Animals Flashcards
(159 cards)
1
Q
How does digestion occur in the hydra (a cnidarian)?
A
Digestions occurs in the gastrovascular cavity which has only one opening. Cells of the gastrodermis secrete digestive enzymes into the cavity for extracellular digestion. Some specialized nutritive cells have flagella that move the food around and some have pseudopods that engulf food particles.
2
Q
What is the gastrodermis of the gastrovascular cavity?
A
It is the lining of the gastrovascular cavity.
3
Q
How does digestion occur in the earthworm?
A
The digestive tract is a long, straight tube. As the earthworm burrows in the ground, the mouth ingests decaying organic matter along with soil. This moves from the mouth through the esophagus and into the crop where it’s stored. Posterior to the crop is the gizzard which grinds up the food with the help of sand/soil and its own muscular walls. The rest of the digestive system consists of intestines, enhanced by typhlosole, aids in chemical digestion and absorption.
4
Q
What is the function of the typhlosole in an earthworm’s digestion?
A
The typhlosole is a large fold in the upper surface of the intestines which enhances absorption by increasing surface area.
5
Q
How does digestion occur in a grasshopper?
A
Similar to the earthworm, the digestive tract is a long tube consisting of a crop and gizzard. The grasshopper has a specialized mouth for tasting food and mechanical digestion. The grasshopper’s gizzard has plates made of chitin to grind up the food. The digestive tract also removes nitrogenous waste (uric acid).
6
Q
Give an overview of digestion in humans.
A
The system has two important functions: digestion and absorption. The digestive tract is about 30 feet long and made of smooth (involuntary) muscles that pushes food along the digestive tract by a process called peristalsis.
7
Q
Define digestion and what is digested in the human digestive system.
A
This is the breaking down large food molecules into smaller usable molecules. Fats are broken down to fatty acids and glycerol, starch into monosaccharides, nucleic acids into nucleotides and proteins into amino acids.
8
Q
Define absorption.
A
This is the diffusion of smaller (already digested) molecules in the body’s cells. Vitamins and minerals are able to be absorbed without being digested.
9
Q
How does digestion occur in the human mouth?
A
Mechanical digestion occurs with the tongue and the teeth. Teeth are indicative of an animal’s dietary habits. Incisors are for cutting, canines for tearing and molars for grinding. Salivary amylase is released by the salivary glands to being the chemical breakdown of starch.
10
Q
How is digestion facilitated in the human esophagus?
A
After swallowing food is directed into the esophagus by the epiglottis and moves down by peristalsis. No digestion occurs in the esophagus.
11
Q
What is the epiglottis?
A
This is a flap of cartilage in the back of the pharynx (throat). It directs food into the esophagus and not into the windpipe.
12
Q
How does digestion occur in the human stomach?
A
Some mechanical digestion occurs and secretes gastric juice that begins digestion of proteins. The acidic environment creates pepsin and also kills germs. The stomach of all mammals contains rennin to aid in the digestion of he protein in milk.
13
Q
What is gastric juice?
A
In the stomach this is a mixture of the enzyme pepsinogen and hydrochloric acid that begin the digestion of proteins. The acidic environment activates pepsinogen to becomes the active enzyme pepsin.
14
Q
What is the cardiac sphincter?
A
It’s a ring of muscle at the top of the stomach that keeps food in the stomach from backing into the esophagus.
15
Q
What is the pyloric sphincter?
A
It’s a ring of muscle at the bottom of the stomach that keeps food in the stomach long enough to be digested.
16
Q
How do ulcers form in the stomach?
A
Excessive acid can cause an ulcer to form in the esophagus, stomach, or duodenum. Helicobacter pylori is a particular bacteria that can cause ulcers and can be treated with antibiotics.
17
Q
How does digestion occur in the human small intestine?
A
Digestion is completed in the duodenum. Intestinal enzymes and pancreatic amylases hydrolyze starch and glycogen into maltose. Bile, which is produced in the liver and stored in the gallbladder, is released into the small intestine as an emulsifier to break down fats. Peptidases continue to break down proteins. Nucleases hydrolyze nucleic acids and lipases break down fats.
18
Q
What are some peptidases present in the small intestine?
A
Trypsin and Chymotrypsin
19
Q
How does absorption occur in the human small intestine?
A
Millions of fingerlike projections called villi and microvilli, in conjunction with the lacteal, absorb all the nutrients that were previously released.
20
Q
What is the structure of the villus in the small intestine?
A
The capillaries of the villus absorb amino acids, vitamins, and monosaccharides. The lacteal (contained in the villus) is a small vessel of the lymphatic system which absorbs fatty acids and glycerol. Each epithelial cell has microscopic microvillus that increase nutrient absorption.
21
Q
What function does the human large intestine play in absorption?
A
The large intestine or colon serves three main functions: egestion, vitamin production, and removal of excess water. If too much water is removed constipation occurs and diarrhea is occurred is too little water is removed.
22
Q
Define egestion.
A
Egestion is the removal undigested waste.
23
Q
Describe the last 7-8 inches of the human gastrointestinal tract?
A
That last 7-8 inches are called the rectum. It stores feces until their release and the opening at the end of the tract is called the anus.
24
Q
What is respiration and how does it occur?
A
Respiration is the exchange of oxygen and carbon dioxide between the external environment and the cell of body. It occurs passively through diffusion.
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What conditions must respiratory surfaces meet?
Respiratory surfaces must be thin, moist and have large surface areas.
26
How do simple animals such as sponges and hydra complete gas exchange?
Gas exchange occurs over the entire surface of the organism wherever cells are in direct contact with the environment.
27
How does an external respiratory surface in earthworms and flatworms work?
This means that diffusion of O2 and CO2 occurs at the skin. Oxygen is carried by hemoglobin dissolved in blood.
28
How does an internal respiratory system work in arthropods and crustaceans?
Air enters the body through spiracles and travels through a system of tracheal tubes into the body, where diffusion occurs in sinuses or hemocoels. In arthropods, oxygen is carried by hemocyanin which is similar to hemoglobin but with copper at its core atom instead of iron.
29
How do gills work?
They take advantage of concurrent exchange to maximize the diffusion of respiratory gases.
30
What is the pathway through which air enter the lung?
Air enters the nasal cavity where is is moistened, warmed and filtered, From there the air passes through the larynx and down the trachea and into the bronchi.
31
How does air pass through the lungs?
From the bronchi air moves to the tiniest bronchioles and end in microscopic air sacs called alveoli where diffusion of gases occurs.
32
How does air get drawn into the lungs?
As the rib cage expans, the diaphragm contracts and lowers which causes the chest cavity to expand. The internal pressure in the lungs is lower than the atmospheric pressure. Thus, the air is drawn in by negative pressure.
33
How do CO2 levels affect breathing rates?
The medulla in the brain, contains the breathing control center, sets the rhythm of breathing and monitors CO2 levels in the blood by sensing changes in pH of the blood. CO2 dissolves in the blood to form carbonic acid therefore the higher the CO2 concentration the lower the pH. A blood pH lower than 7.4 causes the medulla to increase the rate of breathing.
34
What is hemoglobin?
It is an allosteric molecule. The respiratory pigment that can combine loosely with four oxygen molecules forming oxyhemoglobin and carry it through the blood. The closer it binds to the oxygen the more difficult it is to unload.
35
Describe how hemoglobin binds to oxygen.
It exhibits cooperativity, meaning once it binds with one oxygen molecule it binds more easily to 3 other molecules. In addition, it is sensitive to pH because a drop in pH lowers the affinity for oxygen.
36
What is the Bohr shift?
CO2 dissolves in water to form carbonic acid and actively respiring tissue which release large quantities of CO2 and lower the pH of its surroundings. This induces hemoglobin to release its oxygen at the cells where needed.
37
Explain the saturation-dissociation curves for hemoglobin.
The further to the right the curve is, the less affinity the hemoglobin has for oxygen.
38
How is carbon dioxide transported?
Very little is transported by hemoglobin. Most CO2 is carried in the plasma as part of the reversible blood buffering carbonic-acid-bicarbonate ion system.
39
What is the carbonic-acid-bicarbonate ion system?
First, CO2 combines with water to form carbonic acid, this is catalyzed by carbonic acid anhydrase in red blood cells. Second, carbonic acid dissociates into a bicarbonate ion and a proton. The protons are given up in the plasma and lowers the blood pH or taken up by bicarbonate ion which raises blood pH.
40
How do animals with no circulatory system function?
This is true for sponges and hydra; all their cells are in direct contact with the environment.
41
How do animals with a closed circulatory system function?
This is true for earthworms and humans; the blood is pumped by the heart through arteries, veins and capillaries.
42
How do animals with open circulatory systems function?
This is true for grasshoppers - anthropod blood is colorless and don't carry oxygen; after blood is pumped by the heart into an artery it leaves the vessel and seeps through spaces called sinuses/homocoels as it feeds body cells then, blood moves back to veins and then the heart
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Component of Blood: Plasma
Liquid portion of the blood that contains clotting factors, hormones, antibodies, nutrients, dissolved gases and wastes. It maintains the proper osmotic potential of the blood; 300 mosm/L.
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Component of Blood: Red Blood Cells
Erythrocytes; Carry hemoglobin and oxygen. They don't have a nucleus and live about 120 days. They're formed in the bone marrow and recycled in the liver.
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Component of Blood: White Blood Cells
Leukocytes; Fight infection and are formed in the bone marrow. They dies fighting infection and are a component of pus. One type - B lymphocyte - produces antibodies.
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Component of Blood: Platelets
Thrombocytes; These are cell fragment formed in the bone marrow from megakaryocytes. They clot blood.
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Blood Clotting
It begins with the release of clotting factors from platelets and damaged tissue. Then, complex interactions such as the activation of inactive plasma proteins occur. Anticlotting factors normally circulate in the plasma and prevent the formation of a clot or thrombus which can cause damage is there is no injury.
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Artery and Arteriole
Function: carry blood away from the heart under enormous pressures
Structure: walls made of thick, elastic, smooth muscle
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Vein and Venule
Function: carry blood back to the heart under very little pressure
Structure: thin walls with valves to prevent back flow; they are located within skeletal muscle, which propels blood upward and back to heart as the body moves
50
Capillary
Function: allows for distribution of nutrients and wastes between cells and blood
Structure: walls are on-cell thick and so small that blood cells travel single file
51
Heart
It is located beneath the sternum is about the size of a clenched fist. It beats about 70 beats per minute and pumps about 5 quarts of blood per minute.
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Heart: Structure
Two atria receive blood from the body cells and two ventricles pump blood out. Cardiac muscles cells have the ability to contract even when removed from the heart.
53
Sinoatrial Node
This pacemaker sets the timing of contractions in the heart. It's locates on the wall of the right atrium and generates electrical signals to the atrioventricular that trigger ventricles to contract. It's influenced by two sets of nerves, hormones such as adrenaline and body temperature.
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Electrocardiogram
EKG: It detects electrical impulses that travel through the cardiac and body tissues to the skin.
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Blood Pressure
It is lowest in the veins and highest in the arteries. Normal, resting, adult blood pressure is 120/80.
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Systolic Pressure
Measurement of the pressure when the ventricles contract.
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Diastolic Pressure
A measure of the pressure when the heart relaxes.
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Pathway of Blood in the Heart
Right Atrium → Right atrioventricular valve (tricuspid) → Right Ventricle → Pulmonary semilunar valve → Pulmonary artery → Lungs → Pulmonary Vein → Left Atrium → Bicuspid (left AV) Valve → Left Ventricle → Aortic Semilunar Valve → Aorta → To Cells in the Body
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Pathway of Blood in the Body
It circulates through the coronary circulation, renal circulation (kidneys) and hepatic circulation (liver). The pulmonary circulation includes the pulmonary artery. lungs and pulmonary vein.
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Chemical Signals
The endocrine system releases hormones and the nervous system releases neurotransmitters. There;s some overlap for example epinephrine functions as both a fight-or-flight hormone and a neurotransmitter.
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Hormones
Produced in ductless (endocrine) gland and move through the body to a specific target cell.
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Adrenaline
Hormone that produces and immediate, short-lived response.
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Edysone
Alters the development of insects by regulating metamorphosis.
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Tropic Hormones
Stimulate other glands to release hormones and have far reaching affects. For example, the anterior pituitary releases TSH which stimulate the thyroid to release thyroxin.
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Pheromones
Chemical messengers that can reach their target by special means. In the urine of the dog these messengers carry a message between different species.
66
Nitric Oxide
In vertebrates, this gas is produced by one cell and diffuses to and only affects neighboring cells.
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Growth Hormone
Produced by anterior pituitary; stimulates bone growth
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Luteinizing Hormone
Produced by anterior pituitary; stimulates ovaries and testes
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Thyroid-Stimulating Hormone
Produced by anterior pituitary; stimulates thyroid gladn
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Adenocorticotropic (ACTH) Hormone
Produced by anterior pituitary; stimulates adrenal cortex to secrete glucocoticoids
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Follicle-Stimulating Hormone
Produced by anterior pituitary; stimulates gonads to produce sperm and ova
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Oxycotin
Produced by posterior pituitary gland; stimulates contractions of the uterus and milk production by mammary glands
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Antidiuretic Horome
Produced by posterior pituitary gland; promotes retention of water by kidneys
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Throxin
Produced by Thyroid gland; controls metabolic rate
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Calcitonin
Produced by Thyroid gland; lowers blood calcium levels
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Parathormone
Produced by parathyroid gland; raises blood calcium levels
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Cortisol
Produced by adrenal cortex; raises blood sugar levels
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Epinephrine and Norepinephrine
Produced by adrenal medulla; raises blood sugar level by increasing rate of glycogen breakdown by liver
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Insulin
Produced by Pancreas in the islets of Langerhans; lowers blood glucose levels
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Glucagon
Produced by Pancreas in the islets of Langerhans; raises blood glucose level by causing breakdown of glycogen into glucose
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Thymosin
Produced by Thymus; stimulates T lymphocytes
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Melatonin
Produced by Pineal Gland; involved in biorhythms
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Estrogen
Produced by Ovaries; stimulates uterine lining, promotes development and mantenance of primary and secondary characteristics of female
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Progesterone
Produced by Ovaries; promoted uterine lining growth
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Androgens
Produced by Testes; support sperm production and promote secondary sex characteristics
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Hypothalamus
It is the bridge between the endocrine and nervous system. It also contains the body's thermostat and centers for regulating hunger and thirst.
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Hypothalamus: Nervous System
It act as part of the nervous system in times of stress when it sends electrical signals to the adrenal gland to release adrenaline. It acts as a nerve when it secretes gonadotropic-releasing hormone from neurosecretory cells that stimulate the anterior pituitary to secretes FSH and LH.
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Hypothalamus: Endocrine System
It acts as an endocrine gland when it produces oxycotin and anti-diuretic hormone that is stored in the posterior pituitary.
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Feedback Mechanisms
Self-regulating mechanism that increases or decreases the level of a particular substance. (positive- continuing; negative- opposite action)
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Lipid or Steroid Horomone Responses
Diffuse directly through the plasma membrane and bind to a receptor inside the nucleus that triggers the cell response.
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Protein or Peptide Hormone Responses
Cannot dissolve in the plasma membrane so they bind to a receptor on the surface of the cell and once this happens first messengers bind to a receptor on the surface of the cell. This triggers a secondary messenger such as c-AMP and converts the extracellular chemical signal to a specific response.
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Temperature Regulation
Most life exists between 0-50 degrees celsius. On land, temperatures fluctuate enormously so animals must generate their own body heat, seek out a suitable climate or change behavior. Human body temperature is about 37 degrees celsius. The source of heat is the real issue.
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Ecotherms
Animals that gain their body heat from their environment. They have a low metabolic rate so the heat they generate doesn't have an effect on body temperature. They maintain temperature through behavioral means. They include fish, amphibians, and reptiles. It means cold-blooded.
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Endotherms
Animals that use metabolic processes to produce body heat. They're warm blooded. This is very costly energy wise; humans use about 60% of energy to maintain body heat. It gives an advantage because mammals and birds can invade and colonize cold environments.
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Poikilotherm
Animals whose body temperature caries with the environment.
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Hemeotherm
Animals whose body temperature stays constant despite fluctuations in environmental temperature. Ex. mammals (?)
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Torpor
a condition that allows animals to save energy by drastically decreasing metabolic rate; hibernation is an extended form of this
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North-South Cline
The anatomical difference across a geographic range. (Ex. the size of jackrabbits' ears are small in cold, northern regions and large in southern regions)
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Countercurrent Heat Exchange
Mechanism used to warm of cool extremities. For example, when a polar bear puts its paw into ice water, warm core blood flows directly to the paw and warms the chilled blood moving toward the heart
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Osmoregulation
Management of the body's water and solute concentration.
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Osmoregulation: Marine Organisms
The ocean is a strongly dehydrating environment because it is hypertonic to the organism living in it. Fish constantly lose water through their gills and skin so they produce little urine and drink large amounts of water. The extra salt taken in with the water is transported out through the gills.
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Osmoregulation: Freshwater Organisms
Problems are opposite those living in salt water. The environment is hypotonic to the organisms and are constantly gaining water and loosing salt. Freshwater fish excrete copious amount of dilute urine.
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Osmoregulation: Terrestrial Organisms
They have evolved to rid wastes while retaining as much water as possible.
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Excretion: Protista
contractile vacuole
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Excretion: Platyhelminthes
flame cells
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Excretion: Earthworm
Nephridia
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Excretion: Insects
Malpighian tubules
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Excretion: Humans
Nephrons
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Excretion
The removal of metabolic wastes such as CO2 and water for cell respiration, and nitrogenous wastes from protein metabolism.
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Organs of Excretion
skins, lungs, kidney and the liver
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Three Nitrogenous Wastes
ammonia, urea, and uric acid
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Ammonia
Very soluble in water and highly toxic; Excreted generally by organisms that live in water
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Urea
Not as toxic as ammonia; Excreted by earthworms and humans; In mammals, it is formed in the liver from ammonia
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Uric Acid
Pastelike substance that is not soluble in water and therefore not very toxic; Excreted by insects, reptiles and birds with minimum water loss
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Kidney
It is both a osmoregulator and an organ of excretion. Humans have two supplied from the renal artery and renal vein. Humans need to conserve as much water as possible and must balance that with the need to release poisons. The kidney balances the animal's intake of water and salt with the production of urea. Concentrated urine is produced in periods of high salt and low water intake. Dilute urine is produced when there is low salt and high water intake.
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The Nephron
The function unit of the kidney. It consists of a clusters of capillaries, which sits inside the cup-like Bowman's capsule, and connects to a long narrow tube called the Renal Tubule. The nephron carries out its job in four steps: filtration, secretion, reabsorption and excretion.
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Nephron: Filtration
As blood pressure forces fluid from the blood in the glomerulus into the Bowman's capsule filtration occurs. Specialized cells of the capsules are modified into podocytes which along with slit pores increate filtration. It occurs by diffusion and is passive and nonselective. The filtrate includes glucose, salts, vitamins, urea, etc. and diffuses to the Bowman's capsule. Then, the filtrate travels to the proximal tubule.
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Nephron: Secretion
Occurs at the proximal and distal tubules. It is the active and selective uptake of certain drugs and toxic molecules that did not get filtered in the Bowman's capsule. The tubule also secretes ammonia to neutralize acidic filtrate.
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Nephron: Reabsorption
The process by which most of the water and solutes that initially entered the tubule during filrtation are transported back to the peritubular capillaries, thus the body. Starts as proximal convoluted tubule and continues in the loop of Henle and collecting tubule.
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Nephron: Reabsorption & Loop of Henle
The main function is to move salts from the filtrate and accumulate then in the medulla surrounding the loop of Henle and collecting tubule. In this way, it acts as a countercurrent exchange mechanism, maintaining a steep salt gradient surrounding the loop. This gradient ensure that water will continue to flow out of the collecting tubule, thus creating hypertonic urine and conserving urine.
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Nephron: Excretion
Removal of metabolic wastes. Everything that passes into the collecting tubule is excreted from the body. From the collecting tubule or duct. urine passes through the ureter to the urinary bladder. It is stored until it's released through the urethra.
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Hormone Control of the Kidney
Antidiuretic Hormone and Aldosterone respond to different osmoregulatory problems. ADH is released in response to inadequate water intake and excessive sweating. It increases the permeability of the collecting tubules to water so more water can be reabsorbed. Aldosterone is released in response to decrease blood pressure or volume. It causes the distal tubules to reabsorbs more sodium and water thus increasing blood volume.
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Central Nervous System
The Brian and Spinal Cord
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Peripheral Nervous System
All nerves outside the CNS; the sensory function is to convey all information from sensory receptors and nerve endings; the motor function is split into the somatic and automatic systems
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PNS: Somatic System
controls voluntary muscles
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PNS: Automatic System
controls involuntary muscles; is split into the sympathetic and parasympathetic systems
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PNS: Automatic System - Sympathetic
Flight-or-Flight response; increases heart and breathing rate; liver converts glycogen to glucose; bronchi of lungs dilate and increase gas exchange; adrenalin raises blood glucose levels
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PNS: Automatic System - Parasympathetic
Opposes the sympathetic; calms the body; decreases heart and breathing rate; enhances digestion
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The Neuron
Consists of a cell body and cytoplasmic extensions called dendrites and axons
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Neuron: Dendrites
Sensory; receive messages from other cells and carry the electrical signal to the cell body; a neuron can have hundreds
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Axons
transmit an impulse from the cell body outward to another cell; they are wrapped in a fatty myelin sheath that is formed by Schwann cells
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Sensory Neurons
Receive and initial stimulus from a sensory organ.
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Motor Neuron
Simulates effectors (muscles or glands)
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Interneurons or Association Neurons
Reside within the spinal cord and brain, receives sensory stimuli and tansfers the information directly to a motor neuron or the the brain for processing
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Reflex Arc
The simplest nerve response; inborn, automatic and protectice
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Knee-Jerk Reflex
A reflex arc; consists of the sensory and motor neuron; a stimulus is felt on the knee cap and a sensory neuron directs the thigh muscle to contract
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Heat on Hand Reflex
A sensory neuron transmits an impulse to an interneuron in the spinal cord and this sends an impulse to the brain for processing and one to the motor neuron to cause your hand to move from the hot surface.
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Membrane Potential
A difference in electrical charge between the cytoplasm (negative ions) and the extracellular fluid (positive ions). A neuron in a polarized state should have a membrane potential of -70mV. In order for the nerve to fire a stimulus must be strong enough to overcome the resting threshold or resting potential.
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Sodium-Potassium Pump
Maintains polarization of the membrane by actively pumping ions that leak across the membrane. Restores membranes to their original polarized condition by pumping sodium and potassium back to their original position during the refractory period.
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Gated-Ion Channels
Some neurons have these channels that open or close in response to a stimulus and play an essential role in the transmission of electrical impulses.
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Sodium Ion-Gated Channel
When stimulated sodium flows into the cytoplasm, resulting in a decrease in polarization. The membrane becomes somewhat depolarized an it's easier for a nerve to fire.
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Potassium Ion-Gated Channel
When stimulated, membrane potential increases and the membrane becomes hyper polarized so it's harder for the neuron to fire.
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Action Potential
Impulse that is generated in the axon of the neuron. When an axon is stimulated sufficiently and overcomes the threshold, permeability of a region of a membrane changes and the impulse can pass. Sodium channels open and sodium floods into the cell, down the concentration gradient. In response, potassium channels open and potassium floods out. Wave of depolarization are called action potential and lasts a short time.
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Refractory Period
Period in which the sodium-potassium pump repolarizes. It ensures that an impulse moves along an axon in one direction.
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Action Potential to Reaction
When the first action potential is generate it generates a second and so on. This impulse propagates without losing strength. Is the axon is myelinated the impulse travels faster because it leaps from node to node in saltatory fashion.
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All-or-None Event
Action potential's stimulus is either strong enough or it's not. The body distinguishes between the two by frequency.
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The Synapse
The impulse crosses a synapse chemically after traveling down the axon. The cytoplasm at the terminal branch of the presynaptic neuron contains vesicles with thousands of molecules of neurotransmitters. Depolarization causes Ca++ ions to rush into the terminal branch through calcium-gated channels. The rise in Ca++ causes vesicles to fuse with the presynaptic membrane and release the neurotransmitter by exocytosis. The neurotransmitter then, binds with receptors on the postsynaptic side.
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Synapse: Esterase
enzyme that destroys the neurotransmitter when it is released into the synapse
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Acetoylcholine
Stimulates some cells to release nitric oxide which, in turn, stimulates other cells
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Smooth/Involuntary Muscle
makes up the walls of blood vessels and the digestive tract; does not have a straited appearance; under control of the autonomic nervous system
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Cardiac Muscle
makes up the heart and is not striated; generates its own action potential
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Skeletal/Voluntary Muscle
large and multinucleate; works in pairs - while one contracts another relaxes;
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Muscle Fibers
make up every muscle; individual cylindrical muscle cells; each is large and multinucleate; the sarcomere is the functional unit and its boundaries are the Z lines that give skeletal muscle its straition
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Muscle Cells
Contain a sarcolemma that is a modified plasma membrane that surrounds each muscle fiber and propagate action potential. The sarcoplasmic reticulum is a modified ER that contains sacs of Ca++ for muscle contraction. The T system is a system of tubules that connect to the SR to the extracellular fluid.
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The Sliding Filament Theory
Myofibrils run parallel to the length of a muscle cell. They have thick and thin filaments. Thin filaments consist of two strands of actin proteins wound around. The thick filaments are composed of two long chains of myosin molecules each with a globular head with a different function at one end. Troponin and Tropomyosin, in addition to Ca++ ions break and form cross-bridges. Muscles contract as thick and thin filaments slide over each other.
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Neuromuscular Junction
The area where axons of a motor neuron synapse.
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Summation
A twitch caused by a single action potential in a muscle that is extended to a longer contraction when a second action potential arrives before the last one is over.
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Tetnus
What occurs when a large muscle contracts; overlapping series of action potentials that occur at a fast rate
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Acetylcholine Muscle Contraction
The neurotransmitter is released by vesicles from the axon. It binds to receptors on the sarcolemma and depolarizes the muscle cell membrane and sets up action potential. The impulse moves along the sarcolemma into the T system and stimulates the sarcoplasmic reticulum to release Ca++. The ions alter the troponin-tropomyosin relationship and muscle contract.
