Skull and Scalp Flashcards
Outline the functions of the skull.
- houses brain, special sense organs, upper airways and proximal GIT
- provides surfaces for muscular attachments
- facilitates mandibular movements for mastication and speech
The skull without the mandible is called __________.
cranium
The cranium may be subdivided into 2 regions. Name them.
Neurocranium/cranial vault
Viscerocranium/facial skeleton
The neurocranium may be subdivided into two parts, the calvaria (skull cap) and the skull base. Compare them in terms of shape and mode of ossification.
The calvaria are flat bones, formed by intramembraneous ossification (hence may be called membranous neurocranium). Most of them consist of two tables and a diploe.
The bones of the skull base are relatively thicker and are formed by endochondral ossification (hence may be called cartilaginous neurocranium).
Name the four paired paranasal sinuses. (Named according to bones that house them)
maxillary, frontal, ethmoid and sphenoid
Briefly explain three sutural morphologies.
- Interlocked (serrated): has numerous projections that interlock
- Simple (butt-end): the margins of adjacent bones are smooth and meet end-to-end
- Overlap (beveled): border of one bone overlaps the adjacent bone
Identify unique features of the fetal/neonate skull.
- presence of fontanelles
- wider and more sutures
- unilaminar calvarial bones (no diploe)
- prominent frontal and parietal eminences [Diagram]
- relatively large orbits
- contracted (relatively small) viscerocranium due to underdeveloped sinuses
- unerupted teeth and absent alveolar processes (horizontal portion of maxilla that holds the tooth roots)
- rudimentary paranasal sinuses
- cranial base is relatively narrow, short and largely cartilaginous
- ununited bony parts eg. parts of temporal bone
- short, straight and wholly cartilaginous external acoustic meatus
- undeveloped parts: glabella, mastoid process and superciliary arches
- unique mandibular morphology
What is the unique mandibular morphology in neonates? (Hint: consider symphysis menti, the mandibular angle, coronoid and condylar processes, mental foramen)
- right and left mandible is separated by symphysis menti, which is absent in adults
- mandibular angle is obtuse
- The coronoid process is slightly lower than the condylar process. As a person grows, the coronoid process elevates itself quite significantly.
- the mental foramen lies nearer to the base of mandible in children, nearer to the alveolar margin in old people, and midway in adults
What are the extents of the scalp?
Anteriorly: superciliary arches
Posteriorly: superior nuchal lines
Laterally: external acoustic meatus and zygomatic arch
List the layers of the scalp from superficial to deep.
- skin
- subcutaneous dense connective tissue
- the occipitofrontalis muscle (epicranius) and its aponeurosis (galea aponeurotica)
- subaponeurotic loose connective tissue
- pericranium (periosteum of the skull)
Name the two main arteries involved in the blood supply to the scalp as well as their branches.
- Ophthalmic branch of internal carotid artery; gives supratrochlear, supraorbital arteries
- External carotid artery; gives superficial temporal artery, posterior auricular artery, occipital artery
- [Diagram: arteries of the scalp]
They form a rich anastomosis within the dense connective tissue layer of the scalp.
Why do scalp wounds bleed profusely?
- The blood supply to the scalp is made up of many anastomoses.
- The blood vessels to the scalp are adhered to dense connective tissue, preventing the vasoconstriction that normally occurs in response to damage.
- If a deep transverse cut on the skull reaches aponeurosis, frontalis and occipitalis will contract and hence aponeurosis will pull apart.
Why do scalp wounds heal faster?
The scalp is richly vascularized.
Why are scalp wounds often related to menengitis?
(HINT: Think about the bacteria due to the scalp wound. What does it do?)
Bacteria introduced into the scalp through a scalp wound can be transported through emissary veins to the meninges where they may cause meningitis.
What is the clinical relevance of the skin of the scalp?
It has numerous sebaceous glands, hence is a common site for sebaceous cysts.
What is the clinical relevance of the aponeurosis of the scalp?
Wounds on the scalp gape when the aponeurosis is cut transversely. Occipitalis and frontalis will contract hence pulling apart the aponeurosis. This may also contribute to profuse bleeding.
What is caput succedaneum?
This is the swelling/edema of the scalp of a newborn, most often brought by pressure from the uterus or vaginal wall during a head-first delivery. There is reduced venous return, hence accumulation of fluid within the scalp tissues.
State the clinical relevance of the anterior fontanelle in neonatal skulls.
- It can indicate the degree of intercranial pressure (if elevated, anterior fontanelle will bulge and hence we see that in meningitis or in hydrocephaly).
- It can be used as an acoustic window to perform cranial ultrasound.
- It permits access to the superior sagittal sinus.
- Through its lateral angle a needle may be passed into the lateral ventricles of the brain.
What are the regions of the foetal skull?
- Face
- Brow
- Vertex (best type of presentation for delivery since the suboccipito-bregmatic diameter [9.5 cm] is less than diameter of maternal pelvis [10 cm] hence less tedious in terms of vaginal delivery)
- Occiput
Appreciate these regions on a diagram.
Base of the cranial cavity is divided into 3 different fossae. Name them.
Anterior fossa
Middle fossa
Posterior fossa
What does the cranial cavity house?
the brain, meninges, the intracranial portions of cranial nerves, blood vessels and CSF
How can the skull be used as identification in medical legal aspects?
- Determination of sex
- Determination of chronological age
- Determination of racial origin
- Facial approximation
State the sensory innervation of the scalp.
Anterior division receives innervation from CN V
Ophthalmic nerve,
- Supratrochlear nerve
- Supraorbital nerve
Maxillary nerve,
- Zygomaticotemporal nerve
Mandibular nerve,
- Auriculotemporal nerve
Posterior division receives innervation from cervical nerves.
- greater occipital nerve (from dorsal rami of C2)
- third occipital nerve (from dorsal rami of C3)
- lesser occipital and greater auricular (from cervical plexus)
- The cribriform plate is a part of which bone?
- Name the structure that passes through the cribriform plate.
- ethmoid bone
- CN I (olfactory nerve)
Which bone forms the optic canal? Name the structures that pass through the optic canal.
- lesser wing of sphenoid bone
- ophthalmic artery, CN II (optic nerve)
- State the boundaries of the superior orbital fissure.
- What structures pass through the superior orbital fissure?
- greater and lesser wings of sphenoid
- CN III (oculomotor nerve)
- CN IV (trochlear nerve)
- CN VI (abducens nerve)
- CN V1 (ophthalmic nerve - first division of trigeminal nerve)
- superior ophthalmic vein
- State the boundaries of the inferior orbital fissure.
- State the structures that pass through the inferior orbital fissure.
- greater wing of sphenoid bone, zygomatic bone and maxillary bone
- zygomatic nerve [this is a branch of the maxillary division of the trigeminal nerve]
- infraorbital nerve and vessels [infraorbital nerve is the terminal branch of the maxillary nerve]