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Y2 medical pathophysiology > Pathophysiology of the nervous system > Flashcards

Pathophysiology of the nervous system Flashcards

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USMLE® Step 1 flashcards
1
Q

What do interneurones do?

A

Carry signals between sensory and motor neurones.

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2
Q

Why do some people suffer from problems with their nervous system whilst others don’t?

A

Genetic influences

Environmental impact

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3
Q

What are the different possible time frames over which damage to the nervous system can occur?

A

Fast time course events; traumatic events such as strokes, epilepsy or inflammation.

Slow time course events; such as insidious neurodegenration.

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4
Q

What causes the variance of effects of brain injuries?

A

Cause of the injury, location of the injury, severity of the injury, wiring of the brain.

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5
Q

What are the 4 mechanisms of brain injury ?

A

Brain contusion

Increased intracranial pressure

Diffuse axonal injury

Stroke (ischaemic or haemorrhage)

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6
Q

Describe brain contusion causes of brain injury and where they usually occur.

A

Cell death accompanied by haemorrhage.

The soft brain tissue is vulnerable to contusion in head trauma.
The contusion often occurs at a site distant from the point of impact.

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7
Q

Describe how increased intracranial pressure occurs and how it causes brain damage.

A

The intracranial vault is a fixed volume.
Intracranial pressure rises in the brain, blood and cerebrospinal fluid volume increases.
As bleeding occurs, substances are forced out of the cranial vault (CSF first, then arterial blood, then herniation of the brain).
This eventually means that the brain lacks blood supply and so can be mechanically damaged.

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8
Q

Describe how diffuse axonal injuries cause brain damage and where these usually occur.

A

Diffuse form of injury meaning damage occurs over a widespread area.

Involves the shearing of axons in the white matter tracts.
Occurs as brain regions of differing densities and different distances from axis of rotation slide over each other.
The downstream axon will degenerate, meaning other neurones may need to take over.

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9
Q

How do strokes cause brain injury?

A

A loss of blood supply to some or all of the brain will result in cerebral deficit that lasts for at least 24 hours unless fatal.

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10
Q

Define ‘stroke’

A

By rapidly developing clinical symptoms or signs of focal, and at times global loss cerebral function, with symptoms lasting more than 24 hours, or leading to death, with no apparent cause other than that of vascular origin.

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11
Q

If a stroke doesn’t last for 24 hours, what can occur and what is this?

A

A transien ischaemic attack:
A clinical syndrome characterised by acute loss of focal cerebral syndrome with symptoms lasting less than 24 hours and which is thought to be due to inadequate cerebral blood supply as a result of low blood flow, arterial thrombosis or embolism associated with disease of the arteries, heart or blood.

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12
Q

What is the Foramen Magnum/

A

An opening at the base of the skull.

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13
Q

What is herniation?

A

When the brain is squeezed through the foramen magnum.

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14
Q

What may occur due to brainstem herniation?

A

The brainstem is compressed therefore damaging the brain. This may cause the patient to stop breathing and therefore die.

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15
Q

Why is brainstem herniation the most life threatening herniation type?

A

The brainstem keeps you alive by maintaining the regulation of breathing

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16
Q

What effects would you see on the brain tissue during herniation of the brain due to increased ICP?

A

Diffuse swelling (yellow tissue) and expansion of brain tissue into ventricles.

Widening and flatting of gyro on brain surface.

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17
Q

What is encephalitis?

A

Acute inflammation of the brain that causes the brain to push against the skull.

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18
Q

What causes encephalitis?

A

Can be caused by rabies which enters through a bite and travels through the PNS to the CNS.

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19
Q

Which parts of the brain become inflamed during encephalitis and what does this cause?

A

Inflammation of the Meninges which causes Meningitis.

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20
Q

What are brain tumours?

A

Abnormal and uncontrolled cell division leading to production of abnormal mass of cells. This can put pressure on there structures and cause inflammation.

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21
Q

How do brain abscess cause brain damage?

A

They distort and damage surrounding brain areas.

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22
Q

What are the most common types of strokes?

A

Ischaemic

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23
Q

When are ischaemic strokes likely to occur?

A

in trauma, secondary to swelling which compresses nearby arteries.

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24
Q

What are the causes of ischaemic strokes?

A
  • Thrombotic (blood clot formed in situ) or embolic (blockage originates in another part of the body).
  • Atherothombotic cerebrovascular disease
  • Small vessel disease
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25
Q

What are the different types of haemorrhage stroke?

A

Subarachnoid - bleeding around the brain.

Intracerebral haemorrhage - bleeding into the brain.

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26
Q

How do haemorrhage strokes cause brain injury?

A

Decreased oxygen delivery because blood is leaking into brain tissue and not entering the capillary network.
If the blood is leaking into the brain tissue or intracranial vault, the ICP will change. This will then affect supply of blood to the brain.

27
Q

What is the circle of willis and what is its purpose?

A

Multiple blood vessels interconnect and can compensate for each other. This allows blood to shift around the circle to ensure that there is a constant blood supply to all regions of the brain.

28
Q

What vessels move into the circle of willis?

A

1) Left internal carotid in
2) Left vertebral in
3) Right vertebral in
4) Right interior carotid artery in

29
Q

What vessels move out of the circle of Willis?

A

1) Anterior cerebral artery
2) Middle cerebral artery
3) Posterior cerebral artery

30
Q

What are the modifiable risk factors for strokes?

A

High blood pressure, smoking, diabetes, obesity, high cholesterol, irregular heartbeat, inactivity, drug abuse, excessive alcohol use.

31
Q

What are the uncontrollable risk factors for strokes?

A

Increasing age, genetics, race, prior stroke, gender (more common in men)

32
Q

What is an intracerebral haemorrhage and how does this affect the brain?

A

Initial haemotaoma causes increase in local pressure and subsequent rupture of other vessels around the haematoma.
The ICH growth is stopped by increasing counter-pressure from the surrounding tissue.

33
Q

What pre-disposes people to re-bleeding or continuous bleeding in the early stages of haemorrhage?

A

Coagulation disorders and elevated blood pressure.

34
Q

What causes a subarachnoid haemorrhage.

A

Results from the rupture of saccular aneurysms that form on the blood vessels that supply the brain.

35
Q

Where do subarachnoid haemorrhages occur?

A

At bifurcations of the major cerebral arteries of the circle of willis.

36
Q

How are subarachnoid haemorrhages diagnosed?

A
  • Thunderclap headache
  • Xanthochromic lumbar puncture (blood in the CSF not due to traumatic tap)
  • Star patter on CT scan
37
Q

What methods are used to prevent subarachnoid haemorrhages?

A

Clipping of aneurysms used to prevent aneurysms nursing.

Endovascular coils used to promote blood clotting to stop aneurysms rupturing.

38
Q

Describe a Grade I cerebral aneurysm.

A

Asymptomatic, or minimal headache and slight neck rigidity.

39
Q

Describe a Grade II cerebral aneurysm.

A

Headache and moderate neck rigidity.

40
Q

Describe a Grade III cerebral aneurysm.

A

Drowsiness, confusion, or mild focal deficit.

41
Q

Describe a Grade IV cerebral aneurysm.

A

Stupor, moderate to severe hemi paresis, possibly early decerebrate rigidity.

42
Q

Describe a Grade V cerebral aneurysm.

A

Deep coma, decerebrate rigidity.

43
Q

Outline the difference in occurrence of ischaemic and haemorrhage strokes.

A 
Ischaemic = More common
Haemorrhage = Less common
44
Q

Outline the different causes of ischaemic and haemorrhagic strokes

A 
Ischaemic = Atherosclerosis or tumour within brain 
Haemorrhage = Cerebral aneurysms, AV malformations, hypertension
45
Q

Outline the different onset times of ischaemic and haemorrhagic strokes.

A 
Ischaemic = slow
Haemorrhage = sudden
46
Q

Describe the different factors that are likely to bring on ischaemic and harmorrhagic strokes.

A 
Ischaemic = Long history of vessel disease. 
Haemorrhage = Bought on by stress or exertion.
47
Q

Describe previous occurrences or conditions that are likely to cause ischaemic or haemorrhagic strokes.

A 
Ischaemic = history of angina or previous strokes. 
Haemorrhage =  May be asymptomatic before rupture.
48
Q

Describe what effects can occur to the brain in the first 1-2 minutes of a stroke.

A

Compromised neurona function

49
Q

Describe what effects can occur to the brain in the first 4 minutes of a stroke.

A

Permanent injury

50
Q

What are is most effected by an ischaemic event?

A

The ischamic core

51
Q

What effects does the ischamic core experience during an ischaemic event?

A

Low oxygen levels, low ATP levels, low glucose levels and acidosis.

52
Q

What effects does calcium stress have?

A

Can reduce functionality of ion pumps, damage membranes, release calcium from stores, release calcium from mitochondria and overall lead to increased intracellular calcium concentration.

53
Q

What are the effects of high levels of intracellular calcium?

A

Unwanted enzyme activation, cell dysfunction, cellular death, membrane blabbing. Can also increase the stress response.

54
Q

What are the possible mechanisms of calcium stress?

A

Oxidative, mechanical or metabolic.

55
Q

What is an ischameic cascade?

A

When lack of blood flow can initiate a complex series of events which leads to cellular death.

56
Q

What is epilepsy and what are the likely causes?

A

Uncontrolled excitation of the brain.

May be due to; electrolyte imbalance, fever, hypoglycaemia, hypoxia, brain tumours, brain injury or may be idiopathic.

57
Q

What type of seizures can occur in epilepsy - explain each.

A

Grand mal tonic - clonic seizures.

Absence seizures - brief alterations of consciousness (10 seconds approx).

58
Q

What causes seizures?

A

Anything that irritates the brain;

Infections, trauma, drugs, electrolyte imbalances, tumours and stokes, fevers.

59
Q

Why doesn’t an abnormal EEG diagnose epilepsy?

A

Epileptiform abnormalities can be found in 2% of the population; especially in children with autism or ADHD.

60
Q

Explain how excitotoxicity causes neuronal death.

A
  • Seizures result in a massive release of glutamate
  • Glutamate concentration in the synaptic cleft rises rapidly and activates glutamatergic post-synaptic receptors of different types
  • The NMDA receptors are permeable to sodium, potassium and calcium ions. Ligand and voltage gated – ions can flow in presence of lots of glutamate.
  • Must bind glutamate to open channel
  • However, normally magnesium attracted into channel blocks the channel.
  • Excitation of the cell removes magnesium blockade and allows calcium to enter the cell.
  • Calcium then mediates neuronal damage (apoptosis).
61
Q

Why is it such a problem if a neurone dies?

A

Neurones are not mitotic so cannot be replaces.

Information is stored in connections each neurones make so this information is not genetic and so if the neurone disease, a lot of information is lost.

One neurone does not store information, information is stored in circuits so a lot of information can be lost by the damage of one neurone.

62
Q

What Is the treatment goal for epilepsy?

A

No seizures, no side effects and optimum quality of life.

63
Q

What factors choose the type of anti-epileptic medication that should be taken?

A

Type of seizure or epilepsy syndrome.

Coexisting medical conditions.

Dosing and monitoring.

64
Q

When is medication for epilepsy usually given?

A

After a second unprovoked seizure.

Y2 medical pathophysiology (12 decks)

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