The Brain

The effects of strokes

Brain damage is caused by strokes

can cause problems with speaking, understanding speech, reading and writing

lesions in a small cortical area in the left frontal lobe were responsible for deficits in language production

Some patients can recover some abilities after a stroke

Neural plasticity-The ability of nerve cells to change in structure and function. Because of neural plasticity, some patients are able to recover their ability after a stroke.

the structure of brain can remain flexible even in later life and can respond to changes in the environment

Brain structure can functioning is affected by both nature and nurture

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CT- Computerised Axial Tomogrpahy CAT scans

Standard broad-beam X-rays cannot be used for imaging soft tissue as they are only absorbed by denser materials such as bone

CT scans- use thousands of narrow beam X-rays rotated around the patient to pass through the tissue from different angles. each narrow beam is attenuated (reduced in strengh) according to the density of the tissue in its path

The X rays are detected and produces a thin slice of the brain on a computer screen, differernt soft tissues can be distinguished

CT scans- give frozen moment pictures. looking at brain structure not function, used to detect brain disease and monitor the tissues of the brain over the course of the illness

limited resolution so small structures cannot be distinguished

Techniques that do not rely on harmful X rays can be used and have been developed. -MRI

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Magnetic resonance imagine (MRI)

Use magnetic field and radio waves to detect soft tissue

when placed in a magnetic field, the nuclei of atoms line up with the direction of the magnetic field. H atoms in water are monitored because there is high water content in the tissues under investigation, and they line up with the magnetic field

the MRI scanner runs down the center of the tube and another magnetic field is superimposed which comes from the magnetic componnt of high frequency radio waves. These combined fields cause the direction and frequency of spin of the H anuclei to change taking energy from the radio waved.

when the radio waves are turned off, the H nuclei return to their origional alighnement and release energy they absorbed. This energy is detected and a signal is sent to a computer which analyses it to produce an image on the screen.

Different tissues respond differntly so produce contrasting signals and distinct regions. MRI examines tissue in small sections, thin slices, when put together makes a 3D image.

used in diagnosis of tumours, strokes, brain injuries and infections of the brain and spne. can produce finely detailed images of brain structures.

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Functional magnetic resonance imaging

provides information about the brain in action, useful for study into memory, emotion and language and conciousness

fMRI looks at the functions of the different areas of the brain by following the uptake of oxygen in active brain areas.

deoxyhaemoglobin absorbs the radio wave signal where oxyhaemoglobin does not

increased neural activity in brain area result in increased demand for oxygen and increase in blood flow. large increase in oxyhaemologin so less signal is absorbed. the less radio signal the higher the level of activiryty in a particular area. so different areas of the brain will light up accoreding to when they are active

fMRI can produce up to 4 images a second, so can follow the sequence of events over short itme periods.

images are collecrted contunally while the subject alternates between resting and carrying out some tasks such as object recognition, listening or memorising number sequences

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From the eye to the brain

The axons of ganglion cells that make up the optic nerve pass out of the eye and extend to several areas in the brain including the thalamus

the impulses are then sent along further nerones to the primary visual cortex where the information is processed further

before reaching the thalmus, some of the neurones in each optic nerbe branch off to the midbrain, where they connect to motor neurons involved in controlling rh pupil reflex and movement of the eye

ausio signals arrive at the midrain so we can quickly turn our eyes in the direction of a visal or auditoru stimulus

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