Skull and cranial cavity Flashcards
- Describe the arrangement of the layers of the meninges - Explain the locations and flow of blood in the dural sinus - Describe the blood supply to the brain - Explain the clinical consequence of interruption or damage to the venous or arterial blood supply to the head and brain
Layers of the scalp
S C A L P
From superficial to deep:
S-Skin
C- Connective tissue, dense.
A- Aponeurotic layer.
- When lacerated, loses the scalp anchoring properties.
- Connects frontalis to occipitalis.
L- Loose connective tissue.
- Separates upper three layers from pericranium.
P- Pericranium
Innervation of the scalp
Innervated by the trigeminal nerve (CN V) and spinal cutaneous nerves.
Function of meninges
Protection of the brain.
Supports network of blood vessels.
Forms fluid filled cavity to cushion and nourish the brain.
Dura mater
Outermost layer of the meninges that surrounds brain and spinal cord
Divided into two layers:
- Endosteal (outer), lines the skull.
- Meningeal (inner)
Dural sinuses forms between both layers.
Nervous supply to the dura mater
CN V- trigeminal
CN X- vagus
C1-3, sympathetic supply
Blood supply of the dura mater
- Source
- Branches
Middle meningeal artery
- Branch of maxillary artery
Branches into anterior and posterior middle meningeal artery.
Meningeal layer of the dura
Innermost dura mater layer that folds to form septa.
- Folds helps to restrict movement of the brain
Folds:
- Falx cerebri
- Tentorium cerebelli
- Falx cerebelli
Falx cerebri
A fold in the meningeal, dura mater that separates the cerebral hemispheres.
Tentorium cerebelli
A fold in the meningeal, dura mater that separates the cerebral hemispheres from the cerebellar hemispheres.
Falx cerebelli
A fold in the meningeal, dura matter that separates the cerebella hemispheres.
Dura anatomical basis of headaches
Caused by the dura’s sensitivity to stretching.
Extradural haematoma
A collection of blood between the inner skull surface and the endosteal layer of the dura mater.
Can be caused by damage to the middle meningeal artery.
Tentorial herniation
- Mechanism
- Causes
When a part of the brain is squeezed through the tentorium cerebelli due to an increase in intracranial pressure.
- Herniation in temporal lobe
Increase in ICP can be caused by a space occupying lesion like a brain tumour or intracranial haemorrhage.
Arachnoid mater
The middle layer of the meninges.
Avascular layer, contains projections (arachnoid granulations) to transfer CSF to venous sinuses.
Subarachnoid space contains CSF which protects brain from mechanical force.
- This is also the space where structures to and from the brain pass through.
Layers of the meninges
Dura (hard) mater- outermost
Arachnoid mater- middle
Pia (soft) mater- innermost
Cerebrospinal fluid (CSF)
Fluid produced by specialised ependymal cells in the choroid plexus in brain ventricles.
Found in the brain and spinal cord.
- Absorbed by arachnoid granulations in the meninges
Provides buoyancy in the subarachnoid space which protects agains mechanical force.
Pia mater
Innermost, soft, layer of the meninges.
Follows the brain gyri and sulci.
Very vascular structure that forms part of the cerebral arteries entering the brain.
Spinal cord meninges
3 layers that form part of the spinal nerve roots:
- Dura mater (only the meningeal layer)
- Arachnoid mater
- Pia mater
Leptomeningitis
Infection and inflammation in the leptomeninges (arachnoid and pia mater).
Can cause septicaemia if infection enters subarachnoid space and consequently into the blood.
Dural sinuses
Venous channels between the layers of the dura.
- Contains drained blood and CSF from the brain and cerebral veins.
- Drains into the IJV.
Communicates with the veins of the skull and scalp.
Contains no valves or SM- just a thick endothelial wall.
Blood supply to the brain
Main branches:
- Internal carotid, from common carotid artery
- Vertebral artery, from subclavian.
Circle of Willis is formed from their anastomose.
Anterior and middle cerebral arteries- terminal branches
Vertebral artery
Supplies the brain, branches from the subclavian.
Passes within cervical vertebrae and enters through foramen magnum.
Unites to form basilar artery.
Circle of Willis
Anastomose of 2 internal carotid arteries with 2 vertebral arteries.
ICA connects to the posterior cerebral artery by the posterior communicating artery.
Anterior communicating artery connects anterior cerebral arteries together.
Anterior cerebral artery
- Source
- Supply
Source- Internal carotid artery
Part of Circle of Willis
Supplies medial and superior surfaces of the brain + frontal pole
Middle cerebral artery
- Source
- Supply
Source- internal carotid
Supplies- lateral surfaces and the temporal pole.
Posterior cerebral artery
- Source
- Structure
- Supplu
Source- Basilar artery
Part of Circle of Willis- connects to MCA and ICA via posterior communicating artery.
Supplies- inferior surfaces and occipital pole.
Occlusion of vertebral/ ICA
Causes mixing of blood in posterior communicating artery.
- Blood passes back and forth to compensate lack of blood flow.
Neurocranium
The cranium, composed of 8 bones:
- Frontal
- Parietal x2
- Temporal x2
- Occipital
- Ethmoid
- Sphenoid
Intra-sutural bones can appear- extra bones
Viscerocranium
The facial bones: 14
- Nasal 2x
- Maxilla 2x
- Zygomatic 2x
- Nasal conchae x2
- Palatine x2
- Lacrimal x2
- Mandible
- Vomer
Skull
Composed of the cranium (neurocranium) and the facial bones (viscerocranium).
22 bones in total.
Protects the brain and allows attachment for muscles of the face and head.
Cribiform plate
Part of the ethmoid bone
Foramen in the skull that supports the olfactory bulb.
Optic canal
Formed from the sphenoid bone.
Passageway for:
- Optic nerve
- Ophthalmic artery
Superior orbital fissure
Opening of the skull, in the sphenoid bone.
Many structures pass through.
Foramen rotundum
Opening of the skill of the sphenoid bone.
Maxillary nerve of the trigeminal nerve passes through.
Foramen ovale
Opening of the skull in the sphenoid bone.
- Mandibular nerve of CN V passes through.
Foramen spinosum
Opening of the skull in the sphenoid bone.
Passageway for:
- The middle meningeal artery
- Middle meningeal vein
- Meningeal branch of the mandibular nerve.
Internal acoustic meatus
Foramen of the temporal bone.
Passageway fron CN VII and VIII (Facial and vestibulocochlear)
Foramen magnum
Foramen of the occipital bone.
- Passageway for CN XI (accessory)
- Meninges
- Medullar oblongata
Hypoglossal canal
Foramen in the occipital bone
Passageway for CN XII (hypoglossal)
Jugular foramen
Foramen in the temporal bone.
Passageway for nerves IX, X and XI (glossopharyngeal, vagus and accessory)
Foramen lacerum
Foramen in the sphenoid bone
Opening for the internal carotid artery.
Stylomastoid foramen
Opening in the temporal bone.
Passageway for facial nerve (CN VII)
Middle meningeal artery
Supplies the dura mater
Source: Internal maxilla artery
Foramen: Foramen spinosum
Superior sagital sinus
Dural sinus at the superior border of the flax cerebri
Straight sinus
Dural sinus at the falx cerebri and tentorium cerebelli junction.
Drains into the right and left transverse sinus
Receives blood from:
- Inferior sagittal sinus
- Great cerebral vein
Inferior sagittal sinus
Dural sinus at the inferior margin of the flax cerebri.
Drains into the straight sinus.
Transverse sinus
Dural sinus at the posterior and lateral attachments of the tentorium cerebelli.
Drains
Transverse sinus
Dural sinus at the posterior and lateral attachments of the tentorium cerebelli.
Drains from confluence of sinuses and superior posterior sinus.
Drains into sigmoid sinus.
Sigmoid sinus
Dural sinus at the groove of the occipital, temporal and parietal bones.
Drains from the transverse sinus into the internal jugular vein.
Fontanelles
Soft membraneous gaps between sutures in infants.
- The brain expands faster than the skull can grow.
- Provides space for the brain to expand.
Posterior fontanel
Also called
- Lambdoid
- Occipital
Triangular shaped Fontanel formed at the junction between the sagittal and lambdoid suture
Anterior fontanel
Also called:
- Bregmatic
- Frontal
Diamond shaped, between the coronal and sagittal sutures.
Persists until 18 months after birth.
Function:
- Allows the deformation of the skull during childbirth.
- Expansion of the brain after birth.
Clinical significance of fontanelles
Sunken fontanelles= dehydration
Tense/ bulging anterior fontanelle= raised inter cranial pressure
Sphenoidal fontanelle
Also called the anterolateral fontanelle
Located between these bones:
- Frontal
- Sphenoidal
- Parietal
- Temporal
Mastoid fontanelle
Also called the posterolateral fontanelle
Located between these bones:
- Temporal
- Occipital
- Parietal bone
