Lecture 4: White matter, basal ganglia and diencephalon

Question 1

Cerebral white matter is a major contributor to

Answer 1

cerebral volume

Question 2

cerebral white matter is responsible for …

Answer 2

communication (i) between cerebral areas & (ii) between the cerebral cortex & lower CNS centres

Question 3

What does cerebral white matter largely consist of?

Answer 3

Consists largely of myelinated axons bundled into large

tracts

Question 4

Projection tracts

Answer 4

• extend vertically from brain to spinal cord forming internal capsule

it is a white matter tract

Question 5

Commissural tracts

Answer 5

• 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

Question 6

Parts of the corpus callosum seen in a midsagittal section

Answer 6

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

Question 7

Split brain

Answer 7

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).

Question 8

Corpus callosum transection

Answer 8

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

Question 9

Anterior commissure

Answer 9

Includes axons that connect the middle & inferior temporal gyri of the two sides

Question 10

Association fibres

Answer 10

cerebral white matter

• connect lobes & gyri within the hemisphere

Question 11

Basal ganglia is made up of

Answer 11

3 structures - caudate nucleus, putamen, globus pallidus

functionally associated with sub thalamic nuclei and substantial nigra

Question 12

corpus striatum =

Answer 12

caudate nucleus

putamen

Question 13

lentiform nucleus =

Answer 13

putamen

globus pallidus

Question 14

striatum

Answer 14

putamen and caudate nucleus (sometimes called caudate putamen)

Question 15

Pallidum

Answer 15

globus pallidus -external (GPe) & internal (GPi) divisions

Question 16

all of the components of the basal ganglia =

Answer 16

corpus striatum + subthalamic nuclei + substantia nigra

Question 17

The caudate nucleus looks like

Answer 17

a comma that’s turned 90 degrees to the left, there is a head and body and tail

head is most anterior

Question 18

amygdaloid nucleus is part of

Answer 18

the limbic system

Question 19

internal capsule

Answer 19

projection fibres to and from the spinal cord, run deep to lentiform nucleus

Question 20

Posterior limb of internal capsule

Answer 20

between lentiform nucleus and thalamus

Question 21

Anterior limb of internal capsule

Answer 21

between lentiform and caudate nuclei

Question 22

Major connections of the basal ganglia

Answer 22

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

Question 23

Function of the basal ganglia

Answer 23

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.

Question 24

The basal ganglia and its influence on the spinal cord

Answer 24

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

Question 25

At rest - neurons in the basal ganglia

Answer 25

There are inhibitory neurons in the basal ganglia and then from the thalamus there are excitatory neurons, at rest when you do not want to move the neurons that are in the basal ganglia (that are part of the globus pallidus) they are tonically active and they are inhibitory so they are constantly firing and inhibiting the thalamic neurons and because these are inhibitiory on the thalamic neurons you are not getting the generation of movement from the firing of thalamic neurons

Question 26

When the cortex wants movement - neurons in the basal ganglia

Answer 26

inhibition of inhibitory neurons causes movement Inhibitory neuron which is tonically active which means that the thalamic neurons are not firing, to take away the inhibition you have to put in neurons that inhibit them (neurons that inhibit the inhibitory neurons). Cortical/cortex neurons that are excitatory decide they want to do this movement and these excitatory neurons depolarise and cause the inhibitory neuron to release its inhibitory neurotransmitter and this inhibits the other inhibitory neuron therefore taking away the inhibition on the thalamus and then these thalamic neurons are able to fire and they do which can generate a movement. Once the thalamic neurons are active/depolarised then they actually activate the corticospinal tract neurons which then go down to the spinal cord which means that you can actually do the movement.

Question 27

Parkinson's disease cause

Answer 27

substantia nigra dopamine neuron degeneration

Question 28

Motor deficits with Parkinson's disease

Answer 28

- rigidity – tremor (at rest) – difficulty initiating movement – postural instability (leaning forward) – shuffling gait – stiff facial expression (mask-like face)

Question 29

Treatment of Parkinson's disease

Answer 29

(i) replacement of dopamine e.g. leva dopa - most standard treatment (ii) stem cell therapy (iii) deep brain stimulation

Question 30

Diencephalon structure

Answer 30

Contains three- paired structures thalamus, hypothalamus, epithalamus - pairedd meaning that there is one on each side associated with the third ventricle

Question 31

hypothalamic sulcus separates

Answer 31

the thalamus and the hypothalamus

Question 32

thalamus

Answer 32

``` • egg-shaped structure • makes up 80% of the diencephalon • forms the superolateral walls of the third ventricle • contains about a dozen nuclei • can be divided into several groups • interthalamic adhesion (intermediate mass - connects the 2 thalamus to the other side): - a midline connection which joins each thalamus to the other • Plays a key role in relaying sensation, motor activities, cortical arousal, learning and memory ```

Question 33

thalamus role

Answer 33

• Plays a key role in relaying sensation, motor activities, cortical arousal, learning and memory sensory relay station also has a motor component

Question 34

The thalamus is the

Answer 34

gateway to the cerebral cortex

Question 35

Hypothalamus

Answer 35

``` • located below the thalamus (hypothalamic sulcus) • forms the inferolateral wall of the third ventricle • extends from the optic chiasma • superior to the brainstem ```

Question 36

pituitary gland

Answer 36

hypothalamus is closely associated, gives neurone control of pituitary and what hormones it release

Question 37

Main Homeostatic Roles of Hypothalamus

Answer 37

• Autonomic control centre (eg. respiration) • Centre for emotional response (limbic system) • Body temperature regulation (thermosensitive neurons) • Regulation of food intake (appetite and 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)

Question 38

Hypothalamic lesion

Answer 38

Shows that hypothalamus has a role in food intake Leptin deficient - decreases/inhibits food intake, acts on hypothalamus

Question 39

Damage to the hypothalamus

Answer 39

• various neuroendocrine disturbances • autonomic dysfunction (respiratory, cardiovascular and gastrointenstinal systems) • disturbances in temperature regulation, water balance, sexual behavior and food intake • changes the level of consciousness, sleep- wake cycle and emotional behavior Most common cause - tumors Early symptom - visual field defects (encroaching on the optic chiasm or optic tract)