Chapter 25 (Nervous System, Eyes, Ears, Taste, Touch ...



Chapter 25 (Nervous System, Eyes, Ears, Taste, Touch, Endocrine)

The Nervous System (Section 1)

The role of the nervous system is to gather and interpret information regarding our internal and external environment. Our nervous system controls all of our organs and monitors our organs to keep them working properly. Our nervous system is responsible for us speaking intelligently (sometimes not so intelligently), smelling, tasting, hearing, seeing, moving in coordinated fashion, thinking, and experiencing emotions.

The nervous system can be broken down into two divisions. One division is the central nervous system (CNS), which includes our brain and spinal cord. The other division is the peripheral nervous system (PNS), which is our passageways for communication (nerves) that connect all areas of our body to the central nervous system. In a nutshell, all the nerves in our body that extend out from the brain and/or spinal cord are in the PNS.

The Peripheral Nervous System (PNS)

The nerves in this system are called neurons. Each neuron has a cell body (largest central mass area), an axon, and dendrites. Function: Cell Body – collect information to be sent toward or away from the CNS, Axons: carry information away from the cell body it is attached to, Dendrite: carries information to the cell body it is attached to.

Axons can vary in length, some are very short and some are long. Some of the axons are up to a meter long (those running from the cell bodies located near your lower back all the way to your feet). The tip of the axon is branched and is called the axon terminals, which are in contact with dendrites of another neuron. The impulse from the axon is passed to the dendrite and the dendrite carries the impulse to its cell body. Messages are passed from neuron to neuron in this manner.

Special neurons called sensory neurons gather information about what is happening in and around our body and send the information on to the CNS for further processing. Sensory neurons have special dendrites called receptors that detect the changes inside and outside our body.

Neurons that send information to the brain and spinal cord are called motor neurons (motor means to move). When muscles get messages from motor neurons, they respond by contracting (RECALL: muscles only do work by contracting which means they get shorter).

Motor neurons send messages to your glands such as sweat glands (when you are too hot and you need to cool down by sweating). They also send messages to out digestive system when we get hungry or when we eat and the food needs to be digested. This tells our digestive organs to begin functioning.

Nerves are axons bundled together with blood vessels and connective tissue. Nerves are everywhere in our body (think of a few times you have stimulated nerves, like getting a scrape, stumping a toe, biting your tongue, etc.) Most nerves contain the axons from both sensory and motor neurons.

The Central Nervous System (CNS)

The CNS works closely with the PNS. The CNS receives information from all over the body from sensory neurons and responds by sending messages back by motor neurons. The brain is the “control center” for our CNS. The brain has many different jobs to carry out. The processes that the brain controls automatically are called involuntary. An example of an involuntary control is breathing, we do not have to think about breathing and control our diaphragm to inhale and exhale air. We do not have to think about digesting food, it happens through involuntary control of the brain.

Some activities are controlled by your brain and are voluntary. Think about your desire to pick up a quarter (coin) from a tabletop. You have to think about what you want to do and your brain coordinates the activity and tells your arm where to move to and your fingers when to bend in order to grasp the money. This takes many signals from your brain to do this in a coordinated fashion.

Parts of the Brain

Our brain has three parts, the cerebrum, cerebellum and medulla. Each structure carries out specific functions.

The largest portion of your brain is your cerebrum; it is the top or upper portion of your brain that has two hemispheres. It has many convolutions (folds) that increase the area. This is the portion responsible for thinking and storing most memories. The cerebrum controls voluntary actions, like detecting touch, light, sound, odors, tastes, pain, heat, and cold.

The left hemisphere of the cerebrum directs the right side of the body and the right hemisphere directs the left side of the body. This is because the axons cross over to opposite sides of the body in the spinal cord. In order to carry out our daily functions, both hemispheres must work together and most activities involve both hemispheres.

The left hemisphere controls speaking, reading, writing, and solving problems. The right hemisphere controls activities that involve imaginations, appreciation, and creativity.

The second largest part of your brain is the cerebellum. It is located at the back of your brain and right below the cerebrum. It receives information from your skeletal muscles and joints. This helps keep track of the body’s position. This maintains balance when standing on one leg or stretching for an object on a high shelf. If you begin to lose your balance, the cerebellum sends messages to the proper muscles and joints to regain balance and prevent a fall (hopefully, sometimes we can’t compensate and may fall to the ground).

The part of our brain that connects to the spinal cord is the medulla. We cannot live without our medulla because it controls blood pressure, heart rate, breathing and other involuntary activities. If our blood pressure gets too low it sends a message for our vessels to constrict and increase blood pressure. If it allowed the blood pressure to remain low you may faint.

The Spinal Cord

Our spinal cord (part of the CNS) is about the diameter of our thumb. The spinal cord is protected by vertebrae (RECALL where vertebrae are located), which surround the cord. Our vertebrae have a hole in them that allow the spinal cord to run the entire length of our spine. Sensory information goes into the spinal cord and motor information travels out of the spinal cord. The nerve fibers of the spinal cord allow our brain to communicate with our peripheral nervous system.

If the spinal cord becomes damaged or injured, the point below the injury is affected. The nerve impulses (messages) cannot travel from below the injury to the CNS (brain). The brain also cannot send messages to the area below the injury. Many people have spinal cord injuries each year. The area below the injury will become paralyzed (may be temporary or permanent, depending on the injury). Many of the injuries are the result of automobile accidents, but for young people, sports injuries affecting the spinal cord often occur.

We cannot manufacture “synthetic nerves” to replace damaged nerves, so many nerve damages are life long. It is important to take all the precautions to avoid injuries to the CNS and PNS. Safety precautions for children include proper fitting helmets and pads when riding bicycles, skateboards, motorcycles, and scooters. Many injuries that result in children being paralyzed are due to these types of accidents.

Reflexes

If you have ever stepped on a sharp rock or object while bare foot, you probably removed your foot very rapidly to avoid injury. This is a reflex. When you stepped on the object a sensory nerve sent a message to your spinal cord and the spinal cord immediately sent a message to your leg to pull itself off of the object. In the normal situation your sensory nerve would have sent the message to the spinal cord and the spinal cord would forward the message to the brain and the brain would send a message back. In a reflex the sensory message goes to the spinal cord and the spinal cord sends the message right back to the leg muscles. The message is then sent on to the brain. The spilt second it would take to send the message all the way to the brain and get a response may be long enough to cause injury, but going to the spinal cord and back decreases the time and may prevent more harm.

(Section 2) Responding to the Environment

When we detect changes from our environment, our brain interprets the change and responds to them by sending messages by way of motor neurons. We have sensory receptors located all over our body. We can sense heat, cold, pressure, pain, and touch.

Types of receptors: eyes are receptors to light, ears are receptors to sound waves, our tongue has taste buds that sense tastes, and our nose has receptors to sense odors. Another organ that has receptors is the skin; it has touch and pressure, heat and cold receptors.

Our Eyes (responsible for vision)

The parts of the eye: Cornea, Iris, Pupil, Lens, Retina, and Optic nerve. The cornea is the clear part in the front of our eye that protects the eye, but allows light to enter. The iris is the colored portion of our eye that can get thinner or wider to control the amount of eye entering our eye. During bright conditions, the iris is wider to reduce the amount of light entering our eye. During dim or dark conditions, the iris becomes thin to allow much light into our eye. The pupil is a hole in the center of the iris that “looks black”. This is the hole the light passes through to enter our eye. Behind the pupil, we find the lens, which can flex to focus the picture we see. The back “wall” of the eye contains the retina, has the special cells called photoreceptors (rods and cones). The rods function in low light and allow us to see in shades of gray (more like shadows). The cones function in light and allow us to see color. Once the receptors have gathered the information, it is taken to the optic nerve, which transports the image to our brain for interpretation.

Types of Vision: In normal vision, the image is focused directly on the retina. Someone that is nearsighted has the image focused in front of the retina and a person that is farsighted has the image focused behind the retina. Contact lenses can be used to correct this vision imperfection.

Hearing: Our ear is the organ to gather sounds and the sounds are transmitted to the brain in the form of an electrical impulse and interpreted. Our outer ear (the portion we see) funnels the sound waves we detect to the inner ear. The sound waves are directed into the ear canal and strike our eardrum, which is a layer of tissue that begins to vibrate. The eardrum is connected to the ear bones, which will vibrate, and one ear bone is connected to the cochlea. The cochlea has fluid inside, which will vibrate and this stimulates the auditory nerve. The auditory nerve transfers this into an electrical impulse and carries it to the brain, which interprets what we are hearing. This process occurs very rapidly.

Taste: Our tongue contains small folds called taste buds. These taste buds have special cells that send messages to the brain and the brain interprets what we taste. We taste four forms of flavors; sweet, sour, bitter, and salty. The folds or bumps where our taste buds are located are called papilla.

Smell: Our nose also helps us detect tastes. Have you ever noticed, when you are sick and congested that the food you eat does not taste the same as it does when you are not sick? The brain collects the information from our taste buds and nose receptors and interprets the information so our sense of taste is enhanced by our sense of smell. Our sense of small relies on our olfactory nerves, which are the sensory nerves that gather the scents we inhale. The olfactory nerve sends the message as an electrical impulse to the brain and the brain interprets the scent. (Can you believe some people research deodorants and the effectiveness of the deodorants and they sniff underarms all day for the research, WHEW). Some smell foods and determines pleasing ingredients and not so pleasing ingredients in recipes.

Section 3 The Endocrine System

The endocrine system is composed of glands that release chemicals into our bloodstream. The endocrine system controls slower long-term functions, like fluid balance in our body, growth rates, fight or flight responses, and other vital functions.

The glands release chemicals and the chemicals are called hormones. Once in the bloodstream the chemicals are carried to other parts of the body. One example of endocrine glands is the adrenal glands. The adrenal glands are located at the top (right above) of the kidneys. The adrenal glands produce epinephrine also known as adrenaline. This hormone is produced and released when your body needs to prepare itself for danger. It causes your heart rate to increase, breathing to increase and your body to be ready to flee from danger or defend itself for survival. This is known as the “fight or flight” response. You may have noticed these effects when you were scared or angry.

Other endocrine affects: the pituitary gland releases hormones that promote growth of our body. The thyroid gland regulates the proper amount of water in our system and stimulates the birth process in women (contractions during the delivery process of a baby). RECALL: the pancreas is also in the endocrine system and it regulates blood sugar by releasing the hormone insulin. The ovaries in the female release hormones for reproduction purposes and the testes in males release hormones in the male that are involved in reproduction.

The thyroid glands located in your neck increases the rate in which you use energy (controls metabolism). The thymus gland located right above your heart regulates your immune system and helps your body fight disease. We also have parathyroid glands that regulate the amount of calcium in our blood.

How does the body control the endocrine system? The method our body uses is called a feedback loop. Example: if our blood sugar is low, our body signals us it is time to eat. This raises the blood sugar, but the pancreas releases insulin to regulate the amount. If too much sugar is in the blood, the liver is signaled to turn the sugar into glycogen and store it for use as energy at a later time. When the blood sugar returns to a normal level, the pancreas stops releasing insulin. In order to keep our blood sugar levels from falling below normal, our body signals us it is time to eat, and the cycle “loop” begins again.

When someone’s pancreas cannot produce enough insulin, the person has diabetes mellitus. Many of these people can control their blood sugar with the types and amounts of food they consume. Some people must take insulin injections to control their blood sugar.

Some children have pituitary glands that do not make enough growth hormone and they do not grow at the rate they should. If doctors determine this early, they can use prescribed growth hormone and the child will grow to their normal size. If a child’s pituitary glands release more growth hormone than it should the child may grow taller than expected.

Thyroxine: this is a hormone that is produced by our thyroid gland that increases our metabolism. Our thyroid glands need iodine for this to occur properly. We get iodine most of the time through salt that has had iodine added (read a salt box, it should say iodized salt somewhere on the package). If a person does not produce enough thyroxine, they are often fatigued and experience weight gain, and other problems.

Study Guide Section 1

1. The role of the nervous system is to g and

i information regarding our internal and external environment.

2. The nervous system can be broken down into t divisions.

3. The c nervous system includes our brain and spinal cord.

4. The p nervous system is our passageway for communication (nerves) that connects all areas of our body to the central nervous system.

5. The c b collects information to be sent toward or away from the CNS.

6. The a carries information away from the cell body.

7. The d carries information to the cell body it is attached to.

8. Special neurons called s n gather information about what is happening in and around our body and send the information on to the CNS for further processing.

9. Neurons that send information to the brain and spinal cord are called

m n .

10. N are axons bundled together with blood vessels and connective tissue.

11. The brain is the “c c ” for our CNS.

12. The processes that the brain controls automatically are called

i .

13. Our brain has three parts, the c , m and the c .

14. The largest portion of your brain is your c ; it is the top or upper portion of your brain that has two hemispheres.

15. The left hemisphere of the cerebrum directs the r side of the body and the right hemisphere directs the l side of the body.

16. The l hemisphere controls speaking, reading, writing, and solving problems.

17. The r hemisphere controls activities that involve imaginations, appreciation, and creativity.

18. The second largest part of your brain is the c .

19. The part of our brain that connects to the spinal cord is the m .

20. The m is the part of the brain that controls blood pressure, heart rate, breathing and other involuntary activities.

21. Our s c is about the diameter of our thumb and runs the entire length of our spine.

22. When there is an injury to the spinal cord, the portion of the body below the injured area is often paralyzed.

23. When a r occurs, the message from a sensory neuron travels to the spinal cord and the response is sent from the spinal cord to the affected area.

Section 2 Study Guide

1. We have sensory receptors located a over our body.

2. List several types of stimuli that can trigger sensory receptors to perform their job. Heat, Cold, Pressure, Pain, and Touch

3. Our e are receptors to light.

4. Our e are receptors to sound waves.

5. Our tongue has taste buds that sense t .

6. Our nose has receptors to sense s .

7. List the parts and the function of our eyes. (Use the back of your paper for writing room. Include Cornea, iris, pupil, retina, rods, cones and the optic nerve.

8. C l or glasses can be used to correct vision problems related to focus problems.

9. List the parts of our ears related to hearing and explain how “hearing” occurs. (You may have to use the back of your paper) Include: outer ear, eardrum, cochlea

10. Our t contains small folds called taste buds.

11. What are the four tastes we can sense? S ,

B , S , and S .

12. The o nerve sends the message as an electrical impulse to the brain and the brain interprets the scent.

Section 3 The Endocrine System

1. The endocrine system is composed of g that release chemicals into our bloodstream.

2. The glands of the endocrine system release h into the bloodstream.

3. The a glands produce epinephrine also known as adrenaline. This hormone is produced and released when your body needs to prepare itself for danger.

4. The p gland releases a hormone responsible for growth.

5. The t glands release hormones that regulate our metabolism (energy).

6. The o in the female and the t in the male release hormones involved in reproduction.

7. The p is a gland that regulates the blood sugar level by releasing i .

8. The t gland is located right above the heart and helps our body fight disease.

9. The th glands regulate the level of calcium in our blood.

10. When you have to decide to run or take action to survive, we say our fi or fl response has been activated.

Know the information from the notes and study guide and you will do well on the test(s) from Chapter 25. As you learn, always think of how experiences in your life can be applied to the information and the information will be easier to learn.

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