UNIT 3: Compendium Review: Nervous Function

TABLE OF CONTENTS

1. Overview of Nervous System: CNS and PNS

2. Action and Resting Potentials: passage of nerve impulses

3. Reflex Arch: Somatic and Autonomic System

4. Senses

Below I will discuss the importance of the Nervous system and how it ties in with our senses. Above I made a brief table of contents of what I will discuss. As we go about our daily lives, our bodies work hard to keep up with our actions. How exactly are we capable of doing what we do? The 2 parts of the Nervous System I am about to discuss will explain the messages our brains interpret and send to our systems. Each of our senses depend on the sensory receptors it contacts. Hopefully my explanation of the Nervous System and Senses will give you a better understanding of how nerve impulses are transmitted and interpreted.

Overview of Nervous System: CNS and PNS. This system is composed of two major systems: Central Nervous System (CNS) and Peripheral Nervous System(PNS). Giggling at a joke, whispering a secret, smelling the fresh rain, stubbing your toe, dipping into the swimming pool; are all actions occurring in our brain. The brain and spinal cord are part of the CNS; which functions as a control center for our body. While the nerves make up the PNS; which is like a mail carrier, in that they send messages from the brain to the body. "Neurons are the cells that transmit nerve impulses between parts of the nervous system" (Mader 248). The picture to the right is a neuron. Which is composed of 3 different parts. The finger like projections are dendrites(receive information from the environment), the center dot is the cell body(keeps the cell functioning), and the snakelike extension is the axon(takes information away from the cell). Together these structures work to carry nerve impulses either towards the cell body or away from the cell body. There are also 3 different types of neurons in the body: sensory(skin, eyes, nose), inter neurons, and motor(muscles and glands). Wrapped around most axons is a covering known as a mylein sheath. It serves as a protective wrap and as a "nerve regenerat[or] within the PNS" (Mader 249). Multiple Sclerosis (MS) is a disorder that occurs when the mylein sheath becomes injured, which interrupts the nerve impulse flow. I work with a few residents who have this disorder, so its interesting to get more familiar with it. The body is unable to repair any neurons or mylein. A few disabilities in the residents I work with are: loss of muscle strength and control in arms and legs, decrease sensation, and difficulties talking. The cause of this disease is unknown, but the book relates how the immune system may be a factor. "Neurons are the oldest and longest cells in the body" (Faculty article). The packed information of nerve impulses jump across the gap to pass on the information to yet another neuron.

RESTING AND ACTION POTENTIALS: The transportation of nerve impulses can be related to that of a communication network. Resting Potential refers to the axon resting and not sending an impulse. The voltmeter reading at rest is about "-65mV(milivolts), indicating that the inside of the neuron is more negative than the outside " (Mader 250). Note the picture to the right, which shows the molecule action during resting phase. Potassium, since it has a solid line, easily passes through the neuron membrane during resting potential. While the other molecules Chloride and Sodium, have more difficulties. Inside the neuron is like a matching game; for every 3 sodium molecules that exit, the neuron wants 2 potassium molecules to stay inside. Once the match is settled and the molecules are in place, the volts are measure: known as resting potential. Action Potential is known for its speedy impulse of sending information down an axon (as mentioned above, it moves away from the cell body). Since inside of the neuron is negative and the outside is more positive; during action potential the positive charged Sodium molecules are attracted to the inside neuron, which opens up the sodium channels. Once the neuron becomes more positively charged, depolarization occurs. But when the Potassium channels open (negative charged ion) and settle outside of the cell, repolarization occurs. Note the picture to the right, it shows that the sodium and potassium channels opening and closing as the molecules hustle to enter and exit the neuron. After the busy running around, the molecules settle back to where they started, resting.


Information from one neuron flows through to another neuron by crossing a synapse. This transportation is from the many molecules known as neurotransmitters, which make up a synapse. Neurostransmitters are, "stored in synaptic vesicles in the axon terminals" (Mader 252). The synpatic cleft "separates the sending neuron from the receiving neuron" (Mader 252). Neurotransmitters "diffuse across the synaptic cleft where they can bind with receptor sites [..] to influence an electrical response" (Washington article). Similar to a sticky spiders web, some bugs make a lot of movement once attached (start an action potential: sending the message) while some bugs are less active while stuck on the webb. In today's field of medicine, there are many drugs that can affect the release of the neurotransmitters. A few common molecules we are aware of are norepinephrine, dopamine, and serotonin. These neurotransmitters have different functions, such as, moods, temperature regulation, and emotions. The common anti depressant Prozac "blocks the removal of serotonin from a synapse" (Mader 253). Synapses send signals to relay a message throughout the body to cells, mostly to muscles and glands.


REFLEX ARCH: SOMATIC AND AUTONOMIC SYSTEM. To start this section, the purpose of describing the reflex arch first is because it is an automatic response to protect against danger. We have all experienced this reflex numerous times. When you grab the hot plate out of the microwave your first action is to quickly pull your hand away (hence dropping the plate). This quick action is actually going through many processes throughout your body. The first impulse is that of the sensory receptors which quickly sends nerve impulses to the "sensory fibers through the dorsal-root ganglia toward the spinal cord" (Mader 263). It then passes on to interneurons, which travel to a synapse connecting with a motor neuron found within the spinal cord. Once with the motor neuron, the impulse attaches to an effector, which causes your physical action. This whole processes is sent to the brain, which reads the information it receives and then sends an action. The Somatic System is part of the PNS, the voluntary body movement. These nerves consist of: skin, skeletal muscles, and tendons. Autonomic system is divided into the sympathetic and parasympathetic division. The ANS "controls homeostatic maintenance of the body's internal state" (Wikipedia). A few examples of these heart rate, breathing, blood pressure, and perspiration. Imagine being pinned under a car, the Sympathetic Nervous System, would quickly fall into this category. During this emergency your body would quickly speed up its control mechanisms. Your heart rate would increase, allows more oxygen flow, increases blood flow to skeletal muscles, and dilates pupils. Many people know this system as the "Fight or Flight" response. The Parasympathetic Nervous System is more of the relaxation phase. This phase includes: relaxed heart rate, constricts the bronchioles since the demand for oxygen is low, pupils constrict, and the digestive system is moving. The picture of the brain to the right just shows how amazing this structure is. All the information it collects and reads, is then interpreted and sent out binding to receptors and performing an action!

To begin, sensory receptors are: " dendrites specialized to detect certain types of stimuli" (Mader 274). The book describes two different types of sensory receptors: exteroreceptors (taste, smell, see, hear, and equilibrium) and interoceptors (blood pressure changes, water/salt balances, and blood pH). There are also 4 categories of sensory receptors: Chemoreceptors(taste and smell), Pain receptors (watch/notify us of danger), Photorecpetors(vision), Mechanoreceptors(hearing: yelling, music), and Thermoreceptors (temperature regulator). The process of sensation was described when I discussed the reflex arch. The sensory receptors related to the spinal cord impulses are: Proprioceptors (muscle tone), Cutaneous Receptors (skin sensitivity ), and Pain Receptors(damaged tissues).

Touch: The skin goes through the process of either a startle reflex with pain or a regular sensation. Below is a picture of the different layers of the skin.


Taste: The book states that humans have about "3,000 taste buds" (Mader 278). The tiny bumps on your tongue are surrounded by taste buds. There are 4 well known tastes we acquire: sweet, sour, salt, and bitter. I really do appreciate the fact that I can taste the difference between foods, because as you age, unfortunately, we loose our sense of taste.


Smell: Interestingly enough, "80-90% of what we perceive as taste actually is due to the sense of smell" (Mader 279). An article states because of this some argue that, "Taste and Smell should likewise be grouped together as one Sense" (wikipedia). The olfactory neurons in the nose provide us with odors. To the right is a picture of the nose, which shows the path of smell, and the top part shows the olfactory nerve.


Vision: The eyes have many different parts, as you can tell by the picture below. We see objects due to the light projecting on the retina. This could be a complex topic, but the main purpose is how we see and even before impulses reach the brain. This sense is anothermany of us take for granted. Not everyone has been blessed with the ability to see the world.

Hear: There are also many parts within the ear, as shown in the picture below. The pathway of hearing occurs when "sound waves enter the auditory canal" (Mader 287). Individuals hear different sounds at different pitches and tones. Some can't hear high squeaky voices, whiles others have difficulties with low tones.

While watching the 4th of July fireworks, I definitely experienced all the senses. Sitting on the grass, I touched the smooth grass blades between my fingers. Each Mike n Ike I plopped in my mouth was tasteful. Just enjoying the outside air was refreshing, as the evening cooled off. As the lights dimmed to God Bless America; the array of colors lite the evening sky and the bang of each firework sounded above.

In conclusion, the nervous system is composed of two main systems: Central Nervous System (brain and spinal cord) and Peripheral Nervous System(nerves). Neurons are packed with information, sending nerve impulses to different parts of the nervous system. The cell body, dendrites, and axons make up the parts of a neuron. Each part works together to interpret the nerve impulses: resting or action potential. I also discussed Somatic as being a voluntary body movement. We experience different reflexes, depending on the situation. Cutting your finger sends sensory receptors on a journey, which eventually reaches the brain. The end reaction is from the brains interpretation. The 5 senses were also briefly touched: touch, taste, smell, hear, and vision. Our world is full of senses that we tend to take for granted. The nervous system constantly sends nerve impulses throughout the system and relaying the messages to our brains to make an action possible.

Works Cited:

http://emc.maricopa.edu/faculty/farabee/BIOBK
picture of brain and neuron
http://en.wikipedia.org/wiki/somatic_nervous_system and sensesquotes
http://faculty.washington.edu/
picture of potentials and quote
http://freda.quyeung.net/5senses/
pictures of 5 senses
Mader, Sylvia S. Human Biology. Boston: McGrawHill Companies, Inc. 2008.