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
What are the three paired structures of the dicephalon?
thalamus,
hypothalamus,
epithalamus
What ventricle is the diencephalon associated with?
The third ventricle
What is the thalamus? How much of the diencephalon does it make up? What does it form?
-egg-shaped structure
-makes up 80% of the diencephalon
-forms the superolateral walls of the third ventricle
On OneNote identify the key areas of the Diencephalon from a mid-sagittal section…
Answers on OneNote
What can the thalamus be divided into?
-Contains about a dozen nuclei (each specialize in relaying a certain type of information)
-Can be divided into several groups (Lateral, Medial, Ventral)
-interthalamic adhesion (intermediate mass): a midline connection which joins each thalamus to the other
What is the key function of the thalamus?
Plays a key role in relaying sensation, motor activities, cortical arousal, learning and memory
What is the thalamus seen as and why?
A gateway to the cerebral cortex as there are different nuclei in the thalamus and each projects to different parts of the cerebral cortex
Describe where the hypothalamus is located…
-located below the thalamus (hypothalamic sulcus)
-forms the inferolateral wall of the third ventricle
-superior to the brainstem
-extends from the optic chiasma
What are the main homeostatic roles of the hypothalamus?
-Autonomic control center (eg. respiration)
-Centre for emotional response (limbic system)
-Body temperature regulation (thermosensitive neurons)
-Regulation of food intake (appetite & satiety centres)
-Regulation of water balance and thirst (thirst centre)
-Regulation of sleep-wake cycles (with pineal gland)
-Control of endocrine system functioning (eg. ovaries, testes to produce egg, sperm)
