Development of head and neck practical

Question 1

what is synchondrosis

Answer 1

a primary cartilaginous joint

mainly found in the developing skeleton eg growth plates

Question 2

Give an example of synchondrosis in a child

Answer 2

mainly found in the developing skeleton eg growth plates

Question 3

give an example of synchondrosis in an adult

Answer 3

an adult example is between the rib and sternum

hyaline cartilage between the 2 bone surfaces with very little movement allowed

Question 4

what are secondary cartilaginous joints and give examples

Answer 4

fibrous disc / fibro-cartilage disc between bones 
found along the midline of the body 
eg intravertebral discs
pubic syphysis
mental symphysis

Question 5

where would you expect to see the spheno-occipital synchondrosis and what is its purpose

Answer 5

between the sphenoid and occipital bones
it allows growth in the base of the skull

remains open until between 16-20 years old

Question 6

what is an ossification centre

Answer 6

an ossification centre is the starting point for bone growth

some bones in the skull develop from several ossification centres, which later fuse into a single bone

Question 7

what is the first ossification centre to appear

Answer 7

the primary ossification centre

Question 8

how many ossification centres does the occipital bone develop from

Answer 8

usually 6 ossification centres (2 paired parts, 2 individual centres)
although 3 parts usually fuse by birth
the rest fuses by around 6/7 years

Question 9

what are the 2 ways in which bones are formed

Answer 9

endochondral ossification
= cartilage model laid down first then replaced by bone

intramembranous ossification
= bone is laid directly down into the mesenchyme (early embryonic tissue)

Question 10

what type of ossification occurs in the skull

Answer 10

both types

Question 11

explain endochondral ossification

Answer 11

> cartilage grows through interstitial growth (cartilage cells can dividie)
blood vessels penetrate into cartilage
when cartilage gets too big it starts to calcify and forms a nice scaffold for the bone to be laid down on top of
we get first pieces of bone laid down = primary ossification centre

Question 12

in long bones where do you find secondary ossifiication centres and what are their purpose

Answer 12

> secondary ossification centres are found at either end of the long bone
they maitain a cartilage plate in between them (synchondrosis / primary cartilaginous joint)
cartilage can keep growing
bone can keep replacing it until all the cartilage is gone and replaced by bone
growth stops

Question 13

names bones that form from endochondral ossification

Answer 13

part of the occipital bone

mandible

Question 14

where does intramembranous ossification occur

Answer 14

rapidly growing bone
specifically ones surrounding the brain
(bone is laid down directly into the mesencyme - presence of the growing bone stumulates the bone to be laid down)

Question 15

what is a fontanelle

Answer 15

membranous areas “soft spots” between bones of the calvarium (neurocranium)

Question 16

why are fontanelles important structures in the developing skull

Answer 16

allow for compression and overlap of bones of the skull during birthing - head can appear slightly distorted for several days following birth
also important for continued rapid growth of brain after baby is born

Question 17

how many fontanelles are there

Answer 17

> 1x anterior
1x posterior
2x mastoid (posterolateral)
2x sphenoidal (anterolateral)

= 6

Question 18

where is the posterior fontanelle found

Answer 18

between parietal and occipital bones

Question 19

where are the sphenoidal fontanelles found

Answer 19

between parietal, sphenoid and temporal bones

Question 20

where are the mastoid fontanelles found

Answer 20

between occipital, parietal and temporal bones

Question 21

where is the anterior fontanelle found

Answer 21

between parietal and frontal bones

Question 22

when does each fontanelle close

Answer 22

approx closure pattern (all postpartum)

posterior = between 1-3 months

sphenoidal (anterolateral) = around 6 months

mastoid (posterolateral) = between 6-18 months

anterior = by around 2 years

Question 23

what are sutures

Answer 23

fibrous joints that dont allow a lot of movement

in adults sutures are seen as lines on the skull
- can completely ossify / disappear

Question 24

name sutures in the skull

Answer 24

coronal suture
sagittal suture
lamboid suture

Question 25

what is the anterior fontanelle called once it is closed

Answer 25

bregma

Question 26

what is the posterior fontanelle called once it is closed

Answer 26

lambda

Question 27

name sutures / symphysis that can be found on the fetal skull but are not as evident on the adult skull

Answer 27

metopoic suture (along the frontal bone)

mental symphysis (middle of mandible)

Question 28

what happens to the metopic suture in an adult

Answer 28

disappears in an adult
usually closes between 2-4 years after birth

10-15% of population may retain suture until adult but it is not know why
no clinical effect on indiividual

Question 29

what happens to the mental symphysis

Answer 29

there is fibrocartilage in it

open around the time of birth
the bones fuse together within the first year of birth

Question 30

what is the sphenoidal fontanelle called when it fuses

Answer 30

pterion
= coming together of 4 bones (thin area of the skull)
> parietal
> frontal
> temporal
> sphenoid

Question 31

what important artery passes inside the pterion

Answer 31

middle meningeal artery

blow to the side of the head can fracture these bones and damage the artery underneath

Question 32

how do the proportions of the facial skeleton (viscerocranium) and bones surounding the brain (neurocranium) changed from the fetal skull to the adult

Answer 32

a facial skeleton catches up to neurocranium
calvarium to faical proportions are approx 8:1 at birth
then 4:1 @ 5 years
and about 2.5:1 in adult life

Question 33

why are the proportions between the viscerocranium and neurocranium different in the fetal skull

Answer 33

brain development most important before birth [in foetal skull the neurocranium surrounding the brain grows quickly because the brain grows quickly]
BUT
skull needs to be small enough for passage through the pelvis during birth

face grows as the dentition develops and in response to muscles of mastication - teeth not required at birth for feeding - there is no need for the face to grow fast during foetal life

Question 34

what is the angle of the mandible like in the foetal skull

Answer 34

obtuse

Question 35

what causes the change in the angle of the mandible to make it less obtuse

Answer 35

forward (the body) and downward (the ramus) growth of the mandible to accommodate developing dentition

Question 36

where is the mastoid process

Answer 36

the bump of bone you can feel behind your ear

Question 37

what does the tympanic ring become

Answer 37

the tympanic plate

Question 38

if you can still see a gap between the 2 parts of the mandible - does this mean the mental symphysis is fibrous or ossified

Answer 38

fibrous

Question 39

how does the mastoid process arise

Answer 39

the neck muscles pull on this bone and cause it to expand

some air cells develop in there as well

Question 40

what is the tympanic ring / plate

Answer 40

opening to the external auditory meatus = opening into ear canal

ring in foetus
grows outwards and forms more of a plate in an adults

Question 41

why do females tend to have a more obtuse angle of mandible than males

Answer 41

male mandibles become squarer with a close to 90 degree angle of mandible, following puberty
males under go a bigger growth spurt with testosterone and other circulating hormones so they develop a bigger muscle mass and these muscles of mastication are growing larger and pulling more on the bone so the mandible is more robust
males = sqaure chin and jaw

Question 42

how can you tell if a tooth is lost antemortem

Answer 42

there is evidence of healing in the socket an d alveolar bone resorption

Question 43

how can you tell if a tooth is lost postmortem

Answer 43

open tooth sockets

no evidence of healing

Question 44

why can ridges be seen on the mandible bone in males

Answer 44

due to enlarged muscles of mastication