Anatomy of the CNS and Skull

Question 1

What are the two broad categories of bone in the skull?

Answer 1

1. Cranium
   * The bones that form the cavity for the brain
2. Facial
   * Bones forming the orbit, mouth and jaws

Question 2

Describe the layers of bone that comprise the skull

Answer 2

The skull is comprised of three layers of bone. Two layers of compact bone on either side of a layer of **spongy cancellous bone **

Question 3

Cite the bones and sutures that comprise the calvaria (skull cap).

Answer 3

Four bones make up the calvaria: Frontal bone, Left and Right Parietal Bones and Occipital Bone.

The coronal suture is anteriorly located in the coronal plane, joining the frontal bone and left and right parietal bones.

The sagittal suture is located in the sagittal plane seperating the left and right parietal bones

The lamboid suture is located posteriorly on the calvaria, seperating the parietal bones anteriorly and the occipital bone posteriorly.

Question 4

What is the Pterion?

Answer 4

The pterion is a set of immobile joints on the lateral skull between frontal, parietal, temporal and sphenoid bones.

The joints form a H-shaped suture patterns.

The middle meningeal artery (MMA) follows the border of the sphenoid bone in this region and is endangered by fractures of the pterion.

Question 5

At what landmark does the horizontal part of the frontal bone project posteriorly?

Answer 5

The **supra-orbital region **demarcates the point at which the horizontal portion of the frontal bone projects posteriorly and sits at the floor of the cranial cavity.

Question 6

Describe the temporal bone

Answer 6

The temporal bone is a flat bone with a number of projections.

The flat part of the bone is known as the squamous part of the temporal bone. There are four projections from the temporal bone:

• **Zygomatic process **articulates with the zygoma/cheek bone
• **Mastoid process **is a thick bony process that projects posteriorly and takes attachment of the sternocleidomastoid muscle
• **Styloid process **is a sharp process that projects inferiorly deep to the mastoid process
• **Petrous process **projects into the cranial cavity and forms part of the cranial floor

Question 7

Describe the Occipital Bone

Answer 7

The occipital bone is a flat bone with a sharp external **occipital protruberance **posteriorly

Question 8

Describe the sphenoid bone

Answer 8

The sphenoid bone sits posterior to the frontal bone, anterior to the occipital bone and medial to both the parietal and temporal bones.

It has a depression in the **body **of the sphenoid bone where the pituitary gland is positioned

The **superior-orbital fissure **divides the lesser wing (anterosuperior) from the greater wing (posteroinferior)

Question 9

Describe the ethmoid bone

Answer 9

The ethmoid bone has a **cribiform **plate **that has perforations that transmits the oligofactory nerves

**Cristae galli **is a superiorly vertical projection running down the length of the middle of the bone.

Question 10

Do the cranial nerves originate within or outside the cranium?

Answer 10

Cranial nerves originate within the cranium and innervate a number of structures outside of the cranium

Question 11

Describe the three cranial fossae of the cranium

Answer 11

The three cranial fossae are tiered, sequentially descending posteroinferiorly.

The **anterior cranial fossa **supports the frontal lobe of the brain. It’s formed from the horizontal plate of the frontal bone, cribiform plate of the ethmoid bone and the **lesser wing of the sphenoid bone. **

The **middle cranial fossa **the temporal lobes of the brain. It’s formed from the greater wings of the sphenoid bone and temporal bones.

The **posterior cranial fossa **supports the occipital lobe of the brain. It is formed from the occipital bone.

Question 12

What structures transmit through deficiencies of the anterior cranial fossa?

Answer 12

Cribiform Plate = Olfactory Nerve

Question 13

What structures transmit through deficiencies of the middle cranial fossa?

Answer 13

Hypophysial fossa = Pituitary gland

Optic canal = Optic nerve

Superior orbital fissure = Nerves to extraoccular muscles and branches of the trigeminal nerve)

Foramen rotundum = Maxillary nerve

Foramen ovale = Manibular nerve

Foramen spinosum = Middle meningeal artery

Question 14

What structures transmit through deficiencies in the posterior cranial fossa?

Answer 14

Internal acoustic meatus = facial and vestibulocochlear nerves

Jugular foramen = IX, X, XI cranial nerves and internal jugular vein

Hypoglossal canal = hypoglossal nerve

Foramen Magnum = spinal cord and spine

Question 15

Annotate the image, identifying the foramen that transmit through the three fossae of the cranial cavity.

Answer 15

Question 16

What are the three layers of the meninges?

Answer 16

In order of superficial to deep:

Dura mater, arachnoid and pia mater

Question 17

What are dural septa?

Answer 17

Dural septa are partitions of the dura mater that project into the major fissures and divisions of the brain.

They prevent rotational displacement of the brain

There are 4 septa:

Falx cerebri, tentorium cerebelli, falx cerebelli and diaphragma sellae

Question 18

Describe the falx cerebri

Answer 18

The falx cerebri is a dural septa in the sagital plane.

It attaches to the christae galli anteriorly, the inferior aspect of the skull linearly and attaches to the anterior aspect of the **occipital protruberance **

Question 19

What is the tentorium cerebelli?

Answer 19

The tentorium cerebelli is a dural septa that rooves over the posterior cranial fossa

It seperates the occipital lobes of the cerebral hemispheres superiorly from the cerebellum inferiorly.

It is a ‘horizontally’ planed dura septa that is shaped like a ‘comma’

Question 20

What is the falx cerebelli?

Answer 20

The falx cerebelli is a vertically orientated dural septae that projects upwards from the posterior cranial fossa the between the hemispheres of the cerebellum.

Question 21

What is the diaphragma sellae?

Answer 21

The diaphragma sallae overlies the pituitary gland that sits in the depression of the sphenoid bone body

Question 22

How many layers of dura mater are present in the skull?

Answer 22

There are two layers; an inner and outer layer.

These two layers are normally positioned together to form a collective thick layer of dura mater.

When these two layers split, they give rise to dural septa that invaginate and adhere to the fissures of cerebral hemispheres

Question 23

What are dural venous sinuses?

Answer 23

Dural venous sinuses are formed by the splitting of the two dural layers in the formation of dural septa.

They are ‘lakes’ of blood and fluid that drain a number of strutures including diploic veins from skull spongy bone, emissary veins that drain the scalp and cerebral veins (?)

Emissary vein drainage hightens the risk of brain infections resulting from lascerations and injuries to the scalp

Question 24

Annotate the missing labels relating to cranial sinuses

Answer 24

Question 25

What is the cavernous sinus?

Answer 25

The cavernous sinus is fromed by the dura that surrounds the sphenoid bone. It is comprised by a number of sinuses collectively known as the cavernous sinus

It is not associated with any dural septa

It can drain fluids from the face via emissary veins - although this non-preffered.

Question 26

What is the confluence of sinuses?

Answer 26

A meeting of sinuses at the interior occipital protruberance.

Depending upon the individual, sinuses meeting here may meet and mix blood; in other people they may not.

The confluence gives rise to left and right transverse sinuses that run in the root of tentorium cerebelli

Question 27

Discuss the path of the transverse sinuses

Answer 27

The respective transverse sinuses are formed at the confluence of sinuses at the interior occipital protruberance.

It runs in the root of tentorium cerebelli to the edge of the petral bone (demarcating the edge of the middle cranial fossa).

The transverse sinus becomes the sigmoid sinus and down to the jugular foramen to exit as the internal jugular vein.

Question 28

Describe the importance and course of the middle meningeal artery (MMA)

Answer 28

The MMA is the largest and most crucial meningeal artery.

It is a branch of the maxillary artery that transmits through the foramen spinosum to enter the internal cranial cavity. It creates a groove in the bone that it transmits through.

It gives rise to multitude of other smaller meningeal arteries.

Question 29

In what plane do the meningeal arteries lie in?

Answer 29

Meningeal arteries run within the extra/epi-dural space

Epidural haemorrhages in this space are dangerous. Due to arterial pressure, blood is loss rapidly.

Epidural haemorrhages become less common in elder people as the dura mater layers increasingly adhere to the skull and decrease the epidural space.

Question 30

In what plane do the superficial cerebral arteries run within?

Answer 30

Superficial cerebral arteries run in the subdural space between the dura mater and arachnoid mater

Veinous haemorrhaging can occur into this space following trauma (including shaken baby syndrome). It is low pressure bleed with slow onset of symptoms. It is more common in the elderly.

Haemorrhaging blood can accumulate until it raises ICP to the point of severe damage/death

Question 31

List the functional roles of the spinal cord

Answer 31

1. Segemental reflexes, inter-segmental reflexes and pattern generation
2. Processing and transmission of somatosensory information (tactile and nociceptive)
3. Relay of descending motor command
4. Relay of descending autonomic commands

Question 32

At what vertebral level does the spinal cord terminate?

Answer 32

Spinal cord terminates at T-12

From T-12 - inferiorly, the **cauda equina **structure of long nerve roots from the lumbar and sacral nerves transmits spinal nerves to their respective vertebral foramen.

Question 33

What is the most common site for performing a lumbar puncture?

Answer 33

L3-4 is the most common site.

The spinal cord does not project this far down - therefore, minimal risk of damaging spinal cord; although spinal nerve are transmitting in this area in the cauda equina.

Question 34

What considerations are important to remember when viewing sections of the spinal column with CT imaging

Answer 34

CT images are viewed in the direction looking up from the feet towards the head in a prone position; this means the dorsal aspect of the spinal column is viewed inferiorly and the ventral aspect superiorly in 2D cross sections. This is inverted to the conventional way of looking at the spinal column from a superior view.

Additionally, white matter is darker than grey matter in CT imaging

Question 35

What does the grey matter and white matter represent in the spinal cord?

Answer 35

The grey matter represents the cell bodies of the neurons within the spinal cord. The dorsal parts of the grey matter are involved in sensory processing, while the ventral parts of the grey matter are involved in motor processing of the spinal cord.

The majority of white matter are nerve tracts that are descending or ascending in the spinal cord.

Question 36

What’s the difference between intraspinal communication and propriospinal connections?

Answer 36

Nothing - the two terms are synonymous

The terms describe the manner in which spinal cord segments communicate with each other via intraspinal/propriospinal tracts. These tracts do not project to/from the brain.

Question 37

Describe the organisation and distribution of a-motor neurons within the spinal cord

Answer 37

As a-motor neurons are involved in the motor processing pathways, the cell bodies of the a-motor neurons are located within the ventral aspect of grey matter within the spinal cord.

Broadly speaking, there are two bundles of a-motor neurons in the ventral horn: medial and lateral bundles.

a-motor neurons that innervate more distal structures as part of the spinal nerve are positioned more laterally; more proximal innervations are found medially.

Question 38

What constitutes a motor unit?

Answer 38

A motor unit is comprised of a single a-motor neuron and the multiple muscle fibres said motor-neuron innervates

Question 39

What constitutes a motor neuron pool?

Answer 39

A motor neuron pool is the collection of a-motor neurons that innervate a specific muscle.

Question 40

Describe the role and organisation of muscle spindles/intramural fibres

Answer 40

Muscle spindles/intramural fibres are modified muscle fibres encased within a connective tissue sheath and are positioned in parallel with extrafusal muscle fibres.

They monitor the amount of stretch within a muscle. They are engineered to detect muscle length; and, therefore, where in space skeletal elements are positioned (proprioreception)

Muscle spindles transmit sensory information via type 1 and type 2 sensory afferent nerve fibres (the fastest in the body).

They also recieve motor innervation via gamma-motor neurons in order to keep them in aligned and parallel with the surrounding extrafusal muscle fibres.

Question 41

Describe the role and organisation of golgi tendon organs

Answer 41

Golgi tendon organs detect and respond to force.

They are positioned within muscle tendons in order to be in series with muscle fibres.

Question 42

What is the difference between a mono-synaptic and poly-synaptic reflex?

Answer 42

Monosynaptic reflexes involve a single synapse within the spinal cord between a sensory afferent neuron and the motor neuron pool of the muscle in question.

Polysynaptic reflexes involve interneurons that allow a single sensory afferent neuron to influence multiple motor neuron pools with either an excitatory or inhibitory affect depending upon the interneuron involved.

Question 43

What is the cross extensor reflex?

Answer 43

The cross-extensor reflex occurs in response to noxious stimuli in the periphery.

The reflex involves activating flexor muscles ( and inhibiting extensors) of the limb incurring the noxious stimulant in order to withdraw from the stimulus.

For this to occur, simultaneous extension (and inhibition of flexors) of the opposite limb must occur to balance the body. This involves inter-neurons crossing to the opposite side of the spinal cord to activate a-motor neurons.

This reflex isn’t particularly important in humans - more important in quadrupeds.

Question 44

Discuss the organisational differences between short and long propriospinal neurons

Answer 44

Long propriospinal neurons are located medially and recieve bilateral input. They tend to spand **vast numbers of spinal segments **and are involved in the co-ordination of gross motor movements.

Short propriospinal neurons are located laterally and recieve ipsilateral input. They span only a few spinal segments. Given their lateral distribution, the lateral motor neurons that they are associated with are responsible for complex dextrous movements of distal innervations.

Question 45

What are upper motor neurons?

Answer 45

Upper motor neurons are any neurons that affect the excitability of lower motor neurons. Typically, they descend from the cortex, brainstem, etc.

Normally, most of the upper motor neurons innervate lower motor neurons via interneurons that are largely inhibitory - thus, a **basal inhibitive tone exists **that signals the spinal cord ‘not to do anything’

Upper motor neuron lesions/damage is characterised by a loss of inhibition downstream from the site of injury. Exaggerated and hyperexcitable motor output results.

Question 46

What are lower motor neurons?

Answer 46

Lower motor neurons lead out into the periphery from the spinal cord.

Question 47

Describe the location of the brainstem and the structures that comprise it

Answer 47

The brainstem is located in the **posterior cranial fossa **

It extends from the mamillary bodies rostrally to the pyramidal decussation caudally.

The brainstem is comprised of the midbrain, pons and medulla

Question 48

Describe the dorsal aspect of the brainstem

Answer 48

Midbrain:

• Two pairs of colliculi (superior and inferior pairs)
• Superior colliculi are important for eye movement control
• Inferior colliculi are important for hearing

Pons:

• Linked to the cerebellum by neural tracts
• Limited by the 4th ventricle
• Along the floor of the 4th ventricle are the facial colliculi formed by the abducens nucleus and CN VII.

Medulla:

• Dorsal columns project rostro-caudally
• Nuclei- gracile and cuneate tubercule lateral to the dorsal columns

Question 49

Describe the ventral aspect of the brainstem

Answer 49

Midbrain:

• Cerebral peduncles present - are giant white matter tracts that transmit from the motor cortex on each side (they ‘support’ the brain)
• **Interpeduncular fossa **lies between the two cerebral peduncles

_Pons: _

• Cerebellar peduncles (superior, middle and inferior) attach and transmit to cerebellum

Medulla:

• Olivary nuclei bulging at the rostral section of medulla
• Bilateral p**yramids **descend to the pyrimidal decussation

Question 50

What is the tectum?

Answer 50

The tectum is the dorsal aspect or roof of the midbrain. It projects over the aqueduct and fourth ventricle

It gives rise to colliculi dorsally at certain levels of the brainstem. These are the superior and inferior colliculi.

Question 51

What is the tegmentum?

Answer 51

The tegmentum is the central core of the pons, midbrain and contiguous portions of the medulla which contain ascending and descending tracts continuous with the spinal cord and higher brain.

It also contains the nuclei of cranial nerves III-XII and reticular formation.

The tegmentum lies dorsally to the other half of the brainstem core - the basis

Question 52

What is the basis?

Answer 52

The basis is the ventral portion of the brainstem core.

The basis is important for descending motor control. It transmits corticospinal tracts of the desceding motor pathways and in addition to connections with the cerebrum and other nuclei.

Question 53

At what regions of the brainstem do cranial nerves exit the brainstem?

Answer 53

The rule of four

4 cranial nerves exit the medulla:

• CN IX - XII

4 cranial nerves exit the pons:

• CN V - VIII

4 cranial nerves exit above the pons

• CN III - IV
• CN I - II exit within the brain itself - not the brainstem

Question 54

Where are the sensory and motor cranial nerve nuclei located?

Answer 54

Location of the motor and sensory columns are developmentally determined - in development they are located adjacent to the ventricular system.

Sensory nuclei develop from the Alar plate and motor nuclei from the basal plate.

This leads to cranial nerve motor nuclei positioning medially near the midline and sensory nuclei laterally in the tegmentum of the brainstem.

Question 55

What are the six columns that house cranial nerve nuclei?

Answer 55

There are three motor (medially) and three sensory (laterally) columns within the brainstem that house cranial nerve nuclei

The three motor columns:

• General somatic motor
• Branchial motor
• General visceral

The three sensory columns:

• General and special visceral
• General somatic
• Special somatic

Question 56

What and where is the reticular formation?

Answer 56

The reticular formation is found at every level of the brainstem and is comprised of millions of small neurons that communicate with both one-another and the cranial nerve nuclei to regulate function of the cranial nerves.

It has two main functional divisions:

Rostral: maintains alert and conscious state; involves midbrain and upper pons reticular formations

Caudal: co-ordinates with cranial nerve nuclei and spinal cord to regulate a variety of important motor reflexes and autonomic functions; involves the pons and medulla reticular formations.

It is continuous rostrally with certain nuclei of the thalamus and intermediate grey matter of the spinal cord

Question 57

What is the structure and function of the rostral reticular formation?

Answer 57

Otherwise known as the ascending reticular activating system, the rostral reticular formation is involved in the modulation of forebrain activity that regulates the alert and conscious state.

It involves midbrain and upper pons reticular formations

Long projections transmit to vast regions of the forebrain and they are defined by the neurotransmitter used:

• Noradrenergic (locus ceruleus)
• Dopaminergic (substantia nigra)
• Serotonergic (dorsal raphe nucleus)
• Cholinergic

Question 58

What is the structure and function of the caudal reticular formation?

Answer 58

The caudal reticular formations of the pons and medulla co-ordinates with cranial nerve nuclei and the spinal cord to regulate a variety of important motor reflexes and autonomic functions.

Example: Venterolateral medullary reticular formation

• GI responses (swallowing + choking)
• Respiratory activities (rhythm, coughing, hiccuping and sneezing)
• Cardiovascular responses

Also the Lateral Medullary - Pontine RF (chewing) and region surrounding the facial nucleus (crying + smiling)

Question 59

What are the three major long fibre tracts/pathways that traverse the brainstem?

Answer 59

Ascending Pathways:

1. Dorsal column-medial lemniscus

• fine touch and vibration
• Crosses in the medulla (medial lemniscus)

2. Anterolateral system

• pain/nociception
• Crosses in the spinal cord
• Three pathways each terminating in either the thalamus, midbrain or reticular formation

3. Corticospinal tract

• Controls motor function
• Crosses at the pyramidal decussation

Question 60

What two arterial systems comprise the circle of Willis?

Answer 60

The circle of Willis is formed from the two arterial systems that enter the head: vertebral/basilar artery system and internal carotid artery systems

These two systems anastomose to form the circle of Willis - which ensures that continued perfusion of the brain can be achieved if one of these systems is damaged and dysfunctional.

The circle of Willis quite variable in terms of the size/volume of blood contribution from each branch of the circle of Willis

Question 61

What is the origin of the vertebral/basilar and internal carotid arterial systems?

Answer 61

The vertebral/basilar system is derived from the subclavian artery - the vertebral arteries branch off this structure. The vertebral arteries ascend in the neck, running in the t_ranserse foramen of the C1-C6 vertbrae_ before entering the skull through the foramen magnum. The left and right vertebral arteries anastomose to produce the basilar artery which contributes to the circle of Willis.

The internal carotid arteries are branches of the common carotid arteries that ascend in the neck to enter the skull via foramen magnum.

Question 62

Discuss the course and distribution of the anterior cerebral artery

Answer 62

The **anterior cerebral artery **supplies the medial parts of the frontal and parietal lobes.

It projects anteriorly along the longitudinal fissure from the circle of Willis to turn upwards and hook around the corpus callosum and supply the medial parts of the superior frontal and parietal cortex.

It particularly supplies territories of the motor and sensory cortices of the lower limb - the medial parts of the topographic organisation.

Question 63

Discuss the course and distribution of the middle cerebral artery

Answer 63

The middle cerebral artery supplies the lateral surfaces of the brain; parts of the frontal, parietal, temporal and occipital lobes + insula

The artery projects laterally in the lateral fissure from the **circle of Willis **

Territories which it provides include the motor and sensory cortices for most of the body (except lower limb), parieto-occipital association areas and language centres (of the dominant side)

Question 64

Describe the course and distribution of the posterior cerebral artery

Answer 64

The **posterior cerebral arteries **supply the medial and inferior surfaces of the temporal and occipital lobes

The **posterior cerebral arteries **runs in the calcarine sulcus projecting posteriorly towards the occipital apex/protruberance

Territories of arterial supply include the visual cortex. The **primary visual cortex (V1) **is located on each side of the calcarine sulcus.

Question 65

What are the four groups of small perforating branches that are associated with arteries of the circle of Willis?

Answer 65

1. Anterior perforating arteries
2. Lateral perforating/lenticulostriate arteries
3. Posterior perforating arteries
4. Pontine perforating arteries

Question 66

Describe the course and distribution of the anterior perforating arteries

Answer 66

Are branches of the anterior cerebral artery that supply the **optic chiasm **and anterior hypothalamus

Question 67

Describe the course and distribution of the lateral perforating/lenticulstriate arteries

Answer 67

Are branches of the **lateral cerebral artery **that supply the basal ganglia and internal capsule of the brain

Question 68

Describe the course and distribution of the posterior perforating arteries

Answer 68

**Posterior perforating arteries **are derived from the posterior cerbral artery.

They supply the ventral midbrain, posterior hypothalamus and thalamus

Question 69

Describe the course and distribution of the pontine perforating arteries

Answer 69

**Pontine perforating arteries **derive from the basillar artery.

They supply the ventral pons.

Question 70

Generally speaking, what types of structures do perforating arteries of the CNS supply?

Answer 70

Perforating arteries supply deep structures directly where they come off the main CNS arteries.

They tend to be long, narrow arteries **susceptible to occlusion **

Question 71

Describe the course and distribution of the Opthalmic and Anterior Choroidal arteries

Answer 71

Both of these arteries are derived from the internal carotid artery prior to the formation of the middle cerebral artery. The opthalmic artery is the first branch and the anterior choroidal artery is second.

The opthalmic artery passes through the optic canal to supply the eye (including retina), top of nasal cavity and frontal scalp.

Anterior choroidal artery follows the c-shaped curve of the ventricles. It supplies deep strucutres of the lateral hemispheres including the optic tracts, lateral ventricles and hippocampus.

Question 72

Discuss the course and distribution of the vertebro-basilar system arteries

Answer 72

Branches of the basilar-vertebral artery system arise at different levels of the brainstem - they supply the brainstem at these levels.

From superior to inferior:

1. Perforating arteries of posterior cerebral artery​
   * Ventral midbrain
2. Superior cerebellar arteries

• Superior cerebellum
• Posterior colliculi of midbrain

3. Pontine perforating branches
   * Pons
4. Anterior inferior cerebellar arteries
   * Anterior inferior cerebellum
5. Posterior Inferior cerebellar arteries

• Posterior inferior cerebellum
• Posterolateral Medulla

6. Vertebral Arteries
   * Anterolateral medulla
7. **Anterior spinal artery **
   * Medial medulla

Question 73

What forms the anterior and posterior spinal arteries?

Answer 73

There is one anterior spinal artery and two posterior spinal arteries.

The anterior spinal artery is derived from both vertebral arteries.

The two posterior spinal arteries are derived from their respective ipsilateral vertebral artery

The spinal arteries recieve additional blood supply from radicular arteries that bring blood from segmental branches of the aorta (e.g intercostal or lumbar arteries) along the length of the spine.

Question 74

What is medial medullary syndrome?

Answer 74

Medial medullary syndrome is the result of a cerebrovascular incident associated with the anterior spinal artery.

Ischemia and infarction of the vascular territory supplied by the anterior spinal artery - the medial medulla - leads to recognisable neurological deficits.

It impacts:

1. Hypoglossal nucleus
   * Ipsilateral paralysis and atrophy of tongue (LMN) - deviation of tongue occurs towards the side of the lesion
2. Medial Lemniscus
   * Contralateral somatosensory deficit
3. Pyramids
   * Contralateral hemiparesis (UMN)

Question 75

Describe the venous drainage of the cerebrum

Answer 75

Cerebral veins run in the subarachnoid space and drain into a series of sinuses.

These venous sinuses are formed as a space between two layer of dura known as the dural septa.

These sinuses eventually drain into the internal jugular veins to rejoin the systemic circulation.

Question 76

What substances can cross the blood brain barrier?

Answer 76

Gases and some lipids are capable of simply diffusing across the BBB;

Glucose and important amino acids are actively transported across the BBB.

It is difficult to target drugs to the CNS. This is also a useful property in distinguising the CNS side effects of non-CNS targeted drugs.

Question 77

What are the five tissue layers of the scalp?

Answer 77

The scalp consists of five layers of tissue:

Skin

• includes hair follicles

**Connective Tissue **

• contains the neurovascular plane; extensive anastomoses between internal and external carotid arteries - lacerations cause profuse bleeding from this dense vascular network
• dense with fat

Aponeurotic Layer

• Is the aponeurosis of the occipitofrontalis muscle

Loose Connective Tissue

Pericranium

Note: layers form the acronym SCALP

Question 78

Why do lacerations to the aponeurosis of the occipitofrontalis cause profuse bleeding?

Answer 78

In addition to the scalp having a rich vascular network, lacerations through the aponeurosis means the superficial layer of the scalp are retracted towards the two muscle bellies of the occipitofrontalis muscle. With the muscle bellies pulling the wound apart, gaping wounds result.

Question 79

What structures keep the blood vessels upon within the scalp?

Answer 79

The connective tissue layer has small fibrous septa that attach to vessel walls and keep them open.
While this **maintains continued perfusion of scalp, it restricts the ability of blood vessels to vasoconstrict in lacerations** - inefficient clotting results.

Question 80

Is there communication between superficial veins of the scalp and the sinuses of the cranium beneath the skull?

Answer 80

Yes

Emissary veins communicate between these two sets of vessels.

Are a potential source of cranial infection

Question 81

What are the four layers of tissue in the face?

Answer 81

1. Skin
2. Connective tissue (dense)
3. Muscles of facial expression
4. Pericranium

(Note: have the same layers as the scalp but have facial muscles instead of aponeurosis and no loose connective tissue layer)

Question 82

Discuss the organisation of the muscles of faccial expression

Answer 82

Facial expression muscles originate from the bone and fascia underlying them and insert into the skin of the face.

Some facial expression muscles encircle orifaces - they are sphincter muscles of that oriface. Dilator muscles radiate out from the corners of an oriface.

All facial muscles are derived from the second pharyngeal arch in development and are supplied by the facial nerve (CN VII)

Question 83

Outline the distribution of the dermatomes of the head

Answer 83

Question 84

Where is the trigeminal ganglion located?

Answer 84

The trigeminal ganglion sits at the apex of the petrous apex.

From the trigeminal ganglion, three branches of the trigeminal nerve arise: opthalmic (V1), Maxillary (V2) and Mandibular (V3)

Question 85

Describe the organisation of the arterial supply to the face and scalp

Describe the organisation of the veinous supply to face and scalp

Answer 85

The arterial supply to the face is derived from either the internal carotid artery or external carotid artery systems

There are two sets of arteries (on each side of the face) that are derived from the internal carotid artery (via opthalmic artery):

Supratrochlear artery most medial forehead distibution.

Supraorbital artery medial forehead distribution arising from the top of the orbit + frontal scalp

The external carotid artery branches to give several main arteries:

Facial artery has an increadibly tortuous course to the inner angle of the eye. It is the main arterial supply to the face.

The occipital artery is given off and runs up behind the ear and supplies the occipital scalp

The posterior auricular artery runs behind the ear and provide blood supply to pterion scalp

Superficial temporal artery runs up to the temples and gives off small terminating branches.

Veins accompany all of the arteries in the face and scalp.

Question 86

What role do emissary veins play in thrombophlebitis of the facial vein?

Answer 86

In patients with thrombophlebitis of the facial vein, pieces of the clot may break off and enter the cavernous sinus via emissary veins, forming a cavernous sinus thrombosis.

From there the inflammation may spread to the dural venous sinuses and the cranial vasculature.

Question 87

Where are lymph nodes positioned in the face and scalp?

Answer 87

1. Submental nodes (under chin)
2. Submandibular nodes
3. Pre-auricular and parotid nodes
4. Mastoid nodes
5. Occipital nodes

Question 88

Describe the course of the facial nerve (CN VII)

Answer 88

1. Enters the internal auditory meatus and runs a tortuous course within it
2. Exits the skull via the stylomastoid foramen
3. Gives off posterior auricular nerve that innervates the occipitalis muscle belly
4. Enters the parotid gland (posteromedial surface) and creates a plexiform arrangement (in pes anserinus)
5. Divides into its five terminal branches

Question 89

Discuss the position, structure and role of the parotid gland.

Answer 89

The parotid gland is a serous salivary gland

It sits inferior to the zygomatic arch and process, Anterior to the mastoid process of the temporal bone, superior to the angle of the mandible and posterior to the masiter muscle. It is superficial to the styloid process.

It is wrapped in a dense fibrous parotid fascia

Question 90

What structures run within the parotid gland from superficial to deep?

Answer 90

1. Cranial nerve VII (Facial nerve)
2. Retromandibular vein
3. External carotid artery
4. Parotid lymph nodes

Question 91

Describe the course of the parotid duct

Answer 91

The parotid duct emerges from the anterior border of the parotid gland. It runs superfically over the masseter muscle and turns inward at the anterior margin of masseter to penetrate the buccanator muscle.

It then enters the mouth.

Question 92

What are the five terminal branches of the facial nerve?

Answer 92

1. Temporal
2. Zygomatic
3. Buccal
4. Mandibular
5. Cervical

Question 93

Where is the retromandibular vein?

Answer 93

The retromandibular vein is located within the parotid gland is formed by the anastomosis of the maxillar and superficial temporal veins.

Question 94

What deficits occur in an injury to the facial nerve?

Answer 94

Injury to the facial nerve will result in full or partial paralysis of facial muscles - poor movement of facial muscles.

Can be due to surgery in the parotid gland region or Bell’s palsy - no known cause of Bell’s palsy.

Question 95

At what regions is the spinal cord enlarged?

Answer 95

The spinal cord changes its shape over the length of its course.

It is enlarged in the cervical and lumbar regions - due to giving off limbs at these regions where more neural control is required.

Question 96

At what vertebral level does the spinal cord end?

Answer 96

Ends around L1/L2

Question 97

Discuss the organisation of the dorsal and ventral roots of the spinal cord

Answer 97

Each spinal nerve is formed by dorsal and ventral roots.

Dorsal roots are sensory.

Ventral roots are motor.

Question 98

Describe the structure and function of dorsal root ganglia

Answer 98

Dorsal root contains neuronal somata (cell bodies) forming a ganglion.

The ganglion is solely comprised of sensory neurons - these fibres have a branched axon where one branch detects stimuli in the periphery and one branch e*ntering the dorsal horn of the spinal cord *via dorsal roots

Question 99

Discuss the structure and function of the blood brain barrier

Answer 99

CSF is different to plasma - neurons are sensitive to fluctuations in ion concentration and the extracellular fluid of the brain must be partitioned from the blood via the blood brain barrier.

The BBB is formed by the endothlial cells of brain capillaries - they prevent pinocytotic transfer and have very tight _tight junctions _

Most transport through the BBB is via active transport

Molecules with increasing lipid solubility demonstrate increased ability to passively diffuse through the BBB