Thursday, January 30, 2014

Parkinson’s disease (PD)


    Both chronic and Progressive, Parkinson’s disease is a movement disorder which commences when dopamine producing cells, in the substantia nigra, begin to malfunction and die over time. Dopamine is a chemical messenger in your body which transmits signals to parts of the brain that coordinate and initiate movement. And in the course of one’s suffering of Parkinson’s disease, these dopamine cells are terminated for unexplained reasons. Their rate of death then picks up consequently stumping the quantity of dopamine production.

    It is estimated that 1 million or so Americans suffer from Parkinson’s, and more than 75% of those victims are diagnosed after reaching the age of 50.  Although the cause is unknown and no major cure is currently present, there are medicating and surgery options to reduce the effect of the symptoms.

    Although there are common symptoms shared by the diseased people, there are many more symptoms that vary and are different between people. The progression of the disease varies in speed between all. Some might suffer more, for their progression is rapid, while others will suffer at a lesser rate, but over a longer time when their symptom worsening is at a slow progression. Such commonly shared sympyoms consist of
1.       Constant shaking tremor of limbs, Face Muscles, and Jaw
    When the disease hasn’t developed as much in one’s brain, 7 out of 10 experience a constant tremor in their hands and legs (sometimes in the face and jaw). It is described as a “beating” movement. It is known as a resting tumor since it occurs more often when the muscle is relaxed.
This indicates that the tremor usually is present after a loss of activity. As the disease progresses more and more, so does the tremor. It will even spread to different parts of the body.
2.       Slowness of movement (Bradykinesia)
    In this symptom, your voluntary muscle movements are slowed down, and they begin to slow down drastically as the disease progresses and worsens. Many will have problems, even with having the ability to start movements. When this is added to stiffening limbs (also a symptom of Parkinson’s) the amount of times a patient stumbles or falls increases. They might even find themselves getting stuck, this is when they cannot begin or stop walking/moving.
3.       Loss of balance and coordination
4.       Stiffness in limbs and trunk
    This is a symptom that includes the stiffness of muscles or inflexibility of them. Because of  the “rigityness” of the muscles, it decreases the rate and length your muscles can stretch to, for it decreases muscle contraction and relaxation. It will even cause cramps in addition to searing pains.

    But often in PD, there are secondary symptoms that are soon to follow. Speech issues such as slurred or stuttering talking habits, a stooped posture (such as leaning forward or backwards) are all caused by a lack of muscle control. There are many more symptoms to follow. More speech changes, loss of facial expression, difficulty in swallowing/drooling, pain, dementia/confusion, constipation, skin problems, depression, fear/anxiety, memory losses/hard time thinking, loss of energy, fatigue, and even urinary problems.

    The cause of Parkinson’s is yet to be solved, chemicals, and mechanisms have been suggested to cause an increasing amount of cell death.  These include…

Oxidative damage (due to stress)
Unstable molecules whose toxic effects are believed to be caused by oxidation are theorized to contribute to cell death, consequently leading to Parkinson’s. Oxidation, in the brain, is hypothesized to cause death and increase damage in tissues. As a result, antioxidants are now to be used as an attempt to slow down the disease.

Mitochondial dysfunction
In our cells, we have small organelles known as mitochondria which break down food suplements and convert it to energy for cell usage. An increasing dysfunction of the mitochondria were found in scientific research to cause cell death to accelerate. So in this theory, scientisits are now investigating if this plays a role in Parkinson’s disease.

Excitotoxicity
Excitotoxicity is the result of an over production of neurotransmitters leading to an increase of cell death. This cause has already been found in Parkinsons’s. Finding a way to now balance the production of neurotransmitants may be able to cause less cases of the disease and slow it down.

There are also genetic factors in which it has been found that 15%-25% of all patients have relatives who have had Parkinson’s . Again, after scientific study, it has been found that there is a defective gene, uncommonly found in families to which Parkinson’s disease may be inherited. 

Other causes include environmental factors which include rural living toxins such as MPTP which cause death to dopmaine and slow down its production.
Credits: Brain disorders source book.



Saturday, January 4, 2014

The Organization of the Human Nervous System



    I think of it this way. Cells. Multiple cells make up tissues. Multiple tissues make up organs and organ systems consist of multiple organs. Similarly, the nervous system is organized in the same way. Neurons and axons make up nerves, nerves make up neural circuits, and neural circuits create neural systems. Neural circuits which share similar tasks, come together to make neural systems.
  
    Such neural systems include sensory systems (observe and process information about the environments like the visual system, auditory system etc.) and the motor systems (reactions to certain input information. They include reflexes and counter balancing some moves).  Associational systems are composed of large numbers of cells and circuits which are located between both motor and sensory systems. Associational systems also carry out some of the most intricate processes and brain functions.

    As you know, the Central Nervous System (CNS) is composed of the brain (all 4 regions), and the spinal cord. And then, there is also the peripheral nervous system (PNS) which is all the cranial nerves which branch off the brain, and the many nerves which branch off the spinal cord. The PNS also includes sensory neurons which link sensory receptors (parts of sensory neurons which receive sensory information) to circuits in the CNS (missed information about neural circuits? Click here to view my previous post about them).


    The movement (motor) portion of the PNS is divided into 2 branches which both rely on one another in various ways. There is the somatic motor division which consists of nerves and axons which connect the brain and spinal cord to skeletal muscles. And, an autonomic nervous system which controls smooth muscles (which are muscles that move with conscious control ex: Biceps) and involuntary muscles. Both are crucial for survival, as they provide you, your muscle controls and gland controls to live. Without the somatic motor system, the autonomic system cannot move arms and legs, and without your autonomic system, you will need to keep remembering to execute many of your involuntary muscle movements!

    The neurons which lie within the PNS are located in ganglia which are lumps of nerve cells and supporting cells. Bundles of peripheral axons come together to make nerves, just like how thread is made of many thin fibers bundled and twisted. Those fibers are like axons. In nerves, all-around the body, lie glia. The only glia in the periphery though, are Schwann cells which lie layers of Myelin to help speed up neural messages.



In the PNS it is ganglia but in the CNS it is known as nuclei. Local accumulations of cells in the CNS are known as nuclei (not to get confused with the other meaning of nuclei – control center in most cells. Nuclei are found throughout the CNS, including the Spinal cord and division of the main area of the brain. In addition, there are cortices (cortex-singular) which are flat sheets of nerve cells. 

Tracts in the CNS consist of axons, just like those in the PNS. And those tracts that cross the midline division of the brain are called commissures. The area that contains axons, tracts, and commissures is known as white matter (named so because of its color due to its heavy content of myelin). On the other hand, gray matter is the large clumps of cell bodies and neuropil (click here for more info about neuropil). It is located in the brain and spinal cord.


Neural Circuits

Neural Circuits

  Neural Circuits have different and unique tasks that process different information and are organized and arranged in specific ways. In addition, they control our senses, moods, movement, etc. The connection format is what distinguishes the circuits. These connections are made of thick lumps of dendrites and axons and glia, which are known as neuropil.
    
    Although different, many have the same characteristics and similar ways processes are carried out. Preeminent is the direction and way that information travels in all circuits. The direction information flows is key to the distinction of the circuit.The 2 types of preeminent is afferent and efferent. Neurons that carry information from the Peripheral nervous system (PNS)(check my post about peripheral nervous system and central nervous system here for more information here) to the central nervous system are called afferent neurons, but those who carry information away from the CNS to the PNS branches, are classified as  efferent neurons. And there are 

    Interneurons (local circuit neurons) which only participate in short-distance routes which their axons extend.

    An example of a neural circuit is the myotatic spinal reflex, also known as knee-jerk reflex. Afferent and efferent play the role of the reflex. When you get your reflexes tested, you get a hammer tap test. This is what, if you have normal reflexes, triggers the knee-jerk reflex.

    So, here is how it works. The process begins after the hammer has tapped your knee. This stretches your tendon which then stretches the sensory receptors in your extensor muscles (the sensory receptor is the pink little dot on the extensor muscles in this diagram). You can see a blue line, a sensory axon, which is afferent. This axon carries the message of the hammer tap to the purple interneuron and the red motor axon. Now, the interneuron stops the yellow flexor muscle motor axon from moving the flexor muscle. Instead, the flexor muscle relaxes.

    Now, the red extensor muscles axon carries the message to the extensor muscles, which then contracts the muscle. Finally, the leg extends.
Credits: Neuroscience 4th edition