Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Medicine year 2 semester 2 > Case 22- Scanning and Memory > Flashcards

Case 22- Scanning and Memory Flashcards

1
Q

CT scanner- how objects appear

A

X-rays attenuated by tissue, interaction with electrons
• Bright object in CT- bone, calcification, blood
• Grey objects in CT- brain tissue, CSF
• Dark objects in CT- fat, air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

CT- dementia

A

In brain atrophy there will be extension of the sulcus and ventricles and increased dark areas.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

CT- head injury with haemorrhage

A

Mass effect causing a midline shift and ventricular effacement, there will be a white area showing the intracranial bleed and swelling of the extra cranial tissue. There is a crescent shape hyperintensity area (white). Bruising will appear as white

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

CT- contrast enhancement

A

Used in a CT to enhance contrast, its IV injectable and is often iodine based. It efficiency blocks x-rays and shows up brightly. Shows a disrupted blood-brain-barrier as the contrast agent can leak out. It enhances a tumour.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Pro’s of CT

A
  • Quick (10 minutes)
  • Good resolution
  • Bone well visualised
  • Good for trauma
  • Cheap to perform (£100)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Con’s of CT

A
  • Uses ionising radiation- 100 times that which is used for an x-ray
  • Relatively poor soft tissue contrast (grey vs white matter)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Mechanism of MRI

A

Soft tissue has 2 major compounds- water and fat. MRI is very good at soft tissue imaging. Magnetic resonance imaging uses the fundamental interaction between:
• Nucleus H atom (proton)put in a magnetic field
• Applied electromagnetic energy
1H are ubiquitous in water and fat. MRI should therefore provide excellent soft tissue contrast.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Process of MRI

A
  • Place object into a very strong magnetic field
  • Bombard with energy in the form of radio-waves- non-ionising with no risks
  • These are absorbed by the nucleus of the 1H atom (proton)
  • The signal is re-radiated (radio frequency) and detected
  • The strength of signal is determined by the amount of water molecules in the tissue and helps build up the image
  • Bone has low amounts of hydrogen ions so does not tend to show up, only soft tissue shows us
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The flexibility of MRI

A
  • MRI provides many different types of image contrast- each can reveal different aspects of the pathology
  • Contrast changes depending on how we excite the MRI signal and when we measure it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

T2 weighted scan

A
  • More fluid structures are bright
  • CSF- white (ventricles and sulci)
  • Grey matter- grey
  • White matter- darker
  • Good for oedema and necrosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

T1 weighted scan

A
  • More fluid structures are dark:
  • CSF- black
  • Grey matter- grey
  • White matter- white
  • Excellent grey matter to white matter contrast, good for looking at areas of anatomical change, for example, measuring the size of the brain, the structure of the brain and the changes that occur due to ageing
  • Complementary contrast to T1w
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Meningioma- MRI

A
  • Tumour is isointense with grey matter
  • White matter changes- oedema
  • Mass effect (spatial distortion)
  • In a T2 scan you get an area of hyperintensity (white) which is peritumour oedema i.e. adjacent to the tumour. Its bright on Proton density indicating that there is more liquid there then there should be
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Contrast enhanced MRI

A

Injected contrast agent (Gadolinium complex), accumulates in tissues by passive diffusion across the Blood brain barrier. Helps show cancer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

MR angiography

A

Shows blood flow in major vessel, the scan is weighted so its sensitive only to moving water. Can only see the blood and the blood vessels. Its performed in 3D. It sensitises to a particular range of flow velocities, a faster flow uses and angiogram, a slower flow uses a venogram.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Diffusion weighted MRI

A

1) Water diffusion is restricted by cellular tissue structures. Measures how far the water molecule can diffuse, the distance the water molecules can move is determined by the size of the cells they are in.
2) Helps give more information about brain tissue.
3) The cell water volume is actively controlled, its energy dependent. It depends on the size of the cell due to pumping water in and out of cells in order to regulate the cell volume.
4) Diffusion is sensitive to ischaemia or axonal injury, as there is less energy and they lose their ability to control the size of the cell.
5) It’s the most sensitive neuroimagine tool used to detect acute ischaemia.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Orientation dependent MRI

A

How far water molecules can move is depended on the orientation of the white matter axons. If the water molecules are perpendicular (across) the axon they will not be able to move a lot, if they are moving along the axon then they will
Diffusion restriction depends on orientation- it is anisotropic.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Diffusion tensor imaging (DTI)

A

• You acquire images sensitive to diffusion in many different direction
• You can model the observed behaviour to identify the primary directs of diffusions
• When diffusion is direction (cylindrical structure) its an Anisotropic structure
• When Diffusion is uniform (spherical structure) it’s an Isotropic structure
Tractography- 3d images of the direction of CSF flow within the brain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Pro’s of MRI

A
  • Excellent soft tissue contrast
  • Wide range of inherent contrasts- T1w, T2w, DWI, MRA, others
  • Good resolution
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Cons of MRI

A
  • Relatively slow
  • Scanner can be claustrophobic
  • Contraindications- medical implants
  • Relatively expensive (£300+)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Methods to assess brain function

A
  • Positron emission Tomography (PET)

* Single Photon Emission Computed Tomography (SPECT)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

PET- from tissue structure to function

A
  • Radiotracer technique
  • Tracer is injected into the patient
  • Tissue distribution is then measured- detect the radioactive particles externally and work out where the radiotracer was inside the body and work out the tissue distribution.
  • The Positron emitting radioisotope is administered to the subject
  • It accumulates in the tissue
  • Positrons are emitted- same molecular size as electrons but positively charged
  • Travels in the tissue and combines with electron
  • Annihilation produces gamma-photons
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

PET- examples

A

The FDG scan is the most commonly used, it is an analogue of glucose. Modified so its taken up by the tissue as if it was glucose but is not metabolised

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

PET- Creating images

A

The coincidence detectors localise the source of the photons, the number of positrons emitted is counted over time, you work backwards to create the image. The hotter colours (red) are in the grey matter (the cortex) and the cooler colours (blue) are in the CSF and white matter. Shows us that the metabolic rate of grey matter is higher then white matter

24
Q

PET- Alzheimer’s disease

A

More blue colour as the metabolic rate has decreased, especially in the Hippocampus. There is also tissue loss (no colour). There will be hypometabolism in the medial temporal lobe
In dementia with Lewy bodies it is cooler in the posterior occipital lobe

25
Q

PET- other common radiotracers

A
  • Flexibility depends in which radiotracer is used
  • Looking at receptors- labelled ligands for each receptors i.e. 18F-DOPA, measures receptor density
  • Other target- Amyloid (C11-PIB), Neurglia
  • Cerebral blood flow (CBF)- labelled water as a diffusible tracer
26
Q

PET= Pittsburgh compound B (PIB)- Amyloid marker

A
  • Research PET ligand
  • Binds to amyloid plaques which are the pathological marker of Alzheimers disease, binds to beta-amyloid
  • High accumulation of tracer suggests Alzheimer’s disease
27
Q

PET= 18F-DOPA uptake

A
  • Used in Parkinson’s disease
  • Fluorinated L-DOPA
  • Precursor to dopamine, accumulates in dopaminergic neurones
  • Significantly reduced uptake in the Putamen in Parkinson’s
28
Q

Single Photon Emission Computed Tomography (SPECT)

A
  • Similar concept to PET
  • The radioactive tracer injected IV- tracer is taken up in the brain, it emits gamma radiation in single photons
  • Helps show blood flow in the brain
  • Can measure activity of the Dopamine transporter (FP-CIT) which is reduced in Parkinsons
29
Q

Blood flow by SPECT- Cerebral Blood Flow (Tc99-HMPAO)

A
  • Tc99-HMPAO tracer
  • It is delivered by perfusion and accumulates in the brain
  • The amount is proportional to cerebral blood flow
  • In dementia and Alzheimers there is reduced yellow and orange colour
30
Q

PET vs SPECT

A

PET has a better resolution then SPECT

31
Q

Pro’s and Con’s of PET

A

Pro’s of PET
• Flexible- metabolic rate/CBF. Amyloid/neurotransmitters
• Very sensitive= pico-nanomole

Cons of PET
• Relatively poor resolution 3-5mm
• Short half life= isotope needs to be prepared locally, full chemistry production
• High radiation dose
• Expensive
• Limited availability
• Need a lot of expensive techniques
32
Q

Pro’s and Cons of SPECT

A 
Pro’s of SPECT
• Long half-life= days, produced offsite and transported
• Flexible- CBF/neurotransmitters
• Sensitive
• Good availability

Cons of SPECT
• Poor resolution- 7mm
• Radiation

33
Q

Imaging summary

A
  • Macroscopic structures- anatomy- gross pathology- CT and MRI
  • Microscopic structures- microvascular- brain connection- MRI
  • Physiological changes- metabolism- perfusion- PET and SPECT
  • Neuro-transmitters- activity- function- PET and fMRI
34
Q

Imaging- Electrophysiology

A

EEG records the changes in electrical activity within the cortex over the fixed time period, signals are produced by postsynaptic potential from thousands of neurones with a similar spatial orientation. The electrical potential is measured by electrodes on the scalp. EEG signals reflect functional changes within the cortex and assess neural degeneration before actual tissue loss or behavioural changes. EEG can help distinguish normal ageing from dementia subtypes
The main shortcoming of EEG is its susceptibility to artefacts that occur due to- blinking, heartbeats, cranial muscle activity.

35
Q

Learning and memory

A

Learning- the process through which new information is acquired by the nervous system
Memory- recovered experiences that can be brought into consciousness and/or changes in behaviour i.e. remembering how to ride a bike

36
Q

Stages of memory formation

A
  • Sensory input is sent to the Occipital cortex and forms a sensory memory which does not last very long
  • The sensory memory is then transferred to short term memory (working memory), remains in short term memory through constant rehearsal i.e. by repeating a phone number. Last seconds to minutes
  • It is transferred it to long term memory. Permanent but information is pruned and lost
  • Information which is not transferred is lost
37
Q

Qualitative categories of memory

A
  • Phylogenetic- unconscious
  • Declarative (available to consciousness)- daily episodes, words meaning, history, facts
  • Nondeclarative (unconscious)- motor skills, associations, priming, puzzle solving skills. Cant bring everything you are doing to consciousness
38
Q

Phylogenetic memories

A

Innate, hardwired into the organism during development i.e. some species are born being able to recognise overflying predators. Within the genetic code

39
Q

Declarative memory

A
  • General knowledge- i.e. capital cities, colours, home numbers etc
  • Personal recollections- i.e. what you had for breakfast, childhood memories
40
Q

Nondeclerative memory- procedural memory

A
  • Not directly accessible to consciousness, though may be able to talk about some of the processes you cant talk about every single step
  • Example of procedural memory- how to ride a bike, throw a ball drive a car, do sums, associations and priming
41
Q

Short term memory- improvements

A

Short term memory can hold 5-9 items at a time, you can increase short term memory by combining information into meaningful chunks. Association learning can also improve memory i.e. you can remember the location of the chess pieces in a game context but not if they are just moved about randomly.

42
Q

Classical conditioning

A
  • Focuses on involuntary/automatic behaviours
  • Involves coupling a neutral signal (unconditioned signal) with a reflex (unconditioned response)
  • Pavlovian- i.e. ring a bell when you serve food and the dog will salivate when you ring the bell even if there is no food available
43
Q

Operant conditioning

A
  • Strengthen or weaken voluntary behaviours
  • Altering probability of behaviour by applying reinforcement or punishment
  • For example, dogs sitting when you say sit as they expect a treat
44
Q

Forgetting vs amnesia

A
  • Forgetting is a normal (and essential) processes.
  • Amnesia is pathological form of forgetting
  • Anterograde amnesia is the inability to create new memories following neurological insult
  • Retrograde amnesia refers to the inability to retrieve memories established prior to neuropathology
45
Q

Episodic memory

A

Episodic memory i.e. the ability to create new memories is reliant on the medial temporal lobe. Long term memory or past memory is not reliant on the medial temporal lobe but is distributed throughout the cortex. Insult to the medial temporal lobe creates anterograde amnesia

46
Q

Medial temporal lobe structures

A

Amygdala, hippocampus and the Para hippocampal gyrus. Enlarged hippocampus correlates with an increased memory

47
Q

Where are long term memories stored

A

Memories appear to be stored in the cortices involved in the original encoding
• Visual cortex for visual memories
• Wernicke’s area for meaning of words
• Temporal lobe for faces and objects etc

48
Q

Storing of non-declarative memory

A

Learning motor skills is associated with:
• Basal ganglia
• Prefrontal cortex
• Amygdala
• Sensory association cortices
• Cerbellum
These memory traces tend to be stored in the brain regions originally involved in processing the information. Short term declarative memory has unknown storage but is presumed to be widespread.

49
Q

Main thing to remember about memory formation

A

What fires together, wires together

50
Q

Summary of long term potentiation

A

When neurotransmitters are released from the pre-synaptic terminal and binds to the post synaptic density, connections are increased.

51
Q

Mechanism of long term potentiation

A

1) CA3 cells are in the striatum pyramidali and send axons which synapse on cells that have their cell bodies on CA1 in the striatum pyramidal.
2) In LTP an electrical current is applied to the CA3 cells which send action potentials and stimulate the CA1 cells. After this every time the CA3 cell is activated there is a higher chance the CA1 cell will also be activated.
3) The connection between the two cells has been strengthened through applying the High Frequency Stimulation.
4) This only works with High frequency stimulation (100 beats per minute) and not other types.

52
Q

Long term potentiation

A

Two cells that fire action potentials at the same time will grow stronger connections. If the action potentials do not match up then the connection will not be made. The long term depression is the loss of connections that are not being used. LTP works because it fires a large number of action potentials, meaning some will coincide with the spontaneous action potentials of the other cell

53
Q

Mechanisms underlying LTP

A
  • Neurotransmitters- inhibitory GABA and the excitatory Glutamate
  • In LTP lots of Glutamate is being released as action potentials are rapidly arriving at the presynaptic neurone
  • Lots of Glutamate is released into the synaptic cleft, so both synaptic densities are saturated.
  • The post synaptic membrane is being constantly depolarised
54
Q

LTP- effects on receptors

A
  • Glutamate has two main receptors, the AMPA and the NMDA receptor.
  • The AMPA receptor opens when Glutamate binds to it, allowing sodium to enter the post synaptic density causing depolarisation.
  • Normally the NMDA receptor is blocked by a Mg+2 molecule, so even when Glutamate binds the channel is still closed.
  • The NMDA receptor only opens if the membrane is being depolarised and the Mg+2 is removed from the pore.
  • So, the NMDA receptors measures both the pre-synaptic and post-synaptic density.
  • The NMDA receptor allow Ca+2 to flow into the cell causing further depolarisation of the cell, it will trigger over signalling pathways induring changes in LTP protein expression which can after a while cause changes in gene expression for long term memory.
55
Q

Memory- conversion of thin spines to thick spines in the dendrites

A

• Spines are protrusions from the dendrites on top of which the post synaptic densities sit, allowing them to be closer to the pre-synaptic terminals.
• The thin spines are thought to be immature spines because they only contain NMDA receptors.
• In long term memory formation, Glutamate is being released but they cant depolarise as Mg+2 is blocking the channel.
• So only when the dendrite is depolarised will the channel open. The Ca+2 released will cause changes resulting in the AMPA receptors being inserted in the membrane.
• After LTP the thin spine will grow and become more active to accommodate for the AMPA receptors. The longer this process goes on, the thicker and more mushroom like the dendrite will appear.
• The mushroom spines hold long term memory and they are very stable
Connections which are not needed are removed

Medicine year 2 semester 2 (47 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions