Structure of the Brain Flashcards
what areas is the brain divided into?
Forebrain
Midbrain
Hindbrain
what is the forebrain responsible for?
cognitive processing
what is grey matter?
outer area
primarily cell bodies and unmyelinated axons
what is white matter?
inner component
mainly myelinated axons
what is the purpose of the myelin sheath?
white matter is white due to the myelin sheath that surrounds the axons to speed up communication between neurones
what part of the brain is more developed in humans than other animals?
the forebrain
what does the forebrain consist of?
the telencephalon and the diencephalon
what parts of the brain makes up the telencephalon?
the telencephalon consists of all the different lobes that make up the forebrain
walnuty bit
what are the major structures within the Telencephalon?
four lobes
limbic system
basal ganglia
what are the four lobes within the brain?
frontal lobe
parietal lobe
temporal lobe
occipital lobe
what does the frontal lobe do?
to do with processing and ordering of events
contains the primary motor cortex and the secondary motor cortex
where is the primary motor cortex located?
at the back of the frontal lobe
what does the primary motor cortex do?
receives information to do with movement and passes it onto the secondary motor cortex
where is the secondary motor cortex located?
in front of the primary motor cortex in the frontal lobe
what does the secondary motor cortex do?
processes information about movement from the primary motor cortex
what does the parietal lobe do?
receives touch senses
contains the primary somatosensory cortex and the somatosensory association cortex
where is the primary somatosensory cortex located?
at the front of the parietal lobe
what does the primary somatosensory cortex do?
receives information to do with the senses and passes it onto the somatosensory association cortex
where is the somatosensory association cortex located?
behind the primary somatosensory cortex in the parietal lobe
what does the somatosensory association do?
processes sensory information from the primary somatosensory cortex
what does the temporal lobe do?
deals with auditory information
contains the primary auditory cortex and the auditory association cortex
where is the primary auditory cortex located?
in the top middle of the temporal lobe but is hidden from view
what does the primary auditory cortex do?
receives information about sound and passes it onto the auditory association cortex
where is the auditory association cortex located?
below the primary auditory cortex in the temporal lobe
what does the auditory association cortex do?
processes sound information from the primary auditory cortex
what does the occipital lobe do?
deals with visual information, responds to visuals
contains the primary visual cortex and the visual association cortex
where is the primary visual cortex located?
at the back of the occipital lobe
what does the primary visual cortex do?
receives information to do with sight and passes it onto the visual association cortex
where is the visual association cortex located?
in front of the primary visual cortex in the occipital lobe
what does the visual association cortex do?
processes visual information from the primary visual cortex
what does it mean if the brain is ipsilateral?
movement/sight on one side of the body is registered on the opposite side of the brain
right brain controls left side and vice versa
how does size work in relation to receptors
The size of the somatosensory cortex and primary cortex relates to the number of receptors in those areas - more receptors in hands, feet, lips, tongue etc
what parts of the brain does the limbic system consist of?
amygdala
hippocampus
fornix
cingulate cortex
septum
mammillary bodies
what does the amygdala control?
emotions
what does the hippocampus control?
memory and learning
left side controls learning
right side controls memory
what parts of the brain does the basal ganglia consist of?
amygdala
caudate
putamen
globus pallidus
what does the caudate control?
controls motion
contains caudate nucleus
what does the putamen and globus pallidus control?
controls smooth movement
break down may lead to tremours in patients with Parkinson’s
where is the diencephalon located?
in the top of the brain stem
what parts of the brain make up the diencephalon?
hypothalamus and thalamus and pituitary gland?
what does the hypothalamus control?
controls sleeping, eating, reproductive behaviour and regulation
anterior hypothalamus keeps you awake
posterior hypothalamus sends you to sleep
lateral hypothalamus controls hunger
what does the pituitary gland control?
hormones
anterior pituitary gland controls endocrine system
what are the 2 ways in which the body communicates?
neural and hormonal communication
what is neural communication?
fast-acting
neurones, axons, etc
electrical activity that moves across axons
what is hormonal communication
slow-acting
hormones and the endocrine system
released from the brain into blood supply to different parts of the organs within the body
what does the midbrain do?
controls movement
what does the midbrain/ mesencephalon consist of?
the Tectum and the Tegmentum
what does the Tectum consist of?
superior colliculi
inferior colliculi
what does the Tegmentum consist of?
reticular formation
cerebral aqueduct
periaqueductal gray
substantia nigra
what does the substantia nigra do?
Has lots of dopaminergic neurones
neurones which have receptors which respond to dopamine
what happens when the substantia nigra doesn’t work properly
Degeneration of Substantia Nigra leads to Parkinson’s disease - low levels of dopamine in that part of the body which is important in movement control - leads to tremours
what does the hindbrain control?
automatic processes
what does the hindbrain consist of?
the cerebellum, the Pons and the medulla oblongata in the reticular formation
what does the cerebellum do?
controls automatic breathing and balance
what does the pons do?
part of reticular formation and controls sleeping, waking and arousal
what happens on day 28 of embryonic development?
the human brain resembles a hollow tube
what happens on day 20 of embryonic development?
the neural plate develops from the outer layer of the back of the embryo
this is induced by chemical signals produced by the underlying layer called the organiser
what kind of cells are the cells of the neural plate?
cells of the neural plate are stem cells which means they can self-replicate (symmetrical replication) and replicate into any type of mature cells or neurones (asymmetrical replication)
what is the name given to cells that can replicate into any type of cell?
totipotent stem cells
what kind of cells do the cells of the neural plate specialise into as the neural tube develops?
the cells specialise into glial cells or future neurones
what do glial radial cells do?
glial radial cells allow other neurones to climb up and move to different parts of the central nervous system
what happens to the neural plate as the cells specialise?
gradually the neural plate folds up to form the neural groove
the lips of the neural groove fuse to form the neural tube
why do neurones migrate?
to create new layers of cells
neurones travel from the neural tube to different parts of the central nervous system
what happens around day 40 of embryonic development
neural proliferation occurs at the centre of the neural tube called the ventricular zone
at this point, cells do not have axons or dendrites etc
by day 40, three swellings are visible which become the fore, mid and hind brain
migration takes place in stages from the inside to out
what are progenitor cells?
original cells in the ventricular zone
these undergo symmetrical division producing similar cells
what happens at week 7 of embryonic development?
asymmetrical division occurs producing 1 progenitor cell and 1 brain cell
what is the first brain cell?
radial glial cell
has long extensions so that other neurons can climb along them
what is the second brain cell?
Cajal-Retzius cells
then neurones are formed
how long does asymmetrical division occur for?
3 months
what happens after asymmetrical division
progenitor cells die via apoptosis to stop symmetrical division which reduces the chance of cancer as the multiplication of new cells is slower
it also stops development at that point
how do cells migrate to different parts of the CNS?
cells migrate from the centre of the neural tube in two ways:
somal translocation
glia mediated migration
what is somal translocation?
extension comes from the top of the cell and stretches to move to a different area
the cell body follows and moves along through the cerebral spine fluid
then the bottom retracts
similar to a lava lamp
what is glia mediated migration?
uses radial cells (first cells to be produced)
radial cells have big long projections which allow other cells to climb them
similar to a climbing rope
how many neurones does the human cerebral cortex contain?
at least 100 billion neurones
how long does the shortest and longest migration take?
Shortest migration takes 1 day
Longest migration takes 5 weeks
what happens once migration occurs?
Once in position they form dendrites and axons connecting with other neurons
Cells forming neural crest go on to form the peripheral nervous system and migrate long distances tangentally, meaning along the CNS, and outwards which is radial migration
the cells are turn into any type of neurones
what did Krubitzer (1998) demonstrate?
Krubitzer (1998) demonstrated plasticity in the brain and how neurones can changed into different cells e.g. visual cells, sensory cells, auditory cells
how did Krubitzer (1998) demonstrate plasticity in the brain and how neurones change into different cells?
Removed area of cortex of an oposum which normally formed visual cortex
Other parts of the brain compensated for this loss and the visual cortex later developed in a different place and caused other areas, audio and somatosensory to be smaller
in what ways does specialisation occur?
specialisation occurs due to axon connections and external stimuli
explain how axon connections causes specialisation to occur
axons from the thalamus spread into the cells of the cerebral cortex and control development of cells in the cerebral cortex
if the axons are cut then development of the cells in the cerebral cortex is stopped
the connection from the thalamus is what tells the cells in the cerebral cortex to keep developing
explain how external stimuli causes specialisation to occur
visual stimuli required to generate the area of occipital lobe which coordinates stereopsis is an example of how external stimulation can control cell development
if there isn’t any visual stimuli when the brain is developing then you are not able to see things in 3D
what is the stereopsis?
the part of the brain which organises how 3D images are formed
what happens after neurones are formed?
new neurones in the cerebral cortex initially connect you everything
as you use the connections these connection will proliferate and survive
if the connection is not used then that the connection will die/ go away
how many more neurones are produced than survive?
50% more neurons produced than survive
how do the unused connections die?
Active process (apoptosis) were contents of cell is neatly packaged and macroglia attracted to remove
what happens if apoptosis doesn’t occur?
If apoptosis blocked can cause cancer, if triggered inappropriately results in neurogenerative disease - this is what happens in patients with Alzheimer’s due to misfolded proteins that causes apoptosis occurs and cells to die
how does the brain change from birth to adulthood?
Volume of brain quadruples between birth and adulthood (Johnson 2001)
Increased dendritic branching, synaptogenesis and myelination
Reduction in synapse density in visual cortex over first 3 years but in prefrontal cortex adult levels out at 14 years
Grey matter grows large in childhood then decreases in adulthood (Amso & Casey 2005)
findings of Maguire et al’s study (2000)
found that taxi drivers have a bigger posterior hippocampus than controls
led to questions:
Is the taxi driver’s big hippocampus due to spatial skills from learning maps or driving skills or are people with bigger posterior hippocampi more likely to become taxi drivers than other people due to them being good at spatial stuff?
findings of Woolett and Maguire’s study (2011)
Longitudinal study to test cause and effect
Position correlation between time spent being a taxi driver and size of posterior hippocampus - increases in size over time
Negative correlation when looking at anterior hippocampus
Overall size of hippocampus stayed the same as the brain compensated for increased posterior hippocampus by decreasing anterior hippocampus
Led to questions:
Is the taxi driver’s big hippocampus due to knowledge or driving skills?
findings of Maguire et al’s study (2006)
Bus drivers and taxi drivers are familiar with London but bus drivers follow an exact route each time
Only taxi drivers had larger posterior hippocampus than controls
So large posterior hippocampus is likely to do with having to work out all different spatial routes
Having to learn about spatial stuff can increase size of posterior hippocampus
explain Knudsen and Brainard’s study (1991)
Placed glasses on owls which altered view by showing things meant to be in their left visual sphere in their right visual sphere instead and vice versa
Found that gradually they were able to adapt and resulted in visual field changing to compensate for this
Auditory stimuli also adapted as if they heard a noise in one side they would respond to the other side
This shows the plasticity of the neurones as the visual and auditory responses both adapted
explain Greenough’s study (1975)
Enhanced environments result in thickened cortex
In rats given lots of things to play with, their brain grew to be larger and there was more blood supply to the cortex
Environment affects brain
explain Draganski et al’s study (2004)
Juggling increases cortex
More control given to the motor cortex of the brain for hands as they need to have better coordination
explain Schooler’s study (2007)
Brain volume decreases less in people who stay mentally active
As you get older, the brain shrinks and some neurones die
If you are mentally active this occurs less and at a slower time
explain Munte, Altenmuller and Janke’s study (2002)
Exposure to music training changed auditory cortex in humans
Found that left temporal lobe was larger as that is where auditory cortex is found and that area of the brain was more active when playing music
Only true of the left side as music is processed in left hand side of the brain
explain Elbert et al’s study (1995)
String musicians were found to have larger somatosensory cortexes and larger motor cortical maps of the hand on the right cortex as they are required to hold down strings with left hand
explain Braun et al’s study (2000)
2 groups had stimulation to finger and thumb
Group 1 - passive exposure - stimulated constantly throughout the day
Group 2 - active exposure - asked to identify which digit was stimulated
Only group 2 saw increase in size of map of finger on cortex as they were aware of the stimulation
where are the areas in which we gain new neurones as we get older?
areas of neurogenesis:
Olfactory bulb and Hippocampus
how and why do we get more neurones forming in the hippocampus?
memories are forming so new neurones are needed to remember and learn
Develops from a granule cell layer from radial-glial-like cells which rapidly proliferate until proper shaped neurones are formed in the hippocampus
properties of new neurones
lower activation energy so are more reactive to stimuli
plasticity threshold leading to preferential recruitment of these cells into functional circuits (Kee et al., 2007)
survival rate of new neurons
over first month over 50% die
what are the 2 ways in which neurogenesis be positively effected?
creation of new cells (neurogenesis) is positively affected by behavioural tasks e.g. spatial learning and enriched environments as this increases your cortex
Gould et al. 1999
what happens if neurogenesis is reduced?
leads to poor spatial learning
occurs in the right hand side of the hippocampus
Barkas et al. 2012
how can you increase neurogenesis?
keeping the brain active increases the number of new neurons and increases the survival of these new neurons
what did O’Leary, Ruff and Dyck (1994) find about neuroplastic response to nervous system damage?
damage to receptor in an area skin means that that connection between the axons and the somatosensory area of the brain dies away
now that area of the brain is doing nothing so an area of the brain next to empty area spreads into this empty area
here new connections between axons and the somatosensory area of the brain are formed but this may be a different area of skin entirely
this can be seen when people loose limbs
what did Pons et al. (1990) find about remapping of somatosensory cortex?
Pons et al (1990) found monkey with severed sensory neurons to their arms had reorganised somatosensory cortex. The face area had expanded into what had previously received inputs from the arm.
This is because the area that receives information from your fingers is close to the area that receives information from the face so the connections between the face and the somatosensory cortex spread into the empty space
how did Ramachandran and Blakeslee (1998) explain phantom limbs?
Ramachandran & Blakeslee (1998) reported the case of Tom who had a phantom limb
Tom felt stimuli in his arm even though it had been removed
This may be because the brain that had previously been receiving signals from the arm was now receiving stimuli from the face as these areas are close in the somatosensory cortex
Stimulation of the face was stimulating the area of the brain that used to be stimulated by the arm
When he was receiving that stimulation of the face it was perceived as being stimulation from the arm that had been amputated as when Tom’s face on the same side as his amputated area was touched he reported feeling sensations from various parts of his phantom hand
All areas of the brain are used up even when the brain is damaged - this leads to the phantom limb effect
