Lecture 4: White matter, basal ganglia and diencephalon Flashcards
Cerebral white matter is a major contributor to
cerebral volume
cerebral white matter is responsible for …
communication (i) between cerebral areas & (ii) between the cerebral cortex & lower CNS centres
What does cerebral white matter largely consist of?
Consists largely of myelinated axons bundled into large
tracts
Projection tracts
• extend vertically from brain to spinal cord forming internal capsule
it is a white matter tract
Commissural tracts
- cross from one hemisphere to the other
- corpus callosum is wide band of myelinated axon tracts (about 300 million axons)
it is a white matter tract
Parts of the corpus callosum seen in a midsagittal section
splenium (most posterior) - temporal and occipital lobes
body - other parts of frontal lobe and parietal lobe
Genu - anterior parts of frontal lobe, part that has the bend in it
rostrum
Split brain
Split-brain patients (due to transection, or being born with no corpus callosum = acallosal)
– no obvious changes in intellect and behaviour – problems with certain tasks such as naming objects
e.g. object in right hand with eyes closed, can be named (because foes to left and broca’s area is on the left); object in left hand can not be named (because goes to right and needs to go across corpus callosum in order to verbalise the name).
Corpus callosum transection
Corpus callosum transection
- a form of treatment in patients with severe and disabling epilepsy
- preventing the spread of epileptic discharge from one hemisphere to the other
Anterior commissure
Includes axons that connect the middle & inferior temporal gyri of the two sides
Association fibres
cerebral white matter
• connect lobes & gyri within the hemisphere
Basal ganglia is made up of
3 structures - caudate nucleus, putamen, globus pallidus
functionally associated with sub thalamic nuclei and substantial nigra
corpus striatum =
caudate nucleus
putamen
lentiform nucleus =
putamen
globus pallidus
striatum
putamen and caudate nucleus (sometimes called caudate putamen)
Pallidum
globus pallidus -external (GPe) & internal (GPi) divisions
all of the components of the basal ganglia =
corpus striatum + subthalamic nuclei + substantia nigra
The caudate nucleus looks like
a comma that’s turned 90 degrees to the left, there is a head and body and tail
head is most anterior
amygdaloid nucleus is part of
the limbic system
internal capsule
projection fibres to and from the spinal cord, run deep to lentiform nucleus
Posterior limb of internal capsule
between lentiform nucleus and thalamus
Anterior limb of internal capsule
between lentiform and caudate nuclei
Major connections of the basal ganglia
Receive inputs from substantia nigra &
motor cortex and send signals back to these regions
Access to motor neurons in the cerebral cortex is through the thalamus. NO direct access.
Hence have cortical-basal ganglia-thalamic-cortical loop
Function of the basal ganglia
Motor Control
- inhibit unnecessary movements
- acts as a brake so that only have ordered exquisite movement when needed - preventing movement when you do not actually want to move
- brake can be released by input (has to go through the loop) from the cerebral cortex and the substantia nigra to start movement
Regulating attention and cognition.
The basal ganglia and its influence on the spinal cord
The basal ganglia influence the function of spinal cord motor neurons indirectly (compared to cerebral cortex, direct synaptic input)
the inhibitory neurons of the basal ganglia affect the spinal cord indirectly through the thalamus and the cortex compared to the cerebral cortex which has a direct effect on the spinal cord motor neurons by the crticospinal pathway