Lecture 4- Diencephalon and cerebellum

What are the four main parts of the diencephalon?

Thalamus, hypothalamus, subthalamus, and epithalamus (pineal gland).

Which ventricle is associated with the diencephalon, and what forms its walls?

The third ventricle; superolateral walls formed by the thalamus, inferolateral walls by the hypothalamus

What percentage of the diencephalon does the thalamus make up?

About 80%.

What is the thalamus shaped like and how many nuclei does it contain?

It is egg-shaped, containing ~12 nuclei.

What connects the two thalami across the third ventricle?

The interthalamic adhesion

Why is the thalamus known as the “gateway to the cerebral cortex”?

Because almost all sensory information (except olfaction) must pass through it before reaching the cortex for conscious processing

Beyond sensory relay, what other functions does the thalamus serve?

It contributes to cortical arousal, learning, and memory

Where is the hypothalamus located in relation to the thalamus?

Below the thalamus, separated by the hypothalamic sulcus

What part of the third ventricle does the hypothalamus form?

The inferolateral wall

What are the anterior and posterior anatomical boundaries of the hypothalamus?

Optic chiasm (anterior) to the brainstem (posterior)

How does the hypothalamus interact with the pituitary gland?

It releases regulatory hormones that control pituitary secretions, influencing growth, metabolism, reproduction, and stress responses

What is the hypothalamus’ role in the autonomic nervous system?

It acts as the autonomic control center, regulating cardiovascular, respiratory, and digestive activities

How does the hypothalamus regulate emotional behavior?

Through interactions with the limbic system

How does the hypothalamus regulate temperature?

Thermosensitive neurons detect body temperature and trigger heat loss or conservation mechanisms

How does the hypothalamus regulate hunger and satiety?

Via specific nuclei that control food intake—appetite and satiety centers.

What is the hypothalamic thirst center responsible for?

Monitoring water balance and triggering thirst when body fluids are low.

How does the hypothalamus influence sleep-wake cycles?

Works with the pineal gland to regulate circadian rhythms.

What neuroendocrine effects can hypothalamic damage cause?

Disrupted hormone release affecting metabolism, growth, and reproduction

What autonomic effects can hypothalamic damage cause?

Dysregulation of cardiovascular, respiratory, and GI systems

How does hypothalamic damage affect temperature regulation?

Can cause hyperthermia or hypothermia due to loss of homeostatic control

How does hypothalamic dysfunction contribute to obesity?

Damage to satiety centers → unregulated appetite → overeating and weight gain

How can hypothalamic tumors cause visual problems?

By compressing the optic chiasm or optic tract, leading to visual field defects

Where is the subthalamus located?

Between the thalamus, hypothalamus, and midbrain

What is the main functional role of the subthalamic nucleus?

It is part of the basal ganglia circuit and plays a key role in motor control

Where is the pineal gland located?

Attached to the roof of the third ventricle.

What hormone does the pineal gland secrete, and when is it highest?

Melatonin, with peak secretion at night, regulating circadian rhythms

What is “pineal sand” and why is it clinically useful?

Calcium deposits that accumulate in adulthood, visible on CT scans, serving as a radiographic landmark

What percentage of brain volume and neurons does the cerebellum contain?

10% of brain volume, but ~50% of the brain’s neurons

Where is the cerebellum located?

In the posterior fossa, forming the roof of the fourth ventricle

What are the three main layers of the cerebellum?

Cortex (gray matter), arbor vitae (white matter), and deep cerebellar nuclei

What are the folds of the cerebellar cortex called?

Folia

What connects the two cerebellar hemispheres?

The vermis

What covers the posterior cerebellar incisure?

Dura mater

What are the three cerebellar peduncles?

Superior (SCP), middle (MCP), and inferior (ICP)

What is the function of the superior cerebellar peduncle (SCP)?

Connects to the midbrain, mainly efferent output to motor cortex via thalamus

What is the function of the middle cerebellar peduncle (MCP)?

Connects to the pons, carrying afferent input of intended motor commands

What is the function of the inferior cerebellar peduncle (ICP)?

Connects to the medulla, carrying afferent sensory feedback and some efferent signals

What is the role of the spinocerebellum (vermis & intermediate hemispheres)?

Controls posture and coordination of movement

What is the role of the cerebrocerebellum (lateral hemispheres)?

Planning and initiation of voluntary movements

What is the role of the vestibulocerebellum (flocculonodular lobe)?

Controls balance and coordination of head and eye movements

What information does the MCP deliver to the cerebellum?

Intended movement commands from the motor cortex

What information does the ICP deliver?

Actual sensory feedback from muscles, joints, and vestibular system

How does the cerebellum ensure smooth movement?

Deep nuclei compare intended vs. actual movement and send corrections via SCP/ICP

Can voluntary movement occur without the cerebellum?

Yes, but movements are clumsy, uncoordinated, and poorly timed

What are the key symptoms of cerebellar dysfunction?

Ataxia, tremor, nystagmus, headache, vomiting

What is ataxia?

A movement disorder with poor coordination, staggering gait, dysmetria, and slurred speech

What causes tremor in cerebellar disease?

Loss of smooth coordination → involuntary oscillations of limbs/trunk

What is nystagmus in the context of cerebellar dysfunction?

Rhythmic, involuntary oscillation of the eyes

Why are headache and vomiting common signs of cerebellar tumors?

Due to raised intracranial pressure from tumor growth in the posterior fossa