Anatomy Practical 3 Flashcards
how many layers does the scalp consist of
5 layers
name the 5 layers of the skull
- skin
- connective tissue
- aponeurosis
- loose connective tissue
- pericranium
describe the 5 layers of the skull
Skin:
thin, has many sweat & sebaceous glands, abundant arterial supply & venous drainage
Connective tissue:
thick and richly vascularised and is also well supplied with nerves
Aponeurosis:
strong tendinous sheet between muscle bellies of frontalis and occiptalis
Loose connective tissue:
sponge like has potential to distend with many spaces; allows free movement of scalp
Pericranium:
dense connective tissue, periosteum of the calvaria (Skull bones)
what skull bones make up the pterion
frontal
spehniod
parietal
temporal
what structures pass through the superior orbital fissure
oculomotor nerve (III) trochlear nerve (IV) lacrimal, frontal and nasociliary branches of ophthalmic (V1
what structures pass through the inferior oribital fissure
inferior orbital vessels
Inferior division of ophthalmic vein
what are the three layers of the meninges
dura mater
arachnoid mater
pia mater
describe the dura mater
- most outermost layer of the meninges
- dense fibrous membrane composed of a tough external layer and an inner meningeal layer
- inner layer draws away from the outer layer to form dural folds that separate different brain regions from each other
- the largest of the septa is the cerebral falx
what does the cerebral falx do
- separates the two cerebral hemispheres
- the falx becomes continous with the cerebellum tentorium
what does the cerebellum tentorium do
- the cerebellum tentorium separates the cerebllum from the occipital lobe of the cortex
- it covers the posterior fossa structures and supports the occipital and temporal lobes
what is the gap in the falx
- it contains a gap called the tentorial notch
what passes through the tentorial notch
- brainstem and blood vessels pass to enter the middle cranial fossa
what can cause herniate through the tentorial notch
Tumours that occupy this space raise the intracranial pressure and may cause herniation of the temporal lobe (uncus) through this space.
what is the pia attached to
- attached to the brain
what does the subarachnoid space contain
- a network of connective tissue strands
- blood vessels
- nerves and CSF
- they have arachnoid granulations
what type of MRI imaging are there
T1 or T2 weighting - refers to measurements of energy absorbance and release
describe T1
- T1 CSF bone air and blood are black
- fat and bone marrow are white
describe T2
- CSF, bone, air and bloid are white
- fat and bone marrow are black
what is T1 used for whereas what is T2 used for
T1 images are used to reveal soft tissue damage whereas T2 is used for visualising damage involving fluid containing structures
what is the usual cause of death of head injury
- raised intracranial pressure - either the result of brain swelling or of a haemorrhage accumulating inside the skull
what does potential disability
- damage to axons
- hypoxic-ischaemic damage
what are the two important mechanisms involved in head injury
- impact to the head
- movement of the brain
how can you classify the damage seen in head injury in a number of ways
focal or diffuse
describe a focal brain injury
- indicates pathology that can be seen on a CT or MRI scan
describe a diffuse brain injury
- diffuse brain injury refers to microscopic damage which cannot be demonstrated by any of the current imaging techniques but which clinicians diagnose because they have an unconscious patient whose scan shows very little obvious damage
describe a depressed fracture
- a fracture in which an area of the skull i driven inwards
describe a compound skull fracture
- skull is torn - increases risk of infection
describe a skull base fractures
- this is where there is communication with the nasal sinuses
describe a linear closed fracture
- fractures of the vault in which the skin is not broken
- these do not usually require treatment
What bone in the orbit are usually broken
- medial and inferior wall
what do orbital fractures often produce
- these often produce intraorbital bleeding producing pressure on the eyeball and black eyes as the blood accumulates in the soft tissue around the eye
what happens in the zygomatic bone is fractured
- double vision often results
- this is either due tot he damage of the supsensory ligament which no longe rholds the eye in the horizontal plane or because a bone fragements/obstructs the recti muscles
where are orbital fractures seen on
CT scan
what can an orbital fracture damage
- it may damage the cavernous sinus and thus the blood/nerve supply to the eye
- infection can sperad to the cavernous sinus via the ophthalmic vein as a result of such fractures
name the haemorrhages that you can have
- extradural
- subdural
- subarachnoid
what haemorrhages need to be treated
- extradural and subdural haemorrhages usually need to be evacuated neurosurgically and can cause death as they act as mass lesions
define
- subfalcine
- tentorial
- tonsillar
- subfalcine - when brain tissue is displaced under the falx cerebri and is aptly named a subfalcine herniation.
- tentorial - Tentorial Subdural Hemorrhage - Subdural hematomas occur between the dura and arachnoid
- tonsillar - Tonsillar herniation is a type of cerebral herniation characterised by the inferior descent of the cerebellar tonsils below the foramen magnum
what can an internal herniation also lead to
- can compress blood vessels, leading to secondary ischaemic damage
- cranial nerves are often also compressed causing clinical signs
what percentage do extradural haemorrhage occur in head injury
Extradural haemorrhage occurs in approximately 10% of severe head injuries and up to 15% of fatal head injuries
what happens in an extradural haemorrhage
- this is where a blood vessel running between the skull and the dura is torn
describe how long it takes for an extradural haemorrhage
- accumulates slowly over a period of hours - this is because the dura is strongly adhered to the inner aspect of the calvaria and the enlarging clot slowly strips the dura from the skull
what ml of extradural can be fatal
Because there is so little reserve volume inside the skull, haematomas of >75 ml are usually fatal
describe what causes subdural haemorrhage
- it is principally caused by movement of the brain and not by impact
- when the head is accelerated the intertia of the brain causes its movement to lag behind that of the skull
- this leads to traction on bridging veins running between the brain and the dura mater which get torn
what is a difference between subdural and extradural ahemorrhage
- subdural there is damage to the axons as well as underlying brain as well
- extradural damage brain tissue is not usually severely damaged
describe subarachnoid haemorrhage
- bleeding in trauma is almost always insignificant seen on the surface of the hemispehres in relation to fracture sites or contusions
what is the difference between a spontaneous subarachnoid haemorrhage and a traumatic subarachnoid haemorrhage
Spontaneous subarachnoid haemorrhage is quite different from traumatic subarachnoid haemorrhage, resulting from rupture of an aneurysm on a vessel of the circle of Willis (e.g. a Berry aneurysm). This latter type of subarachnoid haemorrhage is a form of haemorrhagic stroke.
where abouts to contusions occur on the crests of gyri
Inferior surface of the frontal lobes
Lateral and inferior surfaces of the temporal lobes
Region adjacent to the lateral fissures
Orbital poles
what are contusions
- ## they are merely small superficial areas of haemorrhage in the cortical ribbon
what does laceration mean
- used when the arachnoid and brain are damaged
- usually at the site of a fracture, a contusions or a large intracerebral haematoma
what is the cause of concussion veruss the caused of a number of behavioural and cognitivie deficits
Experimental work suggests that mild reversible axonal injury is the cause of concussion, and that scattered irreversible axonal damage may be responsible for a number of the behavioural and cognitive deficits of mild head injuries.
what does diffuse axonal injury mean
Diffuse axonal injury (‘DAI’) is the term given to widespread damage to axons, caused by acceleration of the head, with or without deceleration
describe a diffuse axonal injury
The patient with DAI is unconscious from the time of injury, remains in prolonged coma, and is severely disabled or vegetative until death, which is usually caused by bronchopneumonia or other infection.
what are many brain tumours due to
Many brain tumours are due to abnormal proliferation in glial cells e.g. astrocyotoma’s and ependymoma’s (lining the 4th ventricle
Others may affect the meninges and some affect the cerebellum such as medulloblastomas
What has a particular poor prognosis
brainstem tumours
what is the most common of the dementia disorder
alzheimers disease
describe dementia
progressive, degenerative disease that attacks the brain and results in impaired memory, thinking and behaviour
what is alzherimers disease cahracterized by
- The disease is characterized by the progressive development of senile plaques and neurofibrillary tangles.
- Two abnormal proteins of very different origin appear in the lesions.
- They are β-amyloid protein (BAP), derived from amyloid precursor protein (APP), which occurs extracellularly as a major component of senile plaques; and phosphorylated tau, which occurs intracellularly as a major component of neurofibrillary tangles.
what can be used to treat alzheimers
Use of medications to treat cognitive decline and memory loss
Referral to appropriate activities such as exercise, recreation and adult day care services
Appropriate treatment of medical or psychological conditions that may contribute to cognitive changes or decline
what are the two kinds of motor symptoms after cerebellar injury
hypotonia
ataxia
describe the two kinds of motor symptoms after cerebellar injury
- HYPOTONIA –manifests as muscle weakness and loss of motor tone. It results in a floppy, loose-jointed, rag-doll like appearance with pendular reflexes and the patient appears “drunk”.
- ATAXIA - which manifests as “errors in the rate, range or force of movement”
what is the cerebellum particularly susceptible to
- the effects of alcohol
what do focal lesions on the cerebellum produce
focal lesions of the cerebellum produce deficits on the same side of the body as the lesion.
what are the most common cerebellar tumours
- Astrocytoma (30%). Most frequently located in the cerebellar hemisphere. Can be surgically removed with good morbidity.
- Medulloblastoma (20%) Malignant and arise from granular layer of cerebellar cortex. Invade 4th ventricle and can block CSF flow.
- Ependymoma (15%) Occur in 4th ventricle and obstruct CSF flow.
what attacks the central nervous system
multiple sclerosis
describe multiple sclerosis and how it causes central nervous system
- destruction of the myelin sheath of CNS axons by the immune cells lead to impaired communication between nerve cells and neurological symptoms such as abnormal sensations, vision problems and weakness
- astrocytes form scars(plaques) where myelin formly existed
