Diencephalon

Question 1

What does the diencephalon consist of

Answer 1

Thalamus and hypothalamus

Question 2

What is important to remember about the thalamus

Answer 2

Core of the brain- relay station- nearly all pathways will have a synapse in thalamus

Question 3

What are the 3 structures found in the diencephalon

Answer 3

Thalamus
Subthalamus- important for neurosurgeons- where electrodes are inserted for brain stimulation treatment in Parkinson’s (to stop tremors- part of basal ganglia)
Hypothalamus

Question 4

Which structure is in close connection with the hypothalamus

Answer 4

The pituitary gland

Question 5

Where is the thalamus found within the brain

Answer 5

Sits ventral to the lateral ventricles
Thalamus divided in two by 3rd ventricle (Some people have a bridge connecting the two halves).
Just below it hypothalamus
Two corticospinal tracts encapsulate thalamus
Can see two subthalmic nuclei- and beneath this the substantia nigra- thalamus well connected with the midbrain below it

Organised into discrete nuclei (thalamus is large area of grey mater)* ( *In neuroanatomy, nuclei are clusters of neurons with a similar functions and connection)=- with the exception of the basal ganglia.
)
Look at midline structures anteriorly it will be the basal ganglia- but the more posterior you go in coronal slices- will see thalamus in midline

Question 6

Summarise the functions of the thalamus

Answer 6

Relay site for numerous inputs/outputs
Key relay centre to cortical sensory areas
Involved in almost all sensory systems (except olfactory- which is limbic system- no emotional connections to thalamus)
Enhances or restricts signals

Question 7

What is the main function of the thalamus

Answer 7

It is a relay centre between the cerebral cortex and the rest of the CNS

Question 8

Describe how thalamic nuclei are named.

Answer 8

They are named based on their location within the thalamus

Question 9

What is the classification of thalamic nuclei based on and what are the four different classes?

Answer 9

The classification is based on the connections of the thalamic nuclei with the cortex
SPECIFIC – connected to primary cortical areas
ASSOCIATION – connected to association cortex
INTRALAMINAR – connected to ALL cortical areas
RETICULAR – not connected to the cortex (some nuclei are part of the reticular activating system)

Question 10

Which nuclei connect with the motor cortex (primary, premotor and supplementary)?

Answer 10

Ventral lateral

Ventral anterior

Question 11

Which nuclei relay sensory information from different parts of the body?

Answer 11

Head – Ventral posteromedial

Below the neck – Ventral posterolateral

Question 12

Which nucleus is connected to the primary visual cortex?

Answer 12

Lateral geniculate nucleus

Question 13

Which nucleus is connected to the primary auditory cortex?

Answer 13

Medial Geniculate Nucleus.

Question 14

Where is the sensory cortex located

Answer 14

In the post-central gyrus (parietal lobe)

Question 15

Describe the projections of the intra-laminar nuclei

Answer 15

Project to various medial temporal lobe structures (e.g. amygdala, hippocampus and basal ganglia)
Amygdala = emotions, fear, anxiety- commonly affected area of the brain in pathology- will present with an inherent fear and anxiety of everything (found in anterior temporal lobe)
Hippocampus = memory (just behind amygdala at floor of fourth ventricle)
Basal ganglia = movement (control of the initiation of movement)

Question 16

Describe the neurones of the intra-laminar nuclei

Answer 16

Mostly glutamatergic neurons (i.e. excitatory)
Loss of neurons in this region associated with progressive supranuclear palsy* and Parkinson’s disease
Mostly motor neurones affected

Question 17

Describe progressive supranuclear palsy

Answer 17

*PSP = rare brain disorder causing problems with walking and balance

Question 18

How do the intralaminar nuclei modulate the activity of the cortex?

Answer 18

The reticular formation projects up to the thalamus to the intralaminar nuclei and the intralaminar nuclei, because of their diffuse cortical projections, can modulate the activity of the cortex

Question 19

Describe the structure of the intra-laminar nuclei

Answer 19

The thalamus is organized around a Y-shaped collection of white matter called the ‘internal medullary lamina’. This splits the thalamus into three sections – the anterior, lateral and medial sections. Each section is composed of several cell groups with particular inputs and functions, and there are also groups of cells inside the medullary lamina.

Question 20

Describe the neurones of the reticular nuclei

Answer 20

Forms the outer covering of the thalamus

Majority of neurons are GABAergic* (e.g. inhibitory)

Question 21

Describe the connections of the reticular nuclei

Answer 21

Unlike other thalamic nuclei, they don’t connect with distal regions, but with other thalamic nuclei
Receive inputs from collaterals of their axons from thalamic nuclei
Therefore, reticular nucleus acts to modulate thalamic activity (negative feedback)

Involved only in the local circuitry of the thalamus as to modulate the internal activity of the thalamus

Question 22

Describe how the reticular nuclei affect cortical activity

Answer 22

The reticular nuclei don’t have any direct connections with the cortex but they do have widespread intrathalamic connections with all other thalamic nuclei so it can influence the flow of information from the other nuclei to the cortex

Question 23

What is meant by the reticular formation and where is it located

Answer 23

core of grey matter that runs through the brainstem and is involved in the reticular activating system
Set of interconnected pathways in the brainstem
Send ascending projections to forebrain nuclei
Ascending reticular activating system (ARAS)

Question 24

Describe the role of the reticular activating system

Answer 24

Involved in consciousness and arousal
Degrees of wakefulness depend on ARAS activity (increased activity = increased wakefulness)
Both intralaminar and reticular nucleus receive inputs from ARAS

§ The reticular formation projects through the brainstem and is controlling of level of consciousness of the brain – and with the cortex connections of the intra-laminar nuclei, all parts of the cortex can be affected by changes of consciousness.

Question 25

Describe the organisation of the hypothalamus

Answer 25

§ Located in the diencephalon below the thalamus. § Divided into the left and right hypothalamus by the third ventricle. § Each side is largely a collection of individual nuclei with separate actions and ipsilateral connections with forebrain structures. § Mammillary bodies lie directly below the hypothalamus.

Question 26

Where is the hypothalamus found

Answer 26

Divided into two by 3rd ventricle (hypothalamic nuclei found at the floor and walls of the 3rd ventricle) Collection of individual nuclei with distinct functions Largely ipsilateral* connections with other nuclei

Question 27

Essentially, what is the hypothalamus involved in

Answer 27

The four Fs: Fighting Fleeing Feeding Mating

Question 28

How is the hypothalamus involved in maintaining homeostasis?

Answer 28

Co-ordinates homeostatic mechanisms by: § Regulating ANS via connections with the spinal cord. § Acting as an endocrine organ via the pituitary gland. § Controlling behaviour via connections with forebrain structures.

Question 29

Which nucleus in the hypothalamus has connections with the ANS

Answer 29

Direct connections with autonomic nervous system Neurons in hypothalamic paraventricular nucleus with direct projections to pre-autonomic neurons in spinal cord Wing shaped nucleus at top of 3rd Ventricle

Question 30

Describe the potential applications of optogenetics in obesity therapeutics

Answer 30

Optogenetic stimulation of GABAergic LH neuron terminals in PVN results in feeding. If we could genetically modify these cells to respond to light and thus stimulate the inhibitory signal with light- it reduce appetite- thus having a potential role in the treatment of obesity.

Question 31

Describe the projections of the paraventricular nucleus

Answer 31

Sends projections to autonomic nervous system and posterior pituitary gland- made up of parvocellular (small) and large magnocellular neurones (large) Parvocellular neurones project to intermediolateral cell column to project onto autonomic neurones- to influence the heart, vasculature and kidneys. Magnocellular neurones project to the posterior lobe of the pituitary gland- to control the release of vasopressin and oxytocin.

Question 32

Describe the role of the PVN in feeding behaviour

Answer 32

PVN also involved in feeding behaviour PVN lesions cause hyperphagia and weight gain PVN receives input from hypothalamic nuclei involved in feeding (such as arcuate nucleus). Optogenetic stimulation of GABAergic LH neuron terminals in PVN results in feeding.

Question 33

Where is the supra-chiasmatic nucleus found

Answer 33

present rostrally (anteriorly) above optic chiasm for circadian rhythm (supraoptic above optic nerves)

Question 34

Describe the role of the supra-chiasmatic nucleus in the circadian rhythm

Answer 34

Light sitmulates melanopsin expressing retinal ganglion cells which travel up the retinohypothalamic tract to the suprachiasmatic nucleus. Neurones then synapse onto the PVN Neurones from PVN synapse onto intermediolateral cell column in spinal cord These neurones synapse in superior cervical ganglion and then synapse on pineal gland to control release of melatonin This controls hours of wake with light-dark cycle.

Question 35

What can lesions in the supra-chiasmatic nucleus lead to

Answer 35

Disrupted cycle May be an early sign in Parkinson's= as pathology travels up the brainstem and so can affect the RAS- leading to REM behaviour sleeping disorders- 80% of such patients progress to Parkinson's.

Question 36

Does the thalamus have ipsilateral or contralateral projections

Answer 36

Each is a collection of individual nuclei with separate functions and connections with ipsilateral forebrain structures.

Question 37

Describe the association nuclei of the thalamus

Answer 37

Association nuclei have more diffuse reciprocal connections with association cortex. The anterior, lateral dorsal and dorsomedial nuclei connect with parts of the limbic system (cingulate and prefrontal cortex). The lateral posterior and pulvinar nuclei connect with the association cortex at the junction of the parietal, temporal and occipital lobes and the prefrontal cortex.

Question 38

The association cortex can be divided into three areas based on thalamic function. What are these three areas?

Answer 38

Prefrontal Cortex Parieto-tempero-occipital Cortex Cingulate Cortex

Question 39

What is thalamic syndrome

Answer 39

Syndrome that develops after thalamic stroke | The symptoms depend on which part of the thalamus has been affected

Question 40

What 3 main changes occur in thalamic syndrome

Answer 40

CHANGE IN SENSATION – reduced, exaggerated, altered PAIN – central, non-localised (not easily treated because normal analgesics have no effect – may need to use opioids or anti-convulsants/anti-depressants) EMOTIONAL DISTURBANCE – the nuclei that transmit information to and from the association cortex are associated with the limbic system

Question 41

Describe the consequences of traumatic brain injury

Answer 41

§ Most damage is from ‘shearing forces’ which damages the axons in the brain (white matter tracts). § Neuroinflammation (microglia activation) in the thalamus from TBI occurs for a VERY long time after an accident. § Damage in the white matter tracts, travels down the axons into the thalamus which causes thalamus inflammation. o Damage, however, does not track back out into the cortex.

Question 42

Describe the associated structures of the hypothalamus

Answer 42

§ Olfactory system. § Limbic system – hippocampus, amygdala, cingulate cortex and septal nuclei. § Behaviour directed towards well-being triggers the reward system in the hypothalamic-limbic circuitry, leading to reinforcement of that behaviour.

Question 43

List the behavioural control influences of the hypothalamus

Answer 43

``` § Eating and drinking. § Expression of emotion. § Sexual behaviour. § Circadian rhythm. § Memory. ```

Question 44

Describe the consequences of hypothalamic damage

Answer 44

§ Structural damage includes: o Craniopharyngioma and other tumours – i.e. glioma, meningioma, dermoid, chordoma, hamardoma. o Inflammatory diseases – Sarcoidosis, Langerhans cell histiocytosis. § Patients with damage to the hypothalamus can have: o Hormone deficiencies. o Diabetes Insipidus and possible adipsia (doesn’t have any thirst at all). o Cannot regulate food intake – infundibular (arcuate nucleus) and PVN. o Forgets things – mammillary bodies. o Temperature fluctuations – preoptic area. o Aggression – pre-frontal cortex.

Question 45

Describe the influences of the hypothalamus

Answer 45

``` § The hypothalamus can influence: o Sexual activity. o Cardiac arrhythmias. o Alzheimer’s disease. o Narcolepsy & Cataplexy – orexin neurones are missing in patients with this. Basically the hypothalamus is involved in everything. ```

Question 46

Where does the hypothalamus sit

Answer 46

Hypothalamus: sits below thalamus, with the optic chiasm and pituitary stalk just rostral to itself