Lecture 5- White Mater, Basal Ganglia, Diencephalon Flashcards
What is cerebral white mater?
-A major contributor to cerebral volume
-Is responsible for communication: (i) between cerebral areas & (ii) between the cerebral cortex & lower CNS centres
-Consists largely of myelinated axons bundled into large tracts
What are projection tracts of cerebral white matter?
Extend vertically from brain to spinal cord forming internal capsule
What are commissural tracts of cerebral white matter? What is a famous example?
-cross from one hemisphere to the other
- corpus callosum is wide band of myelinated axon tracts (about 300 million axons)
What parts can the corpus callosum be divided into as seen in a midsagittal section? Complete diagram on OneNote…
Answers on OneNote
What is spilt brain? How is it sometimes used as a treatment for epilepsy?
Treatment for epilepsy: 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
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
e.g. object in right hand with eyes closed, can be named; object in left hand can not be named. Why? Because information crosses contralaterally to the right hemisphere if in the left hand and then would need to cross the corpus callosum to get to Broca’s area in the left hemisphere. In spilt brain patients this last step can’t occur.
What are anterior commissure white matter tracts?
Includes axons that connect the middle & inferior
temporal gyri of the two sides
What are the association fibers of the cerebral white matter?
connect lobes & gyri within the hemisphere
What 5 structures collectively make up the basal ganglia?
-Caudate nucleus
-Putamen (pod)
-Globus pallidus (pale globe)
-subthalamic nuclei
-substantia nigra
What two structures of the basal ganglia make up the lentiform nucleus?
Putamen (pod) = more lateral
Globus pallidus (pale globe) = most medial
What structures of the basal nuclei make up the corpus striatum?
-Caudate nucleus
-Lentiform nucleus (putamen, globus pallidus)
Fill in the diagrams on OneNote that show the positions of the basal ganglia from different angles…
Answers on OneNote
What major connections do the basal ganglia have?
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
What is the function of the basal ganglia?
Motor Control
- inhibit unnecessary movements
- acts as a brake so that only have ordered exquisite movement when needed
- brake can be released by input from the cerebral cortex and the substantia nigra to start movement
Regulating attention and cognition.
How does the ‘brake’ get released?
-At rest inhibitory neurons act on the positive neurons
-When the cortex decides it wants to create movement/ needs excitement this inhibition is taken away by inhibiting the inhibitory neurons. This is done by the putamen neurons of the basal ganglia which in turn are activated by excitatory cortical neurons.
What is Parkinson’s disease? What are possible treatments?
- substantia nigra dopamine neuron degeneration
Motor deficits:
– rigidity
– tremor (at rest)
– difficulty initiating movement
– postural instability
– shuffling gait (head +shoulders stopped forward, lean further and further forward moving faster and faster)
– stiff facial expression (mask-like face)
-upper and lower limbs showed increased tone in the opposing muscle groups when the joints were passively moved
Treatment:
(i) replacement of dopamine
(ii) stem cell therapy
(iii) deep brain stimulation
