Lecture 23- Ways to study brain function Flashcards Preview

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Flashcards in Lecture 23- Ways to study brain function Deck (55)

How should the brains be studied?

-Neuroscientists are usually seeking reductionist, causal mechanistic explanations of how systems interact to produce system behaviours -key part of neurological diagnosis is to localise the location of damage by examination of site--specific functions


How can one localise the location of brain damage?

-general observations (consciousness, vital signs...) -patient reports -specific functional tests 1. Motor/sensory motor 2.Sensation 3.Cognition


What is 1. Motor /sensory motor functional test to localise brain damage?

-test segmental reflexes (stretch) -test primitive reflexes (Babinksi) -measure strength of muscles, compare the symmetry, see if there is palsy -test balance, posture and gait -cranial nerves (eye movement)


What are segmental reflexes?

-reflexes that go through just one segment of the spinal cord (stretch, clasp knife, cross extension reflex)


What are primitive reflexes?

-reflexes exhibited by babies but not normal adults (due to inhibition from the higher centers) eg. Babinksi sign


What is palsy?

-paralysis involving loss of feeling and uncontrollable movements (shaking)


How is sensation useful as a diagnostic test?

-use pin prick and cotton ball -can determine if Brown Sicard syndrome or any damage in the pain and touch pathways


How do you test cognition to localise brain damage?

-language, orientation and memory tests


What are cranial nerves?

-12 pairs, always left and right of each -rostral to caudal axis -important for clinical diagnosis (determining location of brain damage) -go from the periphery straight to the brain (brainstem, except fro cranial nerve I =olfactory that goes via the olfactory bulb)


What are the two types of cranial nerves?

-sensory and motor (some have autonomic component too)


What is cranial nerve I and what does it do?

-Olfactory nerve, sensory -sense of smell


What is cranial nerve II and what does it do?

-Optic nerve, sensory -vision


What is cranial nerve III and what does it do?

-Oculomotor nerve, motor -eye movements; papillary constriction and accommodation; muscles of eyelid


What is cranial nerve IV and what does it do?

-Trochlear nerve, motor -eye movements


What is cranial nerve V and what does it do?

-Trigeminal nerve, motor and sensory -somatic sensation from face, mouth, cornea; muscles of mastication


What is cranial nerve VI and what does it do?

-Abducens nerve, motor -eye movements


What is cranial nerve VII and what doe sit do?

-Facial nerve, sensory and motor -controls the muscles of facial expression; taste from anterior tongue; lacrimal and salivary glands


What is cranial nerve VIII and what does it do?

-Vestibulocochlear (auditory) nerve, sensory -hearing; sense of balance


What is cranial nerve IX and what does it do?

-Glassopharyngeal nerve, sensory and motor -sensation from pharynx; taste from posterior tongue; carotid baroreceptors


What is cranial nerve X and what does it do?

-Vagus nerve, sensory and motor -autonomic functions of gut; sensation from pharynx; muscles of vocal cords; swallowing


What is cranial nerve XI and what does it do?

-Spinal accessory nerve, motor -shoulder and neck muscles


What is cranial nerve XII and what does it do?

-Hypoglossal nerve, motor -movements of tongue


What are all the areas where the optic nerve projects to?

-Hypothalamus= how much daylight we are exposed to, regulates circadian rhythms

-Pretectum=reflex control of pupils and lens

-Superior colliculus= the unconscious vision, orienting the movements of head and eyes (how blind people catch a ball)

-LGN and striate cortex of course

-test these and see where the damage is, if all functions gone then must be at chiasm or so


What cranial muscles are involved in movement of the eyes?

-III (Oculumotor), IV (Trochlear), VI(Abducens)


What can we learn from testing eye movement in a patient?

-depending on how they can move their eyes we know where the damage might be -cranial nerve VI (if can't pull eye to the side)


What is a sign of early multiple sclerosis?

-cannot move eyes normally


How can the face movement tell us if it is an upper or lower motor neuron sign?

-upper face gets bilateral innervation = from ipsilateral and contralateral

-whereas lower face only contralateral -if one sided leasion then the upper face sth always left


Where in the cortex is the face represented?

-primary motor and cingulate motor area


Why is the monosynaptic stretch reflex dubbed the most important sign in neurology?

-strength of the reflex also measure of what is happening -as it is connected to the descending systems too -MSR= monosynaptic stretch reflex


How is the locomotor pattern generator an indicator of brain damage?

-normally functions in the context of the entire motor control system -can reveal where damage is


What is ataxic gait a sign of?

-cerebellar disease


What is choreaform gait a sign of?

-basal ganglia damge (Huntington's)


What is Parkinsonian gait a sign of?



What is Hemiparetic gait a sign of?



What is Circumducting gait a sign of?

-damage to motor cortex or the cerebellum


What are the direct measurements of brain activity and structure?

EEG, CAT scan, PET scan, RMI, fRMI. MEG


How does EEG work?

measure brain activity by putting electrodes on the head to see what is happening -very poorly localised -spatial resolution is poor= sources of change diffuse out through the brain EEG -works because lot of activity in brain is geometrically organised and temporally synchronized -they exhibit consistent behaviour -dipoles= change in electrical current


What is the brain EEG when we are awake?

-apha rhythm, sometimes beta rhythm (static) -low amplitude, high frequency


What is the EEG like when we sleep?

Go into REM sleep that has almost the same signature as awake (beta rhythm)

-the 4 stages of non-REM sleep

-as go deeper into sleep= increasing coherence -low amplitude high frequency when sleep

-go though cycles when sleeping the 4 stages (Theta and Delta rhythms)


What is REM?

- same as the awake pretty much, that is when we dream -when in REM= difference-only time when we lose muscle tone in the body except for the eyes (the rapid eye movements)


What is MEG?

-magnetoencephalography=measures the normal tiny magnetic fields associated with activity in the brain

-can combine this with MRI and tell where the activity is

-not great in spatial resolution but incredibly good temporal resoultion


What is the resolution of EEG?

-bad spatially; great temporally


What is the resolution of MEG?

-bad spatially; great temporally


Is MRI harmless?

-yes as it uses radio waves, can do it as much as you like


Are PET and CAT scan harmless?

-no, use positron (gamma rays) and X ray respectively -only 3 times a year or so


What does tomo mean?



How does CAT scan work?

CAT scan (computer assisted tomography)= fancy X ray

-if shine electrode at different angles= then different attenuation from the things that are in the brain


How does PET scan work?

PET scan= positron tomography

-chemical you ingest, gives off positrons, annihilate with electrons= gamma ray -see it as energy

-builds up what the structure looked like


What is T1 and T2 MRI?

-left=T1 MRI high resolution

-right=T2 scan, looking at where the fluid is


How does MRI work?

-it is a measure of water density (proton density) -Hydrogen is paramagnetic (spins at random directions), it's like a spinning magnet. Because of all the water, tissue have lots of protons spinning around, but with random orientations of the spin axis -strong magnetic field align the spin axes -radiowaves disrupt this alignment, when they realign= they give off radio waves that we can pick up


What is fMRI?

functional= more active bits of brainhave more blood= haemoglobin= is paramagnetic and works the same way increase in oxygenated blood in active regions


What does combining fMRI and MRI do?

-combine structural and functional MRI can give you lot of information


What are the limits of fMRI?

-doesn't measure neuronal activity directly and it is blind to details such as how many neurons are firing -the signal, boost in blood flow in response to stimulus can be difficult to extract from the noise of routine changes in blood flow and the statistical techniques involved are easy to misunderstand and misuse


What is MR tractography?

water is what you're measuring the behaviour of that - behaves differently when in a tube of axons


How do the techniques of measuring the brain compare with resolution?

-think about what can it do spatial and temporal -PET most harmful