NOTE: AS ALWAYS, USE MY NOTES AT YOUR OWN RISK! MRS. HINDS IS THE INSTRUCTOR. ALWAYS USE HER OPINION AS THE CORRECT OPINION.
YES, THE FOLLOWING NOTES ARE ABSURDLY LONG, BUT THE SUBJECT MATTER REQUIRES IT. DO MY METHOD OF "CIRCLING" THE NUMBERS/LETTERS IN FRONT OF THE FACTS YOU KNOW, THEN GOING BACK THROUGH AND STUDYING WHAT YOU DON'T KNOW...KEEP CIRCLING, REREADING, CIRCLING, REREADING, UNTIL YOU KNOW IT ALL.
THE FOLLOWING WAS DRAWN FROM MY NOTES, NOTES OFF THE WEB, AND FRIENDS' NOTES. Take them with a grain of salt, as they say...
The Art of Guessing?
Here are some suggestions for getting answers to A&P questions that you are unable to solve in the usual manner. This section will also give you some ways to be more efficient at solving A&P problems. Some students may consider "tricking" their way through the test as the “best” way to get a good grade; that is, they use multiple-choice test-taking strategies and essay-answering strategies instead of studying the material in-depth. This approach is not recommended. Most of the time on an A&P exam, the best way to solve a problem is to have studied it! Still, there may be times when you will not know how to read a graph, or will not really understand a multiple-choice question, or believe that you do not have enough information to answer an essay question.
Basically, there are three circumstances in which you should resort to guessing strategies.
1. When you are stuck on a question.
2. When you are short of time.
3. Both of the above.
It does not pay to guess if you are unable to eliminate any of the answers. But the odds of improving your test score are in your favor if you can rule out even one of the answers in a multiple-choice question. The odds in your favor increase as you rule out more answers in any one question.
You have a limited number minutes to complete your test, which contains around 40-100 multiple choice questions. In precise terms this means that you are to read, interpret, think about, and select one answer for a multiple-choice question every few seconds. This may seem impossible, but there are several things that you can do to better your chances of using your time effectively.
1 . Practice: By using the examples in this book, those given out in your class, or found on the Net, you can become familiar with the format and wording of multiple-choice questions similar to those used in the real exam. In addition to increasing your information base, taking practice exams can save you time when you need it most.
2. Words of Totality: Look out for words like "never" and "always" in multiple- choice questions. It is rare for an answer to be true in relation to these words of "totality," but it is still a possibility. When you see these words, focus on them and consider them carefully.
3. Combination Answers: Some multiple-choice answers will contain statements such as "both (A) and (B)" or "all of the above" or "none of these."
Do not be distracted by these choices. Quickly go through each choice independently, crossing off the answers that you know are not true. If, after eliminating the incorrect responses, you think there is more than one correct answer, group your answers and see if one of the choices matches yours. If you believe only one answer is correct, do not be distracted by “A and B” or “all of the above” possibilities.
The Fallacy of "First Guess is Best"
Among test-taking folklore there is the principle that your "first guess is best."
This piece of folklore is misleading, to say the least.
Research indicates that when people change their answers on tests like the A&P exam, about two-thirds of the time they go from wrong to right, showing that the first guess is often not the best. Of course, this does not mean that you should feel free to change your answer on a whim; it means that you should be willing to change your answer for a good reason. A test-taker who holds to the "first guess is best" principle might as well not bother to go back to a guessed question, since he or she would be afraid to change it anyway. Remember, your first guess is not better than a result obtained through good, hard, step-by-step, conscious thinking that enables you to select the answer that you believe to be the best.
Don't guess, anyway. Write the number of the question along the top of your Scantron. Skip that question until after you are through with all the multiple choice questions. Then go back to the ones you didn't answer and try to figure them out. Often, the answer has occurred to you or you might have even found it later along in the test itself! This is more true of the Lab tests, but also true sometimes in Lecture.
Three Stops to Follow: Read, Eliminate, Reread
One of the most helpful strategies for multiple-choice questions is a three- step process: reading, elimination, and rereading. Most people tend to see what they expect to see. In test taking this can be a counterproductive tendency. Most of us have missed a question not because of not knowing it, but by misreading the question!
1 .Read the question quickly but do not skim. It may even pay to quickly read every word. Slow down at words which link by causation such as "due to" and "because" or "as a result of' and at words of totality such as "never" or "always."
2. Eliminate wrong answers one by one. Do not jump to the answer that you think is correct. While elimination may appear to take more time, it is more likely to provide correct answers. In the rush of the test it is easy to select an answer that looks right at first, but on more careful reading does not answer the question. In addition, answer elimination may provide a clue to a misread answer you would have overlooked.
3. Reread the question, as if you were reading it for the first time. Now choose your answer from your remaining answers based on this rereading.
Essays and Short Answer Questions
Write something down, even if you feel you know little about the question. This will usually get you at least one point, and one point can be the difference between passing and failing.
Be sure to answer ALL parts of the question.
Do what the question asks you to do. If you are supposed to discuss something, then discuss it. Don’t just put down a flow chart or a bulleted list. If the question asks you to define something, or give an example, or compare two things, etc etc, then make your reply fulfill the question!
Don’t “hedge your bets” by stating something and then contradicting it later in the essay. You won’t get any points if the instructor notices that you’ve done that.
Nervous System Notes
- Divisions of the nervous system
- memory, learning, language, perception, and response all reside in the nervous system
- Types of neurons
- sensory - carry stimuli from the internal and external environment
- motor - carry signals to effectors - cells that cause things to happen
- interneurons - link neurons together - found mostly in brain and spinal cord
- Neural Anatomy (Fig. 11.3 p. 242N)
- dendrites and axon
- myelin sheath
- insulates the neuron
- fatty covering formed by Schwann cells
- impulse jumps from one node to the next; faster than non-myelinated -- =saltatory conduction.
- Multiple Sclerosis
- destruction of myelin sheath
- loss of signals
- double vision, slurred speech, poor motor control, no fine motor control, partial paralysis
- thin membrane surrounding axon
- functions in regeneration of neuron – the axon can grow using the empty left-over Schwann-cell “pipe” as its guide
- brain and spinal cord have no neurilemma therefore damage is permanent – no Schwann-cell pipe in CNS, oligodendricytes are there
- Reflex Arc
- some stimuli are too dangerous to wait for brain to interpret and respond; e.g., touch a burner
- sensory receptor - spinal cord - interneuron - motor neuron - contract muscles (or other appropriate response) - feel sensation fractions of a second later
- too much time for brain to judge intensity of pain, weigh alternatives, choose a course of action, effect a response
- common reflexes - blink, sneeze, cough, laugh when tickled, curling foot when step on a pebble
- Electrochemical Impulse
- Membrane Potential
- Na+/K+ pump creates huge gradient
- positive charge outside cell
- K+ leaks out along the diffusion gradient but flow back in along the charge gradient
- Na+ flows in along both concentration and charge gradients
- resting potential should be -80mV (outside is assigned a potential of 0) but because of Na+ leaking in, it is slightly less at -70mV (called resting potential)
- Voltage-gated Channels
- Na+ channels open quickly
- Na+ enters neuron
- potential becomes +40 mV (called action potential)
- depolarization opens more gates - positive feedback
- Na+ close when potential becomes positive so no more Na+ enters
- K+ gates open after Na+ gates and K+ diffuses out
- Problem: original polarity now restored but ions are on wrong side of membrane. Na+/K+ pump corrects this.
- note: gates are concentrated at nodes of Ranvier so that the extracellular fluid is in contact with the axon only at the nodes. This is why the impulse "jumps" from node to node.
- Propagation of the impulse
- the signal cannot proceed in both directions because of the refractory period
- Threshold and All-or-None
- stimulus must have a certain minimum intensity to cause a neuron to fire - this is the threshold of the neuron
- smaller, or weaker, stimuli do not provoke a response
- the stimulus causes channels to open and there must be enough of them opened to depolarize the membrane
- increasing a stimulus above threshold does not result in a larger response - this is all-or-nothing.
- If all stimuli above threshold cause a neuron to fire, how do we detect different intensities of stimuli?
- temporal summation - frequency of stimulation - a neuron fires more or less often. A warm object sends less frequent impulses to the brain
- spatial summation - area of stimulation - more neurons fire
- different thresholds - not all neurons have the same threshold. A warm object may trigger only a few neurons while a hot object provides a stimulus above the threshold of more neurons, causing them to fire
- The Synapse
- synapses are small spaces between neurons, between neurons and effectors, or between neurons and sensory receptors
- neurotransmitters are chemicals that bind to receptors on the post-synaptic membrane and trigger the opening of Na+ gates, "transmitting" the signal across the space
- neurotransmitters are contained in vesicles in the cytosol near the presynaptic membrane. Depolarization of the membrane causes the neurotransmitters to be released into the synapse
- enzymes degrade the neurotransmitter quickly (e.g., acetylcholine and cholinesterase). Why is this important? Otherwise, you’d die...the stimulus would just keep coming and coming. Note: some insecticides block the action of cholinesterase; the insect heart and other muscles contract and cannot relax (poor little guy)
- the presence of synaptic vesicles only in the presynaptic membrane and the presence of neurotransmitter receptors only on the postsynaptic membrane ensures that an impulse can only be propagated in one direction
- note: neurotransmitters may have inhibitory effects on some neurons by opening K+ gates and causing hyper-polarization. This means that the resting potential is lower (more negative) and that more Na+ gates would have to open before the neuron can reach threshold and the membrane be depolarized
- acetylcholine (are we sick of acetylcholine yet?!!!)
- excites skeletal muscles
- can inhibit or excite at other locations
- low acetylcholine has been linked to Alzheimer's disease
- norepinephrine - excite and inhibit
- mostly excites but also inhibits some neurons
- in the brain it affects mood, sleep, attention, and learning
- low dopamine has been linked to Parkinson's disease while high dopamine has been linked to schizophrenia
- mostly inhibitory effects
- LSD binds to serotonin receptors and blocks the inhibitory effect which leads to hallucinations. This is BAD!
- so-called "natural pain killers" released in the brain
- block neurotransmitter receptor sites in the brain so neurons relaying messages from sensory neurons don't fire
- heroine, codeine, and morphine are chemically similar to endorphins and have the same effect
More Nervous System Notes
· Communication within body occurs exclusively by chemical signals (hormones) in plants, but animals have both chemical signals and electrical signals and the two systems are intertwined
· nervous system at simplest level provides: sensory input, integration, motor output
Þ sensory input and motor output accomplished by neurons of peripheral nervous system (PNS)
Þ integration accomplished by neurons of central nervous system (CNS)
· neurons specialized cells for transmitting signals throughout body
Þ cell body with nucleus an other organelles
Þ dendrites convey signals from tips toward cell body
Þ axons convey signals from cell body to tips
Þ Schwann cells form myelin sheath covering axons in the PNS of many vertebrates; in CNS glial cells form myelin sheaths
* function to insulate the electrical impulses that move down the axon;
Þ connect to other neurons at synaptic terminals
Þ sensory, motor and integration neurons
· how do nerves transmit signals?
Þ early work done on large neurons from squids
Þ knew muscle cells could be stimulated to contract with electrical signals
Þ at first thought they conducted electrical signals just like electric wire
Þ by inserting microelectrodes into axon, discovered that inside of the cell was more negatively charged than outside (-70mV)
Þ if electrodes inserted along axon, and nerve stimulated, first one electrode would record a spike of positive charge inside the axon and a fraction of a second later, the second in line would record a spike of positive charge
Þ the degree of change in electrical potential in the cell did not respond to changes in stimulation of nerve, but did impact the frequency—the nerve impulse was an all-or-nothing response
· action potentials are electrical signals that flow down axon
· resting potential is term applied to non-stimulated neuron (most cells only occur in this state)
· normally cells more negative inside than outside—why?
Þ inside: neg ions--proteins, amino acids, phosphate are rarer outside the cell; pos ions--K
Þ outside: pos ions Na, some K
Þ membrane potential is -50 to -100 mV = resting potential
Þ ions can’t move thru phospholipid bilayer, thus need transport proteins or ion channels (proteins too)
Þ K and Na diffuse thru ion channels passively and eventually gradient would dissipate—Na-K active pump works in opposition to diffusion
· all cells have membrane potential, only neurons and muscle cells (excitable cells) adapted to change membrane potential
· neurons have gated ion channels that allow nerve to change permeability to different ions
Þ nerve stimulation opens ion channel for Na+, which rushes into cell because of:
* 1. concentration gradient; [Na+] low inside cell
* 2. electrical attraction; Na+ attracted into negatively charged cell interior
Þ nerve stimulation also opens, but more slowly, ion channels for K+, which rush out of cell because:
* 1. [K+ ] low inside cell
* 2. electrical repulsion from the influx of positive charge (Na+) into the cell
· a stimulus will open Na channels; if only a few channels open, the interior of the cell becomes slightly more positive, but if it reaches about -50mV, then it sets of action potential;
· action potential in one part of axon stimulates the adjacent region to depolarize too
· Transmission speed varies
Þ depends on diameter of axon (larger = faster); in invertebrates large axons important in speeding transmission rates (i.e., in thin axons 3m/s to 100m/s in giant axons)
Þ depends on myelin sheaths in vertebrates; saltatory conduction of impulse
· neurons are joined together by synapses
Þ most synapses use a chemical messenger to carry signal across a synaptic cleft
Þ chemical messenger = neurotransmitter which is released from vesicles of the presynaptic neuron
Þ neurotransmitter diffuses across cleft and stimulates the postsynaptic neuron to fire
· many neurons (i.e., sensory neurons) synapse with a single postsynaptic neuron.
Þ firing by postsynaptic neuron depends on summation of stimuli received by the neuron
* some neurons act in an inhibitory manner
* some neurons act in an excitatory manner
* several excitatory synapses releasing neurotransmitters at the same time or nearly so required to stimulate postsynaptic nerve to fire
* omit details
· variety of types of neurotransmitters
Þ serotonin thought linked to mood, and sleep cycles
· organization of nervous systems varies with different animal groups
Þ simple invertebrates with nerve net, without central control, brain, or division into CNS and PNS
Þ bilaterally symmetrical animals have CNS; i.e., planaria have small brain and nerve cord (bundles of neurons)
· evolutionary trends in vertebrates
Þ brain size increases relative to body size in mammals and birds
* fish, amphibians and reptiles show similar ratios of brain size to body size
Þ as size increases, so does compartmentalization
Þ forebrain with the cerebrum especially increases in some mammals, especially humans.
cell bodies of the neurons in the cerebrum are gray matter and located in the cerebral cortex; these neurons integrated complex behaviors and learning, thus “smarter” mammals have more surface area in their cerebral cortex
Notes on THE BRAIN & FIVE SENSES
The human brain is responsible for overseeing the daily operations of the human body and for interpreting the vast amount of information it receives. The adult human brain weighs an average of 1.4 kg, or about 2 percent of the total body weight. Despite this relatively small mass, the brain contains approximately 100 billion neurons. Functioning as a unit, these neurons make up the most complex and highly organized structure on Earth. The brain is responsible for many of the qualities that make each individual unique-thoughts, feelings, emotions, talents, memories, and the ability to process information. Much of the brain is dedicated to running the body, the brain is responsible for maintaining Homeostasis by controlling and integrating the various systems that make up the body.
OBJECTIVES: Describe all the major parts of the brain and their functions. Summarize the functions of the cerebrum, brain stem, and cerebellum. Describe how the brain is protected from injury.
1. THE BRAIN IS THE MAIN SWITCHING UNIT OF THE CENTRAL NERVOUS SYSTEM; IT IS THE PLACE TO WHICH IMPULSES FLOW AND FROM WHICH IMPULSES ORIGINATE.
2. THE SPINAL CORD PROVIDES THE LINK BETWEEN THE BRAIN AND THE REST OF THE BODY.
3. THE BRAIN HAS THREE MAIN PARTS:
A. THE CEREBRUM
B. THE CEREBELLUM
C. THE BRAIN STEM
4. The Brain is a highly organized ORGAN that contains approximately 100 billion neurons and has a MASS of 1.4 Kilograms.
5. The Brain is Protected by a BONY Covering called the SKULL.
6. The Brain is also WRAPPED in THREE LAYERS of CONNECTIVE TISSUE known as the MENINGES.
7. Connective Tissue connects one tissue to another.
8. The INNER most layer, which covers and is bound to the surface of the brain, is called PIA MATER.
9. It is a FIBEROUS LAYER made up of many Blood Vessels which carry FOOD and OXYGEN to the Brain.
10. The OUTER Layer, called the DURA MATER, is composed of Thick Connective Tissue.
11. The ARACHNOID is the THIN, elastic, weblike layer between the PIA MATER and the DURA MATER.
12. Between the Pia Mater and the Arachnoid is a space filled with CEREBROSPINAL FLUID.
13. Cerebrospinal Fluid separates the middle and inner Meninges and fills four interconnected VENTRICLES, or Cavities in the Brain. Within the Ventricles, Cerebrospinal Fluid acts as a Transport Medium for substances that are important to Brain Function.
14. The Cerebrospinal Fluid is a clear liquid that PROTECTS the Brain from mechanical injury by acting as a Shock Absorber.
15. In order for the Brain to perform its functions, it must have a constant supply of Food and Oxygen.
16. If the Oxygen supply to the brain is cut off even for a few minutes, the brain will usually suffer enormous damage. Such damage may result in DEATH.
PARTS OF THE BRAIN
1. THE CEREBRUM IS THE CONTROL CENTER OF THE BRAIN.
2. The LARGEST and most PROMINENT part of the Human Brain is the CEREBRUM. 85% OF THE WEIGHT OF A HUMAN BRAIN.
3. The Cerebrum is responsible for all the VOLUNTARY (CONSCIOUS) ACTIVITIES OF THE BODY.
4. It is the site of INTELLIGENCE, LEARNING AND JUDGMENT.
5. IT FUNCTIONS IN LANGUAGE, CONSCIOUS THOUGHT, MEMORY, PERSONALITY DEVELOPMENT, VISION, AND OTHER SENSATIONS.
6. The Cerebrum takes up most of the space in the cavity that houses the Brain. (SKULL)
7. The CEREBRUM IS DIVIDED INTO TWO HEMISPHERES, THE LEFT AND RIGHT CEREBRAL HEMISPHERES. (Figure 50-3 (a))
8. There is a DEEP GROVE that separates the Two Hemispheres.
9. The Hemispheres are Connected in a region known as the CORPUS CALLOSUM.
10. The right and left cerebral hemispheres are linked by a bundle of neurons called A TRACT.
11. THE TRACT TELLS EACH HALF OF THE BRAIN WHAT THE OTHER HALF IS DOING.
12. The MOST Obvious FEATURE on the surface of each hemisphere are NUMEROUS FOLDS.
13. These FOLDS and the GROVES INCREASE the Surface Area of the Cerebrum. The Ridges are called GYRI, and the grooves are called SULCUS.
14. The Cerebrum, which looks like a wrinkled mushroom, is positioned over the rest of the brain.
15. It contains thick layers of Unmyelinated Neurons, which look GRAY. (OUR "GRAY MATTER")
16. The increased surface area permits the large number of neurons to fit easily within the confines of the Skull.
17. Each Hemisphere of the Cerebrum is divided into Four regions called LOBES. (Figure 50-3 (b))
18. These LOBES are named for the SKULL BONES that cover them, FRONTAL, PARIETAL, TEMPORAL, AND OCCIPITAL LOBES.
19. Scientists have discovered that the LEFT Side of the Body SENDS its Sensations to the RIGHT Hemisphere of Cerebrum, and the RIGHT Side of the body send its sensations to the LEFT Hemisphere.
20. Commands to move muscles are generated in the same way the Left Hemisphere controls the Right side of the body and the Right Hemisphere controls the Left side of the body.
21. The RIGHT Hemisphere is associated with CREATIVITY AND ARTISTIC ABILITY.
22. The LEFT Hemisphere is associated with ANALYTICAL AND MATHEMATICAL ABILITY.
23. Sometimes blood vessels in the brain are blocked by blood clots, causing a disorder called A STROKE.
24. During a Stroke, circulation to an area in the brain is blocked and the brain tissue dies. A severe Stroke in one side of the brain may cause PARALYSIS of the other side of the body.
25. The Cerebrum consists of TWO SURFACES.
A. The FOLDED OUTER SURFACE is called the CEREBRAL CORTEX and consists of GRAY MATTER (UNMYELINATED NEURONS).
B. The INNER SURFACE is called the CEREBRAL MEDULLA, which is made up of bundles of MYELINATED AXONS. THE WHITE MATTER.
26. The Myelin gives the White Mater its White Color.
1. The CEREBELLUM is the SECOND LARGEST part of the Brain, and is located at the back of the Skull.
2. THE CEREBELLUM COORDINATES MUSCLE MOVEMENTS.
3. The Cerebellum coordinates and balances the actions of Muscles so that the body can move gracefully and efficiently.
4. The Cerebellum CONTROLS BALANCE, POSTURE, and COORDINATION.
5. The Cerebellum receives sensory impulses from muscles, tendons, joints, eyes, and ears, as well as input from other brain centers.
6. It processes information about position and controls posture by keeping skeletal muscles in a constant state of partial contraction.
7. The Cerebellum Coordinates rapid and ongoing movements.
8. This is a small CAULIFLOWER SHAPED Structure, while well developed in mammals, is even more developed in BIRDS.
9. Bird performs more complicated feats of balance than most mammals, because they move through the air, as well as, along the ground.
10. Imagine the kind of balance and coordination needed for a bird to land on a branch at precisely the right moment.
11. A Major part of learning how to perform physical activities seems to be related to training the Cerebellum to coordinate the proper muscles.
12. Because the function of the Cerebellum is INVOLUNTARY (not under conscious control), learning a completely new physical activity can be very difficult.
THE BRAIN STEM
1. The BRAIN STEM CONNECTS the BRAIN to the SPINAL CORD.
2. THE BRAIN STEM, WHICH MAINTAINS LIFE SUPPORT SYSTEMS, CONSIST OF THE DIENCEPHALON, MEDULLA OBLONGATA, PONS, AND THE MIDBRAIN.
3. THE BRAIN STEM CONTROLS VITAL BODY PROCESSES.
4. The Brain stem not only coordinates and integrates all INCOMING INFORMATION; it also serves as the place of entry or exit for ten of the Twelve Cranial Nerves.
5. The Upper Brain Stem, the Diencephalon, contains important relay centers for information entering an exiting the brain.
6. The Lower Brain Stem consists of the MEDULLA OBLONGATA, PONS, AND MIDBRAIN.
7. The Lowest Part of the Brain Stem is the Medulla Oblongata (Sometimes just called the Medulla).
8. The Medulla contains WHITE MATER that conducts impulses between the Spinal Cord and Brain.
9. THE MEDULLA CONTROLS INVOLUNTARY FUNCTIONS THAT INCLUDE, BREATHING, BLOOD PRESSURE, HEART RATE, DIGESTION, SWALLOWING, AND COUGHING.
10. Another important part of the Medulla is a GROUP of CELLS known as THE RETICULAR ACTIVATING SYSTEM or RETICULAR FORMATION (RAS).
11. The Reticular Activation System (RAS) actually helps to alert, or awaken, the upper parts of the Brain, including the Cerebral Cortex.
12. Such actions keep the Brain alert and conscious.
13. The RAS also helps to control respiration and circulation and serves as a filtering system for incoming sensory signals.
14. For example, we awaken to the sound of an alarm clock, to a bright light flash, or to a painful pinch because activity in the RAS that arouses the Cerebral Cortex.
15. Just above the Medulla, the brainstem enlarges to form the PONS.
16. PONS MEAN BRIDGE, AND THIS AREA OF THE BRAIN STEM CONTAINS MOSTLY WHITE MATTER THAT PROVIDES A LINK BETWEEN THE CEREBRAL CORTEX AND THE CEREBELLUM.
17. Above the PONS and continuous with it is the MIDBRAIN, THE SMALLEST DIVISION OF THE LOWER BRAIN STEM.
18. AREAS OF THE MIDBRAIN ARE INVOLVED IN HEARING AND VISION.
THE UPPER BRAIN STEM - DIENCEPHALON
THE THALAMUS AND HYPOTHALAMUS
1. The Thalamus and Hypothalamus are found in the part of the brain between the Brain Stem and Cerebrum.
2. The Thalamus, which is composed of Gray Matter, serves as a SWITCHING STATION FOR SENSORY INPUT. With the Exception of SMELL, each Sense Channels its Sensory Nerves through the Thalamus.
3. The Thalamus passes information to the proper region of the Cerebrum for further processing.
4. Immediately Below the Thalamus is the Hypothalamus, which is the CONTROL CENTER for HUNGER, THIRST, FATIGUE, ANGER, AND BODY TEMPERATURE.
5. Parts of the Diencephalon and the Cerebrum are included in an important group of connected Brain Centers called the LIMBIC SYSTEM.
6. The Limbic System includes the Thalamus, the Hypothalamus, some deeper parts of the Cerebral Cortex, and centers in the Temporal Lobes.
7. The Limbic system plays an important role in emotions, memory, and motivation, among other things.
Human experience is effected by both internal and external stimuli. Humans are able to distinguish among many different types of stimuli by means of a highly developed system of SENSE ORGANS. Sensory Systems represent an integration of the functions of the Peripheral Nervous System and the Central Nervous System. The Sensory Division of the Peripheral Nervous System gathers information about the Body's Internal Conditions and External Environment. Sensory Systems translate light, sound, temperature, and other aspects of the Environment to Electrical Signals and transmit these signals, in the form of Action Potentials, to the Central Nervous System, where they are Interpreted.
OBJECTIVES: List and describe the five types of sensory receptors. Describe the structure of the eye and the roles of rods and cones. Identify the parts of the ear responsible for hearing and for maintaining balance. Compare the senses of smell and taste. Explain how taste and smell are detected. Identify the various sense receptors in the skin. Name the parts of the ear and explain the function of each part. Name the parts of the eye and explain the function of each part.
1. There are million of neurons in the body that do not receive impulses from other neurons. Instead these neurons which are called SENSORY RECEPTORS, REACT DIRECTLY TO STIMULATION FROM THE ENVIRONMENT.
2. Many Receptors that enable the Body to RECEIVE INFORMATION from the ENVIRONMENT are located in highly specialized Organs called SENSE ORGANS.
3. Examples of stimulation include: LIGHT, SOUND, MOTION, CHEMICAL, PRESSURE, PAIN OR CHANGES IN THE TEMPERATURE.
4. Once these Sensory Receptors are Stimulated, they TRANSFORM one form of ENERGY from the Environment (LIGHT, SOUND) into another form of ENERGY (ACTION POTENTIAL) that can be transmitted to other neurons. These Action Potentials (IMPULSES) reach the Central Nervous System (CNS).
5. A Sensory Receptor is a Neuron that is Specialized to detect a Stimulus. There are many kinds of Sensory Receptors, and they can be categorized on the Basis of the Type of Stimuli they Respond To:
A. MECHANORECEPTORS - Respond to Movement, Pressure, and Tension.
B. PHOTORECEPTORS (RODS AND CONES) - Respond to Variations in Light.
C. CHEMORECEPTORS - Respond to Chemicals.
D. THERMORECEPTORS - Respond to Changes in Temperature.
E. PAIN RECEPTORS (Nociceptors)- Respond to Tissue Damage - PAIN!
6. THE SENSORY RECEPTORS ARE CONTAINED IN THE SENSE ORGANS.
7. EACH OF THE FIVE SENSES (SIGHT, HEARING, SMELL, TASTE, AND TOUCH) HAS A SPECIFIC SENSE ORGAN ASSOCIATED WITH IT.
8. The MOST familiar Sense Organs are the EYES, EARS, NOSE, SKIN AND TASTE BUDS. These Organs have RECEPTORS that can respond to Stimuli by producing NERVE IMPULSES in a Sensory Neuron.
9. The Receptors CONVERT the ENERGY of a Stimulus into ELECTRICAL ENERGY that can travel in the NERVOUS SYSTEM.
10. Receptors INSIDE the body inform the CNS about the CONDITIONS OF THE BODY.
11. EXAMPLE: TEMPERATURE Receptors throughout the body detect Changes in Temperature. This information travels to the HYPOTHALAMUS, which helps control body temperature.
12. SPECIALIZED CELLS (Receptors) WITHIN EACH SENSE ORGAN ENABLE IT TO RESPOND TO PARTICULAR STIMULI.
13. Messages from Sense Organs to the CNS are all in the form of Nerve Impulses. How does are brain know whether incoming impulse is sound or light?
14. This Information is built into the "WIRING" in the Pathways of Neurons that Synapse with each other, and into the location in the Brain where the information arrives.
15. The Brain knows if the information received is from a Sensory Neuron that comes from LIGHT RECEPTORS CELLS when it gets the message.
HEARING AND BALANCE
The EAR is really TWO Sense Organs in ONE. It not only detects Sound Waves, it also senses the Position of the HEAD, whether it is STILL, MOVING IN A STRAIGHT LINE, OR ROTATING.
Sound is nothing more than Vibrations in the Air around us.
The Sense Organ that can distinguish BOTH PITCH AND LOUDNESS of SOUNDS are the EARS.
The External Ear consists of the visible fleshy part helps to COLLECT Sounds and FUNNEL them into the AUDITORY CANAL. The Auditory Canal connects the External Ear with the TYMPANIC MEMBRANE, also called the Eardrum.
7. The Auditory Canal contains small Hairs and WAX Producing GLANDS that PREVENT Foreign objects from entering the ear.
8. The Auditory Canal extends into the bone of the head, but stops at the EARDRUM OR TYMPANIC MEMBRANE.
9. The Eardrum is the beginning of the MIDDLE EAR.
10. Sound Vibrations STRIKE the EARDRUM and are Transmitted through THREE TINY BONES: THE MALLEUS (HAMMER), INCUS (ANVIL), AND STAPES (STIRRUP).
11. The Stirrup transfers the Vibrations to a thin membrane covering an opening called the OVAL WINDOW.
12. This Membrane transmits the vibrations to the COCHLEA, which begins the INNER EAR.
13. The COCHLEA is SNAIL SHAPED, consisting of Three FLUID FILLED Chambers that are separated by membranes.
14. The Middle Chamber contains the ORGAN OF CORTI, which is the organ of Hearing.
15. When the Fluid Vibrates, tiny Hair Cells lining the Cochlea are PUSHED back and forth, providing Stimulation that is turned into NERVE IMPULSES.
16. These Nerve Impulses are carried to the Brain by the AUDITORY OR ACOUSTIC NERVE.
17. The EARS also contain structures for DETECTING STIMULI that make us aware of our MOVEMENTS and allow us to maintain our BALANCE.
18. Located within the INNER EAR just above the Cochlea are three tiny canals that lie at right angles to each other.
19. They are called the SEMICIRCULAR CANALS BECAUSE THEY EACH MAKE HALF A CIRCLE.
20. The Semicircular Canals and the TWO Tiny Sacs located behind them help us to SENSE BALANCE OR EQUILIBRIUM.
21. Both the Canals and the Sacs are filled with Fluid and Lined with Hair Cells (Mechanoreceptors).
22. There are also Tiny Grains of Calcium Carbonate and Protein called OTOLITHS, Otoliths roll back and forth in response to gravity, acceleration, and deceleration.
23. The Movement of Fluid and Otoliths bend the hair on the Hair Cells, and in turn sends the impulses to the Brain that enable it to determine BODY MOTION AND POSITION.
1. The Sense Organ we use to sense Light is the EYES.
2. The EYE is composed of THREE LAYERS: The OUTER Layer consists of the SCLERA AND CORNEA, The MIDDLE Layer contains the CHOROID, CILIARY BODY, AND IRIS, The INNER Layer consists of the RETINA.
3. The SCLERA (WHITE OF THE EYE) consist of tough white connective tissue. The Sclera helps MAINTAIN the SHAPE OF EYE, and also provides a means of ATTACHMENT for the MUSCLES THAT MOVE THE EYE.
4. IN THE FRONT OF THE EYE, THE SCLERA FORMS A TRANSPARENT LAYER CALLED THE CORNEA.
5. The CORNEA is the part of the eye through which LIGHT ENTERS.
6. Just inside the Cornea is a small chamber filled with FLUID known as the AQUEOUS HUMOR.
7. At the BACK of this chamber, the PIGMENTED CHOROID, WHICH CONTAINS THE BLOOD VESSELS OF THE EYE, BECOMES a disk-like structure called the IRIS.
8. The IRIS (A DIAPHRAGM) is the portion of the eye that gives your eye its COLOR. The Iris controls the amount of Light entering the eye by altering the Diameter of the Pupil.
9. In the MIDDLE of the Iris is a small opening called the PUPIL, through which LIGHT ENTERS THE EYE.
10. The Pupil appears as a small black disk in the CENTER of the Eye. Tiny muscles in the Iris REGULATE the SIZE of the Pupil, controlling the amount of Light to enter the Eye.
11. In DIM LIGHT the Pupil OPENS to INCREASE the amount of Light, In BRIGHT LIGHT the Pupil CLOSES to DECREASE the amount of Light entering the Eye.
12. Behind the Iris is the LENS. Light is Focused by the Lens, which changes shape when pulled by muscles around its edges.
13. The CELLS that form the Lens contain a special PROTEIN called CRYSTALIN. CRYSTALIN is almost transparent and allows light to pass through.
14. Small Muscles attached to the Lens cause it to bend, this enables the eye to FOCUS on close and distant objects.
15. Behind the Lens is a Large Chamber called the VITREAL CHAMBER filled with a transparent Jelly-like Fluid called VITREOUS HUMOR.
16. Special Light Sensitive RECEPTOR CELLS, or PHOTORECEPTORS, are arranged in a layer in the RETINA, at the BACK of the EYE.
17. The PHOTORECEPTORS CONVERT LIGHT ENERGY INTO IMPULSES THAT ARE CARRIED TO THE CNS.
18. THERE ARE TWO TYPES OF PHOTORECEPTORS: RODS AND CONES. We have about 125 million RODS and 7 million CONES on a single Retina.
19. Photoreceptors contain a PIGMENT called RHODOPSIN, that can respond to most wavelengths of light.
20. RODS are extremely sensitive to ALL COLORS of LIGHT, but DO NOT DISTINGUISH DIFFERENT COLORS.
21. CONES are less sensitive than RODS, but they DO RESPOND DIFFERENTLY TO LIGHT OF DIFFERENT COLORS, PRODUCING COLOR VISION.
22. Humans have three kinds of cones. Each type of cone contains a pigment that absorbs different wavelengths of light. When the signals from these three kinds of cone are integrated, a person is able to see all the colors in the visible spectrum.
23. In DIM Light, when only RODS are activated, you may see objects clearly, but not their colors.
24. As the amount of Light INCREASE, the CONES are stimulated and the colors become clear.
25. The Impulses leave the Eye by way of the OPTIC NERVE, and CARRIED to the part of BRAIN Known as the OPTIC LOBE OR OCCIPITAL LOBE. Here the Brain Interprets the visual images and provides information about the external world.
1. The Sense of Smell is a CHEMICAL SENSE, the Cells responsible for smell are Specialized Chemoreceptors called OLFACTORY RECEPTORS.
2. These Cells are located in the Upper Part of the Nasal Cavity.
3. Chemoreceptors contain Cilia that extend into the air passageways of the nose and react to Chemicals in the Air. Chemicals that come into contact with the Chemoreceptors Stimulate them, causing Impulses to be sent to the Brain by the OLFACTORY NERVE.
1. The Sense of Taste is a Chemical Sense.
2. The Cells that are Stimulated by the Chemicals are called CHEMORECEPTORS.
3. The Sense Organ that detects Taste are the TASTE BUDS. NOT THE TONGUE!
4. Most of the 10,000 Taste Buds are embedded between bumps called PAPILLAE on the tongue, but can also be found on the roof of the mouth, on the lips, and in the throat.
5. Humans can detect FOUR main kinds of TASTE: SWEET, SALTY, SOUR, AND BITTER.
6. Each Taste Bud shows a particular Sensitivity to one of these taste. The Sense of Taste is converted to Nerve Impulses in the Taste Buds and transmitted to the Brain by TWO Nerves - The FACIAL NERVE AND GLOSSOPHARYNGEAL NERVES.
7. Many of the Sensation associated with taste are actually SMELL Sensations, You depend on both Senses to detect Flavors in Food. That is why when you have a Cold and Your Smell Receptors are blocked, food seems to have little or no taste.
TOUCH AND RELATED SENSES
1. All Regions of our bodies are sensitive to TOUCH.
2. YOUR LARGEST SENSE ORGAN IS YOUR SKIN.
3. MECHANORECEPTORS located throughout the Skin make it possible to sense touch, pressure, and tension.
4. In humans, the receptors for touch are concentrated in the face, tongue, and fingertips.
5. Body hair also plays an important role in the ability to sense touch. Large numbers of Mechanoreceptors are found in the skin at the base of hair follicles.
6. Our Skin has several different types of Sensory Receptors that are just below the surface of the Skin.
7. Two Types respond to Heat or Cold - THERMORECEPTORS; Two others respond to TOUCH - MECHANORECEPTORS; one Type responds to TISSUE DAMAGE WHICH CAUSES PAIN - PAIN RECEPTORS.
8. Sensory receptors for Hot or Cold are scattered directly below the surface of the skin. There are THREE to FOUR WARM Receptors for every COLD Receptor.
9. Sensory Receptor can be more concentrated in different places of our bodies.
10. The MOST TOUCH-Sensitive areas are the FINGERS, TOES, AND LIPS.
11. Pain Receptors are located throughout the skin. The Sensation of Pain can be experienced as either Prickling Pain (FAST PAIN) or Burning and Aching Pain (SLOW PAIN). Pain receptors are Stimulated by mechanical, thermal, electrical, or chemical Energy.