Lecture 2: Skull plus others Flashcards
How do the vertebral arteries course to the brain?
Come off the subclavian arteries
Travel through vertebral processes of spine
Pass through foramen magnum into cranial cavity
At what level do the internal carotids branch off the common carotids?
C3
What is the carotid sinus?
Bulge in the common carotid, the point at which the internal carotid branches off
How does the internal carotid course to the brain?
Branches off common carotid
Ascends in carotid sheath into carotid canal, posterior to the external carotid - travels forward and comes out of the carotid canal (not foramen lacerum)
Passes through the cavernous sinus (a venous plexus) and emerges inferior to the optic nerves on ventral surface of the brain
Where does the internal carotid emerge in the brain?
Inferior to the optic nerves on the ventral surface
Which venous plexus does the internal carotid and some important nerves pass through and what is the clinical significance of this?
Cavernous sinus
Infection can lead to swelling of cavernous sinus which can squash these nerves aswell as the internal carotid
Which artery does the posterior system in the brain come off?
Vertebral arteries
Which artery does the anterior system in the brain come off?
Internal carotid
The ventral surface of the brain is actually what surface in situ?
The inferior surface
Which sulcus does the middle cerebral artery run in?
The lateral sulcus
Which part of the cerebellum does the posterior inferior cerebellar artery supply?
The posterior inferior part
Which part of the cerebellum does the anterior inferior cerebellar artery supply?
The anterior inferior part
What is the course of the anterior cerebral once it has come off the middle cerebral?
Goes into the longitudinal fissure
Travels anteriorly then loops posteriorly to supply the medial and superior part of the frontal and parietal lobe
What does the anterior cerebral artery supply?
Medial and superior part of the frontal and parietal lobes
What does the middle cerebral artery supply?
Lateral aspect of the cerebral hemispheres
What does the posterior cerebral artery supply?
Runs posteriorly to supply the occipital lobe and the lower part of the temporal lobe
What artery does the posterior spinal arteries branch off and where do they run?
Come off the posterior inferior cerebellar arteries and run along the posterior surface of the spinal cord
Give 5 functions of the skull?
1) Protects the brain
2) Helps to shape the face
3) Supports other structures eg. eyes
4) Channels of the upper airway are bounded by the skull
5) Use the skull to chew food (mandible is part of the skull)
Although the skull protects the brain what is the potential danger of the brain being in an enclosed space?
No room to expand - finite space, can put pressure on brain
Inside shape of the bones of the skull can cause lacerations to the brain
What are the 2 main sections of the skull?
Cranium
Mandible
What 2 parts is the cranium section of the skull made up of?
Viscerocranium
Neurocranium
Which 9 bones of the skull can be seen from a lateral view of the skull?
Frontal bone Occipital bone Temporal bone Parietal bone Maxillae (2 (R & L) bones fused in midline) Mandible Zygomatic bone Sphenoid bone Nasal bone
What is the anatomical name for the ‘eye sockets’?
Orbits
In which bone is the foramen magnum situated?
Occipital bone
The opening to the carotid canal is found in what bone?
Temporal bone
Which bone of the skull contributes to the hard palate?
Maxilla
What are the cranial fossae?
3 regions at the cranial base
Like 3 steps
Have an anterior fossa, a middle fossa and a posterior fossa
What are the 3 foramen found in the sphenoid bone in the cranial base and where are they roughly situated relative to eachother?
1) Foramen rotundum (most anterior - circular shaped)
2) Foramen ovale (posterior medial - oval shaped)
3) Foramen spinosum (posterior lateral)
What parts of the nasal cavity does the ethmoid bone contribute to?
Forms the roof, lateral walls and medial wall of nasal cavity
What is the ciribiform plate?
Part of the ethmoid bone
Has lots of small holes in it through which the nasal nerves pass
What is the most common joint in the skull?
Suture
What is meant by osteogenic?
Produces more bone
How many layers make up a suture and what is the rough structure?
5 layers
Osteogenic layer covered by periosteum, seperated by a central connective tissue layer
How are sutures an important site of cranial growth?
Growth at the bone edges displaces bone away from the suture
What is meant by ossification of sutures in the brain?
Fusion
In which decade of life does ossification of cranial sutures occur?
3rd - 20s
On which surface does ossification of sutures first begin (deep or superficial) and which suture tends to be affected first?
Deep surface
Sagittal suture is usually the first affected
Can ossification of cranial sutures be used to determine age in a post mortem?
No it is too variable
What is craniosynostosis?
Premature sutural fusion
What does craniosynostosis lead to? 4
Often leads to brain being small
Can cause abnormalities in head shape
raised intracranial pressure
Cognitive defects
What is the treatment for craniosynostosis?
Extensive surgical remodelling of the cranial vault
Through what foramen in what bone does the middle meningeal artery pass into the cranial cavity?
Foramen spinosum in the spenoid bone
What is the pterion and why is it clinically significant?
Site on the temporal bone where 3 sutures meet to make a H shape
This is an area of weakness and the middle meningeal artery runs medial to the pterion, and damage to the middle meningeal artery is associated with extradural haemorrhage
What are the 2 main parts to the mandible?
1) Ramus of the mandible
2) Body of mandible
Which 2 processes are found on the ramus of the mandible?
Condylar process - more posterior
Coronoid process - more anterior
Which 2 bones make up the temporomandibular joint?
Condylar process of the ramus of the mandible
Temporal bone
What is the action of the temporomandibular joint?
An anterior and posterior sliding action
In which direction do mandibles dislocate?
Anteriorly
What are the 4 sinuses in the skull?
1) Frontal
2) Maxillary
3) Sphenoid
4) Ethmoid
The pituitary gland lies superior to which sinus?
Sphenoid sinus
By which route is a pituitary tumour normally removed?
Transphenoidal route
Through the nasal cavity
What is a blow out fracture of the orbit?
Object hits the eye, puts pressure on it, this increases the intraorbital pressure which blows out the small delicate bones beneath the eye ball
What are the 3 le fort fractures?
1) Just maxilla separated
2) Maxilla and nasal area separated
3) Whole of viscerocranium separated
Give the 3 general functions of the brain stem?
1) Conduit - allows ascending and descending pathways to reach the thalamus and cerebellum from spinal cord
2) Integrative - contains the respiratory and cardiovascular centers and has a role in conciousness
3) Cranial nerves - originate from here, they are the heads equivalent to spinal nerves and have a role in sight, hearing and gustation
What lies in the gap between the 2 thalami?
The 3rd ventricle
What is the cerebral aqueduct?
Connects the 3rd and 4th ventricles
What are the caudal, rostral, ventral and dorsal relations of the brainstem?
1) Caudally it is continuous with the spinal cord
2) Rostrally it is continuous with the diencephalon
3) Ventrally lies the clivus of the occipital bone
4) Dorsally lies the cerebellum
How many cranial nerves are there and how many arise from the brainstem?
There are 12
10 arise from the brainstem
Which 2 cranial nerves do not arise from the brainstem and where do they arise from?
The olfactory (CN 1) and the optic (CN 2) Arise from the forebrain
What main structures are visible on the ventral surface of the medulla?
The pyramids
The olives
What main structures are visible on the ventral surface of the brain stem?
The pyramids and olives of the medulla
The rounded pons
The cerebral peduncles
What is the name of the junction which seperates the medulla and the pons?
The pontomedullary junction
What seperates the 2 pyramids?
The anterior median fissure
What is the decussation of the pyramids, how does it appear in a specimen?
Crossing over of fibres from the pyramids to the ipsilateral side, appears as a blurring or interruption of the anterior median fissure
What do pyramids contain?
Corticospinal tracts
Contain descending motor fibres
What is the name of the sulcus separating the pyramids from the olives?
Anterolateral sulcus
What is the name of the sulcus emerging dorsal to the olives?
Posterolateral sulcus
Which cranial nerve emerges from the anterolateral sulcus?
Hypoglossal CN XII
Which cranial nerves emerge from the posterolateral sulcus?
Vagus CN X
Glossopharyngeal CN IX
What is the name of the space inbetween the 2 cerebral peduncles?
Interpedunculer fossa
Which cranial nerve emerges from the interpeduncular fossa?
Occulomotor nerve CN III
What is the name of the sulcus seperating the pons from the medulla?
Pontomedullary sulcus
The basillar artery is formed level with what?
The pontomedullary sulcus
What structures can be seen if the cerebellum is removed on the dorsal surface of the brain stem?
The superior and inferior colliculi of the midbrain
The floor of the fourth ventricle
The cerebellar peduncles (specifically the middle one)
The gracile fascicle and tubercle
The cuneate fascicle and tubercle
What 2 parts does the 4th ventricle divide the medulla into?
Open (rostrally) - no central canal, opens out into 4th ventricle
Closed (caudally) - central canal
What is the anatomical name for the floor of the 4th ventricle?
Rhomboid fossa
What is contained in the fascicles and what is contained in the tubercles?
Fascicles - nerve axons
Tubercles - cell bodies
What info is generally carried in the cuneate and gracile fascicles?
Part of the dorsal column pathway - sensory info from the body to brain
Superior colliculus is involved in what?
Vision
The inferior colliculi are involved in what?
Hearing
What is meant by tract/fascicle/lemniscus/peduncle?
Simply means a bundle of white matter
What is the name of a collection of cell bodies in the CNS? And the PNS?
CNS - nucleus
PNS - ganglion
The cerebrum passes info to the cerebellum via which cerebellar peduncle?
The middle cerebellar peduncle
Info from the spinal cord passes to the cerebellum via which cerebellar peduncle?
The inferior cerebellar peduncle
Info is passed from the cerebellum to the cerebrum via which cerebellar peduncle?
The superior cerebellar peduncle
Which cranial nerve is the only cranial nerve to emerge from the dorsal surface of the brainstem and what does it supply?
CN IV - Trochlear nerve
Controls one muscle that moves the eye
What are the caudal and rostral relations of the pons?
Caudally - medulla (pontomedullary junction)
Rostrally - midbrain (pontomesencephalic junction)
A midline groove can be seen on the pons from a ventral view of the brainstem, what is this groove for?
The basillar artery
Where does the trigeminal nerve emerge from?
Mid pontine level
Which nerve emerges from the pontomedullary junction?
Abducens CN VI
Which 2 nerves emerge from the cerebellopontine angle?
Facial CN VII
Vestibulocochlear CN VIII
What is the main feature of the pons when the brainstem is viewed from a dorsal view?
The Cerebellar peduncles
What forms the roof of the 4th ventricle?
The superior cerebellar peduncle
What is the basis pedunculi?
Another word for cerebral peduncle
Which nerve emerges inferior to the inferior colliculi?
The trochlear nerve CN IV
Which structure does the cerbral aquaduct run through?
The midbrain
What is the tectum and where is it found?
Found posterior to the ventricular system
Made up of the superior and inferior colliculi
Found only at the level of the midbrain
What forms the roof of the cerebral aquaduct?
The tectum
Where does the tegmentum lie and where is it found?
Lies anterior to the ventricular system
Found at level of midbrain, pons and medulla
What is contained within the tegmentum?
Cranial nerve nuclei and tract
Reticular formation
Some ascending and descending pathways
Where can the red nucleus and the substantia nigra be found?
In the tegmentum
What does the basal part of the brainstem contain?
Descending fibres from the cerebral cortex
pyramids, cerebral peduncles
What is the main difference seen in cross section of the open and closed medulla?
Closed medulla has a central canal
Open Medulla has no central canal, it is open at the back where the 4th ventricle lies
In cross section will olives be seen in the caudal or rostral medulla?
In the rostral medulla
When the brainstem is viewed at the level of the pons what are the main structures that can be seen?
1) The 4th ventricle
2) Middle cerebellar peduncle
3) Basal pons
4) Groove for basilar artery
What structures can be seen when the closed medullar is viewed in cross section?
Central canal
Cuneate and gracile fascicles dorsally
Pyramids ventrally
Where does the reticular formation lie?
Within the tegmentum of the brain stem
What is the reticular formation?
Not well understood
Complex, multisynaptic network of neurons
What 3 things does the reticular formation include?
1) Reticular nuclei - gives rise to a descending motor pathway - reticulospinal tract
2) Vital autonomic centers - eg. respiratory and cardiovascular
3) Cells giving rise to the Ascending Reticular Activating System (ARAS) - pass to the cortex and involved in conciousness
As well as conciousness and autonomic centers what 3 other things is the reticular formation involved in?
1) Modulates pain
2) Sleep wake cycle
3) Arousal
What is the basal pons?
Its the anterior portion to the pons
What structure within the 4th ventricle forms the CSF?
The choroid plexus
What are the structures at which the cuneate and gracile fascicle terminate called?
The cuneate and gracile tubercle
What is the shape of the cut inferior cerebellar peduncle?
A crescent shape
What is the name of the apex of the cerebellum on its superior surface?
The vermis
What are the 3 lobes of the cerebellum and from which surface can they be seen?
The anterior, middle and posterior lobes
Seen from the superior surface
On what do the bulbs of the olfactory nerves sits?
The ciribiform plate
Which 5 major subdivisions of the brain make up the brainstem?
The midbrain, pons and medulla
What information is carried in the nerve fibres that make up the pyramids?
Motor info, involved in voluntary movements
Where does the median sulcus/median longitudinal fissure lie?
In the midline in the floor of the 4th ventricle
In which region of the brainstem is the central canal expanded to form the fourth ventricle?
Rostral medulla + pons
What structure sits on the roof of the 4th ventricle?
The cerebellum
