Neurological Diseases

     This revision blog post concerns neurological diseases such as tumours, seizures, strokes and degenerative disorders such as Alzheimer's and Parkinson's.


     Neurogenesis (cells growing back) is possible in adults although it is very limited. The diagram below shows the brain in relation to the limbic system.

     The hippocampus and the olfactory bulb are the only areas which can replace neurons. The image below shows the site of most adult neurogenesis. This integrates into hippocampal functioning.

     There are several things which encourage neurogenesis i.e. help to grow neurons:
* Enriched experiences - e.g. learning (lectures is an example)
* Physical exercise (this has been shown in rat studies)


Tumours (cancer)


    Tumours develop through neoplasm or 'new growth' and the duplication of malfunctioning cells. Benign tumours mean that there is no chemical damage but they kills cells through compression. Malignant tumours travel everywhere.
     Encapsulation - does a border exist between the tumour and the brain? If so, the tumour is easier to remove. If not, it is hard to say whether or not all of the tumour has been removed.

The diagram below shows a scan of a benign brain tumour. In the image there is a clear boundary between the brain and the tumour.

The diagram below shows a scan of a malignant brain tumour (the one on the left). The tumour is shown in the form of dark mass, this type of tumour is much more dangerous as bits could break off meaning that there could be small parts of the tumour all over the brain.

Metastases
     Malignant tumours shed cells. These travel through the blood stream as 'seeds'. Being stressed increases cancer as the sugars produced feed it.

Tumours and Damage

Compression - is when the tumour pushes brain tissue aside. Benign tumours occupy space and directly
                       destroy brain tissue. They also indirectly block the flow of cerebrospinal fluid (CSF) and
                       affect normal brain functioning.

Infiltration - occurs with malignant tumours. This is when the tumour invades the surrounding areas,
                   destroying other cells.

     Malignant tumours grow fast, but are sensitive to radiation. Astrocytes (a type of glial cell) are key in making mistakes in duplication.



Epilepsy


     Epilepsy is the manifestation of the electrical nature of the nervous system. Normal activity is desynchronised.
     Seizures are a wave of excitation that is carried across the brain. i.e. lots of neurons fire (almost like a mexican wave). Sometimes it is hard to tell if someone is having a seizure.

     Epilepsy is self-generated and affects approximately 1% of the population. It is more common in children, however they tend to grow out of it. Not only does epilepsy cause convulsions (motor seizures) it also has more subtle effects on things such as:
* thought, mood and behaviour
* viruses, blows to the head and toxins

Categories of Seizure
1) Generalised - whole brain, causes loss of consciousness and symmetrical muscle spasms in both halves of
                          the brain at the same time.
2) Complex Partial Seizures - affect specific areas of the brain

The diagram above shows abnormal EEG (electroencephalogram) activity across the brain.

Grand Mal


     A grand mal seizure is a generalised, tonic-clonic seizure which results in a convulsion. The tonic phase is the first phase of a grand mal seizure in which all of the patients muscles are contracted and rigid. The clonic phase is the second phase of a grand mal seizure in which the patient shows rhythmic jerking movements.
     Grand mal seizures usually either constrict or stop breathing. They also cause the patients' eyes to roll, their face to contort and they often bite their tongue. There is also intense sweating and/or salivation.
     Soon after the seizure, breathing returns and the patient goes into an unresponsive sleep (15 minutes) followed by normal sleep (2 hours).

Petit Mal


     A petit mal (little trouble) seizure occurs in a different type of epilepsy. There are no convulsions and it is most common in children and ceases around puberty. When the patient suffers from a petit mal seizure (sometimes called an absence seizure) they appear to be absent or daydreaming.
     Petit mal seizures a very brief - lasting only 15 seconds or less. When they occur, the patient may simply stop talking momentarily. It may also interfere with school, particularly because the child may be viewed as just having a lack of attention. The patient has no memory of the event although you can sometimes get a sense of when one is about to occur. It has been found that calling the persons name can help to stop the seizure occurring.

Complex Partial Seizures
      Complex partial seizures only involve part of the brain and are associated with the bilateral cerebral hemisphere. There are a wide variety of symptoms and they are usually preceded by an unusual sensation.




Strokes


     Strokes produce permanent brain damage, but depending on the size of the affected blood vessel, the amount of damage can vary from negligible to massive.


Cerebral Haemorrhage - blood vessels burst in the brain and the sufferer has very high blood pressure.

Cerebral Ischemia - the disruption of blood supply to the brain (blockage).

The diagram below shows bifurcation (splitting). The bifurcation occurs where the dark shadow is. When a person has high blood pressure it is hit at a high speed which creates damage. Epinephrine (adrenaline) stimulates sugar release. Sticky sugar gets stuck in the crates.

     Atherosclerotic Plaque can also lead to strokes and is shown in the diagram below. Oestrogen helps to stop plaque forming which is one reason why men die earlier than women.

     A thrombus is a blood clot that forms within a blood vessel particularly when their walls are already damaged. Sometimes thrombi become so large that blood cannot flow through the vessel causing a stroke. If a thrombus blocks coronary artery it causes a heart attack.

Alzheimer's Disease


     Alzheimer's disease is a degenerative brain disorder of unknown origin. It causes progressive memory loss, motor deficits and eventual death. It is a type of senile dementia which appears before the age of 65. It's frequency increases until the age of about 85 years, after that chances fall.

     The diagram above shows brain shrinkage with age. Only hippocampul shrinkage correlates with loss of memory. Alzheimer's Disease causes severe degeneration in the hippocampus but the amygdala and many areas of the cortex are also affected (frontal and temporal).

     Extensive use of brain makes Alzheimer's less likely.

     Early signs of Alzheimer's disease include memory loss of recent events, memory impairment and an inability to follow conversation. In the early stages, some people make up stories in order to fill in the gaps in their memory.
     People who have Alzheimer's are unable to answer questions such as:
* who is prime minister?
* what year is it?
* where are you now?
     They are also unable to care for themselves.

     The diagram above shows the Cholinergic Pathways (ACh). In Alzheimer's disease, problems occur in the area shown as the basal forebrain. In this area there is a mutation in the production of proteins.

Changes associated with Alzheimer's Disease
* Amyloid Plaques - extracellular deposits that consist of a dense core of a protein called B-amyloid.
* Neurofibrillary Tangles - are due to whorls of proteins, caused by plaques and consist of dying neurons.

     These changes cause the basal forebrain to stop producing acetylcholine.

The diagram below shows a normal human brain.

This image shows a brain affected by Alzheimer's Disease. Note how dry and crusty (my lecturer's terms) this is.

The next three diagrams shows the brains degeneration in Alzheimer's Disease. Diagram 1 shows a preclinical brain. Diagram 2 shows a brain with mild Alzheimer's Disease. Diagram 3 shows severe Alzheimer's Disease.

Delusions


     Delusions are a false belief which are firmly maintained in spite of incontrovertible and obvious proof to the contrary. Delusions can be symptomatic of other conditions such as dementia and one can have  more than one type at the same time.

Here are some examples:
* "My neighbour steals from me" - this is a persecutory delusion

* "My husband is an imposter. He looks like him and acts like him, but it isn't him" - this is called capgrass
    syndrome. There is no emotional link.


Confabulation


     Confabulation is a 'filling in' of memory gaps through fabrication. If patients are unable to remember, it is tempting to invent stories. Not all Alzheimer's patients do this.

The graph below shows research by Feinburg and Keenan (2004). They found that people with delusions tend to have right hemisphere damage.

Below is an image from a fMRI scan showing semantic memory i.e. recalling the name of a previous school. Just to point out - it is the orange coloured bits at the top (front) of the brain which you should be looking at.

The image below shows episodic memory i.e. recalling something that happened to you at primary school. If this area is damaged, you won't be able to remember what happened at school.

It is important to note that Alzheimer's Disease is not dementia. It is one cause, however dementia is also caused by strokes and dehydration.




Parkinson's Disease


     Parkinson's Disease is to a great extent, a movement disorder. It affects 1% of those over the age of 65 and is most prevalent in males (x2.5). Parkinson's Disease causes widespread neural degeneration in the substantia nigra (nigrostriatal system).

     When treating Schizophrenia, if a patient is given too much dopamine it can lead to Parkinson's Disease and vice-versa.

This diagram shows the Dopaminergic Pathways. The mesostriatal pathway is also called the nigrostriatal pathway/system. Parkinson's Disease is caused by a lack of dopamine.

Substantia Nigra
     The substantia nigra secretes dopamine which is an important neurotransmitter. When the substantia nigra is 80% degraded, Parkinson's Disease occurs.

Nigrostriatal Pathway
     The nigrostriatal pathway to Caudate Nucleus and Putamen (called striatem when together) is a basal ganglia motor loop.
     When an individual is affected by Parkinson's Disease they have difficulty controlling and planning their movement.

The diagram above shows the Basal Ganglia. The moderation of activities however is initiated elsewhere.

The diagram above shows the links between the primary motor cortex and the nonprimary motor cortex. Messages are sent along the arrows shown. The basal ganglia is in trouble when you have Parkinson's Disease. The cerebellum is in trouble when you are drunk.

This next diagram looks at the link between movement and Parkinson's Disease:

     When you initiate movement, the basal ganglia sends its opinion very quickly - later the cerebellum does the same thing. The cerebellum joins movements e.g. if you reach for a cup, the cerebellum gets you to grip it.

     The image above shows the typical posture of someone with Parkinson's Disease. They suffer from instability and have difficulties in starting and stopping movement. They are also unable to catch themselves if they fall.
     Parkinson's is normally shown in a resting tremor (which diminishes during purposeful movement). It also causes rigidity of the joints - this however, is not the cause of slow movement! In Parkinson's Disease, nigrostriatal neurons disappear or mutate.

Damaged Basal Ganglia
     When the basal ganglia is damaged, an individual has a lack of internal cues to help with movement. Therefore when someone is suffering from Parkinson's Disease, external cues provide helpful feedback e.g. having a line to their bedroom. This helps them to walk around normally. The basal ganglia is important for implicit skill learning and new associations.

The diagram above shows episodic recall ability. This shows that it is not affected by Parkinson's Disease.



So. That was my revision for neurological disorders. It has made me feel slightly depressed. Particularly as I now have 11 and a half hours to go until my biological psychology exam. It is 2.30am and I am definitely in need of some food and some more coffee!!!

xoxo