to structural, electrical or chemical abnormalities in any part of the nervous system.
The Nervous System : Classification and Functions
The nervous system can be classified into two categories:
Central nervous system (CNS) – It is the main constituent of the nervous system and comprises the brain and the spinal cord. The spinal cord helps connect nerve cells from any part of the body to the brain, while the brain translates the electrical impulses sent to it, and relays back instructions for movement to the concerned body part.
Moreover, the brain stores memories and controls our thoughts.
Peripheral nervous system (PNS) – This system consists of 43 pairs of nerve cells that arise from the brain and spinal cord: 12 pairs of nerves arise from the brain and 31 pairs of nerves arise from the spinal cord.
There are two types of sensory neurons: sensory and motor neurons.
Now , what typically happens is that the sensory neurons will respond to pain, touch or any sensation and send signals to the brain and spinal cord. After the CNS processes this information, it sends out signals to the motor neurons which in turn will stimulate the muscles to react or move accordingly.
What’s even more impressive is that one complete cycle from sensory to motor neurons takes only about 0.15 – 0.25 seconds.
Thus, in order for the nervous system to function, the CNS and PNS will have to be working together. If either one of these systems were to get damaged or destroyed, the electrical pathway would be incomplete, meaning the person would not be able to think, move, respond to pain or even perform involuntary functions like breathing, digestion, pumping blood etc.
Credit : unsplash Caption : CNS
Common Neurological Diseases
There are various types of neurological diseases that affect different parts of the the nervous system:
In some parts of the brain called the ” dark region”, there are specific neurons that secrete a chemical substance known as dopamine.
Dopamine is an important neurotransmitter that sends signals from body nerves to the brain, making it important for controlling the movement and emotional response in human beings.
Parkinson’s disease is a progressive, movement disorder in which these dopamine-secreting neurons undergo degeneration and get destroyed. This leads to a decrease in dopamine levels in the brain and causes abnormal brain activity.
The ” dark region” , also known as the substantia niagra, consists of important nerve cells for movement. In this disease, the region visibly starts to disappear.
The cause of Parkinson’s disease is yet unknown. However, this condition is highly linked to genetics.
Clinical diagnosis: There are four main movement signs that are used to detect Parkinson’s disease:
Tremors: Continuous, uncontrollable and involuntary shaking of the body especially the hands.
This usually happens due to the excessive relaxation of muscles when the body is at rest and is also known as ” resting tremors”. However, when the body moves involuntarily, these tremors stop.
Rigidity: The muscles become really stiff and one smooth movement becomes multiple jerky movements.
The person trying to move their hands or legs will actually feel a resistant force acting in the opposite. Sometimes, it can get very tiring and painful.
Slowed down movements: Due to fatigue, stiffness, rigidity and inability to move, movements in the body are slowed down considerably.
Declining posture: Our body usually has a reflex action that maintains our posture. It is known as ” postural reflexes”. In this disease, the functioning of these reflexes get compromised as you will notice that the person is always slouching.
There are medications that can help reduce symptoms but unfortunately none of them can actually stop neurodegeneration.
These medications either increase dopamine signalling or stimulate dopamine receptors by dopamine antagonists.
Credits: unsplash Caption : Important dopamine secreting neurons
The brain has a complex blood supply going in and out. If this blood supply is lost and no blood reaches your brain, then the brain function will be lost too. When this happens, it is known as a stroke.
This cut-off of blood supply can happen in two ways. Either the blood vessel gets blocked or compressed or in some rare cases the blood vessels get ruptured.
When this happens the brain cells that require oxygen from the blood begin to get injured and eventually get destroyed.
However, rupturing of the blood vessels is more dangerous as the blood openly flows into the open spaces of the brain and damages the brain tissues by putting pressure on it.
The rupture of the vessel is known as hemorrhagic stroke and the blockage of the blood vessel is known as ischemic stroke.
These strokes occur very quickly within a few minutes due to a lack of oxygen and glucose.
The damage or seriousness of the stroke can be determined by the location and damage of brain tissues.
There are two common causes for a stroke:
Some heart conditions affect the muscle contraction of the heart. Due to this irregularity, sometimes blood clots are developed in the blood supply of the brain and cause blockage.
The most common cause of strokes is high cholesterol.
Some strokes are temporary,, meaning the blood clots or blockage will only last for 24 hours but sometimes they are permanent and cause life long abnormalities.
Treatment: The most common types of treatment for ischemic stroke is the use of tissue plasminogen activator (TPA) that will dissolve the blood clot.
For hemorrhagic stroke, antihypertensive drugs are administered in order to lower the blood pressure and reduce the amount of blood flowing out of ruptured vessels.
Alzheimer’s Disease and Dementia
Dementia is a condition in which brain cells get damaged leading to loss of memory, comprehension and alertness.
The most common cause of dementia is Alzheimer’s disease. It is a neurodegenerative disease of the neurons in the cortex, the place in the brain that is responsible for critical thinking, speech, decision making and most importantly, memory.
Every neuron has a special type of protein in its cell membrane. These proteins are responsible for helping the neuron grow and repair itself.
However, just like many proteins, they get used, and eventually, broken down, dissolved and recycled.
In case of Alzheimer’s, these proteins do not dissolve and get accumulated near the neurons, forming a clump known as plaques.
These plaques block brain signals between two neurons, making the brain dysfunctional. To make things worse, the immune cells start an immune response against them and cause inflammation in the brain, further damaging the surrounding neurons.
Sometimes, when these plaques are deposited near blood vessels they cause a rupture in the blood supply and damage the cranial tissues.
Another similar structure similar to plaques is known as tangles. The only difference is that tangles are formed inside the neurons and obstruct the internal pathway of electrical impulse and destroy the neurons.
As the brain cells start to get destroyed, the brain physically starts to shrink and the fluid filled cavities start to enlarge.
The trigger of Alzheimer’s disease isn’t very clear but it is highly linked to genetics and environmental risk factors.
As plaque and tangles buildup in the early stages, the symptoms are very mild. As it progresses, it leads to short term memory and loss of motor skills like cycling and eating.
Eventually, it leads to long term memory loss and the person becomes disoriented and complete loss of identity.
Credits: unsplash Caption: Alzheimer’s progression due to old age
Epilepsy is a seizure disorder that is recurring and unpredictable in nature.
A seizure is an event in which every single nerve cell of the brain is active at the same time and sends continuous and uncontrollable flowing impulse to one another.
Neurotransmitters are usually responsible for controlling the entry and stoppage of electrical impulses which are in the form of ions. The neurotransmitters responsible for transmitting impulses are known as excitatory neurotransmitters and the ones that stop the flow of impulse are known as inhibitory neurotransmitters.
What happens in case of epilepsy is that clusters of neurons in some part of the brain starts sending out excessive excitatory transmitters and suppressing the inhibitory neurotransmitters.
Therefore, this causes either too much excitation or too little inhibition.
This can be triggered by many factors including genetic cause, brain injury, tumours or infections.
The person will experience symptoms like jerking movements, loss of consciousness, development of smells, delusional fears but eventually depends on the neurons that are affected. They all mainly experience episodes of seizures.
In fact, seizures play an important role in diagnosing the type of epilepsy in a patient as every epilepsy has distinct types of seizure movements. Other methods of diagnosis indulge MRI, CT scan and ECG imaging.
Treatment : Daily medication like anticonvulsants are given depending on the specific location of the abnormality and age of the person.
Sometimes, surgeries are performed to remove the affected area but this is very dangerous and could lead to brain failure.
Lastly, there are nerve stimulants that control the functioning of the excitatory and inhibitory neurotransmitters.
Credits: unsplash Caption: Meninges: the other protective layer of the brain
The brain and spinal cord is covered with a protective lining called meninges.
The meninges consist of three layers: outer dura mater, middle arachnoid and inner pia mater.
There is a space filled with the cerebral spinal fluid between the arachnoid and the pia mater. This fluid acts as extra protection to the brain and spinal cord and also serves as a form of nourishment.
The space between the two layers also has blood vessels running through it.
Meningitis is a condition wherein the arachnoid and pia mater get inflamed.
There are many factors that can trigger this inflammation. The most common trigger is through Infections that causes damage to the cells.
Others include autoimmune disorders when the white blood cells attack the meninges or reaction to medication that is introduced directly into the cerebral spinal fluid.
There are two causes of infections in meningitis:
Bacteria. They include E.coli, listeria monocytogenes, streptococcus pneumoniae and Neisseria meningitidis.
Fungi. Eg. Enteroviruses, herpes simplex and HIV.
Moreover, these infections can either enter through the skull, cerebral spinal fluid or the bloodstream.
Once the pathogens reach the space cavity, the immune cells respond to this invasion by releasing cytokines. The interaction of cytokinesis and the pathogen causes further inflammation.
Treatment: For Infections, steroids are given to reduce injuries and are followed by antibiotics. Drugs like antivirus, antibacterial and antifungal are given depending on the type of pathogen.