Orders usually ship within 1 business days. If your book order is heavy or oversized, we may contact you to let you know extra shipping is required. List this Seller's Books. Payment Methods accepted by seller. AbeBooks Bookseller Since: May 31, Home Neeta V. Stock Image. Kulkarni, BR Kate Foreword. Published by Jaypee Brothers Medical Pub, New Condition: New Hardcover. Confirmation bias is an unintentional bias caused by the collection and use of data in a way that favors a preconceived notion. The beliefs affected by confirmation bias do not need to have motivation , the desire to defend or find substantiation for beliefs that are important to that person.
Andreas Hergovich, Reinhard Schott, and Christoph Burger's experiment conducted online, for instance, suggested that professionals within the field of psychological research are likely to view scientific studies that agree with their preconceived notions more favorably than studies that clash with their established beliefs.
Nickerson argued that those who killed people accused of witchcraft demonstrated confirmation bias with motivation. Researcher Michael Allen found evidence for confirmation bias with motivation in school children who worked to manipulate their science experiments in such a way that would produce favorable results. In , Peter Cathcart Wason conducted an experiment in which participants first viewed three numbers and then created a hypothesis that proposed a rule that could have been used to create that triplet of numbers.
When testing their hypotheses, participants tended to only create additional triplets of numbers that would confirm their hypotheses, and tended not to create triplets that would negate or disprove their hypotheses. Thus research also shows that people can and do work to confirm theories or ideas that do not support or engage personally significant beliefs. Mental set was first articulated by Abraham Luchins in the s and demonstrated in his well-known water jug experiments.
After Luchins gave his participants a set of water jug problems that could all be solved by employing a single technique, he would then give them a problem that could either be solved using that same technique or a novel and simpler method. Luchins discovered that his participants tended to use the same technique that they had become accustomed to despite the possibility of using a simpler alternative. However, as Luchins' work revealed, such methods for finding a solution that have worked in the past may not be adequate or optimal for certain new but similar problems.
Therefore, it is often necessary for people to move beyond their mental sets in order to find solutions. This was again demonstrated in Norman Maier 's experiment, which challenged participants to solve a problem by using a household object pliers in an unconventional manner. Maier observed that participants were often unable to view the object in a way that strayed from its typical use, a phenomenon regarded as a particular form of mental set more specifically known as functional fixedness, which is the topic of the following section.
When people cling rigidly to their mental sets, they are said to be experiencing fixation , a seeming obsession or preoccupation with attempted strategies that are repeatedly unsuccessful. Functional fixedness is a specific form of mental set and fixation, which was alluded to earlier in the Maier experiment, and furthermore it is another way in which cognitive bias can be seen throughout daily life. Tim German and Clark Barrett describe this barrier as the fixed design of an object hindering the individual's ability to see it serving other functions. In more technical terms, these researchers explained that "[s]ubjects become "fixed" on the design function of the objects, and problem solving suffers relative to control conditions in which the object's function is not demonstrated.
In research that highlighted the primary reasons that young children are immune to functional fixedness, it was stated that "functional fixedness For instance, imagine the following situation: a man sees a bug on the floor that he wants to kill, but the only thing in his hand at the moment is a can of air freshener. If the man starts looking around for something in the house to kill the bug with instead of realizing that the can of air freshener could in fact be used not only as having its main function as to freshen the air, he is said to be experiencing functional fixedness.
The man's knowledge of the can being served as purely an air freshener hindered his ability to realize that it too could have been used to serve another purpose, which in this instance was as an instrument to kill the bug. Functional fixedness can happen on multiple occasions and can cause us to have certain cognitive biases. If people only see an object as serving one primary focus than they fail to realize that the object can be used in various ways other than its intended purpose.
This can in turn cause many issues with regards to problem solving. Common sense seems to be a plausible answer to functional fixedness. One could make this argument because it seems rather simple to consider possible alternative uses for an object. Perhaps using common sense to solve this issue could be the most accurate answer within this context. With the previous stated example, it seems as if it would make perfect sense to use the can of air freshener to kill the bug rather than to search for something else to serve that function but, as research shows, this is often not the case.
Functional fixedness limits the ability for people to solve problems accurately by causing one to have a very narrow way of thinking. Functional fixedness can be seen in other types of learning behaviors as well. For instance, research has discovered the presence of functional fixedness in many educational instances. Researchers Furio, Calatayud, Baracenas, and Padilla stated that " There are several hypotheses in regards to how functional fixedness relates to problem solving.
If there is one way in which a person usually thinks of something rather than multiple ways then this can lead to a constraint in how the person thinks of that particular object. This can be seen as narrow minded thinking, which is defined as a way in which one is not able to see or accept certain ideas in a particular context. Functional fixedness is very closely related to this as previously mentioned. This can be done intentionally and or unintentionally, but for the most part it seems as if this process to problem solving is done in an unintentional way.
Functional fixedness can affect problem solvers in at least two particular ways. The first is with regards to time, as functional fixedness causes people to use more time than necessary to solve any given problem. Secondly, functional fixedness often causes solvers to make more attempts to solve a problem than they would have made if they were not experiencing this cognitive barrier. In the worst case, functional fixedness can completely prevent a person from realizing a solution to a problem. Functional fixedness is a commonplace occurrence, which affects the lives of many people. Unnecessary constraints are another very common barrier that people face while attempting to problem-solve.
This particular phenomenon occurs when the subject, trying to solve the problem subconsciously, places boundaries on the task at hand, which in turn forces him or her to strain to be more innovative in their thinking. The solver hits a barrier when they become fixated on only one way to solve their problem, and it becomes increasingly difficult to see anything but the method they have chosen. Typically, the solver experiences this when attempting to use a method they have already experienced success from, and they can not help but try to make it work in the present circumstances as well, even if they see that it is counterproductive.
Groupthink , or taking on the mindset of the rest of the group members, can also act as an unnecessary constraint while trying to solve problems. This is very common, but the most well-known example of this barrier making itself present is in the famous example of the dot problem. In this example, there are nine dots lying on a grid three dots across and three dots running up and down. The solver is then asked to draw no more than four lines, without lifting their pen or pencil from the paper. This series of lines should connect all of the dots on the paper.
Then, what typically happens is the subject creates an assumption in their mind that they must connect the dots without letting his or her pen or pencil go outside of the square of dots. It is from this phenomenon that the expression "think outside the box" is derived. This problem can be quickly solved with a dawning of realization, or insight. A few minutes of struggling over a problem can bring these sudden insights, where the solver quickly sees the solution clearly. Problems such as this are most typically solved via insight and can be very difficult for the subject depending on either how they have structured the problem in their minds, how they draw on their past experiences, and how much they juggle this information in their working memories  In the case of the nine-dot example, the solver has already been structured incorrectly in their minds because of the constraint that they have placed upon the solution.
In addition to this, people experience struggles when they try to compare the problem to their prior knowledge, and they think they must keep their lines within the dots and not go beyond. They do this because trying to envision the dots connected outside of the basic square puts a strain on their working memory. Luckily, the solution to the problem becomes obvious as insight occurs following incremental movements made toward the solution.
These tiny movements happen without the solver knowing. Then when the insight is realized fully, the "aha" moment happens for the subject. Irrelevant information is information presented within a problem that is unrelated or unimportant to the specific problem. Often irrelevant information is detrimental to the problem solving process. It is a common barrier that many people have trouble getting through, especially if they are not aware of it. Irrelevant information makes solving otherwise relatively simple problems much harder. For example: "Fifteen percent of the people in Topeka have unlisted telephone numbers.
You select names at random from the Topeka phone book. How many of these people have unlisted phone numbers? The people that are not listed in the phone book would not be among the names you selected. They see that there is information present and they immediately think that it needs to be used. This of course is not true. These kinds of questions are often used to test students taking aptitude tests or cognitive evaluations.
Irrelevant Information is commonly represented in math problems, word problems specifically, where numerical information is put for the purpose of challenging the individual. One reason irrelevant information is so effective at keeping a person off topic and away from the relevant information, is in how it is represented. Whether a problem is represented visually, verbally, spatially, or mathematically, irrelevant information can have a profound effect on how long a problem takes to be solved; or if it's even possible.
The Buddhist monk problem is a classic example of irrelevant information and how it can be represented in different ways:. This problem is near impossible to solve because of how the information is represented.
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Because it is written out in a way that represents the information verbally, it causes us to try and create a mental image of the paragraph. This is often very difficult to do especially with all the irrelevant information involved in the question. This example is made much easier to understand when the paragraph is represented visually. Now if the same problem was asked, but it was also accompanied by a corresponding graph, it would be far easier to answer this question; irrelevant information no longer serves as a road block.
By representing the problem visually, there are no difficult words to understand or scenarios to imagine. The visual representation of this problem has removed the difficulty of solving it. These types of representations are often used to make difficult problems easier. Being aware of irrelevant information is the first step in overcoming this common barrier.
Problem solving can also occur without waking consciousness. There are many reports of scientists and engineers who solved problems in their dreams. Elias Howe , inventor of the sewing machine, figured out the structure of the bobbin from a dream. Thinking about the problem, he dozed off, and dreamt of dancing atoms that fell into a snakelike pattern, which led him to discover the benzene ring. As if by a flash of lightning I awoke; and this time also I spent the rest of the night in working out the consequences of the hypothesis.
There also are empirical studies of how people can think consciously about a problem before going to sleep, and then solve the problem with a dream image. Dream researcher William C. Dement told his undergraduate class of students that he wanted them to think about an infinite series, whose first elements were OTTFF, to see if they could deduce the principle behind it and to say what the next elements of the series would be. They were instructed to think about the problem again for 15 minutes when they awakened in the morning.
Some of the students solved the puzzle by reflecting on their dreams. One example was a student who reported the following dream: . I was standing in an art gallery, looking at the paintings on the wall. As I walked down the hall, I began to count the paintings: one, two, three, four, five. As I came to the sixth and seventh, the paintings had been ripped from their frames.
I stared at the empty frames with a peculiar feeling that some mystery was about to be solved. Suddenly I realized that the sixth and seventh spaces were the solution to the problem! With more than undergraduate students, 87 dreams were judged to be related to the problems students were assigned 53 directly related and 34 indirectly related.
Yet of the people who had dreams that apparently solved the problem, only seven were actually able to consciously know the solution. The rest 46 out of 53 thought they did not know the solution. Mark Blechner conducted this experiment and obtained results similar to Dement's.
Coaxing or hints did not get them to realize it, although once they heard the solution, they recognized how their dream had solved it. For example, one person dreamed: . There is a big clock. You can see the movement. The big hand of the clock was on the number six. You could see it move up, number by number, six, seven, eight, nine, ten, eleven, twelve.
The dream focused on the small parts of the machinery. You could see the gears inside. His sleeping mindbrain solved the problem, but his waking mindbrain was not aware how. Albert Einstein believed that much problem solving goes on unconsciously, and the person must then figure out and formulate consciously what the mindbrain has already solved.
He believed this was his process in formulating the theory of relativity: "The creator of the problem possesses the solution. The psychical entities which seem to serve as elements in thought are certain signs and more or less clear images which can be 'voluntarily' reproduced and combined. In cognitive sciences , researchers' realization that problem-solving processes differ across knowledge domains and across levels of expertise e. Sternberg, and that, consequently, findings obtained in the laboratory cannot necessarily generalize to problem-solving situations outside the laboratory, has led to an emphasis on real-world problem solving since the s.
This emphasis has been expressed quite differently in North America and Europe, however. Whereas North American research has typically concentrated on studying problem solving in separate, natural knowledge domains, much of the European research has focused on novel, complex problems, and has been performed with computerized scenarios see Funke, , for an overview. The two approaches share an emphasis on relatively complex, semantically rich, computerized laboratory tasks, constructed to resemble real-life problems.
The approaches differ somewhat in their theoretical goals and methodology, however. The tradition initiated by Broadbent emphasizes the distinction between cognitive problem-solving processes that operate under awareness versus outside of awareness, and typically employs mathematically well-defined computerized systems.
Buchner describes the two traditions in detail. In North America, initiated by the work of Herbert A. Collective problem solving refers to problem solving performed collectively. Social issues and global issues can typically only be solved collectively. It has been noted that the complexity of contemporary problems has exceeded the cognitive capacity of any individual and requires different but complementary expertise and collective problem solving ability.
Collective intelligence is shared or group intelligence that emerges from the collaboration , collective efforts, and competition of many individuals. In a research report, Douglas Engelbart linked collective intelligence to organizational effectiveness, and predicted that pro-actively 'augmenting human intellect' would yield a multiplier effect in group problem solving: "Three people working together in this augmented mode [would] seem to be more than three times as effective in solving a complex problem as is one augmented person working alone".
Henry Jenkins , a key theorist of new media and media convergence draws on the theory that collective intelligence can be attributed to media convergence and participatory culture. Jenkins argues that interaction within a knowledge community builds vital skills for young people, and teamwork through collective intelligence communities contributes to the development of such skills. Collective impact is the commitment of a group of actors from different sectors to a common agenda for solving a specific social problem, using a structured form of collaboration.
After World War II the UN , the Bretton Woods organization and the WTO were created; collective problem solving on the international level crystallized around these three types of organizations from the s onward. As these global institutions remain state-like or state-centric it has been called unsurprising that these continue state-like or state-centric approaches to collective problem-solving rather than alternative ones. Crowdsourcing is a process of accumulating the ideas, thoughts or information from many independent participants, with aim to find the best solution for a given challenge.
Modern information technologies allow for massive number of subjects to be involved as well as systems of managing these suggestions that provide good results. From Wikipedia, the free encyclopedia. For other uses, see Problem disambiguation. This article has multiple issues.
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Thus, it is clear that contraction of cardiac muscle is not totally dependent on nerve supply although the strength and rate of contraction are influenced by both sympathetic and parasympathetic nerves of autonomic nervous system. Microscopic Structure of Cardiac Muscle Cardiac myocytes muscle cells are short uninucleated cells. The nucleus is centrally placed. The muscle cells are joined end-to-end at junctional specializations called intercalated discs, which are visible under light microscope as transverse dark lines arranged like steps in a staircase.
Thus, it should be appreciated that in cardiac muscle, a muscle fiber is made up of a chain of myocytes unlike in the skeletal muscle, where muscle fiber is a single cell.
The muscle fibers are disposed parallel to each other. They branch and anastomose with myocytes of adjacent fibers. The branches are compactly arranged and have the same parallel orientation like the parent fiber. The cross striations of cardiac muscle are not as prominent as found in skeletal muscle. This may be due to less number of myofibrils and more amount of cytoplasm with abundant mitochondria in cardiac myocytes.
Electron Microscopy of Intercalated Disc The intercalated discs are located between the ends of two contiguous myocytes. They have a transverse part corresponding to the step of staircase and a longitudinal part corresponding to the connection between the two steps. At this site, the plasma membranes of the two cells are joined by three distinct types of cell-to-cell junctions namely, macula adherens desmosome , fascia adherens similar to zonula adherens of epithelial cells and.
Smooth Muscle Plain or visceral muscle The smooth muscle is non-striated and involuntary. It functions under the control of both sympathetic and parasympathetic nerves. It occurs in the wall of blood vessels, gastrointestinal tract, biliary tract, respiratory tract, urinary passages, genital ducts including uterus, muscles of eyeball, Mllers muscle in upper eyelid, dartos muscle in scrotum and arrector pili muscles of skin.
Microscopic Structure of Smooth Muscle The smooth muscle fibers are elongated cells with broad central part and tapering ends. The muscle fibers show remarkable variation in length depending on the site. The oval or elongated nucleus is located in the central part of the cell. The acidophilic sarcoplasm contains myofibrils, which are responsible for the longitudinal striations seen under light microscope.
It also contains other cell organelles and inclusions. A network of delicate reticular fibers envelops the muscle fibers to bind the cells to each other and the gap junctions join the neighboring cells to facilitate intercellular transmission of electric impulse. Additional Features of Skeletal Muscles 1.
The arrangement of muscle fibers may be different according to the functional needs. Pennate comb like muscles are characterized by muscle fascicles that are disposed at an oblique angle to the line of contraction of the muscle. There are three types of pennate muscles. In unipennate muscle, the tendon or bone lies on one side and muscle fibers run obliquely from it e.
In bipennate muscle, the tendon or bone lies in the center and muscle fibers reach it from either side obliquely e. In multipennate muscle, there are numerous tendinous septa that receive fibers from various directions as in acromial fibers of deltoid and in subscapularis. The type of muscle contraction depends on whether the joint moves or not. In isometric contraction, there is no movement of a joint but there is increase in the tone of muscle.
On lifting a heavy suitcase, the flexor muscles. In isotonic contraction, the same muscles shorten to hold a baby. Depending on the actions of the muscles, they are divided into following types. Prime mover is the main muscle that performs a particular action, e. Fixator is the muscle that contracts isometrically to stabilize the prime mover. The examples of fixator muscles are quadratus lumborum which fixes the 12th rib during inspiration facilitating contraction of diaphragm and rhomboid muscles fixing the scapula during overhead abduction of arm. Antagonist is the term used for a muscle that opposes the action of a prime mover as exemplified by contraction of triceps brachii the extensor of elbow during flexion movement of that joint.
Synergist is the term used for a muscle, which helps other muscle prime mover in performing its stipulated action. The flexors and extensors of carpus flexor carpi radialis and extensor carpi radialis and extensor carpi radialis longus and brevis and extensor carpi ulnaris contract simultaneously to stabilize the wrist joint when long flexor or extensor muscles of the digits contract. The sensory fibers of the peripheral nerves carry the external and internal sensations to the neurons or nerve cells of CNS. The information is received, processed and integrated in the motor neurons of CNS.
The response or the command of the CNS is taken to the effector organs muscle, glands, viscera, etc. In this way, the nervous tissue governs and co-ordinates the functions of all other tissues and organs of the body. Subdivisions of Nervous System The nervous system is subdivided into central nervous system CNS , which includes brain and spinal cord and peripheral nervous system PNS , which includes peripheral nerves, sensory ganglia, autonomic ganglia and autonomic nerves. The autonomic ganglia and nerves belong to sympathetic and parasympathetic divisions of autonomic nervous system.
The basic components of the nervous tissue are the neurons, neuronal processes, neuroglia, Schwann cells and synapses. The neurons are the. The fascia adherens and desmosomes are seen in the transverse part of the disc. They help to rapidly transmit force of contraction from one cell to another. The gap junctions are present in longitudinal part of the disc. They provide electrical coupling of cells, so that the cardiac muscle can function as physiological syncytium. They are specialized for reception of stimuli, their integration and interpretation and lastly their transmission to other cells.
Neurons give off radiating processes from their cell bodies. These processes are of two types, dendrites and axons. The synapse is a site of close contact between two neurons for easy transmission of information from neuron-to-neuron. The neuroglia cells serve to support the neurons and their processes in CNS while Schwann cells and satellite cells serve similar function in PNS. Classification of Neurons According to the Number of Processes Unipolar Neuron A neuron with a single process is called unipolar neuron. It is found only in the early stages of embryonic development. Pseudounipolar Neurons Fig.
These neurons are found in sensory ganglia of dorsal roots of spinal nerves and cranial nerves also called dorsal root ganglia. The neurons of the mesencephalic nucleus of trigeminal nerve belong to this category. The giant pyramidal cell of Betz is an example of UMN. Their cell bodies are located in ventral horn of spinal cord and in cranial nerve nuclei in brainstem. Their axons leave the CNS to supply the skeletal muscles via peripheral nerve.
Microscopic Structure of Multipolar Neuron The body of neuron is called perikaryon. It contains a euchromatic in which chromatin is uncoiled and active and vesicular nucleus with prominent nucleolus. The area of cell body that gives origin to axon is called axon hillock. The cytoplasm shows characteristic Nissl bodies rough endoplasmic reticulum studded with ribosomes.
The Nissl bodies are basophilic and are dispersed through out the cytoplasm and in the dendrites but absent in axon hillock and axon. They are involved in protein synthesis. The absence of centriole is responsible for inability of the neurons to divide. The neurons are arrested in Go phase of cell cycle.
Bipolar Neurons Fig. They are found in retina, olfactory epithelium and sensory ganglia of vestibular and cochlear nerves. Multipolar Neurons Fig. They are found in gray matter of central nervous system spinal cord, cerebral and cerebellar cortex, intracerebral and intracerebellar nuclei in addition to cranial nerve nuclei in brainstem. According to the Function of Neurons i. Motor neurons conduct impulses to skeletal muscles neurons of ventral horn of spinal cord. Sensory neurons receive stimuli from external and internal environment.
According to the Location of Neuronal Cell Body i. Upper motor neurons UMN belong to CNS as their cell bodies are located in the motor area of cerebral cortex and their long axons become the corticospinal fibers. These fibers terminate on anterior horn cells of. Neuroglia The neuroglia cells are commonly called glia glia means glue cells. They are non-neuronal cells in CNS, where they outnumber the neuronal population. The glia cells are capable of mitotic cell division throughout life.
The glia cells play a role equivalent to connective tissue in other organ systems of the body. Neuroglia cells in CNS i. Oligodendrocytes with few processes are derived from neural tube. They myelinate nerve fibers in CNS. Astrocytes fibrous and protoplasmic types are derived from neural tube. They regulate ionic milieu in CNS. Microglia are derived from mesenchymal cells. Ependymal cells produce CSF in ventricles of brain. Neuroglia Cells in PNS i. Schwann cells lemnocytes or peripheral glia are derived from neural crest.
They myelinate nerve fibers in PNS. Satellite cells capsular gliocytes are present in ganglia. Lipid rich plasma membranes of oligodendrocytes in CNS for example in optic nerve and Schwann cells in PNS for example in sciatic nerve tightly wrap around the axon several times with the help of mesaxon by which the axon is suspended from the plasma membrane surrounding it. Several concentric layers of plasma membrane and its lipid around the axon give the axon an appearance of a Swiss roll.
This forms the myelin sheath. Oligodendrocytes or Schwann cells line up in rows along the length of the axon outside the myelin sheath. Myelin sheath is interrupted at regular intervals at nodes of Ranvier in the peripheral nerve. The node of Ranvier or nodal gap denotes the limit of adjacent Schwann cells. The myelin sheath is necessary for insulation of nerve fiber so that nerve impulse can jump from node-to-node for speed of transmission saltatory conduction. The myelinated fibers impart white color to the white matter in CNS.
Faulty Myelination i. Multiple sclerosis MS is disorder of brain and spinal cord in which the oligodendrocytes undergo degeneration leading to demyelination of nerve fibers which form white matter. The symptoms include muscle weakness, loss of balance and in-coordination of movements. Cognitive symptoms include weak memory and low problem solving capacity. Guillain Barre syndrome GBS is disorder in which the peripheral nerves lose their myelin sheath.
This results in slow transmission of nerve impulses causing muscle weakness and abnormal sensations starting in the legs and spreading towards arms and upper body. Tumors of Neuroglia i. Ependymoma is the tumor arising from ependymal cells. Astrocytoma is a tumor arising from astrocytes. Oligodendroglioma arises from oligodendrocytes.
Schwannoma is the growth of Schwann cells encircling peripheral nerves. Schwannoma of acoustic nerve is an intracranial tumor seen at cerebellopontine angle. Lysosomes are prominent feature of the cytoplasm. They contain hydrolytic enzymes necessary for phagocytosis. Aging neurons show cell inclusions, which are golden brown lipofuscin pigment known as wear and tear pigment derived from lysosomes.
The cell bodies also contain microtubules and microfilaments for internal support , neurofilaments consisting of spiral proteins, plenty of mitochondria and large Golgi complex. Dendrites are the cell processes that are close to cell body. All cytoplasmic contents of the cell body except the Golgi complex are present. They tend to branch and are capable of forming a dendritic tree for networking with processes of other neurons. Axons arise from cell bodies at axon hillock and lack Nissl bodies. There is only one axon per cell and usually it is long. The axons transmit action potential.
Axons terminate by forming synapses with other neurons, muscle fibers and secretory units of exocrine glands. They form the motor fibers of peripheral nerves. The cytoplasm of axon is called axoplasm and its plasma membrane is called axolemma. Axons are either myelinated or nonmyelinated. Synapse is the specialised site of interneuronal contact for cell-to-cell transmission of nerve impulse. The synapse consists of three parts, the terminal botton or presynaptic membrane of presynaptic neuron, synaptic cleft and postsynaptic membrane of postsynaptic neuron.
The terminal bouton contains vesicles filled with neurotransmitter.
The synaptic cleft is a narrow extracellular space between the two neurons. The synaptic vesicles release the neurotransmitter into synaptic cleft. As soon as the neurotransmitter comes in contact with plasma membrane of postsynaptic neuron, action potential is generated by depolarization. The cartilage consists of chondroblasts and chondrocytes.
The ground substance consists of sulfated glycosaminoglycans and proteoglycans with a large proportion of hyaluronic acid. General Features i. The outer covering of the cartilage is known as perichondrium. However, the articular cartilages covering the articular ends of bones are devoid of perichondrium.
The perichondrium is composed of two layers called inner cellular and outer fibrous. The inner cellular layer contains a row of undifferentiated perichondrial cells that have a potential to turn into chondroblasts if occasion demands. The outer fibrous layer contains dense irregular connective tissue and plenty of blood vessels and sensory nerves.
The cartilage is avascular. The nourishment is provided by perichondrial blood vessels by a process of diffusion through ground substance. The cartilage grows by interstitial and appositional processes. By appositional process new cartilage is added to the surface of old cartilage by the cells of perichondrium. By interstitial process new cartilage is added internally to the old cartilage by chondrocytes, which are inside the lacunae and which have.
Thus, appositional growth is called surface growth and interstitial growth is called internal growth. Histological Types of Cartilage i. Hyaline cartilage ii. Elastic cartilage iii. Hyaline Cartilage It is the most commonly occurring cartilage in the body. It is found in the adults in nose, larynx thyroid, cricoid and part of arytenoid cartilages , trachea, extrapulmonary bronchi, intrapulmonary bronchi, articular cartilages and costal cartilages. The hyaline cartilage has a tendency to calcify and ossify as age advances. The hyaline cartilage appears transparent like a glass.
It is covered with perichondrium. It contains homogeneous matrix, invisible collagen fibers and chondrocytes inside lacunae. Just close to the perichondrium there is a layer of chondroblasts that secrete the ground substance. Once the chondroblasts are surrounded by matrix they become mature chondrocytes. The unique feature of chondrocytes is that they retain capacity to divide and continue to secrete the matrix.
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When chondrocytes divide, they form a group of two or four chondrocytes inside the same lacuna. The matrix of hyaline cartilage contains type II collagen fibers, which are masked by the ground substance. It is basophilic and exhibits metachromasia. The matrix is. Elastic Cartilage This cartilage occurs in the pinna of the ear, larynx epiglottis, tips of arytenoids cartilages, corniculate and cuneiform cartilages , nasal cartilages and cartilaginous part of Eustachian tube.
The elastic cartilage looks yellow in color in fresh state due to presence of abundant yellow elastic fibers in its matrix. The elastic fibers branch and anastomose to form a meshwork inside the matrix. It also contains a few type II collagen fibers. The ground substance is basophilic and the chondrocytes are housed in lacunae either singly or in groups of two.
The cells appear closely placed as intercellular ground substance is lesser than in hyaline cartilage. Unlike the hyaline cartilage, elastic cartilage retains its histologic characters throughout life. Fibrocartilage This cartilage is found in secondary cartilaginous joints like symphysis pubis and manubriosternal joint as intraarticular plate of fibrocartilage joining the articulating bones.
The intervertebral discs are composed of ring shaped annulus fibrosus which is a fibrocartilage surrounding the inner nucleus pulposus which is a gelatinous hygroscopic jelly. The fibrocartilages are also found inside the knee joint as menisci and as articular discs in temporomandibular and inferior radioulnar joints. The fibrocartilage consists of minimum ground substance, very few chondrocytes but abundant collagen fibers. The type I collagen fibers are arranged in large interlacing bundles. The chondrocytes are present as single row between the collagen bundles.
The fibrocartilage lacks perichondrium. Osteoarthritis The basic pathology is degeneration of articular cartilages. The articular cartilage is hyaline cartilage without perichondrium that lines the articulating ends of bones. The degeneration of articular cartilages causes difficulty in walking if joints of lower limb like hip and knee are affected. Incapacitation of joints of hand leads to painful day to day activities performed by hands.
Usually in severe cases of osteoarthritis of knee or hip joint, prosthetic replacement of the joint is undertaken. Paradoxically, it is a highly vascular and dynamic tissue in the body. Contrary to our usual thinking, the bone tissue shows a continuous turn over through out life. Components of Osseous Tissue Like any other connective tissue, the bone consists of cells, matrix and fibers. The only difference is that the matrix of bone is mineralized. That is why the bone is a storehouse of calcium and phosphorous.
Bone Cells i. The osteoprogenitor cells are the least differentiated bone forming cells. They are present in the cellular layers of periosteum and endosteum. They are the stem cells of the bone, since they turn into osteoblasts. The osteoblasts are the bone forming cells. During bone development, they are seen on growing surfaces of newly formed bony plates and around interosseous blood vessels.
Osteoblasts are round cells with single nucleus and highly basophilic cytoplasm. They are characterized by a well-developed rough endoplasmic reticulum, Golgi complex and mitochondria as they secrete type I collagen fibers and ground substance of bone matrix osteoid. They are rich in alkaline phosphatase, which they release in blood circulation during ossification.
The alkaline phosphatase is necessary during mineralization of the osteoid. The osteocytes are mature form of osteoblasts. The cell bodies of these cells are trapped inside the lacunae within a bone and their protoplasmic processes extend into small canaliculi, which radiate from the lacunae. The processes of adjacent osteocytes meet each other inside canaliculi at gap junctions, which provide pathway for transport of nutrients. It must be understood that there are no blood vessels inside the lacunae and canaliculi.
The osteocytes are metabolically active, since they play a role in minimal secretion of bone matrix required for maintenance. The osteoclasts are the macrophages of bone tissue blood monocytes being their precursors. They are largest in size among bone cells. They are multinucleated cells having lysosomes containing acid phosphatase. They are intensely eosinophilic due to plenty of lysosomes. A zone of peripheral cytoplasm and plasma membrane adjacent to osseous surface is referred to as ruffled border. Multiple cytoplasmic processes and lysosomes are found along this border.
This way they bring about destruction and resorption of hard.
The territorial matrix is more basophilic and it surrounds the lacunae like a capsule. The interterritorial matrix is less basophilic and is found at some distance away from the lacunae. The activity of osteoclasts is controlled by calcitonin thyroid hormone and parathormone parathyroid hormone. It is the calcium in the bone that makes it opaque in radiographs. The above proportions clearly indicate that bone is the largest store of body calcium. Microscopic Structure of Bone There are two types of bony tissue, spongy and compact depending on the bony architecture.
Structure of Spongy Bone The bony lamellae are arranged as interconnecting rods and plates bony trabeculae. There are spaces between the interconnecting bony tissues. These spaces are called marrow cavities as they are filled with red marrow. The bony lamellae contain collagen fibers. The osteocytes reside between lamellae in specialized lacunae. The processes of osteocytes pass through minute channels called canaliculi, which originate from the lacunae and travel through the lamellae to connect neighboring lacunae to each other.
Spongy bone tissue is present in epiphyses of long bones, e. Similarly spongy bone occurs in head, greater and lesser trochanters in upper end of femur and in the lower end of femur. All short, irregular vertebrae ,flat bones sternum, scapulae and skull bones contain spongy bone tissue.
Structure of Compact Bone The compact bone is found in the diaphysis of long bones. Though the compact bone also has lamellar structure like the spongy bone, the pattern of lamellae is quite unique. There are three different types, Haversian system, interstitial lamellae and circumferential lamellae. Lamellae of Haversian System This pattern of lamellae is known as osteon. Each osteon consists of a centrally located Haversian canal around which lamellae are laid down in concentric rings. The central canal contains capillaries, nerve fibers and areolar tissue.
The lamellae show lacunae, from which radiate minute canals called canaliculi. The bodies of the osteocytes are lodged in lacunae and their processes occupy the. The canaliculi connect the Haversian canal to all the lacunae in that osteon thereby bringing the nourishment from the canal to all osteocytes via canalicular network.
In the long bone, there are many osteons of this pattern. They are all longitudinally oriented. An additional source of blood supply and nerve supply to the compact bone comes from Volkmanns canals. These canals carry blood vessels from periosteal and endosteal surfaces to the osteons. The Volkmanns canals are horizontally disposed and are not surrounded by concentric rings of lamellae. Circumferential Lamellae The outer circumferential lamellae are arranged in parallel bundles deep to the periosteum, encircling the entire bone.
The inner circumferential lamellae are likewise seen deep to endosteum surrounding the marrow cavity. Interstitial Lamellae These lamellae are seen in between the regular osteons as irregular areas of lamellae. Periosteum It is the outer covering of a bone. It is composed of two layers, outer fibrous and inner cellular. The fibrous layer is composed of dense irregular type of connective tissue. The cellular layer consists of osteoprogenitor cells. The periosteum has rich blood supply. A few of periosteal blood vessels enter the bone via Volkmanns canals. The periosteum is very sensitive to various stimuli.
Its outer layer is richly innervated by somatic sensory nerves. The periosteum gives attachments to tendons and ligaments. The collagen fibers of the tendon occasionally enter the outer part of compact bone, where they are embedded in the matrix. Such extensions of collagen fibers from the tendons are called Sharpeys fibers. The periosteum performs several functions like nutrition and protection to the bony tisue.
In the developing bone in both intramembranous and endochondral ossification, the osteoprogenitor cells in the cellular layer of periosteum lay down subperiosteal bone. In well-developed bone too, these cells grow into osteoblasts when bone is injured to help in bone repair. Following example best illustrates the ability of the periosteum to regenerate the bone.
During surgical removal of cervical rib, if the surgeon performs subperiosteal resection, the cervical rib will regenerate from the cellular layer of periosteum that is left behind. The patient will once again suffer from symptoms of cervical rib. Development and Ossification of Bone Embryologically, the bones are mesodermal derivatives. Hence, they develop from undifferentiated mesenchymal tissue. These mesenchymal cells change into osteogenic.
Growth in Diameter of a Bone The bone grows in thickness by subperiosteal deposition of bone tissue by osteoblasts from cellular layer of periosteum.
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This is known as appositional growth. In a long bone, this is corresponding resorption of bone from endosteal side by the osteoclasts. The net result of these two diametrically opposite processes is increase in diameter without increase in width of compact bone. In this way, bone can grow in thickness even after the growth in length stops refer epiphyseal plate below. Bone Diseases due to Nutritional Deficiency i. Scurvy vitamin C deficiency affects the synthesis of collagen in the bone as vitamin C is essential in this process.
The osteoid is scanty and hence the bone tissue is thin. Rickets vitamin D deficiency in children affects the mineralization of osteoid. Vitamin D deficiency leads to poor absorption of calcium and in turn poor mineralization. There are widespread effects of poor mineralization on the skeleton. Osteomalacia is found in adults, who suffer from inadequate intake of vitamin D or of calcium. Osteoporosis is found in old age. Women are more prone to osteoporosis compared to men. When resorption of bone is more than formation of bone, the bone density is reduced and hence they become fragile and prone to fracture due to slightest trauma.
Types of Bones i. Long bones are found in limbs. Their parts are similar to earlier mentioned parts of a developing long bone, except that they lack growth plate. They are. The only exception to this is the clavicle, which is the only long bone without marrow cavity, is a membrane bone and ossifies from two primary centers. The yellow marrow fills medullary cavity and red marrow fills the epiphyses in adults. The hemopoesis production of erythrocytes, platelets, monocytes and granulocytes takes place in red marrow. So, hemopoesis takes place only in the ends of long bones in adults.
There is one subtype of long bones called short long bones like metacarpals, metatarsals and phalanges. These bones have epiphysis at one end only unlike the long bones, which have epiphyses at both ends. Short bones are seen in hands and feet. The examples in the hand are the carpal bones scaphoid, lunate, triquetral, pisiform in proximal row and trapezium, trapezoid, capitate and hamate in distal row.
The examples in foot are the tarsal bones talus, calcaneus, cuboid, navicular and three cuneiform bones. They are composed of spongy bone, so hemopoesis occurs throughout life in them. They are covered with periosteum like the long bones and their articular surfaces are covered with articular hyaline cartilages. Flat bones are seen in bones of the vault of skull, namely frontal bone, parietal bones and occipital bone. Scapula, sternum and ribs are the other examples. The peculiarity of flat bones of skull is that they show sandwich like arrangement of structure.
There are two thin plates or tables of compact bone enclosing a space called diplo, which contains red hemopoetic marrow and diploic veins in spongy bone. The diploic veins open into adjacent dural venous sinuses. Irregular bones are the ones that have complex and atypical shapes. The examples are hip bones, vertebrae, temporal bone, sphenoid, ethmoid, maxilla, etc. The vertebrae and the hip bones are sites of hemopoesis.
Sesamoid bones are like sesame seeds and develop in the tendons of some muscles. The largest sesamoid bone is the patella, which develops in tendon of quadriceps femoris muscle. Smaller sesamoid bone found in lateral head of gastrocnemius is called fabella. There are few more sites where these bones develop. They are devoid of medullary cavity and periosteum. Pneumatic bones are flat or irregular bones containing a large cavity filled with atmospheric air. The bones containing paranasal air sinuses inside them are maxilla, ethmoid, frontal and sphenoid.
The temporal bone houses air containing cavities like middle ear, mastoid antrum and mastoid air cells. Accordingly, if a bone forms directly from osteogenic cells of mesenchyme, the process of ossification is called intramembranous. If a bone forms indirectly from osteogenic cells derived from the cartilage cells of the cartilage model of bone, the process of ossification is called endochondral or intracartilaginous for details of steps in ossification refer to histology texts.
Bones developed by intramembranous ossification membrane bones are spongy bones, the examples being, bones of face including mandible, bones of vault of skull and clavicle. The bones developed by endochondral ossification are called cartilage bones, e. It is covered by periosteum. A tubular cavity called marrow cavity passes through the diaphysis. It contains red marrow in the developing bone. The marrow cavity is lined by cellular layer, which is called endosteum. The diaphysis is the shaft of a long bone. It is the first part to ossify. The primary center of ossification appears before birth in the cartilage model of the bone in the center of diaphysis between 6th to 8th weeks of intrauterine life.
The shaft of the bone is composed of compact bone. The metaphysis is the funnel-shaped region at either end of the diaphysis. It intervenes between the growth cartilage and the diaphysis. It is the most vascular part of developing bone as newly formed spongy bone from ossification zone of growth cartilage is laid down here. There is an anastomotic arterial ring surrounding the metaphysis. Because of its high vascularity and stasis of blood here metaphysis is a site of osteomyelitis in growing children.
Epiphyseal plate or growth cartilage is a thin plate of cartilage located between the metaphysis and epiphysis at either end. This is a region of great activity as it is responsible for linear growth in bone. It consists of five zones, namely zone of resting cartilage closest to epiphysis, zone of proliferation, zone of hypertrophy, zone of calcification and zone of ossification. When full height is achieved, the cartilaginous epiphyseal plate turns into bone.