Read + Write + Report
Home | Start a blog | About Orble | FAQ | Sites | Writers | Advertise | My Orble | Login
 
Google

Living Healthfully - March 2008

The Nervous System (Part 2)

March 31st 2008 10:50
The Central Nervous System

The Brain

The brain is divided in three major parts: the forebrain, midbrain, and hindbrain.

The forebrain is further subdivided into two: the telencephalon and the diencephalon. On the other hand the midbrain is composed of the structures within the mesencephalon. And in turn the hindbrain consists of the metencephalon and the myelencephalon.

The Forebrain

The telencephalon of the forebrain is made up of the cerebrum and the basal ganglia, while the diencephalon is composed of the thalamus, hypothalamus, subthalamus, and epithalamus.


The Cerebrum

The cerebrum consists of two hemispheres (Figure 12), which together form the largest part of the brain. The structures in the left hemisphere have very similar counterparts in the right hemisphere. One hemisphere is connected to the other by means of the massive bundle of nerve fibers known as the corpus callosum. Each hemisphere is composed of an outer and an inner layer (Figure 13). The outer layer is known as the cerebral cortex. The cerebral cortex is composed of the soma or neuronal cell bodies. These structures make the cortex gray (gray matter). On the other hand, the inner layer is composed of the nerve fibers of those somas located in the cortex. Since these fibers are white, they are collectively known as the white matter.



Figure 12. Cerebral Hemispheres




Figure 13. Gray and white matter


The cerebral cortex is heavily folded. The folds are called gyri, and the grooves between them are known as sulci (or fissures if they are unusually deep).

One hemisphere has functions which make it distinct from the other. The left hemisphere controls the right part of the body, while the right hemisphere controls the left part of the body. Usually the dominant of the two hemispheres is the left. Thus more people manifest with right handedness rather than left handedness.

The contralateral functioning of each hemisphere is due to the bifurcations of the nerve fibers either at the cervicomedullary junctions or at the spinal cord. These bifurcations will be further discussed at the latter section of this discourse.

The table below discusses the functions of the dominant and the non-dominant hemispheres of the cerebrum.



To be continued...
54
Vote
Shared on
Comments (2)Comments (2) Add CommentsAdd Comments
[ Link ]
Posted By: Physiotherapy - Category: No Category
   


The Nervous System (Part 1)

March 25th 2008 13:13


THE NERVOUS SYSTEM
The human nervous system consists of around a hundred billion specialized cells (Kahl, 2003), known as neurons. The general function of these neurons is to receive sensory stimuli and to transmit them to effector organs, muscular or glandular.

However aside from the neurons the nervous system also includes cells whose main functions are to support the neurons and keep their fibers intact and well-organized. These cells are collectively known as the neuroglia (Snell, 1997).

Though these two groups of specialized cells differ from each other, they work hand in hand to compliment the endocrine functions in carrying out the bodyÂ’s responses to the ever-changing environment (www.biologymad.com, 2004).

The Two Major Groups of Cells Comprising the Nervous System
Two differentiated cell types comprise the neural tissues. They are the nerve cells (neurons) and the neuroglial (glia) cells (www.sci.uidaho.edu, 2007). The neurons (Figure 1) can be considered as the primary role players, since they are the cells which generally handle the reception and interpretation of sensory stimuli, as well as the organization of the bodyÂ’s responses to such stimuli. But neurons cannot function as they have been destined to function without the enhancements provided by the neuroglia. And so the neuroglial cells are also important in a sense that they provide structural integrity to the nervous system and functional support that enables neurons to perform.

Neurons
A typical neuron varies considerably in size and shape, but each possesses a soma (cell body) from whose surface project one or more processes known as neurites (nerve fibers). Those neurites responsible for receiving information and conducting it towards the cell body are called dendrites. Those neurites that conduct impulses away from the cell body are called axons (Snell, 1997).

Figure 1. A typical neuron


The soma of neurons appears to be gray in complexion and the neurites usually appear to be white because of the myelin sheath covering these fibers.

We can keep the above facts in mind if we are going to classify the neurons according to their structural characteristics. And so if a neuron contains only one projection, that neuron can be classified as a unipolar neuron. But if two fibers project from the soma, that neuron can be considered as a bipolar neuron (Figure 2). In addition, there are instances that a neuron contains more than two neurites. This neuron is a multipolar type of neuron (Figure 3).

Figure 2. Upper portion shows an example of a bipolar neuron, while lower portion shows an example of a unipolar neuron (formerly known as pseudounipolar).


Figure 3. Multipolar Neuron


In the illustrations below, we can observe an example of how the nervous system works. And from these pictures, we can infer that neurons can also be grouped according to their functions (Figure 4).

Figure 4. The knee jerk


The knee jerk is a reflex elicited once the patellar tendon is tapped (by a neurohammer). The force from the neurohammer is being detected by the sensory receptors in the knee region especially in the patellar tendon. The sensory receptors then relay the signal to the sensory nerves which in turn pass the information (that the tendon is being tapped) to the spinal cord. Within the spinal cord there are neurons that connect the sensory neurons to the motor neurons. These are the interneurons. These interneurons integrate the sensory information to the central nervous system and then to the motor neurons, to produce a meaningful response. And after such integration, the central nervous system relays the ideal response to the motor neurons: that is to move the leg towards extension. The motor neurons then pass the information about the appropriate response to the effectors (in this case the quadriceps femoris muscle). The quadriceps, being the effector, thus executes the response and contracts to move the knee towards extension.

In the above scenario, we can observe three groups of neurons: the sensory or afferent neurons, the interneurons, and the motor or efferent neurons.

The afferent or sensory neurons have long axons and transmit nerve impulses from sensory receptors all over the body to the central nervous system. The peripheral sensory neurons form ganglia at the dorsl aspect of the spinal cord and enter the central nervous system via aspect of the spinal cord. Interneurons are also called association neurons exclusively within the spinal cord and the brain. The efferent or motor neurons transmit impulses from the central nervous system to the muscles and glands that carry out the response. They exit the central nervous system via the anterior gray horn cells of the spinal cord.

On the other hand, the nerve fibers can also be classified physiologically. Generally nerve fibers can be classified either as type A or C (Guyton and Hall, 2000). Type A fibers are myelinated fibers, capable of fast conduction of signals and impulses. Type C are unmyelinated fibers, that conduct impulses at low velocities. Type A fibers usually relay sensory impulses for stretch, pressure, vibration and discrimination, as well as motor signals to move the muscles of the body. Type C fibers are capable of relaying painful stimuli from the body to the central nervous system, and can also send reflex responses to effectors.

Neuroglia
There are four groups of neuroglial cells (Snell, 1997). These are the astrocytes, myelin sheath- producing cells, microglia, and the ependymal cells.

Astrocytes
There are two types of astrocytes: fibrous and protoplasmic.

Fibrous astrocytes (Figure 5) are found mainly in the white matter, where their processes pass between the nerve fibers. Each process is long, slender, smooth, and not much branched. The cell bodies and processes contain many filaments in their cytoplasm.

Figure 5. Fibrous Astrocytes


On the other hand protoplasmic astrocytes (Figure 6) are found mainly in gray matter, where processes pass between the nerve cell bodies. The processes are shorter, thicker, and more branched. Their cytoplasms contain fewer filaments.

Figure 6. Protoplasmic Astrocytes


The astrocytes with their branching processes form a supporting framework for the nerve cells and nerve fibers. In the embryo, they serve as scaffolding for the migration of immature neurons. Astrocytes can also be neurotransmitter regulators, limiting the effect of GABA and glutamic acid secreted by nerve terminals. They also serve as storage for glycogen which can be broken down to become energy source for neurons in response to norepinephrine release. They can also become phagocytes cleaning up debris and wastes surrounding neurons.

Figure 7. Nerve Fiber wrapped with myelin sheath


Myelin Sheath-Producing Cells

Myelin sheath is a structure that speeds up the transmission of signals along the nerve fibers (Figure 7). The increased velocity of the transmission is due to the saltatory conduction, when the action potential only occurs from one node of Ranvier to another.
In the central nervous system, the cells that produce the myelin sheath is known as the oligodendrocytes (Figure 8). And in the peripheral nervous system, they are known as Schwann cells (Figure 9)

.Figure 8. Oligodendrocytes


Figure 9. Scwann cells


Microglia

In the normal brain and spinal cord microglia appear to be inactive. However in inflammatory and degenerative lesions of the central nervous system, they proliferate to the sie of lesions and become active phagocytes. Joined by the monocytes of the blood, they work to remove dead cells and debris on sites of lesion (Figure 10)

Figure 10. Microglia


Ependymal Cells

These cells ensure that the cerebrospinal fluid are constantly circulating around the central nervous system in order to facilitate the transport of nutrients and essential substances to the system. Ependymal cells (Figure 11) come in three forms: ependymocytes, tanycytes, and choroidal epithelial cells.

Figure 11. Ependymal cells


The Structural and Functional Organization of the Nervous System
Based on anatomical features the nervous system can be divided into two parts: the central and the peripheral nervous system. While the brain and the spinal cord constitute the central nervous system, the so-called cranial nerves and the spinal nerves form parts of the peripheral. The peripheral nerves connect the central nervous system with the sense organs, i.e. the organs for vision, hearing, smell, taste, perceptional touch, and other effector organs like muscles and glands.

Another way of dividing the nervous system is to look at it from a functional point of view: autonomic and somatic.

The autonomic nervous system is in connection with glands, internal organs, and involuntary muscles. The functions of the autonomic nervous system stand above our will and awareness, in the sense that the autonomic nervous system automatically takes care of the body.

In contrast, the somatic nervous system handles the skeletal muscles of the body, in other words functions of which are governed by our will (Kahl, 2003).

Below are charts that feature the subdivisions of the nervous system.


ANATOMICAL ORGANIZATION



PHYSIOLOGICAL ORGANIZATION



TO BE CONTINUED...
59
Vote
Shared on
Comments (1)Comments (1) Add CommentsAdd Comments
[ Link ]
Posted By: Physiotherapy - Category: No Category
   


Make Use of Your Hormones to Improve Exercise results...the Natural way! (LAST PART)

March 7th 2008 13:30
Glucose Utilization during Exercise- A Function of the Insulin
Insulin, though not mentioned in Table 2, is also important in both aerobic and anaerobic exercise. As discussed, during these two types of exercise, glucose is one of the fuels that energize the body. And so glucose production has been shown to be stimulated by the catecholamines (and at rest, the glucagon). But how can the glucose produced and delivered to the blood be consumed by the cells in the body? The answer to this is through insulin coming from the pancreas.

Insulin facilitates entry of glucose into the cells in order for it to be transformed into energy (glucose utilization). Without insulin, glucose would only be left within the plasma and would be useless. This would also lead to complications as seen in Diabetes Mellitus patients.

The effect of insulin to the body processes is naturally delayed, as seen in Figure 4. We can only observe sudden rush in insulin secretion after exercise (Scheen et al., 1998). This is because the catecholamines limit such secretion during exercise, since the body needs to produce glucose into the blood as energy reserves. And presence of insulin would impede such process.

However after exercise when glucose within the muscle fibers and other cells is depleted, the glucose reserves in the blood have to be mobilized towards the cells to replenish such depletion. This is where insulin comes into play.

Figure 4. Mean profile of Insulin Secretion Rate (ISR) in the resting condition (unshaded) and in the exercise condition (shaded)


The above concepts are useful when choosing what type of exercise a Diabetes Mellitus (DM) patient (especially Type I) is to perform. If we are to exercise a DM patient, what type of exercise is applicable? In order to answer this we have to consider which type of exercise stimulates more glucose production. Obviously this would be the anaerobic type. But as stated glucose produced in this occasion stays in the blood. And so the tendency to have hyperglycemia is natural. And among the normal individuals, this would not be a problem since post-exercise hyperinsulinemia occurs immediately. This hyperinsulinemia would then control excessive blood sugar. But among DM patients, hyperinsulinemia does not take place. And so hyperglycemia remains leading to worsening of the patientsÂ’ conditions.

On the other hand, what happens during aerobic exercise? Scheen et al. (1998) do not deny that glucose in blood increases during aerobic exercise (but not as much as in anaerobic). And together with this insulin secretory rate decreases. Nevertheless this would not be a problem. Since the glucose level during aerobic exercise does not cause hyperglycemia, unlike in anaerobic exercise. Also, increased peripheral blood flow augments total insulin delivery to muscles and thus compensates at least in part for the decreases plasma insulin concentration.

We can therefore conclude that aerobic exercise is better among DM patients than anaerobic exercise. However if we still opt to continue with anaerobic programs, we have to ensure that patient has administered insulin infusion before activity.

Oxidation in Aerobic Activity- A Role of the Thyrotropin and Thyroid Hormones
Another question that has to be answered is this: how does the body constantly sustain oxygen to produce aerobic energy? This is through the thyrotropin (TSH) and thyroid hormones. According to a certain Dr. Kennedy, TSH and the thyroid hormones control the rate of oxidation or oxygen utilization in energy production. Figure 5 shows the increase in TSH in response to aerobic exercise.

Figure 5. Mean plasma TSH during resting condition (unshaded) and exercise condition (shaded).


Without TSH and the thyroid hormones, energy from fats cannot be utilized. This is especially manifested in patients with hypothyroidism, as their physique shows increased fat deposition.

On the other hand excess of these hormones further increases metabolism and fat utilization. This condition results in being ectomorph (as in patients with hyperthyroidism).


Growth in Exercise

Lastly, let us talk about growth in exercise. Growth is another important result of exercise. In an individual exposed to long-term exercise, one of the most significant manifestations of growth is hypertrophy of muscles. We can especially observe this muscle building process during resistance training exercise, which might be considered as anaerobic in nature.

In the case of a muscle fiber, it must be broken down systematically through resistance training. The fiber responds with an increase in the synthesis of new contractile proteins that result in the fiber becoming larger and stronger. This growth response is the result of the presence of potent anabolic (muscle-building) hormones whose function is to promote protein synthesis. And so we can infer that protein synthesis does not only occur to produce energy. It also occurs with the aid of such hormones in order to promote growth especially at the muscular level. The anabolic hormones involved are GH, IGF-1, and the testosterone (Taylor et al., 2000). As more fibers are involved, a greater hormonal response is necessary, and thus greater changes in whole muscle are possible (Stout).

Conclusion
Truly the endocrine system presents different facets of response during exercise. A more comprehensive description of these facets would be more complicated. And so this discourse has presented the basic activities our endocrine glands do in order to sustain homeostasis and provide adaptations to the body in order for it to keep up with the demands of activities. Understanding these basic concepts can give us a huge foundation if we are to pursue more advanced endocrinology. These concepts would also come in handy when we are to choose which exercises are we to prescribe for patients with different conditions and different needs.

And so if we opt to improve strength, agility, and speed, and increase energy storage for immediate use, then anaerobic exercise will be the exercise of choice. It should be since it utilizes our catecholamines and the growth hormones to achieve our goals. Variants of aerobic exercise are those that involve high intensity but low duration exercises, like weights training, sprint, tennis, and even soccer.

But if our goal is weight and fat loss, or even increase in general body endurance then aerobic exercise shall be our choice. It does not only maximize the use of oxygen to burn our fats, it also teaches our body to conserve energy in order to prevent immediate, untimely muscular and cardiovascular fatigue. Aerobic exercise does this through its effect on the bodyÂ’s release of cortisol, thyroxine, and sex hormones. Aerobic activity or exercise includes jogging, brisk walking, marathon run, treadmill exercise for more than 20 minutes, and even cross-country skating.

And lastly take note that the time of the day when we exercise affects the results. And so if we want to maximize the use of our hormones (like growth hormones and thyroid hormones) for improved growth and fat burning, then evening exercise will do the trick.

THE END>>>
80
Vote
Shared on
Add CommentsAdd Comments
[ Link ]
Posted By: Physiotherapy - Category: No Category
   


Make Use of Your Hormones to Improve Exercise results...the Natural way! (Part 3)

March 4th 2008 11:06
The table featured last time shows a simple concept on hormone reactions during exercise. As seen in the table glucose and glycogen breakdown during exercise is mainly the role of the catecholamines- the epinephrine and the norepinephrine. They ensure that these energy sources are available in the blood during activities. However one of the catecholamines, the norepinephrine also contributes to lipolysis or fat metabolism, transforming it to another consumable energy. Free fatty acid (FFA) mobilization that leads to lipolysis is being triggered by the GH. Protein synthesis on the other hand, has been shown to be stimulated again by the GH and others like testosterone, cortisol, and IGF-1. These hormones create and break down protein to provide growth and energy as well (gluconeogenesis).

It is also notable from the table above that each hormone has its own stimulant for release. As mentioned earlier, hormone response depends on the type of activities an individual is performing. As with this discourse, we focus on the reactions of the hormones to the different forms of exercise. And we shall see that the catecholamines are stimulated by performance of moderate to intense exercise. But later on we shall see that the release of these hormones is more sensitive when the body does an intense type of activity (anaerobic). On the other hand, prolonged exercise triggers cortisol release while light to moderate exercises stimulate estrogen release (aerobic). In addition, GH, testosterone, and IGF-1 are activated with any type of exercise but more of the aerobic (Marks and Kravitz, 2000


[ Click here to read more ]
52
Vote
Shared on
Read MoreRead More Add CommentsAdd Comments
[ Link ]
Posted By: Physiotherapy - Category: No Category
   


More Posts
July 2008
4 Posts
June 2008
1 Posts
May 2008
1 Posts
Older Posts
73 Posts dating from February 2007
Email Subscription
Receive e-mail notifications of new posts on this blog:
[ View Blog Summary ] [ Create A New Post ]
Moderated by Physiotherapy
Copyright © 2006 2007 2008 On Topic Media PTY LTD. All Rights Reserved. Design by Vimu.com.
On Topic Media ZPages: Sydney |  Melbourne |  Brisbane |  London |  Birmingham |  Leeds     [ Advertise ] [ Contact Us ] [ Privacy Policy ]