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AOHS Foundations of Anatomy and Physiology I

Lesson 8The Nervous System

Student Resources

Resource Description

Student Resource 8.1 Simulation: Nerve Impulses

Student Resource 8.2 Diagrams: Anatomy of a Neuron

Student Resource 8.3 Reading: Anatomy of a Neuron

Student Resource 8.4 Notes: Organs and Structure of the Nervous System

Student Resource 8.5 Reading: Organs and Structure of the Nervous System

Student Resource 8.6 Lab: Reflexes

Student Resource 8.7 Glossary: The Nervous System (separate Word file)

Student Resource 8.8 Labeling: Parts of a Neuron

Student Resource 8.9 Reading: Spinal Cord Injuries

Copyright © 2014‒2016 NAF. All rights reserved.

AOHS Foundations of Anatomy and Physiology ILesson 8 The Nervous System

Student Resource 8.1

Simulation: Nerve ImpulsesStudent Names:_______________________________________________________ Date:___________

Directions: With your partner, build the model of dominoes according to the instructions below. Then follow the steps and answer the questions.

Your nervous system does its job by transmitting information as electrical impulses through the long axons of individual nerve cells. Falling dominoes can simulate how a nerve impulse is triggered and how the impulse spreads along the cell membrane.

Materials

Eight standard dominoes

Ruler, 30 cm or longer

Roll of masking tape

Directions: Constructing the Model Measure the length of one of your dominoes. Record the length in the margin of this resource.

Cut eight pieces of masking tape, each about the same length as a domino (they don’t need to be exact).

Place the first domino near the end of the ruler. Use a piece of masking tape to make a hinge connecting the back of the domino to the ruler. Figure 1A shows what tape hinges should look like.

Place the second domino on the ruler about three-quarters of a domino’s length from the first domino.

Connect the second domino to the ruler with a tape hinge like you did for the first domino.

Attach the remaining six dominoes in the same way. Measure carefully before taping the dominoes; it’s important that your dominoes are all the same distance apart.

Cut eight more strips of masking tape, each about the length of a domino.

Use these pieces of tape to reinforce the hinges. Wrap each piece of tape around the ruler and the base of the tape hinge. The hinges shown in Figure 1B are reinforced in this way.



Exploring with the Model

1. Place the ruler flat on your desk, and make sure all the dominoes are upright. If necessary, turn the ruler so that the faces of the dominoes are facing you. What might each domino represent?

2. Flick the first domino with your finger to make it fall. Watch and record what happens.

3. Repeat Step 2. What do you have to do before you can flick the dominoes again?

4. Make the dominoes fall several more times and closely observe their reaction each time. Do they all fall at the same speed?

5. Can you make them fall in the reverse direction?

6. Reset the dominoes so that they are upright. Barely touch the first domino with your finger. Record what happens.

7. Do this again several times, using slowly increasing amounts of force on the first domino. Record your observations.

Interpreting Observations

8. What must happen for the dominoes to be in the starting position again?

9. If your finger pushing the domino sets off the action, what does your finger represent?



10. If we make the rule that you can only put your finger on the first domino, is there any way you can stop the last domino from falling?

11. From your observations, what are some things you can say about how a nerve impulse travels along a nerve cell (neuron)?




Diagrams: Anatomy of a NeuronStudent Name:_______________________________________________________ Date:___________

Directions: Complete the charts and label the diagrams as you watch the presentation Anatomy of a Neuron.

Categories of Neurons

Category of neuron What it does How many in an adult?

Parts of a Neuron

Draw an arrow to show which way the nerve impulse travels.



The SynapseLabel the parts of the synapse

What happens when the neurotransmitter has diffused across the synaptic cleft?



The Nerve Impulse, or Action PotentialDescribe what is happening in the illustrations in the space provided under each one.

A.

B.

C.

D.




Reading: Anatomy of a Neuron



It’s hard for us to imagine how much electricity is flowing through our bodies as we watch this presentation, think about what’s in it, and take notes about it. But all of those things—in fact, everything you think, every motion you make, and every sensory experience you have—happens because your neurons are sending electrical signals to each other. We call these signals nerve impulses. How these signals work is the subject of a lot of scientific research right now.



The neurons in your body all specialize in carrying electrical signals, but those signals serve different purposes, and therefore you have different kinds of neurons. First, your body needs to gather information about your environment. Right now neurons in your eyes are sensing the amount of light and the image of this presentation and your ears are hearing a teacher’s voice. Cells that take in sensory information from the environment are called sensory neurons. They send sensory signals to either the brain or the spinal cord, depending on the situation. In either case, sensory neurons are the same, they just have different destinations. The receiving end of a sensory neuron often has receptors that sense the stimulus. In your brain and spinal cord are neurons whose role is simply to connect to other neurons and continue the relay of the message. These cells are called interneurons. Finally, if, for example, sensory neurons in your leg are sensing discomfort, that signal will be passed through your brain or spinal cord to motor neurons in your legs, so that you’ll move your legs and change position.



The number of each kind of neuron that you—or any average adult—has is very different. You have 20 times more sensory neurons than motor neurons. And you have 40,000 times more interneurons than motor neurons. Your sensory and motor neurons are mostly in the parts of your body outside of your brain and spinal cord, carrying out the functions of picking up information from the environment and creating movement and responses. All the rest—99%—is about integrating information, which is the most important activity you do as a conscious being.



The cell body is where all the usual cell functions happen: metabolizing food and creating proteins that the cell needs. In many neurons, the cell body is the biggest part of the cell.



The nucleus of a neuron holds the same DNA as the rest of your cells. Most of your cells, such as your skin cells, divide and make new cells constantly, a process that starts with the DNA in the nucleus. Most of the neurons you will ever have are already present when you’re born, though your brain makes new ones during crucial developmental times like adolescence, and your body can make new neurons under some circumstances. For the most part, though, the process is more about losing neurons: you’re born with many, many neurons in your brain. During adolescence, your brain starts a pruning process and loses the neurons you’re not making use of so that the ones that remain can flourish. It’s similar to how a gardener will prune—meaning “cut back”—plants and tree branches so that the ones still there get more light and nutrients. Bottom line: classes like this one are important to help you keep as many neurons as possible!



Dendrites are tiny branching structures that let the neuron reach out to gather stimuli from other cells or from the environment. From these branching structures, the signal moves toward the cell body. The word dendrite comes from the latin root dendre, which means “tree.” A neuron can have just a few dendrites or thousands of them. In sensory neurons, the dendrites are sensitive to particular conditions or are activated by other specialized cells. In your eyes, the dendrites of the neurons that give you vision are stimulated by neighboring cells that absorb the light. In your fingertips, some of the neurons’ dendrites are stimulated by touch. In interneurons, dendrites receive signals from other neurons. Many neurons in your brain, for example, have many, many dendrites so that they can get information from lots of other brain cells. The dendrites of motor neurons get their information from interneurons in either the central nervous system or the spinal cord.



Axons are where nerve impulses either arrive (from another neuron) or begin. Nerve impulses in neurons are also called action potentials, and they are similar to action potentials in muscle cells. In a muscle cell, the action potential makes the cell contract. In a neuron, the action potential makes the nerve impulse travel down the axon all the way to its end. Remember that a muscle cell is stimulated to contract at the place where it meets an axon. That’s because there is an impulse—or action potential—traveling down the membrane of the axon until it gets to the end of the axon, where it’s transmitted to the muscle cell. Whereas dendrites are often fairly short, axons can be very long. In fact, the longest cells in your body are the neurons that go from the base of your spine down to your toes. These cells are as long as your legs, which in most people is 2 or 3 feet long!



Like any wires that conduct electricity, nerve cells can move their signals faster if they are insulated. The myelin sheath, made of fat and protein, acts as an insulator. The speeding up works this way: the myelin sheath is created by special cells that wrap themselves around the axon. Between these cells are tiny nodes where the cell membrane of the axon is exposed. When the nerve impulse travels down the axon, it skips over the lumps of myelin and the cells that make it, bouncing from node to node, which is faster than traveling the whole length of the axon. The myelin sheath also helps a neuron repair itself after an injury—if you cut your finger, for instance, you get your feeling back in it after it heals. Neurons in your brain and spinal cord don’t have myelin sheaths, which is why they don’t repair themselves easily when they’ve been damaged.



At the very end of the axon are more branching structures called axon terminals. In motor neurons, axon terminals end near muscle cells. In sensory neurons, they may end at junctions with neurons in the brain or interneurons. Axon terminals contain the chemical neurotransmitters, such as acetylcholine, that carry the signal from one cell to the next. A neuron usually has many axon terminals, as you saw previously in the neuromuscular junction, but there are usually fewer axon terminals than there are dendrites.



In the dominoes demonstration we just did, you saw how the dominoes could only fall in one direction. In the same way, a nerve impulse travels only in one direction through a nerve cell. This means that when you take in a stimulus, like touching your hand to something sharp, the signal has to travel in a circle to make its way back to your muscles so that you can move your hand away. A common circle would be: neurons in your skin detect the stimulus and send a signal up your arm to an interneuron in your spinal cord. The signal keeps going forward through the interneuron until it reaches the axon terminals that meet with a motor neuron. That motor neuron, which runs down your arm, keeps the signal moving forward to your muscles, which then pull your arm away. So even though the signal moves up your arm and back, it is moving forward in one direction along a path paved by neurons.



At the end of the axon terminal is a synapse—the junction where a nerve impulse is passed from one cell to another. At a synapse, two neurons (or a neuron and a muscle cell) are very close together, but they don’t quite meet. Because neurons have many axons and many dendrites, they can form lots of synapses with each other. Often, both axons and dendrites form synapses with many other cells. The cell whose axon terminals are part of the synapse is called the presynaptic neuron. It’s the first one carrying the nerve impulse. On the other side of the synapse are the dendrites of the postsynaptic neuron, which will receive the neurotransmitter that’s released into the synapse.



When a nerve impulse reaches the axon terminal, calcium flows into the terminal. That calcium leads the vesicles to the cell membrane. The vesicles fuse with the cell membrane, which makes these tiny sacs open up. They unload their cargo of neurotransmitters into the tiny space between the axon and the next cell, called the synaptic cleft.

In this drawing, the synaptic cleft is between two neurons. There is also a synaptic cleft between the axons of a motor neuron and the muscle fiber it stimulates. Notice that the signal travels through the neuron as an electrical signal but changes to a chemical signal in the synaptic cleft, and back to electrical again in the postsynaptic cell.



Just as a synapse awaits at the end of an axon terminal, receptor proteins in the membrane of the postsynaptic cell await arrival of the neurotransmitters. The receptor proteins have special shapes that recognize the neurotransmitter. When the two connect, it changes the shape of the receptor, which opens ion channels that allow sodium ions to enter the cell. As you may remember, there is much more sodium outside of the cell than inside, and the sodium doesn’t easily diffuse across the cell membrane. But once the neurotransmitter binds to receptor proteins, sodium can easily move into the cell.



In addition to lots of sodium ions outside the cell membrane there is ordinarily a little bit of potassium. Inside the cell membrane, it’s the opposite: lots of potassium and very little sodium. Once the neurotransmitter binds to receptor proteins and changes shape, so that sodium can easily move into the cell, the little patch of cell membrane near the synapse becomes more positive. You can think of this depolarization as the equivalent of putting your finger on the first domino in your neuron model. Nothing has happened yet, but with a little more impetus of some kind, something will.



In your domino model, the “something more” was the necessary push to get the first domino going. In a neuron, the something more is the necessary quantity of sodium crossing the cell membrane to create enough depolarization. Then, like the dominoes falling, once the initial push is strong enough, the depolarization propagates all the way down the cell. Again, like the dominoes, the action potential moves in one direction only, and once it’s started, there’s no going back.



The nerve impulse passing down the cell membrane causes proteins in the membrane to change shape again and allow potassium ions out. What this does is restore the balance of charge back to what it was before this whole process started: the cell is more positive outside and more negative inside. The balance of charge is this way because there are more positive ions outside the cell than inside the cell. But, during repolarization, while the balance of charge is restored, the ions that account for it have swapped places; potassium is now outside and sodium is now inside. If this happens too many times in a row, the cell won’t be able to produce action potentials until it takes a very quick break to return to its resting state.



To set the cell membrane back the way it was, proteins in the membrane use active transport—the sodium-potassium pump—to move sodium ions out of the cell and potassium ions back in. For every three sodiums that move out, two potassiums move in. This means there is more positive charge from sodium ions outside the cell than from potassium ions inside, so the cell is positive outside and negative inside. This active transport is the equivalent of having to put in work from your hands tilting the ruler in order to reset the dominoes. It requires energy to reset your cell membranes. This means that energy is required for all the activity of your neurons and muscle cells, including your thoughts, movements, and heartbeats .




Notes: Organs and Structure of the Nervous SystemStudent Name:_______________________________________________________ Date:___________

Directions: Complete the notes and chart as you watch the presentation Organs and Structure of the Nervous System.

1) Complete the chart.

Nervous system function Category of neuron involved

2) What are the three main organs of the nervous system and the characteristics of each?

a)

b)

c)

3)

System Organs Function

Central nervous system

Peripheral nervous system



4) Complete the chart by filling in the boxes and ovals with notes about each part of the nervous system.

5) What are reflexes?

6) What are three different kinds of reflexes, and what type of muscle is involved?

7) Describe what happens during each of the five parts of a reflex arc:

a)

b)

c)

d)

e)




Reading: Organs and Structure of the Nervous System



In many of our organ systems, the organs involved can perform several duties, and it doesn’t matter which other things are happening at the same time. For example, your bones are always supporting you, and they may also be producing blood cells. You skin may be sweating and protecting your insides from damaging rays at the same time. But the nervous system’s three functions always occur in the same order, because each is dependent on the one before it.

First, sensory neurons gather information about a situation or the environment. Next, interneurons process that information, sometimes integrating sensory input from a variety of sources, and determine what action to take. Lastly, the nervous system will create a response, often involving muscle movement or other reaction in in your body. For example, your ears hear an announcement that it’s almost time for you to go on stage and make a presentation. Your brain processes that input and sends several responses around your body: it tells your legs to walk you toward the podium and it recognizes an emotion of nervousness. In response, your nervous system stimulates your apocrine glands to produce sweat.



The average adult human brain weighs about 3 pounds. The brain is where your thoughts and emotions reside, as well as all your sensory perception and your ability to speak, read, and understand language. Your spinal cord is an extension of your brain stem, the part of your brain that controls survival functions like digestion, sleeping, and reflexes. It’s about as thick as your thumb, and relays messages to and from your brain from all the parts of your body that are below your head and neck. The spinal cord also has the ability to take over processing information if an action is needed quickly. For example, if you put your hand down on a table and discover a cactus there, up goes your hand in a flash. The signal to move away from the cactus doesn’t need to go through your brain; the orders are sent to your hand right from the spinal cord. Nerves are the third organ of the nervous system.



Nerves are the pipelines that bring information from your body to your brain and spinal cord and send instructions back out to the body. They are made of the axons of sensory and motor neurons. The cell bodies of these cells are often in the brain or spinal cord, but their axons run all through your body, bundled together as nerves. Nerves are as long as they need to be; some are only millimeters long, while the nerves that run down your arms and legs are many feet long.

The axons in nerves are covered with myelin sheaths. As you remember, this helps them conduct nerve impulses faster, which is important given how far the impulses have to travel. You have 12 pairs of nerves that run between your brain and parts of your head, and your sensory organs such as your eyes and ears. These are called cranial nerves, because they either start or end in your brain. Cranial nerves control the action of muscles in your head and neck, like your masseter and sternocleidomastoid, and sensory experiences of sight, sound, taste, and smell. You have 31 pairs of spinal nerves, which control the movements and sensations in all of your body below your legs. Spinal nerves also take care of a lot of involuntary functions: digesting your food, breathing in the air, and releasing some hormones like adrenaline from your glands. Many of your nerves contain both sensory and motor neurons, which means one neuron in a spinal nerve may sense that cactus under your hand and another neuron in that same nerve moves your hand away.



What sets these two divisions apart is the organs in them. The brain and spinal cord are the organs of the central nervous system, or CNS, and your nerves are the organs of your peripheral nervous system, or PNS. Your CNS handles the integration of information, and your PNS deals with all the sensory input and motor output.

Let’s stick with our cactus example: The sensory nerve that feels the stab from the cactus is in the PNS. Your body processes that input in your spinal cord, part of the CNS, and then relays a message via a spinal nerve in the PNS to lift your hand. If, on the other hand, you catch sight of the cactus before you put your hand down, a cranial nerve in the PNS sends a message to your brain, part of the CNS, which processes the visual information and sends the message for your arm muscles via spinal nerves in the PNS: “Whoa, don’t put your hand there.” Although we’ll be describing the nervous system in terms of different divisions, it’s important to note that these aren’t physical divisions: the nervous system exists and functions as one unit, but creating divisions helps us organize our thinking to understand how the nervous system carries out its tasks.



The sensory division of the PNS is made of all the neurons that involve your senses: neurons in your eyes, ears, nose, mouth, and receptors for all kinds of sensation in your skin. You also have neurons with receptors in organ systems like the digestive and urinary systems. These receptors detect things in the environment similarly to your sense organs and relay messages to the brain, even though you aren’t aware of what these receptors are sensing.

The motor division is made of neurons that move muscles in response to messages they get from the brain. Remember that many spinal and cranial nerves have both sensory and motor neurons, so just because we describe these neurons as belonging to different divisions, they may be found together in the same organ.



For the most part, different types of muscle tissue are controlled by different divisions of the nervous system. When you wave your hand or make any other voluntary movement, that’s controlled by your somatic nervous system. Some skeletal muscle motions, like reflexes, aren’t voluntary, but they’re still controlled by these neurons. The autonomic nervous system stimulates the many activities of your smooth muscles, such as adjusting your blood pressure and digesting your food, and stimulates your glands.



The job of the autonomic nervous system is to help us regulate many basic body functions. The autonomic nervous system is divided into the sympathetic and parasympathetic nervous systems. They are actually different sets of neurons, and they have different functions. When your body is experiencing stress, either physical or emotional, your sympathetic nervous system is more active. When you’re relaxing or sleeping, your parasympathetic nervous system is doing more. For example, suppose you’re setting out on a jog. When you get going, you start to sweat, your heart beats faster, your blood vessels direct more blood to your legs and less to your intestines. All these things happen because of the effects of the sympathetic nervous system acting on the heart to speed up, the sweat glands to activate, and blood vessels to expand. When you’re doing your after-jog cooldown, your sympathetic nervous system reduces its activity, and as a result your heart returns to its usual pace and you stop sweating. The parasympathetic nervous system helps maintain your resting heart rate and controls most of your gastrointestinal function. These two systems also respond to your emotions. If you get in a fight with your parents, chances are your sympathetic nervous system will get you wound up, making your heart beat hard and your face flush. When you stop huffing and take a deep breath to talk it out with them, these effects of the sympathetic nervous system subside. Most of the time, the two systems are working together to maintain the right balance of readiness and steadiness in your body.



Reflexes are quick, involuntary muscle movements. There are three types of reflexes—innate, functional, and learned. In our example of putting your hand on the cactus, your body handles the movement by connecting sensory and motor nerves via your spinal cord. This is an innate reflex; you don’t have to learn it, but it works on the somatic nervous system. The signal never has go all the way to your brain. Many other reflexes are functional, working on smooth muscle tissue, that are movements you’re completely unaware of. For example, you have tiny, smooth muscles in your eyes that adjust your pupil size in response to the amount of light in the room. Still other reflexes are learned responses that you can take over consciously if you need to but that you usually do out of habit. For example, if you’re driving and see a car turn in front of you, you’ll put on the brakes without thinking, something your brain has learned to do by practicing driving.



Reflex arcs are the simplest circuits in the nervous system, but they can be combined in many ways, responding to an array of stimuli and creating complex actions. While some reflex arcs are quite complex, they all have five steps. In our example here, the reflex arc begins when pain receptors in your hand sense the potential for tissue damage.



Those receptors, which are part of a sensory neuron, initiate an action potential that gets carried to the spinal cord.



The information is passed on and integrated as neurotransmitters stream from the axon of the sensory neuron to affect other neurons. In some cases, the neurotransmitters create an action potential in an interneuron, which then passes the stimulus along—via neurotransmitters from the axon—to a motor neuron. In other cases, like the one shown above, the axon from the sensory neuron meets with the dendrites of a motor neuron, with no “middleman” neuron. In either case, the integration connects the sensory signal to the appropriate motor neuron.



Whether there is an interneuron or a direct connection between a sensory and a motor neuron, the path is the same: the axon meeting the motor neuron releases neurotransmitters that trigger another action potential, which travels down the motor neuron to the neuromuscular junction with a muscle cell.



The axon of the motor neuron then releases acetylcholine, setting off an action potential in the muscle cell and causing contraction. If the motor neuron is effecting a gland, it may release a different neurotransmitter. In the end, the step is the same: the reflex has caused a change.



Reflexes give health care workers insight into a patient’s health. A reflex arc is a circuit: if you test a person’s reflexes and get an abnormal response, it indicates that there is a problem in the circuit, which could be caused by injury or disease.

For example, one important reflex is your plantar reflex. If someone runs the blunt end of an object along the bottom of a person’s foot, from the heel to the toes, that person’s toes will quickly curl up. If this doesn’t happen or is delayed, it means the person may have suffered severe trauma to the spinal cord. To help locate where along the spine the injury is, a health care professional can test reflexes in various parts of the body. Some medical professionals believe that when a person is dealing with chronic or severe pain, it can heighten his or her reflexes and keep the pain level elevated. Some physical therapists use a technique called primal reflex release on such patients in an effort to lessen their reflexes and, with it, the pain they’re experiencing.



Infants are born with some special reflexes that help them learn to walk, find their mother’s breast, and other things that are part of staying healthy and growing into toddlers. If babies are held upright, they automatically make walking or dancing motions. When they’re older, these movements are indeed attempts at steps, but they start out as simple reflexes, even before the baby is learning to walk. If you put your finger in the corner of a baby’s mouth, the baby will turn his head and open his mouth, a reflex that helps him find his mother’s breast to feed. And if you put your finger in the palm of a baby’s hand, he will reflexively grasp your fingers, and squeeze even harder when you try to pull away. These reflexes only last a few months or maybe a year. As adults age, their nervous systems continue to change. Over time, both the brain and spinal cord lose nerve cells, and the neurons may pass signals more slowly than they used to. Some people lose some of their sensory abilities and don’t taste, hear, or see as well. These changes don’t reflect an older person’s ability to think; they seem to be a natural part of the aging process, and as each person ages, his or her nervous system changes in its own unique way.




Lab: ReflexesStudent Names:_______________________________________________________ Date:___________

Directions: With your partner, complete each step and record your observations. Each partner should do each experiment on the other person so there are two sets of observations. When you’re done, compare the results you got from your experiments and respond to the questions.

Somatic ReflexesMost of the reflexes you’re probably aware of are controlled by the somatic nervous system, which means that they involve skeletal muscle. In these experiments, you will test two different reflexes, one that’s innate and one that’s learned, and see if you observe any differences.

Patellar reflexYou need: reflex hammer

1) Your lab partner should sit on the edge of a desk or table where his or her legs can hang freely, not touching the floor. Feel your partner’s knee for a soft spot just below the patella. This is where the ligament is that connects the patella to the tibia. Firmly strike this spot with the reflex hammer, but be careful not to hurt your partner!

What did you see happen?

2) Next, repeat the experiment, but have your partner focus on reciting the alphabet backwards while you are doing the knee tapping. Do you notice any difference in the reflex response?

3) In this reflex arc, the integration happens in the spinal cord. What are the other four parts of this reflex arc? For example, when your finger touches a cactus, a) the receptor organ is touch sensors in the skin, b) the sensory neuron is one that goes from your arm to your brain or spinal cord, c) the motor neuron is the one that goes from your brain or spinal cord to your arm, and d) the effector organs are the muscles in your arm that pull your hand away.

a) Receptor organ:

b) Sensory neuron:

c) Motor neuron:

d) Effector organ(s):



Ruler-catching reflexYou need: ruler

1) Tell your partner to do this with his or her dominant hand. Your partner should bend his or her elbow and hold the thumb and forefinger about an inch apart. Hold up the ruler between your partner’s fingers so that the bottom end of it (zero inches) is at about the same height as the top of your partner’s hand. Your partner should not touch the ruler but should be ready to grab it when you drop it. Tell your partner to keep an eye on the ruler and to catch it when you let go of it. Drop the ruler three times and each time record the distance it fell (the mark on the ruler where your partner caught it) when you dropped it.

Drop # Distance ruler fell

2) Next, repeat the same exercise, but this time, before you drop the ruler, tell your partner to start reciting the alphabet backwards. Record how far the ruler drops each time.

Drop # (with alphabet)

Distance ruler fell

3) In this reflex arc, the integration happens in the brain. What are the other four parts of this reflex arc?

a) Receptor organ:

b) Sensory neuron:

c) Motor neuron:

d) Effector organ:



4) The patellar reflex is innate and goes through the spinal cord. The ruler-catching reflex is learned and goes through the brain. How do you think those differences affected what you observed in your trials in terms of:

a) The time it took for the reflex to occur?

b) The effect of reciting the alphabet while doing the trials?

c) The effect that practice would have on your performance of each of these reflexes?

Autonomic ReflexesLots of reflexes in your body involve smooth muscle controlled by your autonomic nervous system. One example is your salivary glands: when you’re hungry and you smell a pizza, your mouth starts to water. That’s your autonomic nervous system at work getting you ready to eat.

The irises of your eyes, the part that we talk about when referring to eye color, also have reflexes. Doctors often look at the reflexes in the eye because it can help them see whether there has been damage to the specific part of the brain that controls the reflex.

Pupil reflexYou need: a penlight

1) Have your partner face away from the light source in the room. Stand on the left side of your partner and tell him or her to shield the right eye by putting one hand vertically on the right side of his or her nose.

2) Holding the penlight about 4 inches from your partner’s left eye, shine the light into the left eye for a couple of seconds.

What do you see happening to the pupil?

3) Wait a moment for your partner’s eye to readjust, and then shine the light in the left eye again, but this time watch what happens with the right pupil. What do you see?

4) What is the role of this reflex, and why is it important for us that it is automatic?




Labeling: Parts of a NeuronStudent Name:_______________________________________________________ Date:___________

Directions: Refer to the terms across the bottom of the page to label the parts of the neuron.

dendrites cell body axon

nucleus myelin sheath axon terminals




Reading: Spinal Cord InjuriesStudent Name:_______________________________________________________ Date:___________

Directions: Go through the reading and answer the questions.

In the winter of 2012, 16-year-old Jacob Jablonski was a fit, healthy hockey player, out on the ice to win one for his high school team. Then a player on the opposing team skated up behind him and pushed him hard, slamming him face first into the boards surrounding the ice rink and severely damaging his spinal cord. The strong, athletic teenager is now confined to a wheelchair, expected to never walk again.

About 200,000 people in the United States are living with spinal cord injuries. The leading cause of spinal cord injuries (also called SCIs) is auto accidents, though sports incidents like the one described here are also a culprit among teenagers. The vast majority of SCIs—80%—happen in males, and alcohol plays a significant role in about one-quarter of these types of traumas.

Most SCIs begin with a traumatic blow to the vertebral column that fractures or crushes the vertebrae or the discs between them. Displaced fragments of bone can tear the spinal cord or compress the tissue. Gun or knife violence can cause severe damage to the spinal cord, because these weapons can penetrate the vertebrae and do their damage directly to the nervous tissue. In many cases, the spinal cord isn’t completely severed, but as the area around the injury swells up and bleeds, additional damage is done.

Some SCIs are caused by diseases such as osteoporosis, arthritis, and cancer; these injuries usually develop slowly over time.

Question 1: Explain why accidents, sports injuries, and weapons cause spinal cord injury.



Level and type of injury

The spinal cord is the largest nerve in the body. It is the main pipeline of communications between the brain and the entire body below the head and neck. Your spinal cord is surrounded and protected by your vertebrae, which are divided into three major regions—cervical, thoracic, and lumbar. Branching off from the spinal cord are large spinal nerves that stimulate contraction of any skeletal and smooth muscle below your head and neck.

One way medical professionals describe SCIs is by what they call the level of the injury, which refers to where the injury occurred in the spinal cord. They might say, for example, that the injury is a T-2, which means it occurred closest to the second thoracic vertebra. When the spinal cord is injured, a person can lose feeling or movement in the parts of their body that are served by all the nerves below the site of the injury. So describing where the injury is gives clues to how it is likely affecting a patient.

SCIs are also classified as either complete or incomplete injuries. If a person loses all feeling, all sensory and motor ability, the injury is complete. If the patient still shows some function in the areas below the injury, it’s considered incomplete, and there is greater chance that some feeling or movement will return.

Whereas many of the effects of an SCI are visible, the injury may cause some very important effects that are less apparent. The nerves of your spinal cord control not only your voluntary movements but also your breathing, swallowing, bladder control, and many other functions. So a person with SCI may also have difficulty breathing, eating, or regulating his or her heartbeat.

Question 2: If an SCI allowed people to use their arms but not their legs, and they were having trouble digesting food, what nerves would you guess were affected? Which are not?



Treatments

If you’re present when someone gets injured, especially after a blow to the head or back, it’s very important to know what to do so that you can avoid harming that person further. Some symptoms of a spinal cord emergency are:

Floating in and out of consciousness

Weakness in limbs or lack or control of bowels or bladder

Being twisted in an odd position

The most important thing to do is keep the person still and put blankets around their head to keep it in place. Don’t move the person’s head into another position. If you have to move the person, get help so you can keep the head in position and carry the person on a board.

Once a person with an SCI has gotten to the hospital, he or she is often put in an intensive care unit to be sure that his or her breathing and heartbeat is stable. Sometimes doctors will do surgery to remove broken or disc fragments. If a patient reaches the hospital within eight hours of getting injured, doctors will likely give the person a steroid that helps reduce the added damage that can come from inflammation. Many SCI patients are put in traction under the supervision of a medical professional, which can help realign the spine.

Right now, there is no cure for SCIs; once a part of the spinal cord has become injured, it doesn’t repair itself. People living with a SCI have to deal with the impact of their injury every day, though, depending on the extent of the injury, some people can get a good deal of their function back. Physical and occupational therapists can help SCI patients learn to refine what sensation or movement function they have left and provide guidance on ways to make up for lost function. These kinds of professionals also give patients daily exercises and a routine to help them maintain strength. Some patients are able to use devices called functional electrical stimulation systems, which can help them stand, talk, reach their arms out, or grip objects by delivering small electrical impulses to muscles.

Question 3: Explain how a functional electrical stimulation system can help a patient with an SCI.

ResearchThere is a lot of research going on to try to improve the prospects for people with SCIs. Some researchers are focusing on ways to prevent the secondary damage that happens after the initial injury. New drugs are being tested that doctors hope will be effective for weeks after the injury, preventing injured neurons from releasing substances that can damage the cells around them, and finding ways to control the immune system’s response to injury so that it does its job of preventing infection and promoting healing without causing dangerous levels of inflammation.

Other researchers are searching for ways to get spinal cord neurons to regenerate and reconnect to spinal nerves that serve the limbs and other parts of the body. Some researchers are experimenting with



nerve-cell grafts, whereby nerve cells are taken from somewhere in the patient or from fetal spinal cord tissue, with the hope that the tissue will grow and become a functioning part of the spinal cord. So far, the results of these experiments in humans have been inconclusive, but in experiments with animals, some animals have regained some use of their limbs.

Doctors are also very interested in finding ways to use stem cells to regenerate spinal cord tissue. If this technique works, it may be a big step toward helping people with a SCI regain use of their limbs. But researchers still don’t know very much about how stem cells do their work—giving rise to new cells—and how to control new cell growth so that it goes the way it needs to.

In a more futuristic realm, some scientists are looking at ways to reconnect spinal neurons with the rest of the body using engineered materials. One example is functional electrical stimulation (FES) systems. FES systems deliver tiny electrical impulses to a patient’s muscles. Doctors are experimenting with ways to retrain patients’ limbs. These researchers work together with engineers and physical therapists, using a computer to model movements involved in walking. They then support the patient while the patient is moving his or her legs—in essence, getting the legs to repeat, over and over, what the computer says they need to be doing while training the muscles by giving them electrical pulses. In this way, researchers hope that people with a SCI can retrain their paralyzed limbs to respond to stimuli from outside the body, enabling them to walk and reach and do many of the tasks of daily life.

Question 4: Which area of research for helping SCI patients sounds the most promising to you? Why?


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