Unit 4 Compilation
Table Of Contents
Chapter 14:-Digestive system brings nutrient into body
-Mouth Processes food for swallowing
-Pharynx & esophagus deliver food to stomach
-Stomach stores food, digests protein & regulates delivery
-Small intestine digests food & absorbs nutrients & water
-Accessory organs aid digestion & absorption
-Large intestine absorbs nutrients & eliminates wastes
-How nutrients are absorbed
-Endocrine & nervous system regulate digestion
-Nutrition: you are what you eat
-weight control: energy consumed vs. energy spent
-Disorders of digestive tract
-4 characteristics of nervous system
-Nervous system has 2 principal parts
-Neurons are communication cells
-Neurons initiate action potentials
-Neuroglial cells support/protect neurons
-Info is transferred from neuron to its target
-Receptors receive and convert stimuli
-Somatic sensations arise from receptors throughout body
-Vision: detecting & interpreting stimuli
-Disorders of sensory mechanisms
-Pollutants impact air quality
-Pollution jeopardizes scarce water supplies
-Pollution & overuse damage land
Global Warming in News Today
Chapter 14: Digestive System and Nutrition
Nutrients are substances in food that are required for growth reproduction and the maintenance of health.
*Digestive System Brings Nutrients into the Body
Digestive System consists of all the organs that share the common function of getting nutrients into the body.It is made up of the gastrointestinal tract, which is a hollow tube that extends from mouth to anus- it includes the: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.
It also includes 4 accessory organs: the salivary glands, liver, gallbladder and pancreas.
Walls of GI tract are composed of 4 layers:
1-Mucosa: innermost layer of tissue, all nutrients must cross this to enter blood.
2-Submucosa: layer of connective tissue that contains blood vessels, lymph vessels and nerves.
3-Muscularis: responsible for motility, consists of 2 or 3 sub layers of smooth muscle.
4-Serosa: thin connective tissue sheath, surrounds and protects the other 3 layers and attaches digestive system to walls of body cavities.
*5 Basic Processes accomplish digestive system function
1-Mechanical processing and movement- Chewing breaks food into smaller pieces and 2 types of movement mix the contents of the lumen and propel it forward.
2-Secretion-Flud, digestive enzymes, acid, alkali, bile, and mucus are all secreted into GI tract at various places.
3-Digestion-Contents of the lumen are broken down both mechanically and chemically into smaller particles, culminating in nutrient molecules
4-Absorption-Nutrient molecules pass across the mucosal layer of GI tract into blood/lymph.
5-Elminination-Undigested material is eliminated from the body via the anus.
*2 Types of motility aid in digestive processes
Peristalsis-propels food forward; this begins when a lump of food (bolus) stretches a portion of the GI tract, causing smooth muscle in front of the bolus to relax and the muscle behind it to contract. The contractions push the food forward, stretching the next part of the tube and causing muscle relaxation in front and contraction behind. The peristaltic wave of contractions helps to mix the contents of the stomach and push the contents of the esophagus/intestines forward.
Segmentation- mixes good- short sections of smooth muscle contract/relax in a random fashion. Result of this is a back and forth mixing of contents of the lumen. Food particles are pressed against the mucosa, enabling the body to absorb their nutrients. This type of movement occurs primarily in the small intestine as food is digested/absorbed.
*The Mouth processes food for swallowing
**Teeth Bite and Chew Food
Teeth chew food into pieces small enough to swallow. There are 4 types of teeth, each with a specialized purpose: Incisors cut food, and the canines tear it, pre-molars/molars grind and crush food. Children have only 20 teeth, but adults have 32 permanent teeth.
**Tongue positions and tastes food
The tongue helps to position food over teeth and mash it against the roof of the mouth. The tongue consists of a skeletal muscle enclosed in mucous membrane.
**Saliva begins the process of digestion
3 pairs of salivary glands produce fluid called saliva. The parotid gland lies near the back of the jaw, and the sublingual and submandibular glands are located just below the lower jaw and below the tongue. Saliva moistens food making it easier to chew and swallow.
4 ingredients of mucous include: Mucin- which is a mucus-like protein that holds food particles together so they can be swallowed more easily; Salivary amylase- begins the process of digesting carbs; Bicarbonate- maintains the pH of the mouth between 6.5-7.5; Lysozyme- inhibits bacterial growth.
*Pharynx and Esophagus deliver food to the stomach
After we have chewed our food and mixed it w/saliva, the tongue pushes it into the pharynx (throat) for swallowing. The presence of food in the pharynx stimulates receptors and initiates the “swallowing reflex”. The soft palate rises to close off the passageway into the nasal cavity and the larynx rises slightly. The epiglottis bends to close the airway to the trachea temporarily, so we do not inhale the food
Esophagus- muscular tube consisting of both skeletal and smooth muscle that connects the pharynx to the stomach; its lining produces lubricating mucus that helps food to slide more easily. The lower esophageal sphincter, located at the base of the esophagus opens briefly as food arrives and closes after it passes into the stomach. This sphincter prevents reflux of the stomach’s contents back into the esophagus.
*Stomach stores food, digests protein and regulates delivery
Stomach= a muscular, expandable sac that performs the following functions
1-Food Storage- the stomach stores food until it can be digested and absorbed. The stomach shrinks when empty, then expands to 1-3 liters of capacity when we eat.
2-Digestion- It digests proteins using strong acid protein-digesting enzymes. This acid also kills most bacteria. Muscle contractions mix these secretions w/food, assist in mechanically breaking apart food, and push the mixture into the small intestine.
3- Regulation of delivery- Stomach regulates the rate at which food is delivered into the small intestine.
Gastric Juice breaks down proteins
In the mucosal layer there are millions of small openings called gastric pits that lead to gastric glands below the surface. Most of these cells secrete pepsinogen, which is a large precursor molecule that becomes a protein-digesting enzyme called pepsin.
Stomach typically produces 1-2 liters of gastric juice (pepsin mixed w/HC1) per day. The acid gives the stomach an acidic pH of approximately 2. Pepsin and acid in gastric juice dissolve the connective tissue in food and digest proteins and peptides into amino acids so they can be absorbed into the small intestine. Chyme= watery mixture of partially digested food and gastric juice that is delivered to the small intestine
Stomach contractions mix food and push it forward
While your stomach is empty, muscle contractions keep it small. When you eat, contractions cease and the stomach relaxes and stretches to accommodate the food. Stretching signals peristalsis to increase. Each wave of peristalsis starts at the lower esophageal sphincter and moves toward the pyloric sphincter, becoming stronger as it proceeds. Peristaltic wave pushes the chime forward, and when there is nowhere else for it to go, backward again in a squeezing, mixing motion. A peristaltic contraction occurs every 15-25 seconds. It takes 2-6 hours for a stomach to completely empty after a meal. Chyme w/ a high acid or fat content stimulates the release of hormones that slow stomach peristalsis, giving the small intestine more time to absorb the nutrients.
The stomach doesn’t absorb nutrients because it lacks the required cellular transporting mechanisms and because its inner lining is coated w/mucous.
*The small intestine digests food and absorbs nutrients and water
**Small intestine has 2 major functions:
1-Digestion- stomach partially digests proteins to smaller peptides; Protein digestion continues in the small intestine, and here we also digest carbs and lipids.
2-Absorption- Proteins, carbs, and lipids in foods are broken down to single amino acids, monosaccharide’s, fatty acids, and glycerol, which are small enough to be transported across mucosal cells into the blood. Nearly 90% of absorbable nutrients and water is absorbed in the small intestine.
Small intestine consists of 3 different regions: The duodenum is the first region, which is appx 10 inches long, this is where the most digestion occurs; the products of digestion are absorbed primarily in the other 2 segments the jejunum and the ileum, which together are 10 feet long.
The mucosa contains large folds covered with microscopic projections called villi; each epithelial cell of the villi has dozens of smaller, cytoplasmic projections called microvilli. Combined the villi and microvilli enlarge the surface area of the small intestine by more than 500 times.
*Accessory organs aid digestion and absorption
**Pancreas secretes enzymes and NaHCO3
Pancreas-elongated organ that lies just behind the stomach; it has both endocrine and exocrine functions. As an endocrine gland it secretes hormones that regulate blood glucose levels. In its exocrine role it produces and secretes digestive enzymes (which include proteases such as trypsin, chymotrypsin, and carboxypeptidase), pancreatic amylase (which continues digestion of carbs) and sodium bicarbonate (which functions to neutralize stomach acid). 2 pancreatic ducts deliver these secretions to the duodenum, where they facilitate process of digestion.
**The liver produces bile and performs many other functions
Liver is a large organ located in the upper right abdominal cavity. Liver’s primary digestive function is to facilitate the digestion and absorption of lipids by producing bile, which is a water mixture containing electrolytes, cholesterol, bile salts, lecithin, and pigments derived from breakdown of hemoglobin. Bile salts emulsify lipids in the small intestine; they break them into smaller droplets.
Hepatic portal system: carries nutrient-rich blood directly from the digestive organs to the liver via the hepatic portal vein. After passing through the liver, the blood is returned to the general circulation.
**Liver helps to maintain homeostasis by:
-Storing fat-soluble vitamins –storing glucose as glycogen after a meal, and converting glycogen to glucose between meals –Synthesizing and storing some lipids – Destroying worn-out red blood cells –Converting ammonia into less toxic urea
**Gallbladder stores bile until needed
Gallbladder concentrates bile by removing most of the water and stores it until after a meal, when it is secreted into the small intestine via the bile duct.
*Large intestine absorbs nutrients and eliminates wastes
The large intestine absorbs most of the remaining nutrients and water, and stores the now nearly solid waste material until it can be eliminated.
Most of the large intestine consists of 4 regions collectively known as the colon. The ascending colon rises along the right side of the body, the transverse colon crosses over to the left, and the descending colon passes down the left side to the sigmoid colon, which is where feces is stored until defecation.
*How nutrients are absorbed
**Proteins and carbs are absorbed by active transport
In the small intestine enzymes from the pancreas and enzymes secreted by the mucosal layer of the stomach and small intestine itself break down proteins into amino acid. The amino acids are then actively transported into the mucosal cells; eventually they move by facilitated diffusion out of those cells and make their way into capillaries.
**Lipids are broken down, then reassembled
The products of lipid digestion are fatty acids and monoglycerides; because they are non-polar these quickly dissolve in micelles (small droplets of bile and lechtin that have a polar outer surface and a non-polar inner core). Micelles primary functions are to transport fatty acids and monoglycerides to the outer surface of the mucosal cells so they can be absorbed into cells. Once inside the cells the fatty acids and monoglycerides recombine into triglycerides.
**Water is absorbed by osmosis
AS nutrients are absorbed in the small intestine, the concentration of the water in the intestinal lumen becomes higher than in the intestinal cells or in the blood. Higher concentration of water in the lumen represents a strong driving force for the diffusion of water through the epithelial layer of cells of the small intestine and into the blood.
**Vitamins and minerals follow a variety of paths
Fat-soluble vitamins dissolve in the micelles and are absorbed by diffusion across the lipid membrane of the mucosal cell layer. Water-soluble vitamins are absorbed either by active transport or diffusion through channels or pores. Minerals such as sodium, potassium, calcium, phosphate, sulfate and magnesium are electrically charged and hence not lipid soluble; thee are either actively transported or are absorbed by diffusion via specific transport proteins, pores, or channels.
*Endocrine and nervous systems regulate digestion
**Regulation depends on volume and content of blood
Endocrine system and nervous system regulate digestion according to both the volume and content of food. When stomach stretches to accommodate food, neutral reflexes increase stomach peristalsis and secretion of gastric juice. Stretching and presence of protein stimulate the stomach to release the hormone gastrin, which triggers the release of more gastric juice.
When chime arrives in the small intestine, stretching of the duodenum increases segmentation to mix the chime. The duodenum also secretes 2 hormones into the blood stream: secretin- stimulates the pancreas to secrete water and bicarbonate to neutralize acid, cholecystokinin (CCK) – signals the pancreas to secrete more digestive enzymes.
Secretin, CCK, and stretching of the small intestine inhibit stomach motility and stomach secretion; so if chime flows too quickly from the stomach the small intestine will slow stomach activity accordingly.
**Nutrients are used or stored until needed
Regulation of organic metabolism involves interactions between virtually all the organs in the body. Key organs are the pancreas (which secretes insulin and glucagon) and the liver. Lipids, carbs, and proteins can all be converted to storage forms of lipid or carbs, and then recycled according to the body’s needs. When we consume more energy-containing nutrients than we use, our bodies store the excess for future use; over time, these reserves can increase body weight. When we consume fewer energy-containing nutrients than we use, the body draws on these storage forms of energy to make up the difference; if we do this on a regular basis, we lose weight.
*Nutrition-You are what you eat
**MyPyramid plan offers a personalized approach
MyPyramid divides food into 6 groups and gives you recommendations on what to eat from each group. This system includes plans appropriate to different calorie levels of food intake, based on the latest Dietary Guidelines for Americans issued by the USDA and the Dept. of Health and Human Services. If you enter your age, gender, and activity level on the MyPyramid web site, the system will match you with the best plan for your needs.
General recommendations for healthy diet include:
-Eat a variety of foods –Maintain a healthy weight –Eat plenty of fruits, veggies and whole-grain products –Choose a diet low in cholesterol and saturated fat -Use sugar only in moderation -Consume salt and sodium in moderation (less than 2,300mg per day) -Drink alcohol only in moderation (one drink a day for women, or 2 for men)
**Carbohydrates: A major energy source
Carbs= one of the body’s main sources of energy, and many nutritionists recommend that appx 45-65% of our calorie intake come from carbs. Carbs can either be simple or complex; simple carbs (sugars)-are found in natural foods such as fruit and honey, complex carbs-include glycogen and starch, they consist of many sugar units linked together.
**Lipids: Essential cell components and energy sources
Phospholipids and cholesterol make up most of the cell membrane; cholesterol also forms the backbone of steroid hormones and is used to synthesize bile. Fat stores energy, cushions organs, insulates the body under the skin, and stores several vitamins.
Saturated Fats- have 2 hydrogen atoms for every carbon atom in their fatty acid tails. They tend to be solid at room temp, they are found primarily in meat and dairy products. They tend to raise blood levels of LDL cholesterol or “bad cholesterol”.
Unsaturated Fats- they are missing one or more pairs of hydrogen atoms in their fatty acid tails. Every missing pair of hydrogen atoms leads to a double bond between adjacent carbons and kink in the tail, making it more difficult for adjacent molecules to form bonds with each other. These fats are liquids at room temp, they tend to lower blood LDL cholesterol.
The liver can synthesize cholesterol and most of the lipids the body needs but it cannot produce every last one of them. Essential fatty acids= the few fatty acids that our bodies can’t make and must be consumed as food.
**Complete proteins contain every amino acid
Essential amino acids= the amino acids the body can’t produce, that must be ingested in food.
Complete protein-contains all 20 of the amino acids in proportions that meet our nutritional needs.
**Vitamins are essential for normal function
Vitamins= group of at least 13 chemicals that are essential for normal functioning. The body can produce only a few vitamins; our skin synthesizes vitamin D when exposed to sunlight, and bacteria living in the colon manufacture vitamins K, B6, and biotin.
Vitamins fall into 2 groups: fat soluble- are absorbed more readily if there is fat in the diet; and water soluble- absorbed more readily than fat-soluble vitamins, but they are stored only briefly and rapidly excreted in urine.
**Minerals: Elements essential for body processes
Minerals- atoms of certain chemical elements that is also essential for body processes. They are the ions in blood plasma and cell cytoplasm. They contribute to the activity of nerves and muscles.
**Fiber benefits the colon
Fiber- is an indigestible material found in many veggies, fruit and grains; and even though we can’t digest it, we still need a certain amount in our diets. Fiber is beneficial because it makes feces bulky and helps them pass more efficiently through the colon.
Low fiber diets can lead to chronic constipation, hemorrhoids, diverticulosis, and has also been associated w/a higher risk of colon cancer. Doctors recommend eating between 20-35 grams of fiber a day.
*Weight control: Energy consumed versus energy spent
Energy is measured in units called calories. Technically, a calorie is the amount of energy needed to raise the temp of 1 gram of water y 1 degree Celsius.
BMR: Determining how many calories we need
If we want to maintain a stable body weight, the number of calories we consume must equal the number we use. Your daily caloric energy needs are determined by your basal metabolic rate (BMR).
BMR can be influenced by the following factors:
-Gender and body composition: it is higher in males, muscle tissues consumes more energy than fat tissue.
-Age: your BMR declines over time
-Health: some conditions (such as fever) increase BMR, others such as hypothyroidism lower it.
-Stress: norepinephrine and epinephrine raise BMR.
-Food intake: eating increases metabolic rate, whereas fasting and extreme dieting decrease it.
-Genetics: Rates of metabolism vary between individuals; genes play a strong role in your BMR although it hasn’t precisely been determined how so yet.
**Energy balance and body weight
-Healthy weight control involves balancing energy intake against energy expenditure. Fat contains about 9 calories/gram, but carbs and proteins only contain 4. When we eat more calories than we use, the excess energy is stored in specialized cells as fat. Research suggests that overweight people have 2 or 3 times more fat cells than normal weight individuals.
*Disorders of the digestive system
**Disorder of the GI tract
-Lactose intolerance: Difficulty digesting milk- human infants are born w/the enzyme lactase in their small intestines for digesting lactose; however many adults gradually lose the enzyme and with it their ability to digest lactose; which results in lactose intolerance. Symptoms include: diahhrea, gas, bloating, and abdominal cramps after ingesting milk products.
-Peptic ulcers: Painful erosions of the mucosal lining of the stomach or duodenum. Most of them are associated w/ infection by one of the few bacteria that can live in the acidic environment of the stomach called helicobacter pylori. The bacterial infection can lead to chronic inflammation, an increase in gastric acid secretion and damage to the mucosal lining.
-Colon Polyps: noncancerous growths- A polyp is a noncancerous growth that projects from a mucous membrane. They can develop in many areas of the body, including the colon. Polyps can be detected and removed in a colonoscopy.
**Disorders of accessory organs
-Hepatitis: Inflammation of the liver- this is generally caused by viruses or toxic substances. Hep A is transmitted by contaminated food or water and causes a brief illness from which most people recover completely. Hep B travels in the blood or body fluids, so it is usually passed via contaminated needles, blood transfusion, or sexual contact w/infected individuals. Hep C is also transmitted in infected blood, usually through contaminated needles or blood transfusions.
-Gallstones can obstruct bile flow- Excessive cholesterol in bile may precipitate out of solution with calcium and bile salts, forming hard crystals called gallstones. If the crystals grow large enough they can obstruct bile flow and cause intense pain.
**Malnutrition: Too many or too few nutrients
-Malnutrition refers to conditions in which human development and function are compromised by an unbalanced or insufficient diet. Malnutrition can be caused by either over nutrition or undernutrition. Overnutrition can lead to obesity. However malnourishment is far more common deficiencies of one or more nutrients can produce specific effects: for example years of vitamin A deficiency a lead to eye damage and night blindness. In children, undernutrition stunts growth and increases susceptibility to infection.
**Obesity: A worldwide epidemic?
World Health Organization calls obesity a global epidemic; in the US obesity has increased from 12.6% of the population in 1990 to 34% in 2006. Body weight is determined by both internal factors and environmental factors.
*Eating disorders: Anorexia nervosa and bulimia
-Anorexia nervosa= condition in which person excessively diets or stops eating altogether, even to the point of starvation or death. Symptoms include: refusal to maintain healthy body weight; people with anorexia often weight less than 85% of their ideal weight. They have an intense fear of gaining weight, even though they’re underweight. They have a distorted perception or reoccupation with body weight or shape.
-Bulimia= binge and purge condition in which one eats and deliberately vomits or takes other steps to minimize the calories ingested. Symptoms include: recurrent episodes of binge eating, taking recurrent inappropriate steps to prevent weight gain (such as self-induced vomiting, misusing laxatives, and enemas), and preoccupation w/body shape and weight.
Chapter 11: Nervous System- Integration and Control
4 characteristics of nervous system:
-Receives information from many different senses simultaneously
-Nervous system integrates information; integration is process of taking different pieces of info from many sources and assembling the pieces into a whole that makes sense.
-Nervous system is very fast- it can receive info, integrate it and produce response within tenths of a second.
-It can initiate specific responses including muscle contraction, glandular secretion, and even conscious thought and emotions.
*The Nervous System has 2 principal parts
-Nervous system includes the central nervous system (CNS) and peripheral nervous system (PNS). The CNS consists of the brain and the spinal cord; it receives, processes, stores, and transfers information. The PNS has 2 functional subdivisions: the sensory division of the PNS carries information to the brain and spinal cord, and the motor division of the PNS carries information from the CNS to other parts of the body.
The somatic division of the PNS controls skeletal muscles, and the autonomic division of the PNS controls smooth muscles, cardiac muscles, and glands. In turn autonomic division has 2 subdivisions called the sympathetic and parasympathetic divisions.
*Neurons are Communication cells of the Nervous System
-Neurons= cells specialized for communication. They generate and conduct electrical impulses also called action potentials from one part of the body to another. There are 3 types of neurons in the nervous system.
-Sensory neurons= part of the PNS, they are specialized to respond to a certain type of stimulus, such as pressure or light. They transmit info about this stimulus to the CNS in the form of electrical impulses.
-Interneurons= part of the CNS, they transmit impulses between components of the CNS; they receive input from sensory neurons, integrate this info and influence the functioning of other neurons.
-Motor Neurons= part of the PNS, they transmit impulses away from the CNS; they carry nervous system’s output, still in the form of the electrical impulses.
**All neurons consist of a cell body, one or more dendrites, and an axon.
-Cell body= main body of the neuron, it includes the nucleus with its content of DNA, and mitochondria and other cell organelles.
-Dendrites= receive info from receptors or incoming impulses from other neurons.
-Axons= long, slender tube of cell membrane containing a small amount of cytoplasm. They are specialized to conduct electrical impulses.
*Neurons initiate action potentials
**Sodium-potassium pump maintains resting potential
-Sodium potassium pump is essential to the control of cell volume by virtue of its ability to remove osmotic particles from the cell. It is also essential for the development and maintenance of electrical charge across the cell membrane. Each time the sodium-potassium pump goes through a cycle, the net effect is the removal of one osmotic particle and also one positive charge. Sodium-potassium pump removes both osmotic particles and positive charges from the cell at the same time. As a result of the activity of the sodium-potassium pumps and also the presence of negatively charged protein molecules trapped within the cell, the cytoplasm has a slight excess of negative charge compared to the interstitial fluid.
Concentration of sodium is much higher in the interstitial fluid than it is in the cytoplasm, whereas the inverse is true for potassium.
**Graded potentials alter the resting potential
-Resting potential of a neuron undergoes a change when an impulse arrives from another neuron. Every incoming impulse produces a small transient charge in the resting potential in a local area of the membrane. Depending on the type of signal and its strength, the change might be to depolarize (move voltage closer to zero) or hyperpolarize (make it even more negative) the membrane. These transient local changes in resting potential are called graded potentials.
**Action Potential is a sudden reversal of membrane voltage
-If the sum of all graded potentials is sufficiently strong to reach a certain triggering membrane voltage called the threshold, an action potential results.
-Action potential= sudden temporary reversal of the voltage difference across the cell membrane. Once it is initiated, it sweeps rapidly down the axon at constant amplitude and rate of speed until it reaches the axon terminals. An action potential (impulse_ is the only form in which information is transmitted a long distance by the nervous system. These occur because the axon membrane contains voltage-sensitive ion channels that open and close sequentially once threshold has been reached. It has a sequence of 3 events:
1) Depolarization- sodium moves into the axon: when threshold is exceed voltage-sensitive sodium channels in the axon’s membrane open briefly and sodium ions diffuse rapidly into the cytoplasm. The influx of positive ions causes depolarization.
2) Repolarization: potassium moves out of axon- after a short delay the sodium channels close automatically. The reversal of the membrane polarity triggers the opening of potassium channels, which allows more potassium ions to diffuse rapidly out of the cell. The loss of positive ions from the cell leads to repolarization.
3) Reestablishment of the resting potential- Because the potassium channels are slow to close there is a brief overshoot of membrane voltage during which the interior of the axon is slightly hyperpolarized. Shortly after the potassium channels close the resting potential is reestablished.
**Action potentials are all-or-none and self-propagating
-An action potential does not occur unless a certain threshold membrane voltage is reached. Once it is triggered, it always looks exactly the same in form and voltage. A certain amount of pressure-the threshold level- is required to make the action potential start. Too little amount of pressure will cause it to not start, while too much pressure makes it start more quickly. An action potential also continues to propagate itself in the next region of the axon; because of the local spread of electrical current forward from the region of the axon that is currently undergoing an action potential brings the next region of the axon to threshold. Therefore the action potential is propagated continuously down the axon like a moving wave, at a constant rate of speed and amplitude.
*Neuroglial cells support and protect neurons
-Neuroglial cells= provide physical support and protection to neurons and help maintain healthy concentrations of important chemicals in the fluid surrounding them. In the PNS many neuron axons are protected by Schwann cells (which produce fatty insulating material called myelin). During development Schwann cells wrap themselves around a short segment of an axon many times as a sort of insulating blanked, creating a shiny white protective layer around the axon called a myelin sheath. Between adjacent Schwann cells are short uninsulated gaps called nodes of Ranvier, where the surface of the axon is still exposed.
**Myelin sheath around the axon serves 3 important functions:
1) Saves the neuron energy- the insulating layer of myelin prevents some of the slow inward leak of sodium and outward leak of potassium.
2) It speeds up the transmission of impulses- the myelin sheath prevents nearly all leakage of charged ions across the axon membrane except where the axon is bare. When an action potential occurs at a node of Ranvier, then the local depolarizing current spreads much farther within the axon, all the way to the next node of Ranvier. The rate of travel of this local current within the axon is even faster than the rate of travel of a continuously propagated action potential along the unmyelinated axon.
3) Helps damaged or severed axons of the peripheral nervous system regenerate- if a neuron axon is severed, the portion of the axon distal to the cell body may degenerate. Depending on the length of the axon, the regeneration process can take anywhere from a few weeks to more than a year.
*Information is transferred from a neuron to its target
Once an action potential reaches the axon terminals of a neuron the info inherent in it must be converted to another form for transmittal to its target. Neurotransmitter= chemical that is released and crosses the synapse between 2 cells; it transmits a signal from a neuron to its target.
**Neurotransmitter is released
-Presynaptic membrane= cell membrane of the neuron that is sending info, postsynaptic membrane is the membrane of the cell that is about to receive the info, the synaptic cleft= small fluid-filled gap that separates the presynaptic and postsynaptic membranes. Each axon terminal of the presynaptic neuron ends in an axon bulb that contains neurotransmitter stored in membrane-bound vesicles.
**The events that occur during a synaptic transmission follow a pattern
1) Action potential arrives at axon bulb, causing calcium channels in the presynaptic membrane to open.
2) Presence of calcium causes the vesicles to fuse with the presynaptic membrane and release their contents of neurotransmitter directly into the synaptic cleft.
3) Molecules of neurotransmitter bind to receptors on the postsynaptic membrane. This causes certain chemically gated channels to open.
4) Sodium ions diffuse inward, producing a graded depolarization of the postsynaptic membrane in the area of the synapse.
**Neurotransmitters exert excitatory or inhibitory effects
-Scientists have ID’d more than 50 chemicals that can function as neurotransmitters. All are stored in vesicles within the axon bulb and released into the synaptic cleft in response to an action potential. All produce graded potential in the postsynaptic cell. Neurotransmitters are classified as excitatory, inhibitory, or both.
Excitatory= encourage the generation of new impulses in the postsynaptic neuron.
Inhibitory= cause the postsynaptic cell to hyperpolarize, meaning the cell’s interior becomes even more negative than before.
Depending on the type of receptor to which the neurotransmitter binds to then they can be both excitatory and inhibitory.
**Postsynaptic neurons integrate and process information
-The conversion of the signal from electrical to chemical allows the postsynaptic cell to do a lot of integration and info processing. This is because a single all-or-none action potential in the presynaptic neuron does not always cause a corresponding all-or-none action potential in the postsynaptic neuron, as it does in a muscle cell.
One way for the threshold to be reached in a postsynaptic neuron is for the presynaptic neuron to increase their frequency of stimulation, sending lots of action potentials in a short time. In addition to stimulus intensity, other factors affecting whether threshold is reached in the postsynaptic neuron include: 1) how many other neurons form synapses with it, and 2) whether those synaptic connections are stimulatory or inhibitory.
Chapter 12: Sensory Mechanisms
*Receptors receive and convert stimuli
-Stimulus= some change within or outside the body; it is often a form of physical energy such as heat, pressure, or sound waves, but it can also be chemical
Receptor= a structure specialized to receive certain stimuli; it accepts the stimulus and converts its energy into another form.
-Some receptors are evolved from dendritic structures of a sensory neuron; these convert the stimulus into an impulse within the sensory neuron, and if the impulse is powerful enough it initiates an impulse within the sensory neuron.
-When the CNS receives these impulses we often experience a sensation, meaning that we become consciously aware of the stimulus.
**Receptors are classified according to the stimulus
-Mechanoreceptors: respond to forms of mechanical energy, such as waves of sound, changes in fluid pressure, physical touch, or forces generated by gravity/acceleration
-Thermoreceptors: receptors that respond to heat or cold.
-Pain receptors: receptors that respond to tissue damage or excessive pressure/temperature.
-Chemoreceptors: receptors that respond to the presence of chemicals in the nearby area.
-Photoreceptors: receptors that respond to light.
**The CNS interprets nerve impulses based on origin and frequency
-Stronger stimuli activate more receptors and trigger a greater frequency of impulses in sensory neurons. In effect, the CNS gets all the info it needs by monitoring where impulses originate and how frequently they arrive.
**Some receptors adapt to continuing stimuli
-Receptor adaptation= the sensory neuron stops sending impulses even though the original stimulus is still present; this explains why the CNS can ignore one sensation in order to concentrate on another.
Receptors in the skin for light touch and pressure adapt rather quickly; which provides and advantage because they can keep the CNS informed of changes in these stimuli, without constantly bombarding it with relatively unimportant stimuli. Olfactory receptors also adapt quickly, which can be harmful because people can be continually exposed to low levels of hazardous chemicals that they can no longer smell.
-Pain receptors, joint receptors, and muscle receptors adapt slowly or not at all. Their lack of adaptation is advantageous because persistent sensations such as pain alert us to possible tissue damage from illness or injury and prompt us to take appropriate action.
**Somatic sensations and special senses provide sensory information
-Somatic sensations originate from receptors present at more than one location in the body. These sensations include temperature, touch, vibration, pressure, pain, and awareness of body movements and position. The 5 “special senses” (taste, smell, hearing, balance, and vision) originate from receptors that are restricted to particular areas of the body, such as ears and eyes.
*Somatic sensations arise from receptors throughout the body
-Somatic sensations are essential to help us coordinate muscle movements, avoid danger, and maintain body temp. Some somatic sensations contribute to pleasurable feelings as well, such as our response to the gentle touch of a loved one. Receptors that detect somatic sensations are located throughout the body in skin, joints, skeletal muscles, tendons, and internal organs.
*Mechanoreceptors detect touch, pressure, and vibration
-All mechanoreceptors are modified dendritic endings of sensory neurons. Any force that deforms the plasma membrane of the dendritic ending produces a typical graded potential. If the graded potential is large enough to exceed the threshold, the sensory neuron initiates and impulse.
-Unencapsulated dendritic endings= naked dendritic endings of sensory neurons around hairs and near the skin surface signal pain, light pressure and changes in temperature.
-Merkel disks: these are modified unencapsulated dendritic endings that detect light touch and pressure.
-Meissner’s corpuscles: These are encapsulated touch receptors located close to the skin surface that detect the beginning and the end of light pressure and touch.
-Ruffini endings: These are encapsulated receptors that respond continually to ongoing pressure.
-Pacinian corpuscles: These are encapsulated receptors that are located in the dermis that respond to either deep pressure or high-frequency vibration.
**Mechanoreceptors indicated limb position, muscle length and tension
-Muscle spindles: mechanoreceptors that are specialized for monitoring muscle length; for most joints muscle length determines joint position because of the way the muscle is attached to the bones. Muscle spindles are small bundles of modified skeletal muscle cells located within a skeletal muscle. They are innervated by sensory nerves whose dendritic endings are mechanoreceptors that respond to stretch.
**Thermoreceptors detect temperature
-Near the skin’s surface thermoreceptors for heat and cold provide useful info about the external environment. These receptors adapt quickly, allowing us to monitor changes in temp accurately and yet adjust sensory input so it becomes more bearable. Other receptors located in the abdominal and thoracic organs throughout the body monitor internal temperature.
**Pain receptors signal discomfort
-Pain warns us to avoid certain stimuli and informs us of injuries. Pain receptors are unencapsulated endings that respond to injury from excessive physical pressure, heat, light, or chemicals.
Fast pain: also called sharp or acute pain, occurs as soon as a tenth of a second after the stimulus. Receptors for fast pain generally respond to physical pressure or heat and usually are located near the surface of the body. They inform us of stimuli to be avoided.
-Slow pain: this pain generally arises from muscles or internal organs; it may not appear until seconds or even minutes after energy, and it’s due to the activation of chemically sensitive pain receptors by chemicals released from damaged tissue. Referred pain= slow pain from internal organs that is often perceived as originating from an area of the body completely removed from the actual source.
*Vision: Detecting and Interpreting visual stimuli
**Structure of the eye
-Sclera: the tough outer coat also known as the “white of the eye”, this covers and protects it
-Cornea: transparent anterior portion of the eye, it bends the incoming light (or focuses it)
-Iris: a colored, disk-shaped muscle that determines how much light enters the eye
-Pupil: the adjustable opening in the center of the iris, light passes through this to the lens
-Aqueous humor: fluid that nourishes and cushions the cornea and lens.
-Lens: a transparent, flexible structure attached by connective tissue fibers to a ring of circularly arrange ciliary muscle
-Vitreous humor: transmits light to the retina.
-Retina: made up primarily of photoreceptor cells, neurons and a few blood vessels, it absorbs light and converts it into impulses.
-rods= photoreceptors responsible for black and white vision in dim light
-cones: photoreceptors responsible for color vision and high visual activity
-Macula: central region of the retina with the highest density of photoreceptors
-Optic nerve: located at the back of the eye, it carries info to the thalamus to be forwarded to the visual cortex for interpretation.
-Optic disk: area where the axons of the optic nerve and associated blood vessels exit the eye also referred to as the “blind spot” of the eye.
**Regulating the amount of light and focusing the image
-The iris adjusts the amount of light entering the eye with 2 sets of smooth muscle. When bright light strikes the eye, contraction of muscles arranged circularly around the pupil causes it to contract; otherwise the intensity of daylight would overwhelm our photoreceptors and temporarily blind us.
Light entering the eye is focused by the cornea and the lens. The cornea is responsible for bending most of the incoming light. Our ability to regulate the degree to which incoming light is bend and therefore our ability to change focus between near and far objects is accomplished solely by adjusting the curvature of the lens, this is done by the ciliary muscle.
-When ciliary muscle contracts the inner radius of the muscle shrinks reducing the tension on the fibers attached to the lens. This allows the lens to bulge, and we focus on a near object. When the ciliary muscle relaxes, the ring of muscle increases the tension on the lens, stretching and flattening it and bringing more distant objects into focus.
**Eyeball shape affects the focus
-Myopia: common inherited condition in which the eyeball is slightly longer than normal. Even when the lens is flattened maximally, distant objects focus in front of the retina; this causes nearsightedness.
-Hyperopia: occurs when the eyeball is too short and nearby objects focus behind the retina; this causes farsightedness.
**Light is converted into action potentials
-The unique structure of the retina allows us to see in color, adapt to varying light intensities and perceive images of the world around us.
-Outermost layer of retina consists of pigmented cells that absorb light not captured by the photoreceptor cells.
-Next is a layer of photoreceptor cells called rods and cones.
-Rods and cones synapse w/the 3rd layer; a layer of neurons called bipolar cells, which partially process and integrate info and then pass it on to the 4th layer.
-Innermost layer consists of ganglion cells; which are also neurons, and their long axons become the optic nerve going to the brain.
**Rods and cones respond to light
-One end of photoreceptor cells consists of a series of flattened disks arranged to form either a rod or cone shaped structure. These flattened disks contain numerous molecules of a particular light-sensitive protein called a photopigment. A photopigment protein u undergoes a change of shape when it is exposed to energy in the form of light. The change in the photopigment molecule shape causes the photoreceptor to close some of its sodium channels and reduce the amount of neurotransmitter it normally releases.
-There are around 120 million rods and 6 million cones, but only 1 million ganglion cells w/axons going to the brain.
**Rods provide vision in dim light
-Rods all have the photopigment called rhodopsin; it is much more sensitive to light than the photopigments in cones, and therefor in dim light our vision is dependent primarily on rods; rods however do not give us color vision, which is why objects appear less colorful in dim light.
**Cones provide color vision and accurate images
-WE have 3 different kinds of cones: red, green, and blue; each of these contains a photopigment that absorbs energy of red, green, or blue light. We can distinguish a variety of colors because of the way the brain interprets the ratios of impulses coming from the ganglion cells connected to the 3 types of cones. When all 3 types are activated by all different wavelengths we perceive white light; the perception of black is no white at all. Cones require stronger light to be activated because the cone photopigments are much less sensitive to light than the rhodopsin in rods; this is why your ability to distinguish between colors declines in dim light and it becomes difficult to tell whether a dark-colored car is green or red. When light is dim we primarily see w/rods, so we mainly see in black and white.
**Visual Receptors Adapt
-Adaptation depends on rapid adjustment of the pupil by the iris and on adaptation of the rods. The absorption of light by rhodopsin used up the photopigment temporarily; Light energy actually breaks the rhodopsin into 2 molecules, they can resynthesize back into rhodopsin, but only aver a few minutes.
*Disorders of sensory mechanisms
**Disorders of the ears
-Deafness: loss of hearing- it can have many different causes; deafness caused by damage to hair cells is called nerve deafness, because sounds can’t be converted into impulses is sensory nerves; this is usually the result of frequent exposure to loud sounds. Damage to the tympanic membrane or bone of the middle ear is called conduction deafness; in this type the sound waves aren’t transferred to the inner era at all, it can be caused due to arthritis of the middle ear bones.
-Otitis media: inflammation of the middle ear- This usually results from an upper respiratory infection that extends up the auditory tube; the tube may become blocked and trap fluid in the middle ear.
-Meniere’s syndrome: inner ear condition impairs hearing and balance- the cause of this is unknown, but it could be due to excess fluid in the cochlea and semicircular canals. Symptoms include repeated episodes of dizziness and nausea accompanied by progressive hearing loss. Balance is usually affected to the point that people find it hard to even stand upright.
**Disorders of the eyes
-Retinal Detachment: retina separates from choroid- If the retina is torn the vitreous humor may leak through the tear and peel the retina away from the choroid. Most common cause is a blow to the head. The detached region of the retina loses most of its blood supply and its ability to focus an image properly.
-Cataracts: The lens becomes opaque- Cataracts are a decrease in the normal transparency of a lens. If the delivery of nutrients to the lens is not sufficient, these proteins may denature, or clump, making the lens opaque. Most cataracts are age-related or secondary to diabetes or other diseases.
-Glaucoma: Pressure inside the eye rises- This is the condition in which the drainage vessel that drains the aqueous humor becomes blocked; the excess fluid increase pressure inside the eye and compresses blood vessels supplying the retina. Cells of the retina/optic nerve may eventually die, ultimately leading to blindness.
-Age related macular degeneration (AMD) – This is a disease of visual impairment caused by detachment of the retina and degeneration of photoreceptor cells in the macular region of the retina. The most common cause is accumulations of cellular debris between the choroid and the retina.
-Color Blindness: Inability to distinguish the full range of colors- This is when people have the inability to distinguish the full range of colors. Most color blindness is caused by the deficient numbers of particular types of cones. The most common type is red-green color blindness, which is when you’re deficient in red and green cones; people have a hard time distinguishing between the 2 colors and perceive them as the same color. Red-green color blindness is an X-linked recessive trait that is more common in men than women.
Chapter 24: Human impacts, Biodiversity, and Environmental Issues
The human capacity to shape the environment both creatively and destructively is causing global changes in biogeochemical cycles and affecting the populations of nearly all living species.
*Pollutants impair air quality
-The air we breathe is a mixture of primarily nitrogen, and oxygen, w/trace amounts of carbon dioxide. It also contains trace amounts of chemicals or particles that have adverse effects on living organisms, which are known as pollutants. The major concerns regarding air pollution fall into 4 areas: Global warming, destruction of the ozone layer, acid precipitation, and smog production.
**Excessive greenhouse gases lead to global warming
-Greenhouses gases are located in the stratosphere, these gases that allow sunlight to penetrate through them, but as the sunlight is converted to heat, it doesn’t allow them to escape. The most significant greenhouse gas is water vapor, which accounts for appx 60% of the total. The remainder are human made, and consist of CO2, CH4, and N20, with small amounts of CFCs. Together the greenhouse gases produce a greenhouse effect; which allows sunlight to come to Earth but traps most of the heat radiated from Earth on its way to space. Without the greenhouse effect, most of the sun’s heat would radiate away from Earth and the avg temperature would be well below freezing.
The general agreement among scientists today is that the excessive production of greenhouse gases (throughout earth’s history) is increasing the greenhouse effect and raising the average global temperature- this is referred to as global warming.
-The main activities that cause raises in atmospheric CO2 are the burning of fossil fuels for energy (the carbon in fossil fuels comes from decayed plant material, and we release the carbon back into the air as CO2), and deforestation (because the trees would absorb CO2 from the air during photosynthesis).
**CFCs deplete the ozone layer
-Ozone (O3) is found in 2 places in the atmosphere; in the troposphere (layer near the planet surface) ozone is an air pollutant formed by the reaction of oxygen w/automobile exhaust and industrial pollution. Ozone is mildly toxic; it causes plant damage and respiratory distress. Higher up in the atmosphere ozone is actually very beneficial; it forms a thin layer of the stratosphere that helps shield the Earth from UV rays.
In the early 1980s it had become apparent that the stratospheric ozone layer was suffering damage due to CFCs (group of chemicals used in refrigerators, air conditioners, and aerosol sprays). CFCs released near ground level migrate slowly upward toward the stratosphere and decompose, releasing chlorine atoms; these chlorine atoms combine w/ozone and destroy it, producing oxygen. The chlorine molecule can be used over and over in the reaction, so it can destroy as many as 10,000 ozone molecules.
**Pollutants produce acid precipitation
-Major source of acid precipitation is sulfur dioxide, which is released into the air as a result of burning high-sulfur coal and oil for power, a secondary source is nitrogen oxide in automobile exhaust. Sulfur dioxide and nitrogen oxides combine w/water vapor in the air, become sulfuric acid and nitric acid, and dissolve in raindrops, which falls as acid precipitation. This precipitation corrodes metal and stone and damages forests and aquatic ecosystems, particularly in the northeastern United States, southeastern Canada, and Europe.
**Smog blankets industrial areas
-Several pollutants in air react w/each other in the presence of sunlight and water vapor; they form a hazy brown or gray layer of smog that tends to hover over the region where it is produced. Most smog is caused by the burning of fossil fuels by automobile exhausts. Smog contains several chemicals that irritate the eyes and lungs and may lead to chronic respiratory illness.
Smog can become especially troublesome during a thermal inversion; which is when a warm stagnant upper layer of air traps a cooler air mass containing smog, beneath it.
*Pollution jeopardizes scarce water supplies
**Water is scare and unequally distributed
-All of the freshwater on the surface of the land and in aquifers forms less than 1% of Earth’s total water. Over 97% is salty ocean water, and 2% is frozen in glaciers and polar ice caps. Water isn’t evenly distributed among human populations, residents of the more industrialized use 10 to 100 times more water than people in less industrialized countries. When we use water for our own purposes we take it away from other species or limit their normal migration patterns.
**Urbanization increases storm water runoff
-In urban areas, the shift from woodlands and fields to impermeable roads and buildings has caused major stormwater runoff problems. On the U.S. East Coast, stormwater combines w/sewage leading to combined sewage overflow (CSO). 28 billion gallons of CSO impact the New York Harbor each year; this is the major source of pathogens in the area, it causes gastroenteritis, eye and ear infections, skin rashes, respiratory infections, and hepatitis in swimmers and kayakers.
**Human activities pollute freshwater
-Untreated sewage, chemicals from factories, the runoff of pesticides and fertilizers, and rubber and oil from city streets, all must go somewhere. Either they degrade chemically according to their natural cycle of decomposition r they end up in water or soil.
Some water pollutants are organic nutrients that arise from sewage treatment plants, food-packing plants, and paper mills. When those nutrients are degraded by bacteria, the rapid growth rate of bacteria can deplete the water of oxygen, threatening aquatic animals.
-Other water pollutants are inorganic nutrients, such as nitrate and phosphate fertilizers and sulfates in laundry detergents; these cause prolific growth of algae, which die and are also decomposed by bacteria.
Eutrophication refers to rapid growth of plant life and the death of animal life in a shallow body of water as a result of excessive organic or inorganic nutrients; this is part of the process that turns freshwater into marsh, and then dry land.
-Toxic pollutants can become more concentrated in the tissues of organisms higher up the food chain, which is known as biological magnification. Biological magnification occurs because each animal in a food chain consumes many times its own weight in food throughout its lifetime. Best example of biological magnifications the heavy metal mercury. Mercury released into the air or on the land often ends up in aquatic ecosystems, where it accumulates by biological magnification in tertiary consumes such as sharks, tuna, and whales.
**Oil pollution damages ocean shorelines
-In most years several million tons of oil enters the world’s oceans. About 50% comes from natural seepage; therefore some oil pollution is a natural phenomenon. However, 30% of the total oceanic oil pollution is caused by oil disposal on the land that is washed into the sea in streams and rivers. In general when oil is spilled at sea about a quarter evaporates, nearly half eventually is degraded by bacteria, and the remaining quarter eventually settles to the ocean floor. In short term, however an oil spill can cause significant damage to marine and shoreline ecosystems.
*Pollution and overuse damage the land
-The main environmental issue isn’t actually how we pollute the land, but how much of the land we use. WE dam river valleys to produce hydroelectric power, strip mountaintops to find coal, and cut down forests for lumber or to clear space for crops.
-AS the human population grows, people tend to migrate toward cities. Cities often expand into nearby farmland because it is more economical to build where it is relatively flat.
Many people rely almost entirely on their local environment to survive; therefor it’s not uncommon for impoverished rural communities to cut down all trees for fuel and shelter. Stripping the biomass from fragile ecosystems leads to erosion and desertification (transformation of marginal lands into near-desert conditions unsuitable for future agriculture); every year an estimated 15 million more acres become desert.
Global Warming in the News Today
As of today the US, Mexico, Bangladesh, Sweden, the UN, Canada, and Ghana joined together in efforts to start that will help to address the global warming problems caused by more short-lived pollutants from our environment, including soot, methane, and hydrofluocarbon; which as of today account for between 30-40% of global warming.
According to research, the efforts put forth by these countries can lower the earth’s temperature by 0.5 degrees Celsius by 2050, and also reduce the amount of cases of lung and heart disease by the year 2030.