Thursday, March 31, 2011
Fontanelles
In chapter 5, Neil Shubin discusses the plates, rods, and blocks that make up the cranial structure for human heads. Infants are born with fontanelles which clearly provide no protection for the brain. Discuss how fontanelles are key in the formation of the human skull and how a lack of fontanelles would effect the formation of a human.
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Fontanelle is what is known as the "soft spot" on a baby's head. A baby has this instead of a fully developed skull because the child can fit through the birth canal with fewer problems. This helps to show how having a fontanelle is an evolutionary advantage because more of the offspring (and mothers) of the creatures that have fontanelles are more likely to survive the birthing process which will further allow them to survive and reproduce. Although forntanelle are not as strong as skulls, "the membrane covering the fontanelles is extremely tough and difficult to penetrate" (http://en.wikipedia.org/wiki/Fontanelle). Also, these structures allow for the baby's head to grow at a fast rate as the skull sections are moveable. Lastly, the fonanelles can help indicate the healthiness of a baby as if these spots are sunken, then the child is dehydrated. If the spots are swollen, then the brain has had an injury and is swelling.
ReplyDeleteFontanelle is a huge part of the formation of the skull. If a child's fontanelle turned to skull too early, the brain's development and growth would be restricted. The fontanelles will eventually be replaced by bone creating 5 sutures. The posterior fontanelle closes after eight weeks after birth while the anterior fontanelle takes closer to two years to completely be replaced by bone.
http://www.maexamhelp.com/id85.htm
Jackie James
(jackie.james@comcast.net)
Shubin mentions the "plates, blocks, and rods: the theme for skulls" (Shubin 83). Fontanelles are the spaces between these plates that are seen in human infants. There are several evolutionary advantages of babies having fontanelles when they are born. As Jackie pointed out, these "soft spots" help the child fit through the birth canal with fewer problems than if the child had a fully developed skull. This is an evolutionary advantage because the babies are more likely to survive birth if they have fontanelles. Most infants have two fontanelles; an anterior and a posterior. By their second birthday, "the ossification of the bones of the skull causes the fontanelles to close over...the closures eventually form the sutures of the neurocranium" (http://en.wikipedia.org/wiki/Fontanelle). Not only do the fontanelles enable the bones of the skull to flex, allowing the child's head to pass through the birth canal, they also go through ossification, or osteogenesis, which allows to the skull to develop into a much stronger structure as the child gets older. The formation of the human skull and brain depends on the fontanelles that we have as infants; as Jackie pointed out, the fontanelles allow for the baby's head and brain to grow at a faster rate as well.
ReplyDeleteThere is a clinical significance to fontanelles, which Jackie also mentioned. A sunken fontanelle indicates dehydration, whereas a very tense or bulging anterior fontanelle indicates raised intracranial pressure. The fontanelle may pulsate, and although the precise cause of this is not known, it is perfectly normal and seems to echo the heartbeat.
http://health.nytimes.com/health/guides/symptoms/fontanelles-sunken/overview.html
Hannah Kay (hgkay@aol.com)
Shubin, in chapter 5, describes the plates,blocks, and rods that make up the cranial structure. All of this begins with the developing fetal skull. Of which a major part is the fontanel.
ReplyDeleteBoth Jackie and Hannah go into depth about how fontanels are essential during the birth of a baby. Fontanels are soft spots found on a newborn's skull; they are the patches where skull bones have not yet met. Fontanels are squishy to touch and seem very vulnerable. In fact, they are made up of a fibrous membrane that protects a baby's brain. There are six fontanels on your newborn's skull, but only two are evident. The larger, diamond shaped fontanel is on the top front of the head while the smaller fontanel is placed at the base of the skull.
In human anatomy, a fontanels one of two "soft spots" on a newborn human's skull; although there are six fontanels in the infant's skull: the anterior fontanel, the posterior fontanel, the paired sphenoidal fontanel, the paired mastoid fontanel. The skull of a newborn consists of five main bones: two frontal bones, two parietal bones, and one occipital bone. These are joined by fibrous "sutures" which allow movement that facilitates childbirth and brain growth. The posterior fontanel ossifies(which Hannah and Jackie mention) and closes by the time the newborn is only one or two months old. The fontanels should feel firm and very slightly concave to the touch. A tense or bulging fontanel occurs when fluid accumulates in the skull cavity or when pressure increases in the brain.
(http://cwx.prenhall.com/bookbind/pubbooks/martini10/chapter6/custom3/deluxe-content.html)
Jackie and Hanna believe that the evolutionary advantage of the fontanel is that becauuse the fontanel is present more mothers and babies will be able to survive the the entire process of birth. They then go on to say that this will “further allow them to survive and reproduce” which is advantageous. I totally agree with what they both beleive.
However, there is another evolutionary advantage about the brain that they did not mention. While they seem to make your newborn more vulnerable, fontanels actually make a child's head more sturdy. Without fontanels, a baby's head wouldn't be able to deal with the pressure of passing down the vaginal canal. Otherwise, women's hips would have to be larger or babies would have to be born with smaller brains. In other words, fontanels allow for larger brain capacity.
There are also different relations with fontanels. “Craniosynostosis is a condition in which the sutures close too early, causing problems with normal brain and skull growth.” The premature closing of these sutures can create increased presssure within the skull and can often alter the appearance of the facial structure.
Craniosynostosis is usually inherited either through autosomal recessive of autosomal dominant.
Autosomal recessive means that two copies of the gene are needed to express the condition, one inherited from each parent, who are obligate carriers. Because of this the carrier parents have a 25 percent chance of passing the disorder along to their child with each pregnancy. Autosomal dominant means that only one gene is needed to pass the disorder on to the child and that there will be a 50 percent chance in each pregnancy that the child will have craniosynostosis. In both dominant and recessive, males and females are equally affected.
“Craniosynostosis is a feature of many different genetic syndromes that have a variety of inheritance patterns and chances for recurrence, depending on the specific syndrome present. It is important for the child as well as family members to be examined carefully for signs of a syndromic cause (inherited genetic disorder) of craniosynostosis such as limb defects, ear abnormalities, or cardiovascular malformations.”
(http://www.hopkinsmedicine.org/neurology_neurosurgery/specialty_areas/pediatric_neurosurgery/conditions/craniosynostosis/)
-Adnan Jahan
(adnanjahan@gmail.com)
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