Majed Sharayha
Posts : 130
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Join date : 2011-08-23
Age : 31
 |  Subject: Dr.Shreen, Sheet #1 - 522012 "Corrected"  Mon Feb 06, 2012 8:04 pm | |
| link for download ---> Click here------------------------------------------------------------------------------------------ The skull
The cranium (skull) is divided into two parts :-
1-Brain box which is the skull itself &the upper fixed part (skull proper)
2-Mandible which is the lower mobile part of the skull
The skull is viewed from different aspects.
We’ve 6 aspects or norma:-
• Anterior aspect: norma frontalis
• Superior aspect: norma verticalis
• Lateral aspect: norma lateralis
• Posterior aspect: norma occipitalis
• Inferior aspect (viewed from inside skull): norma basalis interna
• Inferior aspect (viewed from outside skull): norma basalis externa
Now, the special features of each norma will be discussed in detail.
Special features:
1- NORMA VERTICALIS:
A) Bone composition:
It consists of 4 bones:-
• Anteriorly: frontal bone (forms the forehead)
• Behind frontal bone on either side: 2 parietal bones
• Posteriorly: occipital bone
B) Sutures (joints between the bones)
The sutures in the skull are of the fibrous joint type
There are 3 sutures in total:
1. Coronal suture: which divides the skull into anterior &posterior aspects & joins frontal bone with 2 parietal bones
2. Sagittal suture: which divides the skull into right &left aspects &joins 2 parietal bones with the occipital bone
3. Lambdoid suture: which joins the 2 partial bones with the occipital bone
C) Points where sutures meet:
To understand this point we’ve to keep in mind that there are differences between the skull of an adult and a newborn:
1. Bregma: the point at the junction of the sagittal and the coronal suture
In newborns this point is not fully formed. Rather a membrane is found which allows for the development and growth of the brain. This is known as the Anterior fontanel
-it’s rhomboid in shape
-it’s an anterio-posterior breadth of 3 fingers
Every 6 months,1 finger breadth closes so complete closure occurs at 1.5 years of age
2. Lambda: the point which is located at the junction of the saggital &lambdoid sutures
In newborns, this point is formed by a membrane and is known as the Posterior fontanel
- It’s triangular in shape and has the same function as the anterior fontanel
- Complete closure occurs at 6 months of age
Functions of the ant. and post. fontanels:
In newborns, the brain is not well developed and fontanels provide space which allows for the growth of the brain
Development of the brain is completed by the second year which coincides with the closure of the ant. And post. fontanels to form the bregma and the lambda respectively.
*If there were premature closure of the fontanel there will be microcaffalis (small head size) & abnormal brain development are associated with a small fontanel or early fontanel closure which induces mental retardation
*But if there were delayed closure this may be due to growth retardation or in the case of hydrocaffalis may be caused by high levels of CFS in the ventricles ,so we will have increased brain size and delayed closure of the fontanels
C) Foramina:
Located in the parietal bone so called parietal foramina transmitting emissary veins which allow for communication between extracranial &intracranial veins
SCALP:
It is the soft tissue which covers the Norma verticalis and extends anteriorly to the eyebrows & posteriorly to the highest mucal line (found in the Norma occipitalis )
Layers of the scalp :
Formed by 5 layers which are (from outside to inside) :-
1-skin
2-connective tissue
3-Aponeurosis (epicranial )
4-loose connective tissue
5-Pericranium
Use the word ((SCALP))as a key to memorize the order of the layers
In detail,
1- Skin: contains hair follicles
2-connective tissue: dense fibrous tissue that contains superficial blood vessels.
It is firmly adherent to the layers superficial and deep to it so from the surgical point of view the first 3 layers are categorized as a single layer
Also the dense fibrous tissue is firmly adherent to the adventitia of the blood vessels keeping them permanently opened. So, in case bleeding occurs the blood vessels can’t constrict to stop the bleeding and perfused bleeding results
3-Aponeurosis: the only muscular layer in the scalp. It’s also called Galia Aponeurotica
4-Loose areolar connective tissue: (Dangerous area of the scalp) this is the only layer where distesion may occur so collection of inflammatory exodate and pus occurs in this layer
Veins passing through this layer can pass infection form outside the scalp to the inside (reason for being a dangerous zone)
5- Pericranium: periosteum covering outer surface of the skull
Occipto-frontalis muscle:
It consists of four bellies: two frontal &two occipital bellies
Origin:
Frontal bellies: originate from the skin above the eyebrows ( no bony attachment)
Occipital bellies: originate from the highest mucal line in the occipital bone (bony attachment)
Insertion:
The two bellies join and insert in the aponeurosis (the third layer of the scalp) or the galia aponeurotica
Action:
The main action of this muscle is made by the frontal bellies
This is because the frontal bellies are larger
The action is forming transverse wrinkles in the forehead and raising the eyebrows
Nerve supply:
Supplied by the facial nerve (cranial nerve no. 7)
The frontal belly is supplied by the temporal branch of the facial nerve
The occipital belly is supplied by the posterior auricular branch of the facial nerve
*the facial nerve exits the skull and passes to the parotid gland then divides into 5 branches.
Arterial supply of the scalp:
All the head and neck is supplied by the common carotid arteries
The common carotid arteries originate from the brachiocephalic artery (right) and the left common carotid both of which are branches of the arch of the aorta
The right and left common carotid arteries are the further divided into
External carotid artery: supplies structures outside head and neck
Internal carotid artery: supplies structures present inside the skull
For the scalp, we’ve 5 arteries on each side.
From the midline outwards:
1-supratrochlear artery (from inside orbit, turns around a cartilage trochlea)
2-supraorbital artery (from inside orbit)
3-superficial temporal artery
4-posterior auricular artery (behind the ear)
5-occipital artery
The first and second arteries are branches of internal carotid artery (inside orbit)
The last three pass outside the skull and are branches of external carotid artery
Innervation of the scalp:
We’ve 10 nerves on each side
5 in front of the auricle and 5 behind the auricle
The nerves in front or behind the auricle consist of 4 sensory nerves and 1 motor nerve
Motor innervation:
In front of the ear: temporal branch of the facial nerve (innervating frontal bellies)
Behind the ear: posterior auricular branch of the facial nerve (innervating occipital bellies)
Sensory innervation:
In front of the ear: (anterior to posterior)
supratrochlear nerve (innervating stem)
supraorbital nerve(innervating stem)
zygomaticotemporal nerve (innervating non hairy area of the temple )
auriculotemporal nerve (innervating hairy area of the temple )
*zygoma: cheek bone
Behind the ear:
great auricular nerve (root value c2+c3)
lesser occipital nerve (root value c2)
great occipital nerve (root value c2)
third occipital nerve (root value c3)
*All sensation in front of the auricle are carried by branches of the trigeminal nerve (cranial nerve no. 5)
All sensation behind the auricle are carried by branches of the cervical nerves
*All spinal nerves are divided into anterior rami (innervating the body) and posterior rami (innervating back)
The great auricular nerve &lesser occipital nerve originate from ventral rami
The great occipital nerve &third occipital nerve originate from posterior rami (back)
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CORRECTION: HANEEN NIDAL EL-DALI
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